Cantilever strain gauge devices for intraoperative measurement and interpretation of bone density during spinal surgery

Abstract

Provided are bone quality and / or strength measuring devices. In some implementations, the devices include a body and a detector disposed therein designed to interact with a bone, determine the quality and / or strength thereof, and communicate an evaluation thereof to a user. In some implementations, the detector includes at least one contact pad at least a portion of which is configured to deflect away from a bone surface when the at least one contact pad comes into contact with the bone surface, which in some implementations the degree to which the portion deflects away from the bone surface is indicative of the quality and / or strength of the bone surface. Also provided are methods for determining if a region of a bone is appropriate for placement of an orthopedic hardware piece and methods for reducing risk of a complication of spinal surgery associated with failure of an orthopedic hardware piece.

Description

CANTILEVER STRAIN GAUGE DEVICES FOR INTRAOPERATIVE MEASUREMENT AND INTERPRETATION OF BONE DENSITY DURING SPINAL SURGERYCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application No. 63 / 540249, filed on September 25, 2023, the entire contents of which are incorporated herein by reference.GOVERNMENT INTEREST

[0002] This invention was made with government support under grant number 5U01HL152392 awarded by the National Institutes of Health. The government has certain rights in the invention.TECHNICAL FIELD

[0003] The presently disclosed subject matter relates generally to a medical device that can measure mechanical bone quality (strength) intraoperatively during spine surgery.SUMMARY

[0004] In some implementations, devices include hardware and / or software that provides visual, auditory, and / or tactile feedback depending on the measurement taken to thus provide a user with guidance to management of poor bone quality measurements. More particularly, the presently disclosed subject matter relates to devices with single or double contact pads that are designed to deflect away from bone when inserted into a pilot hole, wherein the degree to which the contact pads deflect is indicative of mechanical bone quality (strength).

[0005] This Summary lists implementations of the presently disclosed subject matter, and in many cases lists variations and permutations of these implementations of the presently disclosed subject matter. This Summary is merely exemplary of the numerous and varied implementations. Mention of one or more representative features of a given implementation is likewise exemplary. Such an implementation can typically exist with or without the feature(s) mentioned; likewise, those features can be applied to other implementations of the presently disclosed subject matter, whether listed in this Summary or not. To avoid excessive repetition, this Summary does not list or suggest all possible combinations of such features.BRIEF DESCRIPTION OF DRAWINGS

[0006] Figures 1 A and IB are depictions of aspects of a device of the presently disclosed subject matter. In Figure 1 A, a force (F) inherent in the device is opposed by a bone surface (not depicted) encountered by the device. This opposing force is detected and quantified by a strain gauge present on a cantilever beam of the device. Figure IB is a schematic of the strain gauge.

[0007] Figure 2 is depiction of how when a stronger bone will provide a greater resistive force against the device, resulting in greater cantilever deflection and thus greater measured strain.

[0008] Figures 3A and 3B are depictions of how the opposing forces are encountered and measured in a bone. In Figure 3 A, a double device (i.e., a device with 2 contact pads that encounter the bone surface) or a single device are employed. In the dual device (left side of Figure 3 A), the two contact pads are forced closer to each other when they encounter a bone surface, and the degree to which they approach each other can be quantified as a measure of bone strength and / or quality. In the single device (right side of Figure 3 A), a single contact pad is deflected away from the bone surface, and the degree to which the contact pad is deflected can be quantified as a measure of bone strength and / or quality. Figure 3B is a depiction of a single device.

[0009] Figures 4A-D show an example of a single device of the presently disclosed subject matter. As shown, a stronger bone surface will cause more deflection of the contact pad. In those implementations in which the contact pad surface also includes sensors to detect physical contact along the length of the contact pad and the bone surface, the greater deflection will be accompanied by less contact between the contact pad and the bone surface. The degree to which the contact pad maintains contact with the bone surface can also be measured in addition to the degree to which the contact pad is deflected.

