Arthroplasty jigs and related methods

Description of equivalent WO 2007097853 A2

ARTHROPLASTY DEVICES AND RELATED METHODS

CROSS-REFERENCE TO RELATED APPLICATIONS

0003[0001] This application claims the benefit of priority, under 35 U.S.C. § 119(e), to U.S. Pat. Appl. Serial No. 60/773,491, filed on February 15, 2006, and U.S. Pat. Appl. Serial No. 60/780,757, filed on March 9, 2006, both of which are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

0005[0002] The methods and apparatuses described herein relate generally to the field of implants, as well as jigs that may be used to assist in positioning implants at a target site. More specifically, the methods and apparatuses described herein relate to the field of arthroplasty jigs, including the production of arthroplasty jigs and the alignment of arthroplasty jigs at a target site.

BACKGROUND

0007[0003] Over time and through repeated use, bones and joints can become damaged or worn. For example, repetitive strain on bones and joints (e.g., through athletic activity), traumatic events, and certain diseases (e.g., arthritis) can cause cartilage in joint areas, which normally provides a cushioning effect, to wear down. When the cartilage wears down, fluid can accumulate in the joint areas, resulting in pain, stiffness, and decreased mobility.

0008[0004] Arthroplasty procedures can be used to repair damaged joints. During a typical arthroplasty procedure, an arthritic or otherwise dysfunctional joint can be remodeled or realigned, or an implant can be implanted into the damaged region. Arthroplasty procedures may take place in any of a number of different regions of the body, such as a knee, a hip, a shoulder, or an elbow.

0009[0005] One type of arthroplasty procedure is a total knee arthroplasty (TKA), in which a damaged knee joint is replaced with prosthetic implants. The knee joint may have been damaged by, for example, arthritis (e.g., severe osteoarthritis or degenerative arthritis), trauma, or a rare destructive joint disease. During a TKA procedure, a damaged portion in the distal region of the femur may be removed and replaced with a metal shell, and a damaged portion in the proximal region of the tibia may be removed and replaced with a channeled piece of plastic having a metal stem. In some TKA procedures, a plastic button may also be added under the surface of the patella, depending on the condition of the patella.

0010[0006] Accuracy in implant alignment is an important factor to the success of a TKA procedure. A one- to two-millimeter translational misalignment, or a one- to two-degree rotational misalignment, may result in imbalanced ligaments, and may thereby significantly affect the outcome of the TKA procedure. For example, implant misalignment may result in intolerable post-surgery pain, and also may prevent the patient from having full leg extension and stable leg flexion.

0011[0007] Preoperative planning may be used prior to some TKA procedures to help determine where to position an implant and how to align the implant. Certain preoperative planning methods may include making these determinations based on a two-dimensional image of the target site. In some cases, though, the two-dimensional image may not provide sufficient guidance for precisely replacing a patient's diseased knee with an implant. For example, a physician may rely on certain landmarks of the target site, as shown in the two-dimensional image, for determining placement of an implant. Examples of knee region landmarks that may be relatively easily viewed in a two-dimensional image include the medial and lateral epicondyles of the distal region of the femur. However, the corresponding bone regions in the body typically are covered with soft tissue. This soft tissue may cause the landmarks to be partially obscured or completely hidden when the physician is trying to position an implant at the target site, and may make it especially difficult to view the landmarks when the physician is using a relatively small incision. Moreover, using such landmarks to position an implant at a target site may have added difficulty in that the locations and sizes of the landmarks can vary greatly from one patient to another. As a result, a landmark-based technique that is used for one patient may not be suitable for use with another patient. For at least the reasons provided above, a physician using a landmark-based approach may experience difficulty during surgery, such as difficulty in accessing the rotational axis. Because of this difficulty, many surgeons opt to rely significantly on their intuition and previous experience to guide them in a TKA procedure. The result can be inconsistent surgical outcomes, given the highly complex nature of the human knee, with its six degrees of freedom and features, such as dimensions and alignment, that can vary greatly from one patient to the next. [0008] In certain TKA surgeries, a robot is employed to machine the distal region of the femur and/or the proximal region of the tibia based on, for example, image-based preoperative planning. The robot may form cavities that may be used for attachment of prosthetic implants. While robot-assisted TKA procedures may be successful in terms of accuracy of alignment, they can require relatively long incisions and result in relatively long surgery times. Furthermore, the cost of a robot-assisted TKA procedure, including the capital cost, can be relatively high (e.g., two to three times the cost of a traditional TKA procedure).

0012[0009] In some TKA surgeries, an imageless navigation system is employed, in which planning is done intraoperatively (i.e., during the operation), without the use of preoperative radiographic images. The navigation system can assist surgeons in positioning prosthetic implants, and may thereby enhance the longevity of the implants. However, the navigation system may not provide information regarding the optimal alignment of an implant. Furthermore, the capital equipment cost associated with a navigation system can be relatively high, and the use of a navigation system may result in a longer incision, a higher surgical cost, and a longer duration of surgery, as compared to traditional surgery.

0013[0010] Implants that are implanted into a damaged region may provide support and structure to the damaged region, and may help to restore the damaged region, thereby enhancing its functionality. Prior to implantation of an implant in a damaged region, the damaged region may be prepared to receive the implant. For example, in a knee arthroplasty procedure, one or more of the bones in the knee area, such as the femur and/or the tibia, may be treated (e.g., cut, drilled, reamed, and/or resurfaced) to provide one or more surfaces that can align with the implant and thereby accommodate the implant. However, prior to treating any regions of a bone, it is important to correctly determine the location at which the treatment will take place. In some methods, an arthroplasty jig may be used to accurately position a finishing instrument, such as a cutting, drilling, reaming, or resurfacing instrument. The arthroplasty jig may, for example, include one or more apertures and/or slots that are configured to accept such an instrument.

0014[0011] A relatively high number of arthroplasty procedures are performed every year in the United States, and throughout the rest of the world. More specifically, in the United States alone, more than 300,000 people underwent TKA surgeries in 2005. By 2008, it is expected that approximately 1,000,000 people per year across the globe will have a TKA surgery. Accordingly, it would be desirable to improve the success rate of arthroplasty procedures, in terms of both efficiency and effectiveness. It would also be desirable to be able to meet demand for arthroplasty devices by manufacturing arthroplasty jigs and/or implants, including customized arthroplasty jigs and/or implants, relatively efficiently.

