# Patent

## Title
Patient-specific tools and implants

## Abstract

A method for preparing a femoral neck for receiving a neck implant includes resecting a femoral head from a femoral neck of a patient according to a pre-operative patient-specific plan. The method also includes removing only cancellous bone from the femoral neck and proximal femoral bone of the patient using a patient-specific broach. The patient-specific broach has a three-dimensional cutting surface matching as a negative mold a cortical/cancellous bone interface surface of the femoral neck of the patient.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a divisional of U.S. application Ser. No. 13/041,665 filed on Mar. 7, 2011.
The disclosure of the above application is incorporated herein by reference.


INTRODUCTION
The present teachings provide a bone-preserving design for a hip prosthesis. More specifically, the present teachings are directed to patient-specific femoral neck implants and associated tools and methods
SUMMARY
The present teachings provide various methods, tools and implants for preparing a femoral neck to receive a neck implant.
The present teachings provide a method for preparing a femoral neck for receiving a neck implant. The method includes obtaining image data of a proximal femoral bone and femoral neck of a patient by a medical imaging method and constructing a three-dimensional image model of the proximal femoral bone and neck of the patient using the image data. The method further includes identifying a three-dimensional cortical boundary surface at an interface between cortical and cancellous bone of the patient using the image model. A patient-specific broach having a three-dimensional cutting surface closely matching and complementary to the cortical boundary surface of the patient using the image model is designed and manufactured.
Another method according to the present teachings includes resecting a femoral head from a femoral neck of a patient according to a pre-operative patient-specific plan. The method further includes removing only cancellous bone from the femoral neck and proximal femoral bone of the patient using a patient-specific broach having a three-dimensional cutting surface closely matching and complementary to a cortical/cancellous bone interface surface of the femoral neck of the patient.
The present teachings provide a femoral neck implant. The femoral neck implant includes a body for implantation into a femoral neck of a patient. The body has a patient-specific cross-section of variable size and shape along a longitudinal axis of the body and a patient-specific three-dimensional outer surface that closely nests and conforms complementarily to a cortical boundary surface corresponding to a cortical/cancellous bone interface surface of the femoral neck of the specific patient after removing only the cancellous bone from the femoral neck. The neck implant can include a neck portion extending from the body and configured for coupling with a femoral head implant.
The present teachings provide a femoral neck cutting tool, such as a broach for preparing a femoral neck for a femoral neck implant. The cutting tool includes a body having a patient-specific cross-section of variable size and shape along a longitudinal axis and a patient-specific three-dimensional outer cutting surface that closely nests and conforms complementarily to a cortical boundary surface corresponding to a cortical/cancellous bone interface surface of a femoral neck of the specific patient and configured for removing only the cancellous bone from the femoral neck of the patient. The cutting tool can include a non patient-specific coupling component for engaging a non patent-specific driver tool.
The present teachings also provide a patient-specific guide for preparing a femoral neck of a patient for receiving a femoral neck implant. The patient-specific guide includes a first wall having a first inner surface with a patient-specific inner bore therethrough, and a peripheral wall extending from the first wall. The first inner surface is configured to mate with a resected surface of the femoral neck. The peripheral wall includes a three-dimensional patient-specific peripheral inner surface configured to mate in only one position with an outer peripheral surface of the femoral neck after resection.
Further areas of applicability of the present teachings will become apparent from the description provided hereinafter. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present teachings.



BRIEF DESCRIPTION OF THE DRAWINGS
The present teachings will become more fully understood from the detailed description and the accompanying drawings, wherein:
FIG. 1 is a perspective view of a patient-specific neck implant according to the present teachings;
FIG. 1A is a perspective view of a patient-specific neck implant according to the present teachings;
FIG. 2 is an environmental view of the neck implant of FIG. 1;
FIG. 3 is a plan view of the proximal femur showing a resection of the femoral neck at a plane C;
FIG. 4 is an environmental view showing a patient-specific broach for the femoral neck implant;
FIG. 5 is a perspective view of a patient-specific broach according to the present teachings;
FIG. 6 is a plan view of a driver tool for the broach of FIG. 5;
FIG. 7 is a plan view of the driver tool of FIG. 6 coupled to the broach of FIG. 5;
FIG. 8 is a flow chart of a method according to the present teachings;
FIG. 9 is a flow chart of a method according to the present teachings;
FIG. 10 is an exploded environmental view of a patient-specific cutting guide for a neck implant according to the present teachings; and
FIG. 10A is an environmental view of the cutting guide of FIG. 10.