[0010] Figure 5 is a graph of tests of block surfaces with differing compressive strengths and the strain detected by an exemplary device of the presently disclosed subject matter. It is noted that in one example (indicated with the broken circle), the hole size was incorrectly drilled too large, resulting in a deviation from the observed curve.

[0011] Figures 6A-B depict an exemplary dual device of the presently disclosed subject matter. This exemplary dual device is 3D printed from a titanium allow, has a 4 mm diameter at the tip of the contact pads, each of which has a thickness of 0.5 mm. A strain gauge is present between the contact pads and the tapered handle.

[0012] Figure 7 of a graph of tests of exemplary devices under various conditions of block strength.

[0013] Figures 8A-B depicts an exemplary device of the presently disclosed subject matter wherein the section of the device comprising the contact pad(s) and part of the adjacent neck is designed to not only interrogate the bone surface by also create the hole in the bone into which the device is inserted.

[0014] Figures 9A-B are a depiction of an exemplary single device inserted into a vertebra, Shown are red / yellow / green lights that provide an evaluation of the bone surface as well as a digital readout of the bone strength and / or quality detected.

[0015] Figures 10A-B show a photograph of a prototype of a device of the presently disclosed subject matter. Shown are the device with handle and a tip and strain gauge, with electronics included to display the strain detected.

[0016] Figures 11A-C are photographs of an exemplary single device of the presently disclosed subject matter inserted into test blocks of three different compressive strengths.

[0017] Figures 12A-B are top and side views of a probe tip, according to some implementations.

[0018] Figure 13 is a schematic view of a probe tip and system for intraoperative measurement and interpretation of bone density during spinal surgery, according to some implementations.DETAILED DESCRIPTION

[0019] While the following terms are believed to be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

[0020] All technical and scientific terms used herein, unless otherwise defined below, are intended to have the same meaning as commonly understood by one of ordinary skill in the art. Mention of techniques employed herein are intended to refer to the techniques as commonly understood in the art, including variations on those techniques or substitutions of equivalent techniques that would be apparent to one of skill in the art. While the following terms are believedto be well understood by one of ordinary skill in the art, the following definitions are set forth to facilitate explanation of the presently disclosed subject matter.

[0021] Following long-standing patent law convention, the terms “a”, “an”, and “the” refer to “one or more” when used in this application, including the claims.

[0022] The term “about”, as used herein to refer to a measurable value such as an amount of weight, time, etc., is meant to encompass in some implementations variations of ±20%, in some implementations ±10%, in some implementations ±5%, in some implementations ±1%, in some implementations ±0.1%, in some implementations ±0.5%, and in some implementations ±0.01% from the specified amount, as such variations are appropriate to perform the disclosed methods.

[0023] As used herein, the term “and / or” when used in the context of a list of entities, refers to the entities being present singly or in any possible combination or subcombination. Thus, for example, the phrase “A, B, C, and / or D” includes A, B, C, and D individually, but also includes any and all combinations and subcombinations of A, B, C, and D.

[0024] The term “comprising”, which is synonymous with “including” “containing”, or “characterized by”, is inclusive or open-ended and does not exclude additional, unrecited elements and / or method steps. “Comprising” is a term of art that means that the named elements and / or steps are present, but that other elements and / or steps can be added and still fall within the scope of the relevant subject matter.

[0025] As used herein, the phrase “consisting of’ excludes any element, step, or ingredient not specifically recited. For example, when the phrase “consists of’ appears in a clause of the body of a claim, rather than immediately following the preamble, it limits only the element set forth in that clause; other elements are not excluded from the claim as a whole.

[0026] As used herein, the phrase “consisting essentially of’ limits the scope of the related disclosure or claim to the specified materials and / or steps, plus those that do not materially affect the basic and novel characteristic(s) of the disclosed and / or claimed subject matter. For example, a method of the presently disclosed subject matter can “consist essentially of’ one or more enumerated steps as set forth herein, which means that the one or more enumerated steps produce most or substantially all of the intended result to be produced by the claimed method. It is noted, however, that additional steps can be encompassed within the scope of such a method, providedthat the additional steps do not substantially contribute to the result for which the method is intended.

