Patient-specific glenoid prostheses for partially modified scapula

Abstract

A method comprises outputting a user interface of a surgical planning system, wherein the user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient; and determining a bone-facing surface of the patient-specific glenoid prosthesis having a native-facing portion and a modified-facing portion, wherein the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula.

Description

PATIENT-SPECIFIC GLENOID PROSTHESES FOR PARTIALLY MODIFIED SCAPULA

[0001] This application claims priority to U.S. Provisional Patent Application 63 / 632,894, filed April 11, 2024, the entire content of which is incorporated herein by reference. BACKGROUND

[0002] In a total shoulder arthroplasty (TSA), a glenoid prosthesis is implanted into a glenoid fossa of a patient’s scapula and a humeral prosthesis is implanted into the patient’s humerus. The glenoid prosthesis and the humeral prosthesis replace the native articulating surfaces of the patient’s shoulder joint. In a reverse total shoulder arthroplasty (TSA), the glenoid prosthesis has a glenosphere (i.e., a hemispherical articulating surface) and the humeral prosthesis has a concave surface that articulates relative to the glenosphere. In an anatomical TSA, the glenoid prosthesis has a concave surface and the humeral prosthesis has a hemispherical articulating surface that articulates relative to the concave surface of the glenoid prosthesis.

[0003] The glenoid prosthesis may include a baseplate and a patient-specific augment element. In general, the baseplate comprises a disc-shaped object. The glenosphere and the augment element may be attached to opposite sides of the baseplate. The augment element occupies a space between the baseplate and the patient’s scapula. The shape of the patient-specific augment element is specific to the native shape of the patient’s glenoid fossa. In other words, the patient-specific augment element may be contoured to mate with the corresponding contours of the patient’s glenoid fossa. Thus, the glenoid prosthesis is implantable on the patient’s glenoid fossa without reshaping the patient’s glenoid fossa during surgery. SUMMARY

[0004] This disclosure describes patient-specific glenoid protheses for a partially modified scapula and a computerized planning system for planning implantation of the patient-specific glenoid prosthesis. As described herein, the planning system may output a user interface that represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient. The planning system may determine a bone-facing surface of the patient-specific glenoid prosthesis having a native-facing portion and a modified-facing portion. The native- facing portion is shaped to conform to an unmodified bone surface of the scapula. Themodified-facing portion is shaped to conform to a modified bone surface of the scapula. The modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position. The unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position.

[0005] In one example, this disclosure describes a method comprising: outputting, by one or more processors implemented in circuitry, for display on a display device, a user interface of a surgical planning system, wherein the user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient; adjusting, by the one or more processors, the planned implantation position based on indications of user input to adjust the planned implantation position; and determining, by the one or more processors, a bone- facing surface of the glenoid prosthesis, the bone-facing surface of the glenoid prosthesis having a native-facing portion and a modified-facing portion, wherein the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula, wherein: the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position.

[0006] In another example, this disclosure describes a patient-specific glenoid prosthesis comprising: an articulation element comprising an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide, an augment element; and a baseplate, wherein: the articulation element and the augment element are configured to be attached to opposite sides of the baseplate, the augment element is configured to occupy a space between a scapula of a patient and the baseplate, a bone-facing surface of the glenoid prosthesis has a native-facing portion and a modified-facing portion, the native- facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula, the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis atthe planned implantation position, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position.

[0007] In another example, this disclosure describes a patient-specific guide comprising: a structure defining a lumen configured to guide a guide pin to a preoperatively planned location on a scapula of a patient at a preoperatively planned orientation; one or more patient-specific unmodified bone contact surfaces that are shaped to conform to respective unmodified guide contact surfaces of the scapula, wherein each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of the patient-specific guide and will not be intra-operatively modified during a surgery to implant a patient-specific glenoid prosthesis; and one or more patient-specific modified bone contact surfaces shaped to conform to respective modified guide contact surfaces of the scapula, wherein each of the modified guide contact surfaces is a surface of the scapula that will contact the one of the patient-specific modified bone contact surfaces of the patient- specific guide and will be intra-operatively modified during the surgery to implant the glenoid prosthesis.

[0008] The details of various examples of the disclosure are set forth in the accompanying drawings and the description below. Various features, objects, and advantages will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0009] FIG.1 is a conceptual diagram illustrating an example computing system in which one or more techniques of this disclosure may be performed.

[0010] FIG. 2 is a conceptual diagram illustrating an example user interface for positioning a glenoid prosthesis in accordance with one or more techniques of this disclosure.

[0011] FIG. 3A is a conceptual diagram illustrating an example user interface showing a 3- dimensional (3D) model of a patient’s scapula and a 3D model of a glenoid prosthesis.

[0012] FIG. 3B is a conceptual diagram illustrating an example user interface showing a 3D model of a patient’s scapula and a 3D model of a glenoid prosthesis in accordance with one or more techniques of this disclosure.

[0013] FIG. 3C is a conceptual diagram illustrating a user interface that includes controls for adjusting a planned implantation position of a glenoid prosthesis on a scapula in accordance with one or more techniques of this disclosure.

[0014] FIG. 4 is a conceptual diagram illustrating an example user interface of a planning system that allows a user to control whether the planning system is able to plan a surgery that involves manual bone preparation for a patient-specific glenoid prosthesis, in accordance with one or more techniques of this disclosure.

[0015] FIG. 5 is a conceptual diagram illustrating an example user interface for selecting positions of feet of a patient-specific surgical guide, in accordance with one or more techniques of this disclosure.

[0016] FIG.6A is a conceptual diagram illustrating an example user interface showing a model of a patient-specific guide positioned on a patient-specific model of a scapula, in accordance with one or more techniques of this disclosure.

[0017] FIG. 6B is a conceptual diagram illustrating an example patient-specific guide from a medial-to-lateral perspective, in accordance with one or more techniques of this disclosure.

[0018] FIG.7 is a flowchart illustrating an example operation of planning system in accordance with one or more techniques of this disclosure. DETAILED DESCRIPTION

[0019] In cases where a glenoid fossa has a severe deformity, a glenoid prosthesis may have a customized (e.g., patient-specific) augment element that conforms to the patient’s native bone. In other words, the augment element matches the natural, unmodified contours of the patient’s scapula. Such a customized augment element may be especially helpful when bone loss is so severe that there is an insufficient amount of bone remaining to ream a flat surface within the glenoid fossa for seating a non-patient-specific glenoid prosthesis.

[0020] There is a further subset of cases where the surgeon would like to position the glenoid prosthesis at a given location, but doing so would require the thickness of the augment element to exceed a maximum allowed thickness (i.e., require the augment to exceed an “envelope” for the glenoid prosthesis). The “envelope” refers to a range of allowable sizes and dimensions. For example, the anterior rim of the glenoid fossa may be so severely eroded that an appropriately positioned glenoid prosthesis would have an augment that is greater than a maximum allowed size. In other examples, certain areas on the glenoid face or rim may include one or more osteophytes. If such osteophytes were allowed to remain, the augment elementmay need to be larger, which may force the augment element to exceed the “envelope” for the glenoid prosthesis. In still other examples, one or more portions of the glenoid prosthesis (e.g., the glenosphere) may collide with parts of the scapula when the glenoid implant is at a desired position.

[0021] To address this subset of cases, the surgical planning system includes a feature that allows the surgeon to plan a total shoulder arthroplasty (TSA) that involves removing an area of the scapula so that a bone-facing surface of the glenoid prosthesis sits partially on the modified surface of the scapula and partially on the native surface of the scapula. In some examples, removing an area of the scapula includes removing osteophytes in a particular area. In some examples, an area on the rim of the glenoid fossa may be removed to form a flat surface. The surgical planning system may output, for display on a display device, a user interface of a surgical planning system. The user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient. The surgical planning system may adjust the planned implantation position based on indications of user input to adjust the planned implantation position. The surgical planning system may determine a bone-facing surface of the patient-specific glenoid prosthesis, the bone-facing surface of the patient-specific glenoid prosthesis having a native-facing portion and a modified-facing portion, wherein the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula. The modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position. The modified bone surface will at least partially contact the glenoid prosthesis after implantation of the glenoid prosthesis at the planned implantation position. The modified bone surface excludes any surface created in the scapula for a fixation hole (e.g., a peg hole, keel slot, screw hole, etc.) that may also be formed. The unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position. The surgical planning system may output manufacturing data that enables a manufacturing system to fabricate the patient-specific glenoid prosthesis.

[0022] FIG.1 is a conceptual diagram illustrating an example system 100 in which one or more techniques of this disclosure may be performed. In the example of FIG.1, system 100 includes a computing system 102, a manufacturing system 104, and Mixed Reality (MR) visualization device 120. Computing system 102 is configured to assist one or more users in generating asurgical plan for an orthopedic surgery, such as a total shoulder arthroplasty (e.g., an anatomical total shoulder arthroplasty or a reverse total shoulder arthroplasty) or other type of surgery. Manufacturing system 104 is configured to manufacture patient-specific prostheses according to surgical plans generated by computing system 102. In some examples, manufacturing system 104 also generates patient-specific instruments, such as drill guides, pin guides, cutting guides, or other types of surgical instruments, according to the surgical plans generated by computing system 102. MR visualization device 120 may provide intra-operative guidance. In some examples, system 100 does not include MR visualization device 120.