DESCRIPTION OF VARIOUS EMBODIMENTS
The following description is merely exemplary in nature and is in no way intended to limit the present teachings, applications, or uses.
The present teachings provide patient-specific tools and implants designed for a conservative hip procedure that conserves a portion of femoral neck of a specific patient.
As described in commonly assigned U.S. application Ser. No. 11/756,057, filed on May 31, 2007, during a preoperative planning, imaging data of the relevant anatomy of a patient can be obtained at a medical facility or doctor's office. The imaging data can include, for example, a detailed scan of a pelvis, hip, knee, ankle or other joint or relevant portion of the patient's anatomy. The imaging data can be obtained using MRI, CT, X-Ray, ultrasound or any other imaging system. The imaging data obtained can be used to construct a three-dimensional computer image of the joint and prepare an initial pre-operative plan that can include bone or joint preparation, including planning for resections, milling, reaming, broaching, implant selection and fitting, design of patient-specific guides, templates, tools and alignment protocol for the surgical procedure.
Computer modeling for obtaining three-dimensional computer images of the relevant patient's anatomy can be provided by various CAD programs and/or software available from various vendors or developers, such as, for example, from Materialise USA, Plymouth, Mich. The computer modeling program can be used to plan a preoperative surgical plan, including planning various bone preparation procedures, selecting or designing/modifying implants and designing patient-specific guides and tools including patient-specific prosthesis components, and patient-specific tools, including reaming, broaching, milling, drilling or cutting tools, alignment guides, templates and other patient-specific instruments.
The pre-operative plan can be stored in any computer storage medium, in a computer file form or any other computer or digital representation. The pre-operative plan, in a digital form associated with interactive software, can be made available via a hard medium, a web-based or mobile or cloud service, a cellular portable device to the surgeon or other medical practitioner, for review. Using the interactive software, the surgeon can review the plan, and manipulate the position of images of various implant components relative to an image of the anatomy. The surgeon can modify the plan and send it to the manufacturer with recommendations or changes. The interactive review process can be repeated until a final, approved plan, is sent to the manufacturer.
After the surgical plan is approved by the surgeon, patient-specific implants and associated tools, including, for example, alignment guides, cutting/milling/reaming/broaching or other tools for the surgical preparation of the joint or other anatomy portion of the specific patient can be designed using a CAD program or other three-dimensional modeling software, such as the software provided by Materialise, for example, according to the surgical plan. Computer instructions of tool paths for machining the patient-specific tools and/or implants can be generated and stored in a tool path data file. The tool path data can be provided as input to a CNC mill or other automated machining system, and the tools and implants can be machined from polymer, ceramic, metal or other suitable material depending on the use, and sterilized. The sterilized tools and implants can be shipped to the surgeon or medical facility for use during the surgical procedure.
Patient-specific components or tools or portions discussed below are generally constructed by a surgical plan approved by the surgeon using three-dimensional images of the specific patient's anatomy and made to closely conform and mate substantially as a negative mold of corresponding portions of the patient's anatomy, including bone surfaces with or without associated soft tissue. MRI scans, for example, allow modeling of soft tissue, such as articular cartilage, and modeling of bone portions of different densities, such as inner surfaces matching cortical and cancellous bone, as discussed below.
The present teachings provide a bone-preserving design for a hip prosthesis and associated tools. The procedure can conserve as much of the natural femoral neck 82 of the patient as determined by the surgeon depending on the specific patient by providing a patient-specific femoral neck implant 100 for supporting a femoral head implant 150, as illustrated in FIGS. 1, 1A and 2.