[0027] With respect to the terms “comprising”, “consisting essentially of’, and “consisting of’, where one of these three terms is used herein, the presently disclosed and claimed subject matter can include the use of either of the other two terms. Similarly, it is also understood that in some implementations the methods of the presently disclosed subject matter comprise the steps that are disclosed herein, in some implementations the methods of the presently disclosed subject matter consist essentially of the steps that are disclosed, and in some implementations the methods of the presently disclosed subject matter consist of the steps that are disclosed herein.

[0028] Disclosed herein are designs of a class of medical devices that can measure bone quality and / or strength intraoperatively during spine surgery. In some implementations, the devices include software and indicators that provide the user with feedback regarding the severity of bone quality and / or strength deficits that are measured to provide a user (e.g., a spinal surgeon) with guidance to management of undesirably low bone quality and / or strength measurements.

[0029] Spine surgery, particularly in osteoporotic patients, can be risky due to failure of bone to support metal implants. Ideally, hardware such as screws, plates, etc. should be placed only at bone areas that are sufficiently strong to bear the loads required for adequate repair. The DEXA scan is the gold standard to evaluate bone quality, but has drawbacks. Particularly, it is not always available, does not measure local bone strength, and assumes bone homogeneity. However, it is clear that bone quality and / or strength is not homogenous (Banse et al., 2001), so even a DEXA scan can provide inadequate information to a surgeon.

[0030] Several strategies can be employed to address attachment difficulties at areas of weak bone, including but not limited to use of multiple points of fixation, longer constructs, addition of crosslinks, anterior column support, undertapping, and cement augmentation. However, when and which to employ can be unclear during the operative procedure, and as such, bone strength data can better inform a surgeon so the best decisions with respect to orthopedic repair can be made.

[0031] Thus, in some implementations the presently disclosed subject matter relates to devices and methods for determining bone strength in real time, quickly and specifically along several or many locations under consideration for surgical intervention. By way of example and notlimitation, in some implementations a screw path is mechanically probed to determine vertebral body cancellous bone strength.

[0032] The overall general design concept for a device of the presently disclosed subject matter is depicted in Figures 3, 4, 6, 8, and 10. With particular reference to Figures 3A and 3B, a device of the presently disclosed subject matter is in some implementations essentially cylindrical and of a size appropriate for insertion into a screw path hole produced in a bone to be tested. The device can have two opposing contact pads (i.e., a dual device; left side of Figure 3 A) or can have one contact pad (i.e., a single device; right side of Figure 3A), although it is noted that devices with 3, 4, or more contact pads are also within the scope of the presently disclosed subject matter.

[0033] In some implementations, at least a portion of the device, optionally include the contact pad(s), is disposable and designed to be replaced frequently either during use for any particular subject or for use in different subjects at different times. As such, in some implementations a removeable cap facilitates quick and easy removal of a used contact pad assembly from the probe body and replacement of the same with a contact pad assembly, after which the removeable cap can be replaced on the probe body for subsequent use.

[0034] In some implementations, the probe body can be introduced into a bone to be tested (depicted in Figure 9). In some implementations, the probe body can further comprise a force sensor. The force sensor detects the degree to which the contact pad(s) deflect upon contact with a bone surface. In some implementations, the degree to which the contact pad(s) deflect upon contact with a bone surface is indicative of the quality and / or strength of the bone surface.

