How to Select a Rod for a Pedicle Screw System for Spinal Fusion

Abstract

The method for selecting rods for a pedicle screw system for spinal fixation surgery is performed by determining the positions of a group of screws in a predefined reference system based on the patient's spine and creating an initial patient rod model connecting the screws of the group. A predetermined correction factor may then be applied to the initial patient rod model, and a final patient rod model may then be calculated based on the correction factor. Finally, the final patient rod model is compared to a database of multiple predefined pre-bent rod models, and one predefined pre-bent rod model is selected based on the best fit between the final patient rod model and the multiple predefined pre-bent rod models.

Description

[Technical Field]

[0001] The present invention relates to a method for selecting rods for a pedicle screw system for spinal fusion surgery. [Background technology]

[0002] Spinal fusion is a surgical procedure that permanently connects two or more vertebrae in the spine, eliminating movement between the vertebrae and stabilizing a patient's spinal segment.

[0003] Rods are typically used to connect pedicle screws that are inserted into vertebral bodies to strengthen a patient's spine.

[0004] A pedicle screw is a surgical instrument that allows for strengthening spinal fixation in the event of a patient's spine being damaged, and comprises a tulip and a screw.

[0005] Abnormal spinal curvature (scoliosis or kyphosis), injury to the spinal vertebrae, protrusion of the discs that cushion the vertebrae (herniated disc or nucleus pulposus), or weakening or instability of the spine due to disease are common indications for spinal fusion.

[0006] Pedicle screws are a special type of bone screw designed to be implanted into the pedicle of the spine, providing a means of grasping a spinal segment at any level of the spinal column (cervical, thoracic, lumbosacral).

[0007] Rods are metallic cylindrical implants used in spinal surgery to stabilize spinal segments by connecting pedicle screws inserted into adjacent vertebral bodies to prevent disc movement and allow fusion across the disc space.

[0008] Typically, the rods are bent in the operating room during surgery depending on the position of the screws and the correction required for each patient.

[0009] The rod bending process requires a lot of assumptions, as the rod must be placed into the tulip of the pedicle screw, which is also used as a contact point to correct the spine.

[0010] In addition, correctly bending the rod, especially during surgery, is a complex procedure that must be performed taking into account various parameters, such as the optimal curvature to apply to the rod to achieve the desired correction.

[0011] Therefore, it is desirable to enable patients to accept rods with optimal curvature while reducing surgical time. Therefore, patient-specific rods or rod templates that can be used as guides could be of great value to patients and surgeons.

[0012] Additionally, the rod's own properties and / or the patient's physical condition may prevent the rod from properly maintaining the desired bent shape.

[0013] In this regard, for example, a spinal cord that is too stiff may cause undesirable deformation of the rod when it is applied, reducing its effectiveness. Summary of the Invention

[0014] Therefore, there is a need for a patient-specific rod that can be precisely designed, selected, monitored, and specifically verified for its fit to a desired shape based on a three-dimensional model of the spine, thus overcoming the problems of the prior art.

[0015] These and other objects are fully achieved by a method for selecting a rod for a pedicle screw system for spinal fusion surgery having the features defined in independent claim 1 and a system for selecting a rod for a pedicle screw system for spinal fusion surgery having the features defined in independent claim 15.

[0016] Preferred embodiments of the invention are defined in the dependent claims, the subject matter of which is understood to form an integral or integral part of this description. [Brief explanation of the drawings]

[0017] Further characteristics and advantages of the invention will become apparent from the following description, given purely as a non-limiting example, with reference to the accompanying drawings, in which: [Figure 1A] 1 shows a block diagram illustrating the steps of a method for selecting a rod for a pedicle screw system for spinal fixation according to the present invention. [Figure 1B] 1 shows a block diagram illustrating the steps of a method for selecting a rod for a pedicle screw system for spinal fixation according to the present invention. [Figure 1C] 1 shows a block diagram illustrating the steps of a method for selecting a rod for a pedicle screw system for spinal fixation according to the present invention. [Figure 2] 1 shows a possible implementation of the method of the present invention. [Figure 3] 1 illustrates a system for selecting rods in a pedicle screw system for spinal fusion. DETAILED DESCRIPTION OF THE INVENTION

[0018] Briefly, the method of selecting rods for a pedicle screw system for spinal fusion surgery according to the present invention uses optical or electronic tracking technology to define the location of screws, specifically pedicle screws, to be implanted in a patient.

[0019] In particular, the screws are provided in at least one group consisting of all screws placed along the spine in the same / corresponding positions within each of the vertebrae involved to perform a spinal fusion procedure.