[0023] Computing system 102 may include one or more computing devices. In one example, computing system 102 includes a personal computer used by a surgeon. In this example, the personal computer may generate a surgical plan without interaction with other computing devices. In other examples, computing system 102 includes a server device and a client device (e.g., a personal computer). In such examples, the server device may generate a surgical plan based on input initially received via the client device. In any case, one or more computing devices of computing system 102 may output user interfaces for display to a user and may receive, directly or indirectly, indications of user input.

[0024] Computing system 102 includes one or more processors 106, a storage system 108, a communication interface 110, and a display device 112. In other examples, computing system 102 may include more, fewer, or different components. The components of computing system 102 may be in one or more computing devices. For example, processors 106 may be in a single computing device or distributed among multiple computing devices of computing system 102, storage system 108 may be in a single computing device or distributed among multiple computing devices of computing system 102, and so on. In some examples, computing system 102 is a personal computer, a system of computing devices, one or more server devices, or a system comprising one or more other types of computing devices. Processors 106, storage system 108, communication interface 110, and display device 112 are communicatively coupled.

[0025] Processors 106 may be implemented in circuitry and include one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), hardware, or any combinations thereof. In general, processors 106 may be implemented as fixed-function circuits, programmable circuits, or a combination thereof. Fixed-function circuits refer to circuits that provide particular functionality and are preset on the operations that can be performed. Programmable circuits refer to circuits that can be programmed to perform various tasks and provide flexiblefunctionality in the operations that can be performed. For instance, programmable circuits may execute software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. In some examples, one or more of the units may be distinct circuit blocks (fixed-function or programmable), and in some examples, the one or more units may be integrated circuits.

[0026] Processors 106 may include arithmetic logic units (ALUs), elementary function units (EFUs), digital circuits, analog circuits, and / or programmable cores, formed from programmable circuits. In examples where the operations of processors 106 are performed using software executed by the programmable circuits, storage system 108 may store the object code of the software that processors 106 receives and executes, or another memory within processors 106 (not shown) may store such instructions. Examples of the software include software designed for surgical planning. Processors 106 may perform the actions ascribed in this disclosure to processors 106.

[0027] Processors 106 may output data (e.g., a user interface, models, etc.) for display. Outputting data for display may include one or more of processors 106 generating and sending signals to a display device (e.g., display device 112) that the display device can directly use to display the data. Outputting data for display may include one or more of processors 106 outputting data for transmission to another computing device (e.g., another computing device of computing system 102) that processes the data to generate signals that a display device (e.g., display device 112) may directly use to display the data.

[0028] Processors 106 may receive indications of user input from one or more users. Processors 106 may receive an indication of user input directly from a user input device (e.g., keyboard, mouse, touchscreen, etc.). For instance, in an example where computing system 102 is implemented on a single computing device, processors 106 may receive the indications of user input from one or more user input devices of the computing device. In other examples, processors 106 may receive the indications of user input by way of one or more computing devices. For instance, in an example where computing system 102 is implemented using a server device and a client device and processors 106 are located in the server device, processors 106 may receive indications of the user input from the client device. For example, processors 106 may receive an indication from the client device that the user has selected a displayed element, typed specific text, and so on.

[0029] Storage system 108 may store various types of data used by processors 106. Storage system 108 may include any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. Examples of display device 112 include a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.

[0030] Communication interface 110 that allows computing system 102 to output data and instructions to and receive data and instructions from a medical imaging system, manufacturing system 104, or other devices via one or more communication links or networks. Communication interface 110 may include hardware circuitry that enables computing system 102 to communicate (e.g., wirelessly or using wires) to other computing systems and devices. Example networks may include various types of communication networks including one or more wide-area networks, such as the Internet, local area networks, and so on. In some examples, the network may include wired and / or wireless communication links.

[0031] In the example of FIG.1, storage system 108 stores medical image data 114, plan data 116, and a planning system 118. In other examples, storage system 108 may store more, fewer, or different types of data or units. Moreover, the data and units illustrated in the example of FIG. 1 are provided for purposes of explanation and may not represent how data is actually stored or how software is actually implemented. Planning system 118 may comprise instructions that are executable by processors 106. For ease of explanation, this disclosure may describe planning system 118 as performing various actions when processors 106 execute instructions of planning system 118.

[0032] Planning system 118 is a system that may help a surgeon plan an orthopedic surgery as part of a pre-operative planning process. Planning system 118 may be an instance of a computer-assisted orthopedic surgery (CAOS) system. In some examples, planning system 118 may also assist users during a surgery. For instance, planning system 118 may output navigation information to one or more devices (e.g., monitors, head-mounted displays, etc.) to a user during a surgery to help the user execute a surgical plan. Planning system 118 may generate plan data 116 that describes a surgical plan for a patient developed using planning system 118.

[0033] During the pre-operative planning process, planning system 118 may help the surgeon select parameters of a patient-specific orthopedic prosthesis for implantation into a patient and may automatically design the patient-specific orthopedic prosthesis according to the selected parameters. For ease of explanation, this disclosure may refer to orthopedic prostheses assimply prostheses. Planning system 118 may use medical imaging data 114 during the pre- operative planning process and / or at other times. Medical imaging data 114 may include one or more of x-ray images, CT images, MRI images, images generated based on other medical imaging techniques, or models generated based on such images.

[0034] Planning system 118 may output a user interface for display to a user. The user interface may display a virtual glenoid prosthesis model displayed relative to a virtual scapula model. The virtual scapula model is a representation of at least a portion of a scapula of a patient. In other words, planning system 118 may generate, and output within the user interface, an image in which the virtual glenoid prosthesis model is displayed relative to the virtual scapula model. The virtual glenoid prosthesis model is a representation of a glenoid prosthesis to be implanted on the scapula. In response to receiving indications of user input, planning system 118 may rotate the glenoid prosthesis model and virtual scapula model in three dimensions to allow the user to see the glenoid prosthesis model and virtual scapula model from any angle.

[0035] The virtual glenoid prosthesis model and the virtual scapula model may be 3- dimensional (3D) models. For example, the virtual glenoid model and the virtual scapula model may each be a 3D mesh comprising vertices, edges, and faces. Such meshes may include hundreds or thousands of such vertices, edges, and faces. A relatively high density of vertices may be involved with the meshes, especially since a high degree of accuracy may be needed to ensure matching between the patient’s bone and portions of a glenoid prosthesis that will contact the patient’s bone. Generating images based on the 3D meshes may include performing a rendering process that applies shaders to the vertices, projects the vertices to a 2-dimensional plane, and applies other image process actions (e.g., lighting effects, texturing, etc.). Given the number of vertices involved, rendering may be performed in a Graphics Processing Unit. In such examples, a 3D virtual scapula model may be generated (e.g., by planning system 118 or another system) based on a computed tomography (CT) scan and / or other type of medical imaging of the scapula. In some examples, the virtual glenoid prosthesis model and the virtual scapula model may additionally or alternatively be 2-dimensional (2D) models. In such examples, the virtual scapula model be displayed as a 2D slice of the scapula and the 2D virtual glenoid prosthesis model may be displayed as an outline of the glenoid prosthesis.

[0036] Planning system 118 may receive indications of user input to adjust various parameters of the glenoid prosthesis. Example parameters may include types of prostheses, positions of prostheses, and so on. Different types of prostheses are associated with different parameters. For example, parameters of a glenoid prosthesis in a total shoulder arthroplasty may include a lateralization / medialization of the glenoid prosthesis, an inclination of the glenoid prosthesis,a version / anteversion of the glenoid prosthesis, a size of an articulating surface (e.g., radius of a glenosphere, diameter of a concave articulating surface, etc.), eccentricity of the articulating surface, and so on. In some examples, planning system 118 may automatically recommend one or more parameters of the glenoid prosthesis.

[0037] A glenoid prosthesis includes a baseplate, an articulation element, and an augment element. The baseplate may comprise a disk-shaped metal element. The augment element is attached to a bone-facing side of the baseplate. The baseplate may define one or more screw holes. After the placement of the baseplate and augment element onto the patient’s scapula, the surgeon may fix the baseplate and augment element to the patient’s scapula by passing fixation screws into the patient’s scapula through the screw holes of the baseplate. In some instances, one or more of the fixation screws also pass through corresponding screw holes defined in the augment element.

[0038] The articulation element and the augment element are attached to opposite sides of the baseplate. Thus, the articulation element is attached to a non-bone-facing side of the baseplate. The articulation element includes an articulation surface, such as a glenosphere or a concave articulation surface. The articulation element may include a polyethylene element that serves as the articulation surface. The baseplate may have one or more attachment elements used for attaching the articulating element to the baseplate. For instance, the attachment elements of the baseplate may include a cone-shaped protrusion that defines a threaded bore. The articulation element may have a corresponding attachment member that fits over the cone-shaped protrusion. During surgery, after the baseplate and augment element are fixed to the patient’s scapula, the surgeon may position the articulation element on the cone-shaped protrusion and may pass a screw through the articulation element into the threaded bore of the cone-shaped protrusion to secure the articulation element to the baseplate.