BRIEF SUMMARY

0016[0012] Described here are methods and devices that may be used to efficiently manufacture arthroplasty jigs configured for use at specific target sites, as well as methods and devices that may be used to enhance the positioning and alignment of an arthroplasty jig at a target site. The methods and devices described here include certain features that may enhance the customization of an arthroplasty procedure, and may thereby result in reduced procedure time and recovery time, as well as a reduced likelihood of complications.

0017[0013] Some of the methods described here comprise forming an arthroplasty jig, such as a knee arthroplasty jig. In some variations of the methods, the arthroplasty jig may be formed from a near-shape arthroplasty jig blank having at least one feature specific to a target site to be matched by the arthroplasty jig. In certain variations of the methods, the arthroplasty jig may have a first configuration, and may be formed from a near-shape arthroplasty jig blank having a second configuration approximating the first configuration.

0018[0014] Arthroplasty jig blanks, and methods of forming arthroplasty jig blanks, are also described herein. Some of the arthroplasty jig blanks comprise a jig blank body, are configured to be formed into an arthroplasty jig, and have at least one feature specific to a target site to be matched by the arthroplasty jig. Certain of the methods comprise forming a near-shape arthroplasty jig blank that is configured to be formed into an arthroplasty jig, and that has at least one feature specific to a target site to be matched by the arthroplasty jig.

0019[0015] The target site to be matched by the arthroplasty jig may be, for example, a left knee or a right knee, and/or may be a valgus knee, a varus knee, or a neutral knee. In some variations, the target site to be matched by the arthroplasty jig may be a femur. In certain variations, the target site to be matched by the arthroplasty jig may be a tibia.

0020[0016] The arthroplasty jig that is formed from the near-shape arthroplasty jig blank may be a customized arthroplasty jig, and/or may be a femoral arthroplasty jig or a tibial arthroplasty jig. In some variations, the method may comprise adding at least one patient- specific feature, such as a cavity, to the near-shape arthroplasty jig blank to form the arthroplasty jig. The patient-specific feature may be added to the near-shape arthroplasty jig blank using, for example, a milling process. In certain variations, forming the arthroplasty jig from the near- shape arthroplasty jig blank may comprise machining the near-shape arthroplasty jig blank.

0021[0017] Some of the methods may comprise forming a plurality of near-shape arthroplasty jig blanks that are configured to be formed into an arthroplasty jig, and that have at least one feature specific to a target site to be matched by the arthroplasty jig. In certain variations of the methods, one or more near-shape arthroplasty jig blanks may be formed using injection-molding technology.

0022[0018] Surface-matching devices, which may be used to position an arthroplasty jig at a target site in a body of a subject, also are described herein, along with related methods. Some of the surface-matching devices comprise at least one block and at least one pin extending from a portion of the block, and are configured to position an arthroplasty jig at a target site in a body of a subject. Certain of the methods comprise positioning a surface-matching device at a target site in a body of a subject, where the surface-matching device comprises at least one block and at least one pin extending from a portion of the block, and the surface-matching device is configured to position an arthroplasty jig at a target site in a body of a subject.

0023[0019] Some variations of the surface-matching devices may comprise a plurality of pins. One or more of the pins of a surface-matching device may have an end that is configured to contact at least one of bone and cartilage when the surface-matching device is positioned at a target site in a body of a subject. The surface-matching devices may be configured to position an arthroplasty jig, such as a knee arthroplasty jig, at a target site in a knee of a subject.

BRIEF DESCRIPTION OF THE DRAWINGS

0025[0020] FIG. IA is an illustrative view of a knee of a subject in extension.

0026[0021] FIG. IB is an illustrative view of the knee of FIG. IA in flexion.

0027[0022] FIG. 2 is a perspective view of femoral and tibial osteotomies and implants. [0023] FIG. 3 is a flowchart representation of a method of designing and manufacturing arthroplasty jigs.

0028[0024] FIG. 4A is an illustration of two-dimensional images of multiple segmentations of a femur of a. subject.

0029[0025] FIG. 4B is a three-dimensional anatomical computer model of a distal portion of a femur formed from the images of FIG. 4A.

0030[0026] FIG. 5A is an illustration of two-dimensional images of multiple segmentations of a tibia of a subject.

0031[0027] FIG. 5B is a three-dimensional anatomical computer model of a distal portion of a tibia formed from the images of FIG. 5 A.

0032[0028] FIG. 6A is a front view of a three-dimensional model of a distal portion of a femur of a subject.

0033[0029] FIG. 6B is a side view of the model of FIG. 6 A.

0034[0030] FIG. 6C is a front view of a femoral implant. '

0035[0031] FIG. 6D is a side view of the femoral implant of FIG. 6C.

0036[0032] FIG. 6E is a perspective view of a femoral implant and a distal portion of a femur of a subject.

0037[0033] FIG. 7A is a perspective view of a three-dimensional computer model of a proximal portion of a tibia of a subject.

0038[0034] FIG. 7B is a side view of a tibial implant including a load-bearing component.

0039[0035] FIG. 7C illustrates a shape-fitting method.

0040[0036] FIGS. 8 A and 8B illustrate a shape-fitting method for a femoral implant.

0041[0037] FIG. 8C is a perspective view of the femoral implant of FIG. 8A. [0038] FIGS. 8D and 8E illustrate a shape-fitting method for a tibial implant.

0042[0039] FIG. 9A is a perspective view of a femoral arthroplasty jig.

0043[0040] FIG. 9B is a perspective view of a tibial arthroplasty jig.

0044[0041] FIG. 10 is a perspective view of a femoral cutting jig.

0045[0042] FIG. 11 is a flowchart representation of a method for forming arthroplasty jigs-

0046[0043] FIG. 12 A is a perspective view of a near-shape femoral arthroplasty jig blank.

0047[0044] FIG. 12B is a perspective view of a near-shape tibial arthroplasty jig blank.

0048[0045] FIG. 13 A is a front view of a near-shape femoral arthroplasty jig blank.

0049[0046] FIG. 13B is a front view of a femoral arthroplasty implant.

0050[0047] FIG. 14A is a front view of a near-shape tibial arthroplasty jig blank.

0051[0048] FIG. 14B is a front view of a tibial arthroplasty implant.

0052[0049] FIG. 15 is a perspective view of a near-shape femoral arthroplasty jig blank undergoing a milling process.

0053[0050] FIG. 16 illustrates the use of customized femoral and tibial arthroplasty jigs on a femur and a tibia of a subject, respectively.

0054[0051] FIG. 17 is a perspective view of a distal portion of a femur of a subject and a proximal portion of a tibia of the subject, after resection using customized arthroplasty jigs.