Referring to FIGS. 1 and 1A, an exemplary patient-specific neck-preserving (“neck implant” for short) 100 can include a body or stem 102 for introduction into the femoral neck 82 as described below and an optional flange or collar 104 for abutment on a resected surface 90 corresponding to a resection plane C of the femoral neck 82 (shown in FIG. 4). A neck implant 100 without the collar 104 is illustrated in FIG. 1A. The neck implant 100 can also include a neck portion 106 which can be coupled to a corresponding bore 152 of the femoral head implant 150 using a taper-to-taper connection or other type of coupling. The stem 102 of the neck implant 100 is designed to be patient-specific with a three-dimensional outer surface 108 that is complementary and closely nests and conforms to a cortical/cancellous interface surface 88 where the cortical and cancellous bone layers meet (referred to as cortical boundary surface 88 after the cancellous bone is removed) of the femoral neck 82 of the patient only in one position. Identifying the cortical/cancellous interface 88 enables removing only the cancellous bone 84, thereby conserving the hard cortical bone unmodified for engaging the complementary outer surface 108 of the neck implant 100.
Specifically, the neck implant 100 is designed during the pre-operative plan based on a three-dimensional computer model of the femoral neck 82 of the patient as reconstructed from MRI, CT, X-ray or other scans of the patient. Referring to FIG. 3, the cortical/cancellous interface surface 88 between the cortical bone 86 and the cancellous bone 84 is illustrated after a planar neck resection C is made to separate the natural femoral head from the portion of the femoral neck 82 to be preserved below resected surface 90. As can be seen from FIG. 2, the neck implant 100 can be sized and shaped such that it does not extend beyond the femoral neck 82 into the intramedullary canal of the femoral bone of the patient. The neck implant 100 has a patient-specific depth into the femoral neck 82 and a patient-specific angle relative to the femur. Further, because the cortical/cancellous interface surface 88 has a variable size and shape cross-section, the neck implant 100 has a corresponding variable size and shape cross-section along a longitudinal axis A of the neck implant 100, which is also specific to each patient. For simplicity, the neck implant 100 is shown in FIG. 1 with a variable oval/elongated and tapering cross-section 103, 103′ (in two different locations), although it should be understood that this geometry is merely exemplary and that the shape and size cross-section 103 along the body of the neck implant 100 is patient-specific and mirrors the corresponding shape and size of the cortical/cancellous interface surface 88 along the femoral neck 82 of the specific patient. The cross-section 103 can be oval or elongated and decreasing or tapering in size, but not necessarily linearly. Further, the cross-section 103 may be and generally is non-symmetric for a specific patient. The neck portion 106 of the neck implant 100 can also be designed to be aligned to a patient-specific articulation direction along a second axis A′ which may be at an angle to the longitudinal axis A of the neck implant A, as illustrated in FIG. 2. The neck portion 106 can be also adjusted for an out-of-plane angle or neck version adjustment.
Referring to FIGS. 3-5, to remove only the spongy cancellous bone 84 while preserving substantially all the cortical bone 86, a patient-specific cutting tool, broach or other bone-removing tool 200 can be designed during the preoperative plan based on the three-dimensional computer model of the neck 82 of the patient. Specifically, the broach 200 is designed to have a body 201 with an outer peripheral three-dimensional cutting surface 202 extending from a proximal end surface 204 to a distal end surface 210 of the body 201 that closely nests and conforms or matches and is complementary to the cortical/cancellous interface surface 88 only in one position and such that only cancellous bone 84 is removed and the cortical boundary surface 88 is exposed and maintained. Similarly to the neck implant 100, the broach 200 is also a patient-specific and has a variable in shape and size cross-section 203, which is generally oval/elongated and tapering, but not necessarily linearly, along a longitudinal axis B of the broach. Further, the cross-section 203 may be non-symmetric for a specific patient. The cutting surface 202 is provided with cutting teeth and channels or grooves for moving bone chips away from the cavity created by the broach 200, as shown in FIG. 4.