[0039] The augment element occupies a space between the baseplate and the scapula. The augment element includes a porous metallic material that allows for bony ingrowth. The augment element may be manufactured using an additive manufacturing process. The additive manufacturing process may form the augment element directly on the baseplate.

[0040] In some examples, a central peg extends from the augment element. The central peg is a cylindrical element. When the central peg is inserted into a peg hole formed in the patient’s scapula, the central peg provides mechanical support for the glenoid prosthesis. In other examples, a keel extends from the augment element and serves a similar purpose as the central peg.

[0041] Patients have differently shaped glenoid fossae. For instance, different patients have differently sized glenoid fossae or have glenoid fossae of different depths. Additionally, injuries, arthritis, or other conditions may lead to bone loss of the glenoid fossa. In other instances, a patient’s glenoid fossa may have a congenital deformation. Such deformations, especially along a rim of the glenoid fossa may lead to instability and dislocation of the shoulder joint. In some cases, the patient’s humeral head is medially displaced as bone loss on a rim of the patient’s glenoid fossa progresses. In many cases, the bone loss is asymmetric. For instance, bone loss may be greatest along an anterior, posterior, inferior, or superior rim of the glenoid fossa. The areas and amounts of bone loss differ among individual patients.

[0042] Since patients have differently shaped glenoid fossae, the shape of an augment element of a glenoid prosthesis may be specific to the patient. In other words, a bone-facing surface of the augment element may have a negative geometry of a corresponding part of the scapula. In this way, the bone-facing surface of the augment element may mate with the corresponding part of the scapula. By matching the surface of the scapula in this way, the bone-facing surface of the augment element may fit flush with the corresponding part of the scapula.

[0043] As mentioned above, planning system 118 may output a user interface for display that shows a virtual prosthesis model relative to a virtual bone model. Planning system 118 may receive indications of user input to position the baseplate of the glenoid prosthesis relative to the virtual bone model of the patient’s scapula. Planning system 118 may determine a shape of the augment element based on a space between the baseplate and the patient’s scapula. For instance, planning system 118 may determine the shape of the augment element by performing a Boolean subtraction of the scapula from a virtual cylinder extending from the virtual baseplate. In another example, planning system 118 may determine the shape of the augment element by projecting rays from points on the virtual baseplate toward the virtual scapula and determining points of intersection of the rays with the virtual scapula.

[0044] An envelope for a surgery defines limitations on the range of values of parameters of the surgery. For instance, the envelope may define a maximum allowable inclination / declination of the glenoid prosthesis, a maximum allowable version / anteversion of the glenoid prosthesis, a maximum and minimum lateralization / medialization of the glenoid prosthesis, and so on. The envelope may also define limitations on the size of the augment element. For instance, the envelope may specify a maximum thickness of the augment element. Thickness may be defined in a direction perpendicular to a plane of the baseplate. The maximum thickness limitation on the augment may exist because the structural integrity of the augment element may decrease with greater thickness, especially if the augment elementincludes one or more relatively thin protrusions. For example, if the face of the glenoid fossa and the posterior rim of the glenoid fossa are severely eroded, the augment element may extend a significant distance towards the medial border of the scapula. In this example, the posterior side of the augment element may become progressively thinner and weaker toward the medial end of the augment element. In some cases of severe deformity, limiting the thickness of the augment element to the maximum thickness may result in an augment element that does not provide sufficient support for the glenoid prosthesis. Additionally, the envelope may define a minimum thickness of the augment element.

[0045] In accordance with one or more techniques of this disclosure, planning system 118 allows the user to plan a TSA in which a bone-facing surface of the glenoid prosthesis has a native-facing portion and a modified-facing portion. The native-facing portion is shaped to match an unmodified bone surface of the scapula, and the modified-facing portion is shaped to match a modified bone surface of the scapula. The modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at a preoperatively planned implantation position. The preoperatively planned implantation position may be selected by the user of planning system 118. In some examples, the modified bone surface at least partially contacts the glenoid prosthesis after implantation of the glenoid prosthesis at the position. The unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the position.

[0046] A bone-facing surface of an augment element of the glenoid prosthesis includes the native-facing portion of the bone-facing surface of the glenoid prosthesis. In some examples, the bone-facing surface of the augment element also includes at least part of the modified- facing portion of the glenoid prosthesis. Thus, in such examples, a baseplate-facing surface of the augment element may occupy an entire area of the bone-facing surface of the baseplate. In other examples, a bone-facing surface of the baseplate includes the modified-facing portion of the bone-facing surface of the glenoid prosthesis. Thus, in such examples, a baseplate-facing surface of the augment element does not occupy the entire area of the bone-facing surface of the baseplate.

[0047] The surgeon may modify the shape of the scapula to reduce the lateralization of the bone-facing surface of the baseplate. Reducing the lateralization of the bone-facing surface of the baseplate may reduce the thickness of the augment element, allowing the thickness of the augment element to remain within the limitations defined in the surgical envelope. Modifyingthe shape of the scapula may involve removing an area on or near a rim of the glenoid fossa. For instance, if there is severe erosion on the posterior area of the glenoid fossa, the surgeon may remove an area on the anterior area of the glenoid fossa. The surgeon may use one or more tools to modify the shape of the scapula. For example, the surgeon may modify the shape of the bone using a cutting burr, an osteotome, rongeurs, a saw, or another type of tool.

[0048] In some examples, the surgeon may modify the scapula to remove osteophytes from glenoid fossa. If the osteophytes were allowed to remain, the augment element may need to have greater thickness in order to accommodate the osteophytes. For example, an osteophyte may extend laterally from an area of the scapula that is close to the desired position of the baseplate. In this example, the baseplate would have to be more lateral than the desired position so that the osteophyte could be accommodated within an indentation of the augment element.

[0049] In some examples where the surgeon modifies the scapula, the surgeon may select a thicker baseplate or a differently sized articulating surface to compensate for the modification to the scapula. For example, planning system 118 may automatically recommend one or more parameters of the baseplate and / or articulating element based on the selected position of the glenoid prosthesis. In other words, planning system 118 may determine, based on the planned implantation position, one or more parameters of the articulation element or the baseplate.

[0050] In some examples of automatically recommending one or more parameters of the baseplate and / or articulating element, planning system 118 performs a bony impingement analysis. The bony impingement analysis involves determining collision points and associated ranges of motion between the collision points. The collision points are points at which the humeral bone and prosthesis models collide with the scapula bone model / glenoid prosthesis model when the humeral bone model and humeral prosthesis model are virtually moved relative to the scapular bone model and the glenoid prosthesis model. Detecting a collision may involve evaluating whether a point (e.g., a vertex) of the humeral bone model or humeral prosthesis model is within or beyond a plane (e.g., face) defined between a set of points (e.g., vertexes) of the scapula bone model / glenoid prosthesis model. Planning system 118 may virtually move the humeral bone and prosthesis models relative to the scapular bone model and glenoid prosthesis model by calculating updated 3-dimensional positions of vertices that make up the models according to standard affine motion equations. If the determined ranges of motion are insufficient, planning system 118 may repeat the bony impingement analysis with different combinations of parameters of the baseplate and / or articulating element. For instance, planning system 118 may repeat the bony impingement analysis with differently sized baseplates, different articulation element eccentricities, different positions, and so on. Planning system 118may continue to repeat the bony impingement analysis until a combination of parameters of the baseplate and / or articulating element is identified that achieve one or more stopping conditions. Such stopping conditions may include acceptable ranges of motion, avoiding collisions that lead to scapular notching, and so on. In some examples, planning system 118 may use a Nelder-Mead optimization algorithm to explore the combinations of parameters. Planning system 118 may recommend parameters of the identified combination.

[0051] In one example, the available baseplates may include a baseplate having a 25-millimeter (mm) diameter and a baseplate having a 29-mm diameter. In this example, the 29-mm baseplate may be initially selected. However, if the geometry of the patient’s scapula does not allow the surgeon to place the baseplate inferiorly enough on the glenoid fossa to satisfy the surgeon, e.g., due to risk of scapular notching, planning system 118 may perform automatically recommend use of the 25-mm baseplate, which would allow the center of the baseplate to be positioned 2 mm more inferior. Scapular notching may occur following a reverse total shoulder arthroplasty when a medial margin of the articulation element of the humeral prosthesis repeatedly collides with the patient’s scapula.

[0052] In other examples, planning system 118 uses a trained machine learning model to recommend parameters of the baseplate and / or articulation element. For example, planning system 118 may use a trained machine learning model that generates a point cloud representing a recommended baseplate and / or articulation element, e.g., as described in Patent Cooperation Treaty (PCT) publication WO 2023 / 172621, the entire content of which is incorporated by reference.