0055[0052] FIG. 18 is a perspective view of a distal portion of a femur of a subject after resection and drilling.

0056[0053] FIG. 19 A is an illustration of preoperative planning data of a distal portion of a femur of a subject. [0054 J FIG. 19B is an illustration of preoperative planning data of a proximal portion of a tibia of a subject.

0057[0055] FIG. 2OA is a perspective view of a computer-aided point-to-point matching process for a distal portion of a femur of a subject.

0058[0056] FIG. 2OB is a perspective view of a computer-aided point-to-point matching process for a proximal portion of a tibia of a subject.

0059[0057] FIG. 21 A is a perspective view of a femoral multi-pin guided device.

0060[0058] FIG. 21 B is a perspective view of a tibial multi-pin guided device.

0061[0059] FIG. 21C is a schematic diagram of a computer-aided manufacturing process for forming multi-pin guided devices.

0062[0060] FIG. 22 is a perspective view of arthroplasty jig instruments being placed on a distal portion of a femur of a subject and a proximal portion of a tibia of a subject, using multi-pin guided devices.

DETAILED DESCRIPTION

0064[0061] Described here are arthroplasty jigs, and methods of making and using arthroplasty jigs, having features that may provide for enhanced alignment and positioning of the arthroplasty jigs at a target site. Certain of the methods described here comprise forming arthroplasty jigs from near-shape arthroplasty jig blanks having at least one feature specific to a target site to be matched by the arthroplasty jigs. Because the near-shape arthroplasty jig blanks already have one or more features directed to the configuration of the target site, they may be used to form arthroplasty jigs relatively efficiently. Also described here are devices that may be used to enhance the alignment and positioning of an arthroplasty jig at a target site. This enhanced arthroplasty jig alignment and positioning may, in turn, result in enhanced implant alignment and positioning at the target site. As the alignment and positioning of an implant are improved, the result may be a decreased likelihood of follow-up surgery (e.g., to adjust the alignment of the implant), and/or an increase in the useful life of the implant. Additional results may include reduced procedure time and fewer complications during and/or after surgery. Moreover, fewer resections and/or holes may be made when an arthroplasty jig is properly positioned and aligned at a target site. It should be understood from the outset that while knee arthroplasty jigs are described in detail here, one or more of the features or methods described here may be employed with other types of arthroplasty jigs, such as arthroplasty jigs that are suited for use in the hip, shoulder, elbow, etc.

0065[0062] Turning now to the figures, FIG. IA shows a knee (100) of a subject in extension, and FIG. IB shows knee (100) in flexion. Knee (100) is located at the juncture between the distal end of a femur (101) and the proximal end of a tibia (102) . All human knees share certain anatomical features, including articular cartilage (103), a patella (104), an anterior cruciate ligament or ACL (105), and collateral ligaments (106). However, the dimensions of these features are not identical from one person to the next. Furthermore, alignment can vary among different people. For example, one person may have a valgus knee, while another person may have a varus knee, and a third person may have a neutral knee. As a result of these and other variations, the positioning and alignment of a knee implant can be different for different people. Thus, in order to ensure longevity of a knee implant, the implant should be positioned with high translational and rotational accuracy.

0066[0063] In some variations of an arthroplasty procedure, one or more arthroplasty jigs may be employed to help prepare the damaged region for an implant, and to increase the likelihood that the implant will be correctly positioned and aligned at a target site in the damaged region. The arthroplasty jigs may be used, for example, to aid in the correct placement of finishing instruments, such as cutting, drilling, reaming, and resurfacing instruments. As an example, some arthroplasty methods may include using an arthroplasty jig to accurately position a reciprocating saw blade. The reciprocating saw blade may be used, for example, to cut the damaged bone region to provide one or more planar surfaces. The planar surfaces may assist in the alignment and positioning of an implant at a target site in the damaged bone region. Arthroplasty jigs may also be used, for example, to position one or more pins that secure an implant to a target site in the damaged bone region.

0067[0064] In some variations, an arthroplasty jig may help to position finishing instruments that are used to form a relatively high number of cuts and/or apertures in a damaged bone region. For example, arthroplasty jigs may be used during a TKA procedure to form at least ten resections in a damaged knee region that allow implants to be attached to a distal region of the femur and a proximal region of the tibia. [0065] FIG. 2 illustrates exemplary osteotomy cuts that may generally be formed on the distal region of a femur (200) and the proximal region of a tibia (202), using one or more arthroplasty jigs. The cuts are used to help attach or press-fit a femoral implant (204) to femur (200), and a tibial implant (206) to tibia (202). Femoral implant (204) includes a load-bearing component (208), and tibial implant (206) includes a load-bearing component (210). The load- bearing components of the implants may be formed of, for example, one or more plastics. Examples of processes that may be conducted to provide the osteotomy cuts include the following: intermedullary drilling to enter a femoral medullary canal (212); forming a distal femoral resection (214) that is configured to mate with femoral load-bearing plastic component (208); drilling a right femoral stem hole (218) that is configured to mate with a right stem (220) of femoral implant (204) (which is located on a side of femoral implant (204) that is not shown); drilling a left femoral stem hole (219) that is configured to mate with a left stem (221) of femoral implant (204); forming an anterior femoral resection (222) that is configured to mate with a planar surface (224) of femoral implant (204); forming an anterior femoral chamfer resection (223) that is configured to mate with a planar surface (225) of the femoral prosthetic implant; forming a posterior femoral resection (226) that is configured to mate with a planar surface (228) of femoral implant (204); forming a posterior femoral chamfer resection (230) that is configured to mate with a planar surface (232) of femoral implant (204); forming a tibial resection (234) that is configured to mate with a planar surface (236) of tibial implant (206); and forming a tibial stem feature punch (238) that is configured to mate with a feature (240) of tibial implant (206).

0068[0066] The cuts and holes described above with reference to FIG. 2 are illustrative, and are not meant to be limiting. A process of preparing a bone region for one or more implants may include forming more cuts and/or holes than described above, or fewer cuts and/or holes than described above. Furthermore, different combinations of cuts, holes, grooves, ridges, etc. may be used. Examples of instruments that may be used to prepare a target site for an implant include distal resectors, anterior-posterior (AP) sizers, sliding 4-in-l cut blocks, tibial resectors, offset tibial templates and punch towers, femoral impactors, handles/styluses, etc.