[0020] In other words, the screws are divided into different groups, each group consisting of all the screws that are aligned or substantially aligned along the spine when in use.

[0021] For example, the screws may all be applied along the central axis of each vertebra, thus defining only a single group.

[0022] Alternatively, the screws may be placed along the left and right sides of each vertebra, thus defining a first group (e.g., screws placed on the left side) and a second group (e.g., screws placed on the right side).

[0023] An initial patient rod model (its shape) is then calculated based on the pedicle screw locations for that particular group, and additional correction factors can be applied based on either preoperative planning or user experience.

[0024] The initial patient rod model defines the shape that the rods that are joined to the group must have in order to effectively correct the deficiencies that the spinal fusion surgery must address.

[0025] Correction factors are applied based on parameters identified during sagittal balance simulation or based on the surgeon's assessment and need for under- or over-correction of the rod, depending on multiple factors, particularly the curve or flexibility of the spine, or the corrective maneuver to be performed.

[0026] By introducing correction factors, it is possible to obtain a final patient rod model that corresponds to the ideal shape that the rod should assume to achieve optimal performance after application.

[0027] In a further step, a database is searched, the database containing a plurality of predefined pre-bent rod models, each having a different curvature, shape, material, and length from one another, and then one predefined pre-bent rod model is selected based on the best fit between the final patient rod model and the plurality of predefined pre-bent rod models.

[0028] Additionally, the location at which the rod should be cut on the cranial and caudal sides is calculated.

[0029] Finally, a physical rod corresponding to the selected predefined pre-bent rod model is prepared, then cut according to the plan and subsequently implanted in the patient.

[0030] In general, physical rod preparation can be performed by taking an already bent rod that conforms to the shape of a selected pre-bent rod model, or by selecting a straight rod that is then bent according to the information provided by the pre-bent rod model.

[0031] In this regard, the pre-bent rod model may include or depict specific instructions (e.g., location of bend, direction, degree of bend) that indicate the bending procedure to be performed on the straight rod to produce the desired shape.

[0032] More particularly, FIG. 1 shows a block diagram of the steps of the method for selecting rods of a pedicle screw system for spinal fusion according to the present invention as summarized above.

[0033] In a first step 10, the positions of at least one group of screws are determined in a predefined reference system based on the patient's spine using an electronic or optical tracking system (camera or similar optical sensor).

[0034] The optical system may be an external optical system or may be an optical system placed on each screw and mounted in series to determine its position relative to the other screws in the same group.

[0035] In a second step 20, an initial patient rod model is created that connects the groups of screws (aligned substantially along a straight line).

[0036] The term "substantially aligned along a straight line" means that the connected screws are in a straight line.

[0037] As will be explained in more detail below, the entire procedure may be applied to more than one rod, as can be seen in Figure 2, which shows a photograph (top and side views) of a three-dimensional portion of a patient's spine 100, where reference numerals L1, ..., L5 indicate two opposing screws belonging to two separate and different groups. Lines 102, 104 indicate the initial patient rod model of two different rods that are coupled to the screws of each group.

[0038] In a further step 30, correction factors based on pre-operative planning and / or the preferences and techniques described above are applied to the initial patient rod model.

[0039] Thereafter, in step 40, a final patient rod model is calculated based on the correction factors of step 30.

[0040] In a further step 50, the final patient rod model is compared to a database of a plurality of predefined pre-bent rod models, and then one predefined pre-bent rod model is selected based on the best fit between the final patient rod model and said plurality of predefined pre-bent rod models.

[0041] Advantageously, in a further final step 60, the best fitting rod is selected from the database by calculating the difference between the selected predefined pre-bent rod model and the final patient rod model and selecting the rod with the smallest difference, indicating the cranial / caudal position at which to cut the rod.

[0042] The rod may be, for example, 600 mm long, with a 200 mm lordotic curve and a 400 mm kyphotic curve. However, a patient may require a 375 mm long rod with a 150 mm lordotic curve and a 225 mm kyphotic curve. Based on this information, the method of the present invention determines to cut 175 mm at the top and 50 mm at the bottom.

[0043] In addition to the above, the method also preferably includes a step 70 of setting up a bent rod corresponding to the pre-bent rod model.

[0044] The setup may be performed by selecting a rod according to a pre-bent rod model (70b) and preparing a bent rod by bending the rod to replicate the shape of the final patient rod model, or alternatively by simply selecting an already bent rod (70a).

[0045] That is, the starting rod may be a straight rod, or it may be an already pre-bent rod, which may (or may not) require some adjustment to best fit the shape of the final patient rod model.