[0035] Thus, in some implementations the force sensor further comprises an indicator and / or a detector that detects whether the bone is suitable or unsuitable to be used as an attachment point for orthopedic hardware (e.g., a screw). In some implementations, the indicator and / or detector acts in a binary fashion with respect to a pre-selected minimum bone quality and / or strength in that if the bone has a quality and / or strength that is less than the pre-selected minimum, the indicator and / or detector relays a signal that is observable by the user. In some implementations, the signal is a visual signal. By way of example and not limitation, if the indicator and / or detector acts in a binary fashion to display a visual signal, a light of one color (e.g., red) or type (e.g., flashing) can indicate that the bone is unsuitable, whereas a light of another color (e.g., green) or type (e.g., steady on) can indicate that the bone is suitable. By way of a further example and notlimitation, if the indicator and / or detector acts in a ternary fashion to display a visual signal, a light of a first color (e.g., red) or type (e.g., off) can indicate that the bone is unsuitable, a light of a second color (e.g., yellow) or type (e.g., flashing) can indicate that the bone is borderline unsuitable, and a light of a third color (e.g., green) or type (e.g., steady on) can indicate that the bone is suitable. A device with such an indicator is depicted in Figure 9. Other observable and / or perceptible signals can also be employed, including but not limited to auditory signals and / or tactile signals. Any combination of signals can also be generated by the probe, including signals that are relayed to a receiver that is in wireless communication with the probe body, is hardwired to the probe body, or both (e.g., WiFi, Bluetooth, and / or infrared communication).

[0036] In some implementations, the probe body, force sensor, contact pad(s), etc. are made of a material that is resistant to degradation by techniques designed to sterilize the devices. Such sterilization techniques include chemical sterilization and heat sterilization (e.g., autoclaving).

[0037] The devices and methods of the presently disclosed subject matter are applicable to a full range of spine procedures and not just to measurement during pedicle screw approaches as exemplified herein, and can provide measurements at multiple points. This is in contrast to the DensiProbe (Deckelmann et al., 2010; see also Hoppe et al., 2015), which is limited to a single measurement. In some implementations, the presently disclosed subject matter allows for vertebral axial compressive strength measurement, which can be important in spinal instrumentation. The DensiProbe device also measures at only one point 15-20 mm in the vertebrae transpedicular direction only, a limitation that is addressed by the presently disclosed subject matter.

[0038] The presently disclosed subject matter thus identifies and addresses certain underlying causes of pedicle screw failure. Most pedicle screws fail in the cancellous bone near the tip of the screw, especially in osteoporotic bone. Thus, in some implementations the presently disclosed subject matter directly measures the bone quality at different segments along the screw path. If predictable failure of the cancellous region can be identified, then screw failure or revision surgery can be avoided.

[0039] Bone Compression Test: Bone compression tests using cadaver vertebrae were employed in order to ascertain mechanical characteristics of cancellous bone. Based on literature, a 4 mm2surface area was estimate to require approximately 10 MPa of stress and a deflection above a 0.1 mm to reach the yield point. A compression test using a 6.25 mm diameter cylinder yielded 3.91MPa of stress, a value consistent with poor bone quality. Additional compression tests determine the potential yield range of cancellous bone. In addition, mechanical characteristics of plastics (e.g., those commercially available from General Plastics, Inc.) that mimic a range of expected mechanical properties of cancellous bone are tested.

[0040] Device Design and Testing: Many design concepts were tested before the cantileverbased mechanism disclosed where was employed to directly probe the mechanical properties of the underlying bone. Two exemplary devices are disclosed herein: (1) an “active device” where the surgeon can actively probe sites of interest; and (2) a “passive device” where the surgeon translates the probe through the screw path. Each model can be designed to cause mechanical indentation in weak bone without damaging strong bone.

[0041] Active Device Design: The cantilever-like behavior of the active model is driven by a piston to engage indentation (Figure 9). The piston can be manually controlled by a torque- and / or force-limited torsional mechanism on the back end. Bone strength is determined by measurements of deflection and applied torque and / or force. In some implementations, the exemplary device has control over both force and displacement; the operator can choose where to engage the indenter along the pedicle screw path within the vertebra.