0069[0067] In certain variations, an arthroplasty jig may be customized to correspond to a particular patient's anatomy. As described above, while individual human knees share some characteristics, they also can differ from each other in certain ways, such as alignment. The use of a customized arthroplasty jig may enhance the precision of any cuts or other modifications that are made to a damaged region, such as a damaged knee region, during surgery to repair or restore the damaged region. For at least these reasons, customized arthroplasty jigs can provide for an effective and efficient arthroplasty procedure.

0070[0068J FIG. 3 is a flowchart representation of a method (300) for forming and using customized arthroplasty jigs using preoperative planning. The preoperative planning portion (302) of the method is an attempt to best determine the parameters and features of a target site prior to surgery, so that the positioning and alignment of one or more implants at the target site during surgery can be optimized.

0071[0069] As shown in FIG. 3, preoperative planning portion (302), described with reference to a knee arthroplasty, proceeds as follows. First, after a patient has undergone magnetic resonance imaging (MRI), computed tomography (CT), and/or one or more other medical imaging processes, the patient's imaging data is sent to a preoperative planning computer program. Upon receipt of the data, the computer program converts the data (e.g., two- dimensional MRI images) into three-dimensional anatomical computer models of the knee joint (304) with the aid of a medical imaging conversion computer program. For example, current commercially available MRI machines use 8 bit (255 grayscale) to show the human anatomy. Therefore, certain components of the knee, such as the cartilage, cortical bone, cancellous bone, meniscus, etc., can be uniquely viewed and recognized with 255 grayscale. The specialized medical converging software recognizes the anatomy of the knee and shapes the knee using mathematical algorithms, such as sequences of n^Λ order polynomials, where n > 3. A technique such as surface-rendering is then used to construct a three-dimensional model of the knee joint. Examples of medical imaging computer programs that may be used here include Analyze (from AnalyzeDirect, Inc., Overland Park, KS), open-source software such as the Insight Toolkit (ITK, www.itk.org) and 3D Slicer (www.slicer.org), and Mimics (from Materialise, Ann Arbor, MI). The resulting three-dimensional anatomical computer models of the knee joint include the cortical bone of the femur and the tibia, as well as articular cartilage attached to the distal region of the femur and the proximal region of the tibia. The computer program typically automatically excludes the rest of the soft tissue, as well as the cancellous bone, from the three-dimensional computer models, although in some variations the computer program may not automatically exclude the rest of the soft tissue and/or the cancellous bone. [0070] Once the three-dimensional computer models of the knee have been formed, the appropriately sized knee implants (here, femoral and tibial implants) are selected (306). This selection process may be accomplished with the aid of a computer program including one or more selection algorithms. Example of suitable computer programs include SolidWorks® software (from SolidWorks Corp., Concord, MA), and Pro/Engineer and Pro/Mechanica (both from Parametric Technology Corp.). These computer programs are only exemplary computer programs, and one or more other computer programs may be used as appropriate. In some variations, the process of selecting the appropriately sized knee implants may be conducted by one or more surgeons, bioengineers, other qualified medical professionals, etc., by using a computer graphic method to compare the critical dimensions of the implant computer models to those of the three-dimensional computer models of the knee. Critical dimensions that may be compared include, for example, the anterior-posterior (A-P) extent inequality constraint, the medial-lateral (M-L) extent inequality constraint, and the lateral condyle radii inequality constraint. Other critical dimensions may alternatively or additionally be employed. In some variations, one or more of the above-described computer software programs may be used in comparing an implant computer model to a knee computer model.

0072[0071] After the implant selection process has been completed, a shape-fitting (also known as surface-matching) process is performed (308). The shape-fitting process may be conducted with the aid of a computer program employing one or more shape-fitting algorithms. For example, shape-fitting between a patient's condyle surface and an implant's condyle surface may be accomplished using any of a number of different methods, including but not limited to point-to-point optimization and normal surface vector-to-vector optimization. Alternatively or additionally, the shape-fitting process may be conducted by one or more surgeons, bioengineers, other qualified medical professionals, etc., using a computer graphic method that includes superimposing different implant computer models onto the three-dimensional computer models of the knee. Examples of computer software that may be used to achieve this shape-fitting process include SolidWorks® software (from SolidWorks Corp., Concord, MA), and Pro/Engineer and Pro/Mechanica (both from Parametric Technology Corp.). The surgeon can then evaluate whether the implant sizes have been properly selected (310). If not, then the process is repeated, starting with implant selection (306). If the selected implants are of appropriate sizes, however, then the preoperative planning portion of the method is complete. [0072] The data gathered from preoperative planning is then sent to the hospital for surgical preparation (312), and to an arthroplasty jig manufacturer for production of one or more customized arthroplasty jigs (314). In some variations of the method, only one of these steps may be performed, while in other variations of the method, both of these steps may be performed. The hospital, upon receiving the preoperative planning data, can prepare the required sets of surgical instruments, keeping the selected implant sizes in mind. The arthroplasty jig manufacturer can use the preoperative planning data to fabricate a customized arthroplasty jig (e.g., a single-use arthroplasty jig) for use in surgery. After the appropriate preparation has taken place, the instrumentation and the arthroplasty jig or jigs are sent to an operating room (316), where an arthroplasty surgical procedure is conducted.

0073[0073] As described above, during a preoperative planning process, three- dimensional computer models of a knee region may be formed from one or more two- dimensional images of the knee region. FIG. 4 A shows multiple two-dimensional anatomical images (400) of a distal femur region of a knee taken using, for example, MRI or CT technology, or another imaging technology. A three-dimensional model (402) of the distal femoral region, shown in FIG. 4B, may be reconstructed based on the multiple two-dimensional images of FIG. 4A. Similarly, FIG. 5A shows multiple two-dimensional anatomical images (500) of a proximal tibial region of a knee, and FIG. 5B shows a three-dimensional model (502) of the proximal tibial region, which may be reconstructed based on the images of FIG. 5 A.