[0053] After the surgeon has selected a desired position of the baseplate and planning system 118 has determined the bone-facing surface of the patient-specific glenoid prosthesis, planning system 118 may output manufacturing data. The manufacturing data may indicate the size and type of the baseplate, the size and type of the articulation element, and a shape of the augment element. Manufacturing system 104 may use the manufacturing data to obtain and fabricate components of the patient-specific glenoid prosthesis. For example, manufacturing system 104 may use an additive manufacturing process to form the augment element on the baseplate. In other examples, manufacturing system 104 uses a system that cuts down a larger piece of material to form the augment element. In some examples, a mesh may be used to represent the shape of the augment element. Manufacturing system 104 may be configured to form the augment element based on coordinates of vertices in the mesh with high accuracy. Thus, the techniques of this disclosure may enable the manufacture of patient-specific augment elements that are closely match the patient’s scapula, including modified and unmodified bone surfaces.

[0054] In some examples, planning system 118 generates a physical patient-specific guide that helps the surgeon insert a central guide pin (e.g., a guide wire) into the patient’s glenoid fossa at a location and orientation specified using planning system 118. The surgeon may insert a cannulated drill bit over the central guide pin to form a hole for the central post of the glenoid prosthesis. The surgeon removes the central guide pin after the central post is formed. In some examples, the patient-specific guide helps the surgeon insert a rotational alignment pin into the patient’s scapula. The rotational alignment pin may interact with a notch or hole of the glenoid prosthesis and / or insertion tool to ensure that the glenoid prosthesis is attached to the scapula at the correct rotational alignment.

[0055] The patient-specific guide may include a plurality of patient-specific bone-contacting surfaces. The bone-contacting surfaces of the patient-specific guide may conform to the surface of the patient’s bone. In some examples, the patient-specific guide is used prior to modifying the scapula to allow implantation of the patient-specific glenoid prosthesis at a planned implantation position. Accordingly, the bone-contacting surfaces of the patient-specific guide may conform to unmodified areas of the scapula, even if the surgeon eventually modifies one or more of those areas to allow for implantation of the patient-specific glenoid prosthesis. In general, having the bone-contacting surfaces of the guide conform the patient-specific guide conform to the unmodified areas of the scapula may allow for more secure and accurate placement of the patient-specific guide.

[0056] Alternatively, the bone-contacting surfaces of the patient-specific guide may include one or more bone-contacting surfaces designed to conform to areas of the patient’s scapula that were modified to allow for implantation of the patient-specific glenoid prosthesis and bone- contacting surfaces designed to conform to one or more unmodified surfaces of the patient’s scapula. In such examples, the guide may only sit properly on the patient’s scapula if the patient’s scapula has been modified according to the preoperative plan. Thus, the surgeon may repeatedly use the patient-specific guide during the surgery to test whether enough bone tissue has been removed. In some examples, two patient-specific guides may be fabricated, one of which has bone-contacting surfaces designed to conform to areas of the patient’s scapula that will later be modified and one of which has bone-contacting surfaces designed to conform to modified surfaces of the patient’s scapula. In some examples, manufacturing system 104 manufactures the patient-specific guide.

[0057] In some examples, a mixed reality (MR) visualization device 120 presents a mixed reality visualization to the surgeon (or other user) to guide the surgeon on insertion of the central guide pin and / or rotational alignment pin. In some examples, MR visualization device120 includes a see-through display that allows the surgeon to see virtual elements in addition to directly seeing real world objects through the see-through display. Microsoft HOLOLENS ™ is an example of such an MR visualization device. In some examples, MR visualization device 120 includes an opaque display that allows the surgeon to see virtual elements superimposed on images of the real world captured by one or more cameras. Apple VISION PRO ™ is an example of such an MR visualization device. Thus, MR visualization device 120 may also be characterized as an Augmented Reality (AR) visualization device. In this disclosure, MR is to be understood to encompass AR.

[0058] In some examples where MR visualization device 120 is used, MR visualization device 120 may display virtual elements that guide the surgeon with respect to areas of the scapula to modify to allow implantation of the patient-specific implant at the planned implantation position. For instance, MR visualization device 120 may display a virtual element that outlines or highlights the area of the scapula to remove. A system (e.g., planning system 118, visualization device 120, etc.) may generate the virtual element based on a virtual scapula model (e.g., a 3D mesh) that represents one or more portions of the scapula, such as a modified bone surface of the scapula and / or an unmodified bone surface of the scapula. In some examples, MR visualization device 120 provides real-time feedback to the user to indicate locations of areas to remove. For instance, MR visualization device 120 may overlay a color map on the scapula with colors corresponding to depths of bone tissue to remove. The colors may be determined based on distances between vertices of 3D meshes representing a native bone surface of the scapula and a modified bone surface of the scapula. MR visualization device 120 may update the color map in real time as the surgeon removes bone tissue. In some examples, the surgeon removes the bone tissue using uses a tool that has an attached optical marker. A tracking system (e.g., MR visualization device 120 or another device) may track the position and orientation of the optical marker. Since a tip of the tool is at a known position relative to the optical marker, the tracking system may determine the position of the tip of the tool and therefore how much bone tissue has been removed. The use of mixed reality in this way may increase the accuracy with which the user is able to reshape the scapula for implantation of the patient-specific glenoid prosthesis.

[0059] In some examples, conventional monitors display guidance to the user on removal of bone tissue. For example, one or more display screens may be positioned within the operating room and may be configured to display intra-operative guidance on removal of the bone tissue.

[0060] FIG.2 is a conceptual diagram illustrating an example user interface 200 for positioning a glenoid prosthesis in accordance with one or more techniques of this disclosure. Planningsystem 118 may output user interface 200 for display to a user. User interface 200 includes windows 202A – 202D. In the example of FIG.2, window 202A shows a first 3D representation of a glenoid prosthesis 204 at a position relative to a 3D representation of a scapula 206 along an anterior-to-posterior axis. Window 202B shows a second 3D representation of glenoid prosthesis 204 at the same position relative to 3D virtual bone model of scapula 206 as window 202A but along a lateral-to-medial axis. Window 202C shows a 2D representation of the position of glenoid prosthesis 204 relative to a 2D representation of scapula 206 (e.g., a 2D slice of CT data) in a transverse plane (i.e., along a superior-inferior axis). Window 202D shows a 2D representation of the position of glenoid prosthesis 204 relative to a 2D representation of scapula 206 (e.g., a 2D slice of CT data) in a frontal plane (i.e., along an anterior-to-posterior axis). In some examples, planning system 118 may rotate the views in windows 202A or 202B in response to receiving indications of user input. In some examples, planning system 118 may change the level of the slices shown in windows 202C and 202D in response to receiving indications of user input.

[0061] Glenoid prosthesis 204 includes a baseplate 208, an articulation element 210, and an augment element 212. In the example of FIG. 2, baseplate 208 includes a central post 214. In other examples, central post 214 is a part of augment element 212. As seen in windows 202A, 202C, and 202D, a medial tip of central post 214 extends through a medial surface of scapula 206. As seen in window 202B, baseplate 208 defines a set of screw holes 216.

[0062] Furthermore, window 202B shows a modified area 218 of scapula 206 and an unmodified area 220 of scapula. Modified area 218 is an area of scapula 206 that will be modified during the surgery to implant glenoid prosthesis 204. Modified area 218 includes a modified bone surface 222 that will result from modification of scapula 206 during the surgery to allow implantation of glenoid prosthesis 204 at the planned implantation position. In some examples, modified bone surface 222 at least partially contacts glenoid prosthesis 204 after implantation of glenoid prosthesis 204. In some examples, all of modified bone surface 222 contacts glenoid prosthesis 204 after implantation of glenoid prosthesis 204. In other examples, such as the example of FIG. 3A (which is described in greater detail below) a portion of a modified bone surface does not contact the glenoid prosthesis. Furthermore, in some examples, no portion of the modified bone surface contacts the glenoid prosthesis. For instance, in such examples, an area of the rim of the glenoid fossa of the scapula may be removed to make room of an articulation element of the glenoid prosthesis, but the resulting modified bone surface does not actually contact the articulation element. Unmodified area 220 is an area of scapula 206 that will not be modified during the surgery to implant glenoid prosthesis 204 at theposition. Unmodified area 220 includes an unmodified bone surface 224 of scapula 206 that will contact glenoid prosthesis 204 after implantation of glenoid prosthesis 204 and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the position.

[0063] A user can observe from windows 202A – 202D that the bone-facing surface of glenoid prosthesis 204 includes a native-facing portion 226 and a modified-facing portion 228. The native-facing portion 226 is shaped to conform to unmodified bone surface 224 of scapula 206. Modified-facing portion 228 may be shaped to conform to modified bone surface 222.

[0064] FIG.3A is a conceptual diagram illustrating an example user interface 300 shown a 3D model of a patient’s scapula 302 and a 3D model of a glenoid prosthesis 304 in accordance with one or more techniques of this disclosure. Glenoid prosthesis 304 includes a baseplate 306, an articulation element 308, and an augment element 310. Planning system 118 may display augment element 310 differently depending on whether the bone-facing surface of augment element 310 is able to make full contact with scapula 302, given the selected position of glenoid prosthesis 304 and the limitations of the surgical envelope. For example, planning system 118 may display augment element 310 in red or blue, depending on whether the bone- facing surface of augment element 310 is able to make full contact with scapula 302, given the selected position of glenoid prosthesis 304 and the limitations of the surgical envelope.