Referring to FIGS. 5-7, the patient-specific broach 200 can be coupled to a non-custom driver tool 300 by providing a coupling interface between the proximal end surface 204 of the broach to a distal surface 314 of the driver tool 300. The coupling interface can include, for example, a broach coupling component 220, such as a finger or rod or other protrusion 208 extending from the proximal end surface 204 of the broach 200 to be received in a corresponding bore or other opening 312 defined through the distal surface 314 of the driver tool 300. The coupling interface can also include a driver coupling component 320, such as an opening or bore 206 defined through the proximal end surface 204 for receiving a distal portion 316 of a retractable bar or rod 310 of the driver tool 300. The driver tool 300 can include a body 302, a handle bar 304, and a proximal flange 318 for impaction. The retractable rod 310 extends along the length of the body 302 and is biased by a proximal spring 308. The rod 310 can be deployed for engaging the broach 200 by using a trigger 306 which can be operated by holding with one hand the handle 304 and squeezing the trigger opening 305 with an index finger. The broach 200 can be held securely with the driver tool 300, as shown in FIG. 7 and inserted into the femoral neck 82 to remove the cancellous bone 84 and expose the cortical/cancellous interface surface 88 for receiving the patient-specific neck implant, as shown in FIGS. 1 and 2.
Referring to FIGS. 8 and 9 according to present teachings, image data from CT, MRI, X-ray, ultrasound or other scanning of the proximal femoral bone 80 and femoral neck 82 of a patient are obtained at block 400. For modeling the cortical/cancellous interface and identifying the cortical boundary surface 88, the image data may be obtained from MRI scanning or other methods that provide differentiation of bone and tissue layers based on density, composition or other parameters. A three-dimensional computer image model of the proximal femoral bone 80 and femoral neck 82 of the patient can be constructed at block 402 using commercially available software, as discussed above. The three-dimensional cortical boundary surface 88 can be visible and identified and confirmed in the image model at block 404 by the surgeon. A neck resection plane can be selected and corresponding patient-specific femoral alignment guides and/or femoral head resection guides can be designed, as discussed, for example, in commonly assigned U.S. application Ser. No. 12/893,306, filed Sep. 29, 2010 and U.S. application Ser. No. 12/486,992, filed Jun. 18, 2009 of the cross-reference section, and incorporated herein by reference. A patient-specific broach 200 having a three-dimensional cutting surface 202 matching and complementary to the cortical boundary surface 88 in only one position can be designed at block 406 using the computer image model of the patient's anatomy. A patient-specific neck implant 100 having a three-dimensional surface 108 matching and complementary to the cortical boundary surface 88 in only one position can be designed and manufactured using the computer image model of the patient's anatomy (block 408). The implant 100 can be impacted into the femoral neck 82 and can also be porous coated for bone in-growth. As discussed above, other patient-specific tools, including femoral alignment/cutting guides to be used for resecting the femoral head, can also be designed and manufactured using the image model of the patient's anatomy according to the pre-operative plan.