[0042] Passive Device Design: This probe generates a force from passive cantilever flexing. The cantilever probe tip can be initially cocked back and subsequently released once it reaches a set position. The probe translates along the screw path and cantilever deflection (correlating to bone strength) is collected along the path. The tip indents weak bone whereas sufficiently strong bone deflects the cantilever, thus preventing damage to strong (i.e., good) bone. Several probe tip designs have been numerically modeled to deliver a bending moment that results in a 10 MPa load.

[0043] Alternative Materials: Testing of true-scale implementations (approximately 4 mm in diameter) using 3D-printed titanium is performed. Numerical models indicate that stronger materials (i.e., stronger than polymer) can be advantageous to test exemplary devices at the devices’ true-scale. Further, surgeons can provide feedback as to their preference towards an active design or passive design.

[0044] Force and Deflection Transducers: alternative methods for detecting probe deflection are tested. Two exemplary methods are optically based displacement sensors and strain gauges. The successful implementation of these transducers provides measurements beyond “strong” or“weak”, providing precise quantifiable measures of bone quality thus giving the best-possible information to surgeons. Such measurements also enable surgeons to provide the best possible corrective action depending on the degree of bone degradation.

[0045] Translation System: to address a mechanism for the controlled displacement of the device, a surgeon can manually insert and translate the probe itself. The development of a thread-based translational system such that a surgeon can manually rotate a collar that precisely translates the probe head according to the thread count of the translating screw is employed. Incorporating the translation system with force and deflection transducers enables sophisticated and unprecedented mechanism of mapping of the interior bone strength.

[0046] Testing of Exemplary Devices: both designs were 3D printed with PLA plastic at a larger scale (3x) for assessment. Geometrical modifications were made (based on hands-on observations and numerical models) and incorporated into the next set of scaled-up devices that are printed out of nylon through the University of Louisville’s Rapid Prototyping Center. The foam blocks in Figure 10C are commercially available at a variety of specified strengths. Prototype testing occurs with the insertion of these probes inserted in predrilled holes in the foam blocks. Prototype measurements will be verified with respect to foam block strengths.

[0047] 3D Printed Devices from Titanium: Numerical models show that atrue-scale probe device can created from a stronger material (i.e., stronger than polymers) to generate sufficient forces necessary for proper operation. Titanium devices are thus created via additive manufacturing through the University of Louisville’s Rapid Prototyping Center.

[0048] Optical Displacement Transducers: Displacement sensors are an exemplary method for measuring probe deflection. Fiber optic displacement sensors from Philtec Fiberoptic Sensors are as small as 0.5 mm in diameter with sub-micrometer resolution, and can thus be employed in the devices of the presently disclosed subject matter.

[0049] Strain Gages: In some implementations, a strain gage mounted to the probe itself can also provide measurements of deflection. For example, linear strain gages from Micro-Measurements can be as small as 2 mm2and a variety of configurations are commercially available. In some implementations, sensing via Wheatstone bridge circuitry is employed.

[0050] Torque and / or Force Limited Operation & Precise Translation: In some implementations, a torque- and / or force-limiting driver is employed in the devices of the presently disclosed subject matter. A variety of commercial torque- and / or force-limiting drivers are available (ex: Bradshaw Medical and In’ Tech Medical) to control the force delivered from the active probes of the presently disclosed subject matter. Translation for the rotary probe can involve a simple system consisting of a rotary encoder couples with a threaded collar.

[0051] Data Acquisition: In some implementations, a data acquisition system is employed to simultaneously acquire and log measurements from the probe. The National Instruments USB- 6003 multifunction I / O device can be employed for this purpose, with Lab View software employed to run the I / O instrument.

[0052] Device Mapping Accuracy: An exemplary device is tested in a randomized bone block sandwich of variable bone quality to test, demonstrate, and validate the exemplary device’s mapping accuracy.

[0053] The exemplary device is then deployed in a cadaver spine to demonstrate clinical feasibility. Cadaver vertebrae are microCT and / or DEXA scanned to determine bone density, which is correlated to output from the exemplary device deployed.