[0065] Planning system 118 may determine one or more regions of the scapula to remove to achieve the modified bone surface. Planning system 118 may output, in the user interface, an indication of the one or more regions of the scapula to remove to achieve the modified bone surface. For example, FIG. 3A also shows an outline 312 indicating an area of scapula 302 to remove to allow implantation of glenoid prosthesis 304 at the planned implantation position. Planning system 118 may determine the regions of the scapula to remove to achieve the modified bone surface in one of a variety of ways. For instance, planning system 118 may determine the region of the scapula to remove as an area of the scapula that is lateral to a bone- facing side of the baseplate at the specific position of the patient-specific glenoid prosthesis.

[0066] FIG. 3B is a conceptual diagram illustrating an example user interface 340 showing a 3D model of a patient’s scapula 342 and a 3D model of a glenoid prosthesis 344 in accordance with one or more techniques of this disclosure. In the example of FIG.3B, a line 346 indicates an area of scapula 342 to be removed given the current position of glenoid prosthesis 344.

[0067] FIG.3C is a conceptual diagram illustrating a user interface 360 that includes controls for adjusting a planned implantation position of a glenoid prosthesis 362 on a scapula 368 in accordance with one or more techniques of this disclosure. User interface 360 includes window 364 and window 366. Window 364 shows a representation of glenoid prosthesis 362 and a CTslice of a patient’s scapula 368 and humerus 370 from a superior-to-inferior perspective. Window 366 shows a representation of glenoid prosthesis 362 and a CT slice of the patient’s scapula 368 and humerus 370 from an anterior-to-posterior perspective.

[0068] As shown in window 364, glenoid prosthesis 362 includes a baseplate 372, an articulation element 374, and an augment element 376. Planning system 118 may display augment element 376 differently depending on whether the bone-facing surface of augment element 376 is able to make full contact with scapula 368, given the selected position of glenoid prosthesis 362 and the limitations of the surgical envelope. For example, planning system 118 may display augment element 376 in red or blue, depending on whether the bone-facing surface of augment element 376 is able to make full contact with scapula 368, given the selected position of glenoid prosthesis 362 and the limitations of the surgical envelope. In the example of FIG. 3C, the bone-facing surface of augment element 376 is not able to make full contact with scapula 368 in area 378. Hence, the surgeon may want to remove bone tissue in order to allow implantation of glenoid prosthesis 362 at the planned implantation position.

[0069] In some examples, planning system 118 may determine that a depth measure exceeds a predefined depth threshold. The depth measure may be a length of a virtual line orthogonal to a bone-facing side of baseplate 372 from the bone-facing side of baseplate 372 to a closest point on scapula 368. Based on the determination that the depth measure exceeds the predefined depth threshold, planning system 118 may determine that the augment exceeds the depth limit of the envelope (and therefore a gap, such as area 378, exists). Accordingly, in some examples, based on the determination that the depth measure exceeds the predefined depth threshold, planning system 118 may output a warning for display on the display device (e.g., display device 112).

[0070] User interface 360 also includes controls 380 for controlling an orientation of glenoid prosthesis 362. Thus, planning system 118 may update the superior, inferior, anterior, or posterior orientation of glenoid prosthesis 362 in response to receiving indications of user input to controls 380. User interface 360 includes controls 382 for adjusting an anterior / posterior position of glenoid prosthesis 362, controls 384 for adjusting a medial / lateral position of glenoid prosthesis 362, and controls 386 for adjusting a superior / inferior position of glenoid prosthesis 362. Thus, planning system 118 may update the position of glenoid prosthesis 362 in response to receiving indications of user input to controls 382, 384, and 386.

[0071] FIG. 4 is a conceptual diagram illustrating an example user interface 400 of planning system 118 that allows a user to control whether planning system 118 is able to plan a surgery that involves manual bone preparation for a patient-specific glenoid prosthesis, in accordancewith one or more techniques of this disclosure. Specifically, user interface 400 includes a toggle element 402 that enables and disables planning of a surgery that involves manual bone preparation for a patient-specific glenoid prosthesis. Manual bone preparation involves modifying a portion of the scapula. If manual bone preparation is disabled, planning system 118 may prevent the user from positioning the glenoid prosthesis at a position that would require modification of the scapula. Thus, planning system 118 may output, for display on a display device, a user interface feature (e.g., toggle element 402) that enables and disables an ability of the surgical planning system 118 to plan a total shoulder replacement surgery that involves modification of the scapula to allow implantation of patient-specific glenoid prostheses having bone-facing surfaces that have native-facing portions and modified-facing portions. Based on the ability being enabled, planning system 118 may be allowed to adjust the planned implantation position of the patient-specific glenoid prosthesis to a position at which modification of the scapula is required to allow implantation of the glenoid prosthesis at the planned implantation positions.

[0072] User interface 400 also includes features 404 that enable the user to select various surgical parameters. For instance, in the example of FIG. 4, features 404 enable the user to select a surgery type (e.g., anatomical or reverse), an implant type (e.g., a family of prostheses) a baseplate diameter, a post type (e.g., centered, offset), a post length, a glenosphere diameter, and a glenosphere type (e.g., centered, eccentric).

[0073] Additionally, user interface 400 includes information elements 406 that provide information to the user. In the example of FIG. 4, information elements 406 indicate a post engagement length and an augment thickness. The post engagement length indicates a length of the post that is engaged with the scapula. The augment thickness indicates a maximum thickness of the augment element. Information elements 406 also include an element indicating whether the surgery involves glenoid reaming.

[0074] User interface 400 also includes a window 408 showing glenoid prosthesis 204 and scapula 206. In FIG. 4, an outline 410 surrounding the modified bone surface 224 is shown. User interface 400 also includes a button 412 to instruct planning system 118 to compute a shape of the augment element.

[0075] As mentioned above, planning system 118 may compute a patient-specific surgical guide. Planning system 118 may output manufacturing data that enable manufacturing system 104 to fabricate the patient-specific surgical guide. Manufacturing system 104 may use an additive manufacturing process (e.g., 3D printing) to fabricate the patient-specific guide. In other examples, manufacturing system 104 may use a process that cuts down a block of materialto fabricate the patient-specific guide. The patient-specific surgical guide has a central lumen that guides installation of a guide pin (e.g., guide wire) into the face of the glenoid fossa. The surgeon may use a cannulated drill bit fitted over the guide pin to drill a hole into the scapula. A central fixation peg of the glenoid prosthesis is inserted into the hole. The surgical guide may also include a lumen that guides installation of a rotational alignment pin into a location on the scapula within the face of the glenoid fossa or the rim of the glenoid fossa. The rotational alignment pin engages a notch on an outer rim of the glenoid prosthesis and a notch in a prosthesis insertion tool to ensure that the glenoid prosthesis has the correction rotational alignment relative to the scapula when the surgeon is installing the glenoid prosthesis.

[0076] As part of the process of planning the surgery, a surgeon may choose four different points on the edge of the glenoid fossa. These points will establish the position of the feet of the guide. FIG. 5 is a conceptual diagram illustrating an example user interface 500 for selecting the positions of feet of a patient-specific surgical guide. User interface 500 includes a patient-specific 3D model of a patient’s scapula 502. Planning system 118 may receive indications of user input to select locations 504 on the rim of the glenoid fossa of scapula 502. In the example of FIG.5, the user selects the locations on unmodified areas of scapula 502. In FIG.5, one of locations 504 is on the posterior part of the glenoid fossa and three points are on the anterior part of the glenoid fossa. In other examples, the surgeon may choose different locations for the points, but would generally avoid the lower posterior area because retractors are typically used in that area to hold back soft tissue overlaying the shoulder. Thus, the points of contact of the feet are on the glenoid rim, e.g., on the anterior and posterior part of the glenoid fossa.

[0077] Planning system 118 may also indicate a location 506 of a rotational alignment hole or rotational alignment pin. The rotational alignment hole is located within the anterior-superior quadrant. Orientation of the rotational alignment hole may change slightly depending upon the rotation of the planned glenoid prosthesis.

[0078] FIG. 6A is a conceptual diagram illustrating an example user interface 600 showing a model of a patient-specific guide 602 positioned on a patient-specific model of a scapula 604, in accordance with one or more techniques of this disclosure. Planning system 118 may automatically compute patient-specific guide 602 based on the selected points (see FIG.5). In some examples, planning system 118 computes patient-specific guide 602 based on previous surgical planning. Patient-specific guide 602 is not reusable.

[0079] In addition to receiving input to indicate the selected points on the glenoid rim, a central location on the glenoid is identified (e.g., by the surgeon, planning system 118 software, or acombination thereof). A trajectory of a pin to enter the glenoid at the central point is also identified (e.g., by the surgeon, planning system 118, or a combination thereof), e.g., using controls 380 (FIG.3C).