0074[0074] The three-dimensional models of FIGS. 4B and 5 B above may be obtained using either a surface rendering technique or a volume rendering technique. Surface rendering is an imaging technique that starts with a process such as iso-surfacing, iso-contouring, surface extraction, or border-following. After this process is complete, three-dimensional models having polygon meshes are constructed for display using, for example, conventional geometric rendering techniques. Volume rendering is an imaging technique for visualizing three- dimensional arrays (which are widely used for representing image information) of sampled two- dimensional data. Using either of the above-described surface or volume rendering techniques, cortical bone and articular cartilage of the femur and the tibia are extracted to construct three- dimensional models of these regions while filtering out other anatomy. Surface rendering techniques and volume rendering techniques are described, for example, in Foley et al., Computer Graphics: Principles and Practice (Addison Wesley, 1990); Glassner, Principles of Digital Image Synthesis (Morgan Kaufmann, 1995); Pharr et al., Physically Based Rendering (Morgan Kaufmann, 2004); Dutre et al., Advanced Global Illumination. (AK Peters, 2002); Jensen, Realistic Image Synthesis Using Photon Mapping (AK Peters, 2001); Shirley et al., Realistic Ray Tracing (AK Peters, 2nd ed., 2003); Glassner, An Introduction to Ray Tracing (Academic Press, 1989); Cohen et al., Radiosity and Realistic Image Synthesis (AP Professional, 1993); Akenine-Moller et al., Real-Time Rendering (AK Peters, 2nd ed., 2002); Gooch et al., Non-Photorealistic Rendering (AK Peters, 2001); Strothotte et al., Non-Photorealistic Computer Graphics (Morgan Kaufmann, 2002); and Blinn, Jim Blinn's Corner - A Trip Down the Graphics Pipeline (Morgan Kaufmann, 1996), all of which are hereby incorporated by reference in their entirety.

0075[0075] FIGS. 6A and 6B show front and side views, respectively, of a three- dimensional model of the distal region of a femur (600), and FIGS. 6C and 6D show front and side views, respectively, of a three-dimensional model of a corresponding femoral implant (602). Based on a coordinate system (604) (shown in FIG. 6A), a point A(X y₁) is defined where dx/dy = 0 on the boundary curve represented by x = fi(y) (which represents the medial/lateral epicondyle shape). Similarly, a point B(x₂,y₂) is defined where dx/dy = 0 on the boundary curve represented by x = f₂(y) (which represents the lateral/medial epicondyle shape). Line (AB), which connects point A to point B, is referred to as the transepicondyle axis. Additionally, a point C(x3,y3) is defined where dy/dx = 0 on the curve represented by y = gi(x), and a point D(x4,y₄) is defined where dy/dx = 0 on the curve represented by y = g₂(x). Line (CD), which connects point C to point D, is referred to as the anterior-posterior axis, or the AP axis. Length (Ll) of line (AB) is referred to as the M-L extent, and length (L2) (shown in FIG. 6B) is referred to as the A-P extent. The M-L and A-P extents provide information that may be used in selecting an appropriately sized femoral implant. The corresponding implant dimensions (Dl) and (D2), shown in FIGS. 6C and 6D, respectively, typically should closely match with, or be less than, lengths (Ll) and (L2), respectively.

0076[0076] FIG. 6E is a perspective view of three-dimensional computer models of the distal region of femur (600) and the corresponding femoral implant (602). Once the appropriate femoral implant size has been determined, the transepicondyle axis (line (AB)) and the AP axis (line (CD)) can be referenced to provide initial translational and rotational positions along the x-, y-, and z-axes (shown in a coordinate system (606)) of femoral implant (602).- Moreover, the surface profiles of the condyles, represented by the functions y = hι(x) and y = h₂(x), and the corresponding implant surface profiles of the condyles, represented by y = h₃(x) and y = Iu(X), are closely superposed to provide final translational and rotational positions of the femoral implant with respect to the three-dimensional computer model of the distal region of femur (600).

0077[O077] FIGS. 7 A and 7B are perspective views of three-dimensional computer models of the proximal region of a tibia (700) and a corresponding tibial implant (702) including a load-bearing component (704). The articular surface of the tibial plateau (706) on tibia (700) is represented by the function fi(x,y,z) = 0, and the load-bearing surface (708) on tibial implant (702) is represented by the function f₂(x,y,z) = 0, based on an x,y,z-coordinate system. A computer can be used to surface match the tibial plateau surface to the load-bearing surface by superposing the two functions. Additionally, the Is^ distance (gk) between the normal vector on the surface element of the tibial surface at (xi,y;,Zj) and the corresponding point (XJ^ZJ) on the implant-bearing surface is measured as shown in FIG. 7C. The optimal surface matching is achieved when the minimum value J = MINIMUM (SUM (from 1 to k) (g_k^A2)^A(l/2)).

0078[0078] FIGS. 8 A and 8D are graphical representations of a femoral implant (800) being shape fitted onto a distal region of a femur (804), and a tibial implant (802) being shape fitted onto a proximal region of a tibia (806), respectively. This preoperative shape fitting may, for example, result in optimal knee joint motion after a TKA procedure. After the positions of femoral implant (800) and tibial implant (802) have been set graphically, the distal femoral cut plane (808) formed from points Ai, B₁, Ci, and Di (shown in FIGS. 8A-8C), as well as the two drill hole directions (vj) and (v₂) (shown in FIG. 8C), are determined. Additionally, the proximal tibial cut plane (814) formed from points Ej, Fi, Gj, and Hj (shown in FIGS. 8D and 8E) is determined. This information may then be incorporated into the femoral and tibial arthroplasty jig designs. More specifically, distal femoral cut plane (808) is incorporated into the jig design for a femoral arthroplasty jig, and the stem hole direction vectors (V₃) and (v_j) (shown in FIG. 8B) also are determined. Furthermore, proximal tibial cut plane (814), which is determined by the shape-fitting method, is incorporated into the jig design for a tibial arthroplasty jig. This procedure can be automatically incorporated into a computer program without the manual use of a graphical interface. [0079] As described above, customized arthroplasty jigs may be formed using three-dimensional computer models. The arthroplasty jigs may be manufactured using any of a number of different methods, including rapid production methods such as computer numerical control (CNC) machining, stereolithography apparatus (SLA) methods, and/or one or more other rapid prototyping technologies.

0079[0080] Examples of arthroplasty jigs are provided in FIGS. 9A and 9B. FIG. 9A shows a femoral arthroplasty jig (900), and FIG. 9B shows a tibial arthroplasty jig (902). Femoral arthroplasty jig (900) has an interior matching surface (904), and tibial arthroplasty jig (902) has an interior matching surface (906). Interior matching surfaces (904) and (906) may be created based on three-dimensional computer models of the femur and the tibia, such as the three-dimensional computer models described above. When the interior matching surfaces are created from these three-dimensional computer models, they may have shapes and/or cavities including damaged bone and articular cartilage. These shapes and/or cavities may eventually allow the arthroplasty jigs to form a precise match, during arthroplasty surgery, with the distal region of the corresponding femur and the proximal region of the corresponding tibia. Interior surfaces (904) and (906) thus may serve as reference surfaces for mechanical registration to precisely position saw guiding slots (908) and (910) for the femoral distal and tibial planes, and drill holes (912) and (914) for stem holes on the arthroplasty jigs. Once arthroplasty jigs have been formed based on three-dimensional computer models, the arthroplasty jigs may be packaged, sterilized, and shipped to a designated hospital.