[0054] As shown in FIGS. 12A-B, a probe tip 20 is a handheld surgical device that will provide a quantified measure of bone strength in situ during surgery. No additional surgical steps are required to use the probe tip 20, and it can be incorporated within current surgical procedures. The probe tip 20 includes an insertion tip 24 sized to be inserted into a pedicle track drilled into a bone. In some implementations, the insertion tip 24 defines a diameter that is similar to a diameter of the pedicle track. A strain gauge mounting pad 28 is formed adjacent the insertion tip 24 and defines a reduced thickness compared to the insertion tip 24. In some implementations, the mounting pad 28 defines a width equal to the diameter of the insertion tip 24 but a reduced thickness. The mounting pad 28 is designed to flex. The mounting pad 28 is connected to an extended shaft 32 by a tapered shaft segment 36 and a wire channel 40 extends through the extended shaft 32 and the tapered shaft segment 36 to provide wire management. In some implementations, the extended shaft 32 includes a threaded shank 44 that is sized to receive a threaded stuff of a handle 46. In some implementations, the threaded shank 44 includes male threads sized to be received by female threads of the handle 46.

[0055] As shown in FIG. 13, the probe tip 20 includes a strain gauge 44 connected to the mounting pad 28 (e.g., via adhesive) and structured to send strain information indicative of a strain on the mounting pad 28. The strain information is receivable by a controller 48 having a processor 52 and a memory device 56. In some implementations, circuits of the controller 48 are provided in the form of machine or computer-readable media that is executable by a processor, such as processor 52. The computer readable program code may be executed on one processor, multiple co located processors, multiple remote processors, or any combination of local and remote processors. Remote processors may be connected to each other through any type of network (e.g., CAN bus, etc.). In another configuration, the circuits of the controller 48 are implemented as hardware units, such as electronic control units. As such, the circuits of the controller 48 may be implemented as one or more circuitry components including, but not limited to, processing circuitry, network interfaces, peripheral devices, input devices, output devices, sensors, etc. In some implementations, the circuits of the controller 48 may take the form of one or more analog circuits, electronic circuits (e.g., integrated circuits (IC), discrete circuits, system on a chip (SOCs) circuits, microcontrollers, etc.), telecommunication circuits, hybrid circuits, and any other type of “circuit.” In this regard, the circuits of the controller 48 may include any type of component for accomplishing or facilitating achievement of the operations described herein. For example, a circuit as described herein may include one or more transistors, logic gates (e.g., NAND, AND, NOR, OR, XOR, NOT, XNOR, etc.), resistors, multiplexers, registers, capacitors, inductors, diodes, wiring, and so on). The circuits of the controller 48 may also include programmable hardware devices such as field programmable gate arrays, programmable array logic, programmable logic devices or the like.

[0056] The hardware and data processing components used to implement the various processes, operations, illustrative logics, logical blocks, modules and circuits described in connection with the implementations disclosed herein (e.g., the processor 52) may be implemented or performed with a general purpose single- or multi-chip processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, or, any conventional processor, or state machine. A processor also may be implemented as a combination of computing devices, such as a combination of a DSPand a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0057] The memory device 56 (e.g., memory, memory unit, storage device) may include one or more devices (e.g., RAM, ROM, Flash memory, hard disk storage) for storing data and / or computer code for completing or facilitating the various processes, layers and modules described in the present disclosure. The memory device 56 may be communicably connected to the processor 52 to provide computer code or instructions to the processor 52 for executing at least some of the processes described herein. Moreover, the memory device 56 may be or include tangible, non-transient volatile memory or non-volatile memory. Accordingly, the memory device 56 may include database components, object code components, script components, or any other type of information structure for supporting the various activities and information structures described herein.