[0080] After the points on the glenoid rim, the central point, and the rotational alignment hole are selected, planning system 118 may project these points from the scapular surface to an imaginary plane situated generally parallel to the glenoid face. In particular, the guide includes the plurality of feet 606 that couple along the rim of the glenoid fossa. On the bone-facing side of each of feet 606, the surface is a negative of the surface of the glenoid where the foot is to contact to scapula 604. This way, the foot contacts to the glenoid without having gaps. On the other end of each foot (i.e., non-bone-facing side), each foot is connected to a ring 608. In some cases, spokes 610 connect one or more of feet 606 to ring 608. Stated another way, patient- specific guide 602 forms a hub-and-spoke configuration, where the hub forms ring 608, and each spoke couples to a foot. The bone-facing surfaces of spokes 610 may or may not touch scapula 604. In some examples, one or more of feet 606 may be positioned on modified areas of the glenoid rim and one or more of the feet may be positioned on the native, unmodified area of the glenoid rim. In other examples, each of feet 606 are positioned on unmodified areas of the glenoid rim.

[0081] In FIG. 6A, the bone-facing side of ring 608 has a surface that is a negative of the surface of the glenoid fossa where ring 608 touches scapula 604. This way, ring 608 attaches to the glenoid cavity without having gaps. Accordingly, patient-specific guide 602 is patient- specific to glenoid fossa and rim of glenoid fossa, and attaches to scapula 604 with minimal gaps. The arc-shaped area within ring 608 and surrounding a structure 612 encircling a central lumen 614 allows the surgeon to see the surface of the glenoid bone.

[0082] A first structure 612 defines a central lumen 614 through which a central pin is inserted. A second structure 616 defines a rotational alignment lumen 618 through which a rotational alignment pin is inserted. In some examples, the bone-facing sides of structures 612, 616 are not patient specific, are generally flat, and do not contact scapula 604. This may allow the surgeon to see the contact points of pins onto scapula 604 prior to drilling the pins into scapula 604 and may allow bone debris to exit scapula.

[0083] FIG.6B is a conceptual diagram illustrating an example patient-specific guide 652 from a medial-to-lateral perspective, in accordance with one or more techniques of this disclosure. Similar to patient-specific guide 602, patient-specific guide 652 includes a plurality of feet 656A – 656D (collectively, “feet 656”), a ring 658, a structure 662 that defines a central lumen 664, a second structure 666 that defines a rotational alignment lumen 668. Patient-specificguide 652 includes patient-specific modified bone contact surfaces 670 that are shaped to conform to respective modified guide contact surfaces of the scapula. Patient-specific guide 652 also includes patient-specific unmodified bone contact surfaces 672 that are shaped to conform to respective unmodified guide contact surfaces of the scapula.

[0084] Thus, planning system 118 may generate a model of a patient-specific guide 602, where patient-specific guide 602 defines a central lumen 614 configured to guide a guidewire into scapula 604 at a preoperatively planned position on scapula 604 and at a preoperatively planned orientation. The model of patient-specific guide 602 may include a mesh comprising vertices, edges, and faces. Patient-specific guide 602 includes one or more patient-specific unmodified bone contact surfaces (e.g., patient-specific unmodified bone contact surfaces 672 in FIG.6B) that are shaped to conform to respective unmodified guide contact surfaces of the scapula. Each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of patient-specific guide 602 and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis. Planning system 118 may output manufacturing data that enables manufacturing system 104 to fabricate patient-specific guide 602. The manufacturing data may include mesh data representing patient-specific guide 602. In some examples, patient-specific guide 602 further includes one or more patient-specific modified bone contact surfaces (e.g., patient-specific modified bone contact surfaces 670 in FIG. 6B) shaped to conform to respective modified guide contact surfaces of the scapula. Each of the modified guide contact surfaces is a surface of the scapula that will contact one of the patient-specific modified bone contact surfaces of patient-specific guide 602 and will be intra-operatively modified during the surgery to implant the glenoid prosthesis. The modified bone surfaces of the scapula may include, but are not necessarily limited to, the modified guide contact surfaces of the scapula, and vice versa. In some examples, the surgeon may determine that the modified bone surface has been formed when each of the patient-specific unmodified bone contact surfaces of patient-specific guide 602 are flush with the unmodified guide contact surfaces of the scapula and each of patient-specific modified bone contact surfaces of patient-specific guide 602 are flush with the modified guide contact surfaces of the scapula.

[0085] The baseplate and augment element of a patient-specific glenoid prosthesis define holes through which a surgeon passes fixation screws into the patient’s scapula. The fixation screws hold the glenoid prosthesis into the scapula. As mentioned above, the guide includes a rotational alignment lumen 618 that guides insertion of a rotational alignment pin. The rotational alignment pin may help to prevent the glenoid prosthesis from rotating relative toscapula while the glenoid prosthesis is being installed onto the scapula, including while the surgeon is drilling holes for the fixation screws and installing the fixation screws.

[0086] In examples where the rotational alignment pin remains in the scapula during this process, the rotational alignment pin should not align with any of the screw holes (i.e., holes created in the scapula for the fixation screws). Planning system 118 allows the surgeon to select positions of the screw holes. After the surgical planning system receives the selection of the positions of the screw holes, the surgical planning system automatically determines a position of the rotational alignment hole of the guide in order to avoid the screw holes. In other words, planning system 118 may automatically select a position on the outer rim of the central ring (e.g., ring 608) of the patient-specific guide so that the rotational alignment pin does not interfere with the screw holes.

[0087] In some examples, planning system 118 computes multiple patient-specific surgical guides. The patient-specific guides may be similar in general shape and function to those of FIG. 6A and FIG. 6B. However, the bone contact surfaces of a first patient-specific guide are shaped to conform to the native, unmodified guide contact surfaces of the scapula and do not include any bone contact surfaces that conform to modified guide contact surfaces of the scapula. A surgeon may use this first patient-specific guide during surgery before modifying the shape of the scapula, e.g., to place one or more guide pins, holes, or marks. A second patient-specific guide may have patient-specific modified and unmodified bone contact surfaces, e.g., as described above with respect to FIG. 6A and FIG. 6B. The surgeon may use the second patient-specific guide to verify proper bone removal and / or perform other surgical tasks. Use of the first patient-specific guide may lead to greater accuracy and stability while inserting the guide pins, drilling holes, etc., than would be possible with just the second patient- specific guide. The use of the second patient-specific guide may enable verification of proper bone modification.

[0088] FIG. 7 is a flowchart illustrating an example operation of planning system 118 in accordance with one or more techniques of this disclosure. In the example of FIG.7, planning system 118 may output, for display on display device 112, a user interface of planning system 118, where the user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient (700). The glenoid prosthesis may comprise a baseplate, an articulation element, and an augment element. The articulation element and the augment element are configured to be attached to opposite sides of the baseplate. The articulation element comprises an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide. The augment element may be configuredto occupy a space between the scapula and the baseplate. A native-facing portion of the glenoid prosthesis may include a native-facing surface of the augment element that has a patient- specific shape that conforms to the unmodified bone surface of the scapula. Furthermore, in some examples, the bone-facing surface of the augment element is further shaped to conform to the modified bone surface of the scapula. In other examples, a portion of the baseplate is configured to contact the modified bone surface of the scapula after implantation of the glenoid prosthesis at the planned implantation position.

[0089] Planning system 118 may adjust the planned implantation position based on indications of user input to adjust the planned implantation position (702). For instance, planning system 118 may receive an indication of user input to adjust the planned implantation position via controls 380, 382, 384, 386 (FIG.3C).

[0090] Planning system 118 may determine a bone-facing surface of the patient-specific glenoid prosthesis where the bone-facing surface of the patient-specific glenoid prosthesis having a native-facing portion and a modified-facing portion (704). In other words, planning system 118 may generate a shape of a bone-facing surface of the glenoid prosthesis. The native- facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula. The modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position. In some examples, at least part of the modified bone surface contacts the glenoid prosthesis after implantation of the glenoid prosthesis at the planned implantation position. The modified bone surface may result from modification of at least a portion of the glenoid rim or glenoid face. In some examples, the modified bone surface may result from removal of one or more osteophytes. In this disclosure, the term modified prosthesis contact surface (or modified bone surface) applies with respect to areas other than fixation holes (e.g., for a peg, keel, screws, etc.). The unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position. Determining the bone-facing surface of the patient-specific glenoid prosthesis may include determining the shape of the bone-facing surface of the patient-specific glenoid prosthesis. For example, planning system 118 may generate a 3D mesh representing the bone-facing surface of the patient-specific glenoid prosthesis. In some examples, planning system 118 generates a point cloud representing a volume of the augment element.

[0091] In some examples, after determining the bone-facing surface of the patient-specific glenoid prosthesis, planning system 118 may output manufacturing data that enables manufacturing system 104 to fabricate the patient-specific glenoid prosthesis. The manufacturing data may indicate the size and type of the baseplate, the size and type of the articulation element, and a shape of the augment element. Manufacturing system 104 may use the manufacturing data to obtain and fabricate components of the patient-specific glenoid prosthesis. In some examples, planning system 118 may provide intra-operative guidance to a surgeon to form the modified bone surface.

[0092] The following is a non-limiting list of clauses in accordance with one or more techniques of this disclosure.

[0093] Clause 1. A method comprising: outputting, by one or more processors implemented in circuitry, for display on a display device, a user interface of a surgical planning system, wherein the user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient; adjusting, by the one or more processors, the planned implantation position based on indications of user input to adjust the planned implantation position; and generating, by the one or more processors, a shape of a bone-facing surface of the glenoid prosthesis, the bone-facing surface of the glenoid prosthesis having a native-facing portion and a modified-facing portion, wherein the native- facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion faces at least a portion of a modified bone surface of the scapula, wherein: the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position.