0080[0081] In some variations, an arthroplasty jig may be designed, based on implant size, to assist with anterior, anterior chamfer, posterior, and posterior chamfer cuts. An example of such an arthroplasty jig is shown in FIG. 10. As shown in FIG. 10, an arthroplasty jig (1000) has a flat surface (1002) and two stems (1004) and (1006), corresponding to the femoral distal cut plane and two drill holes, respectively. Arthroplasty jig (1000) also includes four saw- guiding slots: an anterior cut slot (1008), an anterior chamfer cut slot (1010), a posterior cut slot (1012), and a posterior chamfer cut slot (1014). While the dimensions of arthroplasty jig (1000) may not be patient-specific, they may be determined according to the size of a selected femoral implant. This implant size information may be sent to the surgeon in advance, so that the surgeon can prepare all of the necessary instrumentation prior to the surgery. [0082] In some variations, methods for forming arthroplasty jigs may include using near-shape arthroplasty jig blanks. In other words, the arthroplasty jig blanks may be predesigned to include certain features that are shared by certain patients. For example, a near- shape arthroplasty jig blank may be designed to be used to form an arthroplasty jig for a subject having a valgus knee. Advantageously, near-shape arthroplasty jig blanks may be mass- produced, and thereafter, individual near-shape arthroplasty jig blanks may be customized for a specific patient. The fact that the near-shape arthroplasty jig blanks already incorporate certain features that will be retained in the arthroplasty jigs may allow the near-shape arthroplasty jig blanks to be used to produce customized arthroplasty jigs relatively rapidly.

0081[0083] FIG. 11 is a flowchart representation of a method (1100) for forming customized arthroplasty jigs, such as single-use arthroplasty jigs, using near-shape arthroplasty jig blanks. First, near-shape femoral and/or tibial arthroplasty jig blanks are formed using one or more injection molding techniques, thermal plastic press forming techniques, and/or other plastic forming technologies (1102). The arthroplasty jig blanks may all be of the same size, or may have different sizes. For example, in some variations, six different sizes of one type of arthroplasty jig blank may be formed. Each of the arthroplasty jig blanks has a left or right knee orientation. The arthroplasty jig blanks may be mass-produced, and typically are not initially patient-specific.

0082[0084] Next, appropriate sizes for a specific patient's femoral and/or tibial arthroplasty jigs are selected (1104) based on information gathered during preoperative planning (1106). The selected arthroplasty jig blanks may then undergo a marking/labeling process (1108) using, for example, laser technology, printing technology, machine engraving, and/or adhesive labeling. Examples of information that may be included on the arthroplasty jig blanks include patient names, doctor names, company logos, barcodes, etc. Marking and labeling are described, for example, in U.S. Pat. Appl. Serial No. 11/642,385, filed on December 19, 2006, which is hereby incorporated by reference in its entirety. Next, a machining process is performed to add patient-specific features to the femoral and tibial arthroplasty jig blanks, in . addition to other features, such as guiding slots and/or holes (1110). The resulting patient- specific arthroplasty jigs may then undergo a cleaning process (1112) and a packaging process (1114). Thereafter, the packaged arthroplasty jigs may be sterilized (1116) using, for example, gamma radiation, e-beam radiation, and/or one or more other methods. The sterilized arthroplasty jigs may then be shipped to designated hospitals (1118).

0083[0085] FIG. 12A shows a near-shape femoral arthroplasty jig blank (1200), and FIG. 12B shows a near-shape tibial arthroplasty jig blank (1202). Although these near-shape arthroplasty jig blanks do not include patient-specific features, they have shapes that are similar to the shapes of the arthroplasty jigs that will eventually be formed from them. Use of near- shape arthroplasty jig blanks to form customized arthroplasty jigs may accelerate the arthroplasty jig manufacturing process (e.g., relative to a process in which arthroplasty jigs are formed from feature-less arthroplasty jig blanks). Dotted lines (1204) and (1206) represent the locations on the near-shape arthroplasty jig blanks at which patient-specific features will be added during an arthroplasty jig formation process, such as the arthroplasty jig formation process described above with reference to FIG. 11. It should be noted that these are only exemplary locations at which patient-specific features will be added, and other locations may alternatively or additionally be used. Features (1208) and (1210) are included on near-shape femoral arthroplasty jig blank (1200) and near-shape tibial arthroplasty jig blank (1202), respectively, and are configured to function as reciprocal saw guides. Relatively thick areas of the near-shape arthroplasty jigs (relative to other areas of the jigs) may represent the location of drill holes that may provide a long and stable bushing. An example of a relatively thick area is area (1212) of near-shape femoral arthroplasty jig blank (1202), which has a thickness (Tl). In some variations, the corresponding thickness of the femoral arthroplasty jig that results from femoral arthroplasty jig blank (1202) may be equal to or less than about 30% of thickness (Tl).

0084[0086] In some variations, one or more of the features of a near-shape arthroplasty jig blank may be designed or selected based on the corresponding implant that will be used. As an example, FIGS. 13A and 13B are front views of a near-shape femoral arthroplasty jig blank (1300) and its corresponding femoral arthroplasty implant (1302). There are, for example, six different sizes of Vanguard™ prosthetic femoral arthroplasty implants (manufactured by Biomet, Inc.). It is believed that these six different sizes may cover more than 90% of total knee arthroplasty surgeries. The dimensions of the near-shape arthroplasty jig blanks can be designed and selected with reference to the dimensions of one of these implants, or with reference to another appropriate implant, such as the Triathlon® Knee System (from Stryker® Orthopaedics), the P.F.C.® Sigma Knee System (from DePuy), etc. [0087] As shown in FIGS. 13 A and 13B, near-shape femoral arthroplasty jig blank (1300) has a width (Wl) that is greater than the corresponding implant width (W2). The difference between width (Wl) and width (W2) may be, for example, at least three millimeters. Similarly, near-shape femoral arthroplasty jig blank (1300) has a height (Hl) that is greater than the corresponding implant height (H2). The difference between height (Hl) and height (H2) may be, for example, at least three millimeters. Additionally, in some variations, an arthroplasty ig may have a thickness of from four millimeters to ten millimeters. If the near-shape femoral arthroplasty jig blanks are modeled based on the Vanguard™ femoral arthroplasty implants, for example, then there may be at least six near-shape femoral arthroplasty jig blanks available, which may cover 90% of TKA patients' knees. However, any resulting arthroplasty jigs may be modified. For example, in some variations, the outer boundary of an arthroplasty jig may be further machined down (e.g., to provide a smaller arthroplasty jig size for a minimally invasive TKA surgery). Furthermore, an arthroplasty jig for a knee that is much bigger or much smaller than the sizes of the available near-shape arthroplasty jig blanks may be made using one or more other manufacturing technologies, such as selective laser sintering (SLS), SLA methods, etc.