[0046] In other words, the pre-bent rod model may define a rod that requires less effort / bending to achieve a desired shape equivalent to the final patient rod model, or it may define a rod that provides instructions for processing a straight rod to achieve the desired final shape.

[0047] Once the pre-bent rod model has been defined, it is then possible to select a rod and, only if necessary, bend it in a particularly quick and easy manner to reproduce the shape of the final patient rod model.

[0048] Ideally, if a perfect match is found between the pre-bent rod model and the final patient rod model, it would even be possible to simply select the corresponding already bent rod without further manipulation before coupling it to the corresponding screw.

[0049] To ensure an optimal match between the final patient rod model and the bent rod, it is possible to perform check procedures aimed at ensuring that the bent rod correctly maintains its deformation and thus the desired shape.

[0050] The above checking procedure is carried out, inter alia, by comparing the bent rod and the final patient rod model at certain predefined measurement points (80) and measuring the distance between each measurement point on the bent rod and the corresponding measurement point on the final patient rod model (90).

[0051] The points may be a set of consecutive points for performing a check procedure to verify the overall shape of the rod, or may correspond to a set of specific reference points of interest, such as the points where the rod is coupled to the screw (i.e., the position of the tulip), to allow for a faster and easier check procedure.

[0052] Generally, if at least one distance exceeds a predetermined threshold, i.e., if the shape of the rod differs significantly from the shape of the final patient rod model, step 100 of modifying at least one parameter of the bent rod is performed.

[0053] The parameters include, in particular, the shape of at least a portion of the bent rod, and therefore, modifying the parameters may be performed by bending at least a portion of the bent rod until at least one distance that was too high to be tolerated falls below a predetermined threshold.

[0054] Alternatively, if it is not possible to produce a satisfactory bent rod even by subsequent bending / correction steps applied locally to specific portions of the bent rod that are found to be far from the desired shape, it is possible to select another rod and subsequently prepare a new bent rod that is better suited to correctly reproduce the shape of the final patient rod model.

[0055] In this scenario, the checking procedure can also be repeated for a new bent rod obtained by selecting and / or bending another rod.

[0056] In particular, the alternative rod may be a rod that exhibits different physical characteristics (eg, length, cross section, material, initial shape, etc.) than the rod originally used.

[0057] Advantageously, the claimed method can be implemented to specifically perform the application of rods in spinal fusion surgery or similar procedures aimed at improving / stabilizing a patient's spine.

[0058] The rod may be a bent rod that has been prepared and checked according to the procedural steps described above, or may be an already bent rod.

[0059] Indeed, as explained above, the pre-bent rod model may correspond to a set of instructions showing how to bend a straight rod to obtain a particular shape, or it may simply depict the shape of an already bent rod that is present, for example, in a storage unit and that can be selected and used without the need to perform further preparation steps such as bending and / or checking procedures.

[0060] In this regard, the method further comprises a step 110 of preparing the applied bent rod by connecting said bent rod to all the screws of the same group.

[0061] Operationally, the rods are placed in contact with the screws belonging to the same group (i.e., the screws aligned at the same position along the spine) and then bonded to their tulips and blocked.

[0062] However, the spine may be too stiff for the applied bending rod, causing its deformation.

[0063] To ensure that the rod maintains the correct shape (and optimally addresses the problem requiring the spinal fusion surgery to be performed), further check procedures similar to and corresponding to those performed on the bent rod can be performed before applying the screws.

[0064] In particular, the procedure may be performed by comparing (120) the applied bent rod and the final patient rod at predefined measurement points and measuring (130) the distance between each measurement point of the applied bent rod and the corresponding measurement point of the final patient rod model.

[0065] Also, in this situation, the comparison of the applied bent rod with the final patient rod may be performed using a set of consecutive measurement points along the entire length of the rod, or by identifying a set of individual points.

[0066] Preferably, the measurement points correspond to the position of the tulips of all screws connected / coupled to the rod.

[0067] In other words, the proposed method may be performed by identifying the positions of the screws, calculating a specific rod model depending on those positions, then selecting / preparing and applying the rods corresponding to the calculated model, and finally re-measuring the positions of the screws (specifically their tulips) to check whether their actual positions after the introduction of the bent rods are still identical to the positions measured at the beginning of the process when the rods were not yet present.

[0068] Also, if at least one distance exceeds a predetermined threshold, i.e., if the shape of the applied bent rod (and therefore the position of the screws) differs significantly from the shape of the final patient rod model, step 140 may be performed to modify at least one parameter of the applied bent rod.