[0094] Clause 2. The method of clause 1, wherein: the glenoid prosthesis comprises a baseplate, an articulation element, and an augment element, the articulation element and the augment element are configured to be attached to opposite sides of the baseplate, the articulation element comprising an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide, the augment element is configured to occupy a space between the scapula and the baseplate, and the native-facing portion of the glenoid prosthesis includes a native-facing surface of the augment element that has a patient-specific shape that conforms to the unmodified bone surface of the scapula.

[0095] Clause 3. The method of clause 2, wherein the modified-facing portion of the glenoid prosthesis includes a modified-facing surface of the augment element that has a patient-specific shape that conforms to the modified bone surface of the scapula.

[0096] Clause 4. The method of any of clauses 2-3, wherein a portion of the baseplate is configured to contact the modified bone surface of the scapula after implantation of the glenoid prosthesis at the planned implantation position.

[0097] Clause 5. The method of any of clauses 2-4, further comprising: determining, by the one or more processors, that a depth measure exceeds a predefined depth threshold, the depth measure being a length of a virtual line orthogonal to a bone-facing side of the baseplate from the bone-facing side of the baseplate to a closest point on the scapula; and based on the determination that the depth measure exceeds the predefined depth threshold, outputting, by the one or more processors, a warning for display on the display device.

[0098] Clause 6. The method of any of clauses 2-5, further comprising determining, by the one or more processors, based on the planned implantation position, one or more parameters of the articulation element or the baseplate.

[0099] Clause 7. The method of any of clauses 1-6, wherein the modified bone surface of the scapula results at least in part from modification of a portion of a glenoid rim of the scapula.

[0100] Clause 8. The method of any of clauses 1-7, wherein the modified bone surface of the scapula results at least in part from removal of one or more osteophytes.

[0101] Clause 9. The method of any of clauses 1-8, wherein the method further comprises: outputting, by the one or more processors, for display on the display device, a user interface feature that enables or disables an ability of the surgical planning system to plan a total shoulder replacement surgery that involves modification of the scapula to allow implantation of patient-specific glenoid prostheses having bone-facing surfaces that have native-facing portions and modified-facing portions; and based on the ability being enabled, allowing, by the one or more processors, the surgical planning system to adjust the planned implantation position of the glenoid prosthesis to a position at which modification of the scapula is required to allow implantation of the glenoid prosthesis at the planned implantation position.

[0102] Clause 10. The method of any of clauses 1-9, wherein: the method further comprises determining, by the one or more processors, one or more regions of the scapula to remove to achieve the modified bone surface, and outputting the user interface comprisesoutputting, by the one or more processors, in the user interface, an indication of the one or more regions of the scapula to remove to achieve the modified bone surface.

[0103] Clause 11. The method of any of clauses 1-10, further comprising: generating, by the one or more processors, a model of a patient-specific guide, wherein the patient-specific guide defines a lumen configured to guide a guidewire into the scapula at a preoperatively planned position on the scapula and at a preoperatively planned orientation, the patient- specific guide includes one or more patient-specific unmodified bone contact surfaces that are shaped to conform to respective unmodified guide contact surfaces of the scapula, wherein each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of the patient-specific guide and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis; and outputting, by the one or more processors, manufacturing data that enables a manufacturing system to fabricate the patient-specific guide.

[0104] Clause 12. The method of clause 11, further comprising fabricating the patient- specific guide based on the manufacturing data.

[0105] Clause 13. The method of any of clauses 11-12, wherein the patient-specific guide further includes one or more patient-specific modified bone contact surfaces shaped to conform to respective modified guide contact surfaces of the scapula, wherein each of the modified guide contact surfaces is a surface of the scapula that will contact one of the patient- specific modified bone contact surfaces of the patient-specific guide and will be intra- operatively modified during the surgery to implant the glenoid prosthesis.

[0106] Clause 14. The method of clause 13, wherein the modified bone surface has been formed when each of the patient-specific unmodified bone contact surfaces of the patient- specific guide is flush with the unmodified guide contact surfaces of the scapula and each of the patient-specific modified bone contact surfaces of the patient-specific guide is flush with the modified guide contact surfaces of the scapula.

[0107] Clause 15. The method of any of clauses 1-14, wherein the method further comprises providing, by the one or more processors, intra-operative guidance to a surgeon to form the modified bone surface.

[0108] Clause 16. The method of any of clauses 1-15, further comprising outputting, by the one or more processors, manufacturing data that enables a manufacturing system to fabricate the glenoid prosthesis.

[0109] Clause 17. The method of any of clauses 1-16, further comprising fabricating the glenoid prosthesis.

[0110] Clause 18. The method of any of clauses 1-17, wherein the modified-facing portion of the glenoid prosthesis contacts the portion of the modified bone surface after implantation of the glenoid prosthesis at the planned implantation position.

[0111] Clause 19. The method of clause 18, wherein the modified-facing portion of the glenoid prosthesis has a patient-specific shape that conforms to the portion of the modified bone surface of the scapula.

[0112] Clause 20. A system comprising: a memory; and one or more processors implemented in circuitry and communicatively coupled to the memory, the one or more processors configured to perform the methods of any of clauses 1 – 19.

[0113] Clause 21. The system of clause 20, further comprising a manufacturing system configured to fabricate a glenoid prosthesis or a patient-specific guide generated using the methods of any of clauses 1-19.

[0114] Clause 22. A non-transitory computer-readable medium having instructions stored thereon that, when executed by one or more processors of a computing system, cause the computing system to perform the methods of any of clauses 1 – 19.

[0115] Clause 23. A patient-specific glenoid prosthesis comprising: an articulation element comprising an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide, an augment element; and a baseplate, wherein:

[0116] the articulation element and the augment element are configured to be attached to opposite sides of the baseplate, the augment element is configured to occupy a space between a scapula of a patient and the baseplate, a bone-facing surface of the glenoid prosthesis has a native-facing portion and a modified-facing portion, the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula, the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to implant the glenoid prosthesis, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at a planned implantation position.

[0117] Clause 24. The patient-specific glenoid prosthesis of clause 23, wherein the native-facing portion of the glenoid prosthesis includes a native-facing portion of the augment element has a patient-specific shape that conforms to the unmodified bone surface of the scapula.

[0118] Clause 25. The patient-specific glenoid prosthesis of any of clauses 23-24, wherein the modified-facing portion of the glenoid prosthesis includes a modified-facing surface of the augment element that has a patient-specific shape that conforms to the modified bone surface of the scapula.

[0119] Clause 26. The patient-specific glenoid prosthesis of clause 25, wherein a portion of the baseplate is configured to contact the modified bone surface of the scapula after implantation of the glenoid prosthesis at the planned implantation position.

[0120] Clause 27. The patient-specific glenoid prosthesis of any of clauses 23-26, wherein the modified bone surface of the scapula results at least in part from modification of a portion of a glenoid rim of the scapula.

[0121] Clause 28. The patient-specific glenoid prosthesis of any of clauses 23-27, wherein the modified bone surface of the scapula results at least in part from removal of one or more osteophytes.

[0122] Clause 29. The patient-specific glenoid prosthesis of any of clauses 23-28, wherein the modified-facing portion of the glenoid prosthesis contacts the portion of the modified bone surface after implantation of the glenoid prosthesis at a planned implantation position.

[0123] Clause 30. A patient-specific guide comprising: a structure defining a lumen configured to guide a guide pin to a preoperatively planned location on a scapula of a patient at a preoperatively planned orientation; one or more patient-specific unmodified bone contact surfaces that are shaped to conform to respective unmodified guide contact surfaces of the scapula, wherein each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of the patient- specific guide and will not be intra-operatively modified during a surgery to implant a patient-specific glenoid prosthesis; and one or more patient-specific modified bone contact surfaces shaped to conform to respective modified guide contact surfaces of the scapula, wherein each of the modified guide contact surfaces is a surface of the scapula that will contact the one of the patient-specific modified bone contact surfaces of the patient-specific guide and will be intra-operatively modified during the surgery to implant the glenoid prosthesis.

[0124] While the techniques been disclosed with respect to a limited number of examples, those skilled in the art, having the benefit of this disclosure, will appreciate numerous modifications and variations there from. For instance, it is contemplated that any reasonable combination of the described examples may be performed. It is intended that the appendedclaims cover such modifications and variations as fall within the true spirit and scope of the invention.

[0125] It is to be recognized that depending on the example, certain acts or events of any of the techniques described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the techniques). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially.

[0126] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium and executed by a hardware-based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol. In this manner, computer-readable media generally may correspond to (1) tangible computer- readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave. Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and / or data structures for implementation of the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0127] By way of example, and not limitation, such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. It should be understood, however, that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0128] Operations described in this disclosure may be performed by one or more processors, which may be implemented as fixed-function processing circuits, programmable circuits, or combinations thereof, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Fixed-function circuits refer to circuits that provide particular functionality and are preset on the operations that can be performed. Programmable circuits refer to circuits that can programmed to perform various tasks and provide flexible functionality in the operations that can be performed. For instance, programmable circuits may execute instructions specified by software or firmware that cause the programmable circuits to operate in the manner defined by instructions of the software or firmware. Fixed-function circuits may execute software instructions (e.g., to receive parameters or output parameters), but the types of operations that the fixed-function circuits perform are generally immutable. Accordingly, the terms “processor” and “processing circuity,” as used herein may refer to any of the foregoing structures or any other structure suitable for implementation of the techniques described herein.