[0058] While the term “processor” is briefly defined above, the term “processor” and “processing circuit” are meant to be broadly interpreted. In this regard and as mentioned above, the “processor” may be implemented as one or more general-purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), digital signal processors (DSPs), or other suitable electronic data processing components structured to execute instructions provided by memory. The one or more processors may take the form of a single core processor, multi-core processor (e.g., a dual core processor, triple core processor, quad core processor, etc.), microprocessor, etc. In some implementations, the one or more processors may be external to the apparatus, for example the one or more processors may be a remote processor (e.g., a cloud based processor). Alternatively or additionally, the one or more processors may be internal and / or local to the apparatus. In this regard, a given circuit or components thereof may be disposed locally (e.g., as part of a local server, a local computing system, etc.) or remotely (e.g., as part of a remote server such as a cloud based server). To that end, a “circuit” as described herein may include components that are distributed across one or more locations.

[0059] Implementations within the scope of the present disclosure include program products comprising machine-readable media for carrying or having machine-executable instructions or data structures stored thereon. Such machine-readable media can be any available media that can be accessed by a general purpose or special purpose computer or other machine with a processor. By way of example, such machine-readable media can comprise RAM, ROM, EPROM,EEPROM, or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of machine-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer or other machine with a processor. Combinations of the above are also included within the scope of machine-readable media. Machine-executable instructions include, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing machines to perform a certain function or group of functions.

[0060] The controller 48 is structured to receive the strain information from the threaded shank 44 and determine a bone strength parameter based on the strain information. In some implementations, the controller 48 and the probe tip 20 are calibrated based on known bone strength samples or a calibration apparatus. The bone strength parameter is output by the controller 48 to a display 60. In some implementations, the display 60 is remote from the probe tip 20 (e.g., located on a monitor stand). In some implementations, the display 60 is attached to the handle 46 or molded into the handle 46.

[0061] In some implementations, a bone strength testing procedure includes exposing a vertebrae of a spine, planning a screw trajectory, and drilling a pedicle track into the vertebrae (e.g., approximately 3 mm to 4 mm in diameter). Prior to tapping and / or screw insertion, the probe tip 20 is used to determine bone strength. A surgeon inserts the insertion tip 24 of the probe tip 20 into the pedicle track and acquires bone strength measurements (via the stress information) in real time without any changes to the site preparation. Bone strength is correlated to the applied force on the threaded shank 44 and a quantitative measurement (e.g., the bone strength parameter) is provided to the surgeon via the display 60. Using the measured data and the bone strength parameter, the surgeon can determine the best strategy for the patient including the potential implementation of screw augmentation. There are several screw augmentation strategies including bone cement, supplemental hooks, and segmental fixation. The probe tip 20 is a non-destructive measurement, and no additional surgical preparation is needed for its use.

[0062] Prototyping has demonstrated: (i) correlation between sensor readings and foam block compressive strengths, (ii) consistent readings between different fabricated probes, (iii) consistent readings between different users. Based on extensive testing by the Inventors, the extended shaft 32 was lengthened. Testing also included using the probe tip 20 on a human spine specimen froma cadaver of a 96 year old woman. DEXA scans were acquired of the specimen, vertebrae were prepared and tapped, and probe tip 20 measurements were acquired.

[0063] Summarily, the probes of the presently disclosed subject matter provide at least the following benefits: a competitive advantage over current devices in that direct mechanical measurement of bone quality and / or strength and thus bone suitability for placement of orthopedic hardware is provided; directional measurements in three dimensions can provide better prediction of failure given the non-uniformity in three dimensions of typical bones; the user has the freedom to quickly map multiple sites of interest in real time; and the use of a screw hole as a access point does not destroy the target bone or alter the surgical procedure itself.

Claims

What is claimed is:

1. A bone quality and / or strength measuring device comprising: a body; and a detector disposed therein, wherein the detector is configured to interact with a bone, determine the quality and / or strength thereof, and communicate an evaluation of the bone quality and / or strength to a user.

2. The bone quality and / or strength measuring device of claim 1, wherein the detector comprises at least one contact pad, at least a portion of which is configured to deflect away from a bone surface when the at least one contact pad comes into contact with the bone surface in a manner indicative to the quality and / or strength of the bone surface.