0085[0088] FIGS. 14A and 14B show top views of a near-shape tibial arthroplasty jig blank (1400) and its corresponding prosthetic tibial arthroplasty implant (1402). As with the Vanguard™ prosthetic femoral arthroplasty implants described above, there are six different sizes of Vanguard™ prosthetic tibial arthroplasty implants (manufactured by Biomet, Inc.). However, dimensions (D3) and (D4) of near-shape tibial arthroplasty jig blank (1400) are smaller than the corresponding dimensions (D5) and (D6) of tibial arthroplasty implant (1402). This helps to limit the likelihood of potential interference by soft tissue. Accordingly, near- shape tibial arthroplasty jig blank (1400) may be made to cover 50-90% of tibial articular surface and exposed proximal tibial cortical bone. Additionally, the outer boundary of the resulting tibial arthroplasty jig may be further machined down to provide an optimal fitting of the tibial arthroplasty jig with the tibial plateau during surgery.

0086[0089] FIG. 15 shows a near-shape femoral arthroplasty jig blank (1500) undergoing a milling process (1502) to add patient-specific features (1504) onto the arthroplasty jig blank. The patient-specific features may be added based on preoperative planning information, which may include the anatomical shape of the patient's articular cartilage surface and exposed and side distal femur cortical bone (obtained, for example, from MRI and/or CT images). A machining file may be generated based on this preoperative planning information, and may be used to provide a CNC machine and/or an automated mechanical system (e.g., a robot) with instructions to machine patient-specific cavities and/or other features onto the arthroplasty jig blank.

0087[0090] FIG. 16 is a perspective view of customized (patient-specific) femoral and tibial arthroplasty jigs (1600) and (1602), respectively. Femoral arthroplasty jig (1600) is ^• attached to a distal region of a femur (1604), while tibial arthroplasty jig (1602) is attached to a proximal region of a tibia (1606). Femoral arthroplasty jig (1600) includes a slot (1608) and holes (1610) and (1612), while tibial arthroplasty jig (1602) includes slots (1614) and (1615). These features may be machined, for example, based on preoperative planning information regarding patient-specific anatomical cavity features. Once an incision has been made and the distal region of the femur and proximal region of the tibia have been exposed in the operating room, the customized arthroplasty jigs may be precisely matched with anatomical surfaces of the knee. Moreover, the slots and holes in the customized arthroplasty jigs may be used to guide one or more osteotomy instruments. The osteotomy instruments may be cutting instruments, such as reciprocal saws (1616), (1618), and/or (1620), and/or drilling instruments, such as stem drill (1622). The above-described slots and holes, in addition to jig fixation holes (1624), (1626), (1628), and (1630) on the femoral and tibial arthroplasty jigs, may provide for relatively high-precision cutting and drilling based on preoperative planning.

0088[0091] The arthroplasty jigs and arthroplasty jig blanks described herein may be formed of any of a number of different materials. They may be formed of just one material, or multiple materials, such as a blend of different materials or layers of different materials. Generally, the arthroplasty jigs and arthroplasty jig blanks may be formed of any suitable biocompatible material. Examples of suitable materials include polymers, metals, ceramics, metal alloys, and combinations thereof. Specific examples of polymers include acetal resins (e.g., Delrin^®), polyetheretherketones (PEEK), polycarbonates, polyamides, polyesters, polystyrenes, polyacrylates, vinyl polymers, and polyurethanes. Specific examples of metals and metal alloys include gold, platinum, palladium, stainless steel, cobalt alloys (e.g., Elgiloy^®), and nickel-titanium alloys (e.g., Nitinol™). In some variations, the arthroplasty jig blanks may be formed of one or more plastics. In such variations, the blanks may be formed, for example, using injection molding technology and/or thermal plastic press forming technology. In certain variations, an arthroplasty jig may be intended to be disposable, and in some variations, an arthroplasty jig may be intended to be recyclable. The materials out of which an arthroplasty jig is formed may be selected with these and/or other criteria in mind. As an example, some variations of arthroplasty jigs may be formed of thermoplastic materials, and may be 100% recyclable. Moreover, certain variations of arthroplasty jigs may be formed of two or more layers of different materials, and/or may include one or more coatings.

0089[0092] FIG. 17 shows a distal region of a femur (1700) and a proximal region of a tibia (1702) after they have been resected using customized arthroplasty jigs, such as those described above. Femur (1700) includes a femoral distal cut (1704) and two stem drilling holes (1706) and (1708). Tibia (1702) includes a tibial cut (1710) and a tibial stem cut (1712). These cuts can be important to the successful alignment of prosthetic implants in these regions, such that excellent extension and flexion of the knee joint are provided.

0090[0093] FIG. 18 shows additional different types of cuts that may be made to a femur (1800) during a knee arthroplasty procedure. As shown in FIG. 18, a distal portion of femur (1800) has been resected to provide a femoral distal cut (1802) for the translation position of a femoral implant. The femoral distal cut may be formed using, for example, a distal resector (available as part of the Vanguard™ Knee System, from Biomet, Inc.). Additional cuts that have been made to femur (1800) include a posterior resection (1804), a posterior anterior chamfer resection (1806), an anterior resection (1808), and a posterior chamfer resection (1810). These four resections may be formed using, for example, a sliding 4-in-l cut block (also available as part of the Vanguard™ Knee System, from Biomet, Inc.).