[0069] In this regard, the modification of the parameters of the applied bent rod may be performed by bending at least a portion of the applied bent rod until said at least one distance falls below a predetermined threshold and while said rod is still coupled to the screw.

[0070] If not, it is possible to separate the applied bent rod and add a further bend to it or replace it completely.

[0071] For example, separation of an applied bent rod may be performed by discarding it and selecting another rod (according to the pre-bent rod model), which is then bent according to the final patient rod model and then applied to the corresponding group of screws.

[0072] Advantageously, the above procedure makes it possible to ensure at all times that the selected rod (which is then bent and applied to the screw) actually has and maintains the desired shape.

[0073] The above-described method may be performed to determine / apply a single rod when such a single rod is sufficient to produce the desired effect on the patient's spine.

[0074] Alternatively, the above procedure can be carried out with the aim of providing multiple rods, in particular a pair of rods with a first rod attached to the left side of the spine and a second rod attached to the right side of the spine.

[0075] In particular, the method may be performed to determine, based on the patient's spine, a first group of positions comprising screws placed on the left side of the spine and a second group of positions comprising screws placed on the right side of the spine in a predefined reference system.

[0076] In a further step, both a left initial patient rod model and a right initial patient rod model are created.

[0077] The model is created to connect the first and second groups of screws, respectively.

[0078] Additionally, predetermined correction factors can be applied to the left and right initial patient rod models to compensate for, for example, potential sagittal balance issues associated with the patient's spine.

[0079] Based on the applied correction factors, a final left patient rod model and a final right patient rod model can be calculated.

[0080] Finally, by comparing the left and right final patient rod models with the aforementioned database, it is possible to select corresponding pre-defined pre-bent rod models based on the best fit between each of the left and right final patient rod models and the plurality of pre-defined pre-bent rod models.

[0081] Once the optimum rod shapes have been determined, they can be prepared and applied to each group of screws in turn.

[0082] That is, a first rod (e.g., the rod attached to the left side of the spine) is applied, and only after it has been confirmed that the first rod has maintained its shape is a second rod (e.g., the rod attached to the right side of the spine) applied.

[0083] In particular, the method may be performed to prepare a left-side bent rod by selecting a rod according to a left-side pre-bent rod model, bending it according to a left-side final patient rod model, and repeating the same procedure in a corresponding manner for a right-side bent rod.

[0084] Both rods may then be analyzed through the check procedures described above to confirm their ability to maintain the desired shape (i.e., the shape of the corresponding final patient rod model).

[0085] It is then possible to apply the left bent rod by connecting it to all the screws in the first group.

[0086] The left bent rod may also be checked after being coupled to the screw to ensure that it has not been deformed in an undesirable manner by potential forces exerted on it by the spine itself.

[0087] This step is specifically performed by measuring the distance between each point of the applied left bent rod and the corresponding point of the left final patient rod model.

[0088] If all distances are below the predetermined threshold, the rod is behaving in the desired manner, and therefore it is possible to proceed with the application of the right-hand bent rod by coupling it to all the screws in the second group (which is then itself checked in a similar manner).

[0089] If not, the parameters of the left bent rod are modified (e.g., using the procedure described above) until its shape matches the shape of the left final patient rod model.

[0090] After the right-hand bent rod has been applied, it can be subjected to exactly the same checking procedures as were performed on the left-hand bent rod to verify its ability to maintain the desired shape even under the influence of potential forces exerted on it by the spine itself.

[0091] Alternatively, two rods may be applied simultaneously, coupled to the screws of their respective groups, and the checking procedure carried out only after they are both fixed in place.

[0092] Generally, it is possible to perform the check procedure sequentially for each rod after it is coupled to its respective screw, or in one single step after both rods have been applied.

[0093] The process according to the invention may be carried out by a system of the type shown in FIG. 2, which comprises, inter alia, a processing subsystem 210, a display device 220, a keyboard 230, a pointing device (mouse) 240, and a workstation 200 of known type having a device for connecting to a local area network (network bus) 250.

[0094] In FIG. 2, the workstation 200 is shown as a computer, but it may be any kind of personal device with computing capabilities, such as a tablet, laptop, mobile phone, etc.

[0095] Alternatively, the processing system may be distributed (not shown) with processing subsystems and local or remote peripheral input / output devices.

[0096] The workstation 200 or distributed system is configured to process processing groups or modules and computing programs stored on disk or accessible over a network, suitable for displaying the described processes to display the results on the device 220.