The patient-specific neck implant 100, patient-specific broach 200 and other custom or non-custom tools are sterilized and shipped to the surgeon's site. Referring to FIG. 9, intra-operatively, the natural femoral head can be resected from the femoral neck 82 at a selected position and orientation (plane C in FIG. 4) using, for example, patient-specific alignment guides, patient-specific resection guides, non-custom guides and cutting tools or combinations thereof (block 410). The resection plane C is selected to preserve as much of the natural femoral neck 82 as determined in the pre-operative plan. After the natural femoral head is removed intra-operatively, the patient-specific broach 200 can be used to remove only the cancellous bone 84 from the femoral neck 82 and expose the cortical boundary surface 88 of the femoral neck 82, at block 412. The patient-specific neck implant 100 can then be implanted, for example, by impaction, in only one position (block 414), and mate with the exposed cortical boundary surface 88, as shown in FIG. 2. A femoral head implant 150 can be coupled to the neck portion 106 of the neck implant 100. The femoral head implant 150 can articulate with the natural acetabulum or an acetabular implant 151, as determined and planned by the surgeon for the specific patient.
Referring to FIGS. 10 and 10A, in some embodiments, a patient-specific milling or cutting guide 600 can be used with a milling tool 500 to remove the cancellous bone 84 and prepare the femoral neck 82 for receiving a neck implant 100. The patient-specific milling guide 600 can be designed during the preoperative plan such that it can be mounted only in one position on the femoral neck 82, after the femoral head is resected and removed. The milling guide 600 can include a peripheral wall 602 and a first wall 608. The first wall 608 can be substantially flat and have a first inner surface 609. The peripheral wall 602 extends from the first wall 608 to a second surface 610 that is opposite the first wall 608. The peripheral wall 602 includes a three-dimensional patient-specific peripheral inner surface 604 that is configured to nestingly mate and conform only in one position to a remaining (after resection) three-dimensional outer peripheral surface 83 of the femoral neck 82. The first wall 608 includes a patient-specific bore 606 therethrough. The first inner surface 609 is patient-specific and configured to mate and conform to the resected surface 90, as shown in FIGS. 10 and 10A. The patient-specific bore 606 is sized and shaped during the preoperative plan to be patient-specific for guiding a cutting portion 502 of a milling or other cutting tool 500 to remove the cancellous bone 84 from the femoral neck 82 to the cortical boundary 88 (interface between cortical and cancellous bone) for receiving a neck implant, such as the patient-specific neck implant 100 discussed above. It is noted that the dimensions the patient-specific milling guide 600, including the depth and size the peripheral inner surface 604, is such that the patient-specific milling guide 600 can be mounted over the resected femoral neck 82. In some embodiments, the patient-specific milling guide can include a split or hinge (not shown) along the insertion axis or can be formed in two pieces couplable pieces in clamshell fashion, as discussed in commonly assigned U.S. patent application Ser. No. 12/486,992, filed Jun. 18, 2009 and incorporated herein by reference.
The patient-specific broach 200, the patient-specific milling guide 600 and the patient-specific implant 100 can be manufactured from biocompatible materials using machining, rapid manufacturing by stereolithography, laser welding, computer-assisted manufacturing using numerical machining or robotic controllers. Patient-specific alignment and/or resection guides for resecting and removing the femoral head can also be designed from the image model and manufactured by the above methods according to the pre-operative plan for the patient.
The foregoing discussion discloses and describes merely exemplary arrangements of the present teachings. Furthermore, the mixing and matching of features, elements and/or functions between various embodiments is expressly contemplated herein, so that one of ordinary skill in the art would appreciate from this disclosure that features, elements and/or functions of one embodiment may be incorporated into another embodiment as appropriate, unless described otherwise above. Moreover, many modifications may be made to adapt a particular situation or material to the present teachings without departing from the essential scope thereof. One skilled in the art will readily recognize from such discussion, and from the accompanying drawings and claims, that various changes, modifications and variations can be made therein without departing from the spirit and scope of the present teachings as defined in the following claims.