Claims

What is claimed is:

1. A method comprising: outputting, by one or more processors implemented in circuitry, for display on a display device, a user interface of a surgical planning system, wherein the user interface represents a patient-specific glenoid prosthesis at a planned implantation position on a scapula of a patient; adjusting, by the one or more processors, the planned implantation position based on indications of user input to adjust the planned implantation position; and generating, by the one or more processors, a shape of a bone-facing surface of the glenoid prosthesis, the bone-facing surface of the glenoid prosthesis having a native-facing portion and a modified-facing portion, wherein the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion faces at least a portion of a modified bone surface of the scapula, wherein: the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to allow implantation of the glenoid prosthesis at the planned implantation position, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at the planned implantation position.

2. The method of claim 1, wherein: the glenoid prosthesis comprises a baseplate, an articulation element, and an augment element, the articulation element and the augment element are configured to be attached to opposite sides of the baseplate, the articulation element comprising an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide, the augment element is configured to occupy a space between the scapula and the baseplate, and the native-facing portion of the glenoid prosthesis includes a native-facing surface of the augment element that has a patient-specific shape that conforms to the unmodified bone surface of the scapula.

3. The method of claim 2, wherein the modified-facing portion of the glenoid prosthesis includes a modified-facing surface of the augment element that has a patient-specific shape that conforms to the modified bone surface of the scapula.

4. The method of any of claims 2-3, wherein a portion of the baseplate is configured to contact the modified bone surface of the scapula after implantation of the glenoid prosthesis at the planned implantation position.

5. The method of any of claims 2-4, further comprising: determining, by the one or more processors, that a depth measure exceeds a predefined depth threshold, the depth measure being a length of a virtual line orthogonal to a bone-facing side of the baseplate from the bone-facing side of the baseplate to a closest point on the scapula; and based on the determination that the depth measure exceeds the predefined depth threshold, outputting, by the one or more processors, a warning for display on the display device.

6. The method of any of claims 2-5, further comprising determining, by the one or more processors, based on the planned implantation position, one or more parameters of the articulation element or the baseplate.

7. The method of any of claims 1-6, wherein the modified bone surface of the scapula results at least in part from modification of a portion of a glenoid rim of the scapula.

8. The method of any of claims 1-7, wherein the modified bone surface of the scapula results at least in part from removal of one or more osteophytes.

9. The method of any of claims 1-8, wherein the method further comprises: outputting, by the one or more processors, for display on the display device, a user interface feature that enables or disables an ability of the surgical planning system to plan a total shoulder replacement surgery that involves modification of the scapula to allow implantation of patient-specific glenoid prostheses having bone-facing surfaces that have native-facing portions and modified-facing portions; andbased on the ability being enabled, allowing, by the one or more processors, the surgical planning system to adjust the planned implantation position of the glenoid prosthesis to a position at which modification of the scapula is required to allow implantation of the glenoid prosthesis at the planned implantation position.

10. The method of any of claims 1-9, wherein: the method further comprises determining, by the one or more processors, one or more regions of the scapula to remove to achieve the modified bone surface, and outputting the user interface comprises outputting, by the one or more processors, in the user interface, an indication of the one or more regions of the scapula to remove to achieve the modified bone surface.

11. The method of any of claims 1-10, further comprising: generating, by the one or more processors, a model of a patient-specific guide, wherein the patient-specific guide defines a lumen configured to guide a guidewire into the scapula at a preoperatively planned position on the scapula and at a preoperatively planned orientation, the patient-specific guide includes one or more patient-specific unmodified bone contact surfaces that are shaped to conform to respective unmodified guide contact surfaces of the scapula, wherein each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of the patient-specific guide and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis; and outputting, by the one or more processors, manufacturing data that enables a manufacturing system to fabricate the patient-specific guide.

12. The method of claim 11, further comprising fabricating the patient-specific guide based on the manufacturing data.

13. The method of any of claims 11-12, wherein the patient-specific guide further includes one or more patient-specific modified bone contact surfaces shaped to conform to respective modified guide contact surfaces of the scapula, wherein each of the modified guide contact surfaces is a surface of the scapula that will contact one of the patient-specific modified bone contact surfaces of the patient-specific guide and will be intra-operatively modified during the surgery to implant the glenoid prosthesis.

14. The method of claim 13, wherein the modified bone surface has been formed when each of the patient-specific unmodified bone contact surfaces of the patient-specific guide is flush with the unmodified guide contact surfaces of the scapula and each of the patient- specific modified bone contact surfaces of the patient-specific guide is flush with the modified guide contact surfaces of the scapula.

15. The method of any of claims 1-14, wherein the method further comprises providing, by the one or more processors, intra-operative guidance to a surgeon to form the modified bone surface.

16. The method of any of claims 1-15, further comprising outputting, by the one or more processors, manufacturing data that enables a manufacturing system to fabricate the glenoid prosthesis.

17. The method of any of claims 1-16, further comprising fabricating the glenoid prosthesis.

18. The method of any of claims 1-17, wherein the modified-facing portion of the glenoid prosthesis contacts the portion of the modified bone surface after implantation of the glenoid prosthesis at the planned implantation position.

19. The method of claim 18, wherein the modified-facing portion of the glenoid prosthesis has a patient-specific shape that conforms to the portion of the modified bone surface of the scapula.

20. A system comprising: a memory; and one or more processors implemented in circuitry and communicatively coupled to the memory, the one or more processors configured to perform the methods of any of claims 1 – 19.

21. The system of claim 20, further comprising a manufacturing system configured to fabricate a glenoid prosthesis or a patient-specific guide generated using the methods of any of claims 1-19.

22. A non-transitory computer-readable medium having instructions stored thereon that, when executed by one or more processors of a computing system, cause the computing system to perform the methods of any of claims 1 – 19.

23. A patient-specific glenoid prosthesis comprising: an articulation element comprising an articulation surface over which a corresponding articulation surface of a humeral prosthesis is configured to slide, an augment element; and a baseplate, wherein: the articulation element and the augment element are configured to be attached to opposite sides of the baseplate, the augment element is configured to occupy a space between a scapula of a patient and the baseplate, a bone-facing surface of the glenoid prosthesis has a native-facing portion and a modified-facing portion, the native-facing portion is shaped to conform to an unmodified bone surface of the scapula and the modified-facing portion is shaped to conform to a modified bone surface of the scapula, the modified bone surface of the scapula is a surface of the scapula that will result from modification of the scapula during a surgery to implant the glenoid prosthesis, and the unmodified bone surface of the scapula is a surface of the scapula that will contact the glenoid prosthesis after implantation of the glenoid prosthesis and will not be intra-operatively modified during the surgery to implant the glenoid prosthesis at a planned implantation position.

24. The patient-specific glenoid prosthesis of claim 23, wherein the native-facing portion of the glenoid prosthesis includes a native-facing portion of the augment element has a patient-specific shape that conforms to the unmodified bone surface of the scapula.

25. The patient-specific glenoid prosthesis of any of claims 23-24, wherein the modified- facing portion of the glenoid prosthesis includes a modified-facing surface of the augment element that has a patient-specific shape that conforms to the modified bone surface of the scapula.

26. The patient-specific glenoid prosthesis of claim 25, wherein a portion of the baseplate is configured to contact the modified bone surface of the scapula after implantation of the glenoid prosthesis at the planned implantation position.

27. The patient-specific glenoid prosthesis of any of claims 23-26, wherein the modified bone surface of the scapula results at least in part from modification of a portion of a glenoid rim of the scapula.

28. The patient-specific glenoid prosthesis of any of claims 23-27, wherein the modified bone surface of the scapula results at least in part from removal of one or more osteophytes.

29. The patient-specific glenoid prosthesis of any of claims 23-28, wherein the modified- facing portion of the glenoid prosthesis contacts the portion of the modified bone surface after implantation of the glenoid prosthesis at the planned implantation position.

30. A patient-specific guide comprising: a structure defining a lumen configured to guide a guide pin to a preoperatively planned location on a scapula of a patient at a preoperatively planned orientation; one or more patient-specific unmodified bone contact surfaces that are shaped to conform to respective unmodified guide contact surfaces of the scapula, wherein each of the unmodified guide contact surfaces of the scapula is a surface of the scapula that will contact one of the unmodified bone contact surfaces of the patient-specific guide and will not be intra-operatively modified during a surgery to implant a patient-specific glenoid prosthesis; and one or more patient-specific modified bone contact surfaces shaped to conform to respective modified guide contact surfaces of the scapula, wherein each of the modified guide contact surfaces is a surface of the scapula that will contact the one of the patient-specific modified bone contact surfaces of the patient-specific guide and will be intra-operatively modified during the surgery to implant the glenoid prosthesis.

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