3. The bone quality and / or strength measuring device of claim 2, wherein a degree to which the portion deflects away from the bone surface when the at least one contact pad comes into contact with the bone surface is indicative of the quality and / or strength of the bone surface.

4. The bone quality and / or strength measuring device of claim 3, wherein the degree to which the portion deflects away from the bone surface is detected by a strain gauge in operational communication with the portion that deflects away from the bone surface, and further wherein the strain gauge communicates the evaluation of the bone quality and / or strength to the user.

5. The bone quality and / or strength measuring device of claim 4, wherein the device comprises a single contact pad.

6. The bone quality and / or strength measuring device of claim 4, wherein the device comprises two contact pads that interact with different surfaces of the bone.

7. The bone quality and / or strength measuring device of any one of the preceding claims, wherein the bone quality and / or strength measuring device is of a size such that it can be inserted into a bone screw path introduced into the bone, optionally wherein the size is such that the bone quality and / or strength measuring device fits into the bone screw path with minimal gaps between the body of the bone quality and / or strength measuring device and the surface of the bone screw path.

8. The bone quality and / or strength measuring device of any one of the preceding claims, further comprising an output that provides a visual, auditory, and / or tactile feedback to a user based on the quality and / or strength of the bone determined by the detector.

9. The bone quality and / or strength measuring device of claim 8, wherein the output comprises a visual display that notifies the user that the quality and / or strength of the bone does or does not exceed a pre-selected minimum.

10. The bone quality and / or strength measuring device of any one of the preceding claims, wherein the bone is a bone of the spine, optionally a vertebra.

11. The bone quality and / or strength measuring device of any one of the preceding claims, wherein the device is fabricated at least in part from metal, optionally wherein the metal is titanium and / or an alloy thereof.

12. The bone quality and / or strength measuring device of any one of the preceding claims, wherein the bone quality and / or strength measuring device has a maximum diameter of about 2 mm to about 4 mm.

13. The bone quality and / or strength measuring device of any one of the preceding claims, wherein the bone quality and / or strength measuring device further comprises a plurality of threads on an outside surface of the at least one contact pad such that the bone quality and / or strength measuring device can be used to introduce the bone screw path into the bone immediately prior to and / or simultaneously with the detector interacting with the bone.

14. A method for determining if a region of a bone is appropriate for placement of an orthopedic hardware piece, the method comprising determining quality and / or strength of the region of the bone using the bone quality and / or strength measuring device of any one of claims 1-13, wherein the region of the bone is appropriate for placement of the orthopedic hardware piece if the quality and / or strength of the region of the bone exceeds a pre-determined minimum threshold.

15. The method of claim 14, wherein the bone is a bone of the spine, optionally a vertebra.

16. The method of claim 14 or claim 15, wherein the orthopedic hardware piece is a screw.

17. A method for reducing risk of a complication of spinal surgery associated with failure of an orthopedic hardware piece, the method comprising:(a) selecting a region of a spinal bone, optionally of a vertebra, for possible placement of an orthopedic hardware piece;(b) determining quality and / or strength of the region of the spinal bone using the bone quality and / or strength measuring device of any one of claims 1-13; and(c) placing the orthopedic hardware piece in the region of the spinal bone if the region of the bone has a quality and / or strength that exceeds a pre-determined minimum threshold; or if the region of the bone has a quality and / or strength that does not exceed a predetermined minimum threshold;(dl) repeating steps (a), (b), and (c) until a region of the bone that exceeds a predetermined minimum threshold is identified and then placing the orthopedic hardware piece in the region of the spinal bone; or(d2) placing the orthopedic hardware piece in the region of the spinal bone but also performing a salvage strategy that comprises use of multiple points of fixation, use of an orthopedic hardware piece with a greater length than would have been used otherwise, adding one or more cross links to the orthopedic hardware piece, use of one or more anterior column supports, use of undertapping in placement of the orthopedic hardware piece, use of cement augmentation, or any combination thereof.

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