## Claims

1. method of preparing a femoral neck for receiving a femoral neck implant comprising:
obtaining image data of a proximal femoral bone and the femoral neck of a specific patient using a medical imaging modality;
constructing a three-dimensional image model of the proximal femoral bone and neck of the specific patient using the image data;
identifying a three-dimensional cortical boundary surface at an interface between cortical bone and cancellous bone of the femoral neck of the specific patient using the three-dimensional image model;
resecting a femoral head from the femoral neck of a patient according to a pre-operative patient-specific plan;
removing only cancellous bone from the femoral neck and proximal femoral bone of the patient using a patient-specific broach having a three-dimensional cutting surface matching as a negative mold the cortical boundary surface of the femoral neck;
selecting a patient-specific neck implant having a patient-specific length determined from the three-dimensional image model of the specific patient; and
implanting the patient-specific neck implant having a three-dimensional outer surface matching as a negative mold the cortical boundary surface of the femoral neck of the patient after the cancellous bone is removed.

2. The method of claim 1, further comprising:
coupling a driver tool to the patient-specific broach; and
inserting the broach into the femoral neck of the patient.

3. The method of claim 2, further comprising:
inserting a protrusion extending from a proximal surface of the broach into a bore of a distal surface of the driver tool; and
inserting a distal portion of a retractable rod of the driver tool into a bore defined through the proximal surface of the broach to secure the broach to the driver tool.

4. The method of claim 1, further comprising engaging a proximal flange of the neck implant with a resected surface of the femoral neck.

5. The method of claim 4, further comprising coupling a femoral head implant to a neck portion of the neck implant.

6. The method of claim 1, further comprising coupling a femoral head implant to a neck portion of the neck implant.

7. A method of preparing a femoral neck for receiving a femoral neck implant comprising:
identifying a three-dimensional cortical boundary surface at an interface between cortical bone and cancellous bone of the femoral neck of the specific patient using a three-dimensional model derived from image data gathered about a specific patient;
coupling a driver tool to a patient-specific broach having a three-dimensional cutting surface matching as a negative mold the three-dimensional cortical boundary surface at the femoral neck;
using the driver to insert the broach into a resected portion of the femoral neck of the patient;
removing only cancellous bone from the femoral neck and proximal femoral bone of the patient using the patient-specific broach; and
exposing the three-dimensional cortical boundary surface by removing only the cancellous bone using the patient-specific broach
selecting a patient-specific neck implant having a patient-specific length determined from the three-dimensional model of the specific patient, the patient-specific length configured such that the neck implant does not extend beyond the femora neck into an intramedullary canal; and
implanting the patient-specific neck implant having a three-dimensional outer surface matching as a negative mold the cortical boundary surface of the femoral neck of the patient after the cancellous bone is removed.

8. The method of claim 7, further comprising:
directing bone chips away from a cavity created by the broach.

9. A method of preparing a femoral neck for receiving a femoral neck implant comprising:
identifying a three-dimensional cortical boundary surface at an interface between cortical bone and cancellous bone of the femoral neck of the specific patient using a three-dimensional model derived from image data gathered about a specific patient;
resecting a femoral head from the femoral neck of the specific patient to expose a corresponding resected surface of the femoral neck;
inserting a patient-specific broach into the femoral neck of the patient through the exposed corresponding resected surface of the femoral neck, the patient-specific broach having a three-dimensional cutting surface matching as a negative mold the three-dimensional cortical boundary surface of the specific patient;
removing only cancellous bone from the femoral neck of the patient using the patient-specific broach at least by inserting the patient-specific broach;
exposing the three-dimensional cortical boundary surface by removing only the cancellous bone using the patient-specific broach;
selecting a patient-specific neck implant having a patient-specific length determined from the three-dimensional model of the specific patient, the patient-specific length configured such that the neck implant does not extend beyond the femoral neck into an intramedullary canal; and
implanting the patient-specific neck implant having a three-dimensional outer surface matching as a negative mold the cortical boundary surface of the femoral neck of the patient after the cancellous bone is removed.

10. The method of claim 9, further comprising:
directing bone chips away from a cavity created by the broach.

11. The method of claim 9, further comprising:
coupling a driver tool to the patient-specific broach.

12. The method of claim 11, further comprising securing the driver tool to the broach.

13. The method of claim 11, further comprising inserting a protrusion extending from a proximal surface of the broach into a bore of a distal surface of the driver tool.

14. The method of claim 11, further comprising inserting a distal portion of a retractable rod of the driver tool into a bore defined through the proximal surface of the broach.

15. The method of claim 11, further comprising engaging a proximal flange of the neck implant to the resected surface of the femoral neck.

16. The method of claim 15, further comprising coupling a femoral head implant to a neck portion of the neck implant.