Claims

1. 1. A method for selecting a rod for a pedicle screw system for spinal fixation, comprising: - determining (10) the positions of at least one group of screws in a predefined reference system based on the patient's spine; - creating (20) at least one initial patient rod model connecting the screws of each group; - applying a predetermined correction factor to said initial patient rod model (30); - calculating (40) a final patient rod model based on said correction factors; - comparing (50) the final patient rod model with a database of a plurality of pre-defined pre-bent rod models, and then selecting (60) one pre-defined pre-bent rod model based on a best fit between the final patient rod model and the plurality of pre-defined pre-bent rod models.

2. 10. The method of claim 1, further comprising determining (60) a difference between the selected predefined pre-bent rod model and the final patient rod model to indicate cranial and / or caudal positions for cutting the rod.

3. The method of claim 1 or 2, comprising the step of setting up (70) a bent rod corresponding to the pre-bent rod model.

4. 4. The method of claim 3, wherein the step (70) of setting up a bent rod is performed by selecting (70a) an already bent rod.

5. 4. The method of claim 3, wherein the step of setting up a bent rod (70) is performed by selecting a straight rod (70b) and bending the straight rod according to the pre-bent rod model so as to reproduce a corresponding final patient rod model.

6. - comparing (80) the bent rod and the final patient rod model at predefined measurement points; - measuring the distance between each measurement point of the bent rod and the corresponding measurement point of the final patient rod model (90); A method according to any of claims 3 to 5, comprising a step (100) of varying at least one parameter of said bent rod if at least one distance exceeds a predetermined threshold.

7. The step of varying at least one parameter of the bent rod is carried out according to at least one of the following: bending at least a portion of said bent rod until said at least one distance is below said predetermined threshold; - selecting another rod and bending said another rod to replicate the shape of said final patient rod model.

8. 8. The method according to any one of claims 3 to 7, comprising the step (110) of preparing the applied bent rod by connecting said bent rod to all the screws of the same group.

9. - comparing (120) the applied bent rod with the final patient rod model at predefined measurement points; - measuring (130) the distance between each measurement point of the applied bent rod and the corresponding measurement point of the final patient rod model; The method according to claim 8, comprising a step (140) of varying at least one parameter of the applied bent rod if at least one distance exceeds a predetermined threshold.

10. The step of varying at least one parameter of the applied bent rod is carried out according to at least one of the following: bending at least a portion of the applied bent rod until the at least one distance falls below the predetermined threshold; - separating the applied bent rod.

11. The separating step includes the following substeps: - discarding the applied bent rod; - selecting another rod according to said pre-bent rod model; - bending said further rod according to said final patient rod model; The method according to claim 10, including the substep of connecting said further rod to all the screws of the same group.

12. - determining (10) the positions of a first group of screws, the screws being associated with the left side of said spine, and the second group of screws being associated with the right side of said spine, in a predefined reference system based on the patient's spine; - creating (20) a left initial patient rod model and a right initial patient rod model connecting the first and second groups of screws, respectively; - applying predetermined correction factors to the left and right initial patient rod models (30); - calculating (40) a final left and a final right patient rod model based on said correction factors; - comparing (50) the left and right final patient rod models with a database of a plurality of predefined pre-bent rod models, and then selecting (60) a corresponding predefined pre-bent rod model based on a best fit between each of the left and right final patient rod models and the plurality of predefined pre-bent rod models.

13. - preparing a left bent rod by selecting a rod according to the corresponding pre-bent rod model and bending the rod to replicate the shape of the left final patient rod model; - preparing a right-side bent rod by selecting a rod according to the corresponding pre-bent rod model and bending the rod to replicate the shape of the right-side final patient rod model; - applying the left bent rod by connecting it to all the screws of the first group, - applying the right-hand bent rod by coupling it to all the screws of the second group, and changing at least one parameter of the left-hand bent rod otherwise applied.

14. - measuring the distance between predefined measurement points of the applied left bent rod and corresponding measurement points of the left final patient rod model; - applying the right bent rod only if all of the distances are below a predetermined threshold.

15. 1. A system for selecting rods for a pedicle screw system for spinal fixation, comprising: a workstation (200) having a processing subsystem (210), the processing subsystem (210) comprising: - determining (10) the positions of at least one group of screws in a predefined reference system based on the patient's spine; - creating (20) at least one initial patient rod model connecting the screws of each group; - applying a predetermined correction factor to said initial patient rod model (30); - calculating (40) a final patient rod model based on said correction factors; - comparing (50) the final patient rod model with a database of a plurality of pre-defined pre-bent rod models, and then selecting one pre-defined pre-bent rod model based on a best fit between the final patient rod model and the plurality of pre-defined pre-bent rod models.

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