0091[0094] FIGS. 19A and 19B show three-dimensional computer models based on preoperative planning information of a patient's femur and tibia. The three-dimensional computer models include a model of the femur (1900) and a model of the tibia (1902), and may be formed from multiple segmented images of the patient's femur and tibia, obtained using MRI, CT, and/or one or more other imaging technologies. The preoperative planning that is performed may be based on a traditional TKA surgical method, a shape-matching method, and/or one or more other preferred methods. Once the appropriately sized femoral and tibial implants have been selected based on the results of the preoperative planning, the selected three- dimensional implant computer models (as shown, femoral implant model (1904) and tibial implant model (1906)) are automatically superposed onto the three-dimensional femoral and tibial computer models (1900) and (1902). This may be accomplished using computer-aided graphics including positioning algorithms (e.g., using one or more of the software programs described above). Based on the superpositions between the three-dimensional femoral and tibial computer models and their corresponding three-dimensional implant computer models, certain cut planes and stem directions may be obtained. For example, and as shown in FIG. 19A, a distal cut plane (1908) (formed from points A, B, C, and D) and two femoral stem directions (1910) and (1912) are obtained. Similarly, and as shown in FIG. 19B₅ a tibial cut plane (1914) (formed from points E, F, G₅ and H) and a tibial stem direction (1916) are obtained. These cut planes and stem directions may provide important information with regard to the alignment of prosthetic implants in the preoperative planning process.

0092[0095] FIGS. 2OA and 2OB illustrate a computer-aided point-to-point mapping process that can be used to map a distal portion of a subject's femur, and a proximal portion of the subject's tibia. First, a total number of N points, such as point (2000) and point (2002), are selected on the surfaces of the articular cartilage and bone of a femur (2004) and a tibia (2006). In mapping femur (2004), the distance (such as distance (D7)) between each point on a femoral distal cut plane (2012) formed from points A, B₅ C, and D, to a corresponding point on a parallel reference femoral plane (2008) formed from points Ai, Bi, Ci, and Dj₅ is measured and registered for all N points. Generally, as N increases, accuracy of implant alignment can become enhanced. Tibial mapping is similar, except that the distances are measured from each point on a tibial cut plane (2014) formed from points E₅ F, G, and H, to a corresponding point on a parallel reference tibial plane (2010) formed from points Ei, Fi, Gi, and Hi.

0093[0096] Certain devices may be used to help properly position an arthroplasty jig at a target site. For example, FIG. 21 A shows a multi-pin guided device (2100) that may be used for aligning an arthroplasty jig on a distal portion of a subject's femur, while FIG. 2 IB shows a multi-pin guided device (2102) that may be used for aligning an arthroplasty jig on a proximal portion of a subject's tibia.

0094[0097] Femoral device (2100) includes pin blocks (2104) and (2106) holding N number of pins, such as pin (2108). In some variations, N may be greater than three and less than 1,000. Each pin is a mechanical registration pin in the form of a rod with a rounded edge ^"that is configured to contact cartilage or bone during surgery. Each pin is arranged to match a corresponding distance registered in a point-to-point matching process performed previously (such as distance (D7), described with reference to FIG. 20A). Furthermore, device (2100) includes a drill bushing block (2110) that is positioned between pin blocks (2104) and (2106), and that can provide a surgeon with femoral prosthetic implant stem hole positions. An instrument guiding block (2112) is placed on top of pin blocks (2104) and (2106), to guide an arthroplasty jig to form a femoral distal cut corresponding to plane ABCD (such as femoral distal cut (1802) shown in FIG. 18). Device (2100) further includes a feature (2114) that functions as a mechanical tightening device by firmly securing the multiple blocks and pins for final assembly.

0095[0098] Similarly, tibial device (2102) is a multiple pin-based mechanical jig guiding device. While tibial device (2102) has a different configuration from femoral device (2100), tibial device (2102) has similar components to femoral device (2100). For example, tibial device (2102) includes pins (e.g., pin 2152) and features (2154) and (2156) that function as mechanical tightening devices by firmly securing the multiple blocks and pins of tibial device (2102) for final assembly.

0096[0099] Tibial device (2102) and femoral device (2100) may be assembled manually (e.g., by surgeons, nurses, or any other qualified personnel), or may be assembled using a device such as computer-controlled positioning device (2170), shown in FIG. 21 C. Device (2170) includes a computer program (2172) (e.g., for use with a PC) that controls multiple actuators (2174) or a similar device that push pins, such as pin (2176), into one of the pin blocks (as shown, pin block (2104)). Actuators (2174) also can position all of the blocks of the device based on preoperative planning data. The assembly of multi-pin guided devices may be done either preoperatively (i.e., before a surgical incision) or intraoperatively (i.e., after a surgical incision has been made).

0097[0100] FIG. 22 illustrates the positioning of conventional arthroplasty jig instruments, using multi-pin guided surface-matching devices, on a distal portion of a patient's femur and a proximal portion of the patient's tibia. After the distal femoral portion (2200) and the proximal tibial portion (2202) have been exposed via an incision, the multi-pin guided devices (2204) and (2206) are used to match the surfaces of the femur and the tibia, respectively. The positions are uniquely defined according to the plan (i.e., one-to-one matching). First, stem hole drilling processes (2208) and (2210) are performed with respect to the drill hole bushings (2212), (2214), and (2216) assembled in the multiple pin based mechanical jig guiding devices. A distal resector (2218), which is a conventional TKA jig instrument, is placed with respect to multi-pin guided device (2204) and is firmly fixed onto the anterior side of the femur with multiple nails and/or screws (2220) and (2222). The multi-pin guided surface matching device (2204) may then be removed, and a surgeon may make a femoral distal cut using a reciprocal saw (2224). Tibial resection may be done similarly to the femoral distal resection, as shown.

0098[0101] While the multi-pin guided surface matching devices described above have been described with reference to their use in positioning arthroplasty jigs, in some variations, an arthroplasty jig itself may be in the form of a multi-pin device. The pins may be used, for example, the help accurately position the arthroplasty jig at a target site. Arthroplasty jigs including positioning components are described, for example, in U.S. Pat. Appl. Serial No. 11/642,385, filed on December 19, 2006, which was previously incorporated by reference in its entirety. An arthroplasty jig that is in the form of a multi-pin device may be formed using preoperative and/or intraoperative planning methods, and may be used, for example, in point-to- point matching.

0099[0102] The methods and devices described herein have been described with respect to arthroplasty jigs. However, the features of the methods and devices described herein may apply to some variations of implants, such as arthroplasty implants. Moreover, while arthroplasty procedures have been described, the jigs and implants described herein may be used in any of a number of different procedures, including, for example, spinal surgery.

0100[0103 J While the methods and devices have been described in some detail here by way of illustration and example, such illustration and example is for purposes of clarity of understanding only. It will be readily apparent to those of ordinary skill in the art in light of the teachings herein that certain changes and modifications may be made thereto without departing from the spirit and scope of the appended claims.