Arthroplasty system and related methods

A method of manufacturing an arthroplasty jig is disclosed herein. The method may include the following: generate a bone model, wherein the bone model includes a three dimensional computer model of at least a portion of a joint surface of a bone of a patient joint to undergo an arthroplasty procedure; generate an implant model, wherein the implant model includes a three dimensional computer model of at least a portion of a joint surface of an arthroplasty implant to be used in the arthroplasty procedure; assess a characteristic associated with the patient joint; generate a modified joint surface of the implant model by modifying at least a portion of a joint surface of the implant model according to the characteristic; and shape match the modified joint surface of the implant model and a corresponding joint surface of the bone model.

FIELD OF THE INVENTION

The present invention relates to systems and methods for manufacturing customized arthroplasty cutting jigs. More specifically, the present invention relates to automated systems and methods of manufacturing such jigs.

BACKGROUND OF THE INVENTION

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.

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.

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.

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.

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.

To achieve accurate implant alignment, prior to treating (e.g., cutting, drilling, reaming, and/or resurfacing) any regions of a bone, it is important to correctly determine the location at which the treatment will take place and how the treatment will be oriented. In some methods, an arthroplasty jig may be used to accurately position and orient a finishing instrument, such as a cutting, drilling, reaming, or resurfacing instrument on the regions of the bone. The arthroplasty jig may, for example, include one or more apertures and/or slots that are configured to accept such an instrument.

A system and method has been developed for producing customized arthroplasty jigs configured to allow a surgeon to accurately and quickly perform an arthroplasty procedure that restores the pre-deterioration alignment of the joint, thereby improving the success rate of such procedures. Specifically, the customized arthroplasty jigs are indexed such that they matingly receive the regions of the bone to be subjected to a treatment (e.g., cutting, drilling, reaming, and/or resurfacing). The customized arthroplasty jigs are also indexed to provide the proper location and orientation of the treatment relative to the regions of the bone. The indexing aspect of the customized arthroplasty jigs allows the treatment of the bone regions to be done quickly and with a high degree of accuracy that will allow the implants to restore the patient's joint to a generally pre-deteriorated state. However, the system and method for generating the customized jigs often relies on a human to “eyeball” bone models on a computer screen to determine configurations needed for the generation of the customized jigs. This “eyeballing” or manual manipulation of the bone modes on the computer screen is inefficient and unnecessarily raises the time, manpower and costs associated with producing the customized arthroplasty jigs. Furthermore, a less manual approach may improve the accuracy of the resulting jigs.

There is a need in the art for a system and method for reducing the labor associated with generating customized arthroplasty jigs. There is also a need in the art for a system and method for increasing the accuracy of customized arthroplasty jigs.

SUMMARY

Various embodiments of a method of manufacturing an arthroplasty jig are disclosed herein. In a first embodiment, the method may include the following: generate a bone model, wherein the bone model includes a three dimensional computer model of at least a portion of a joint surface of a bone of a patient joint to undergo an arthroplasty procedure; generate an implant model, wherein the implant model includes a three dimensional computer model of at least a portion of a joint surface of an arthroplasty implant to be used in the arthroplasty procedure; assess a characteristic associated with the patient joint; generate a modified joint surface of the implant model by modifying at least a portion of a joint surface of the implant model according to the characteristic; and shape match the modified joint surface of the implant model and a corresponding joint surface of the bone model.

In a second embodiment, the method may include the following: generate a restored bone model, wherein the bone model includes a three dimensional computer model of at least a portion of a joint surface of a bone of a patient joint to undergo an arthroplasty procedure, wherein the restored bone model is representative of the bone in a pre-degenerated state; generate an implant model, wherein the implant model includes a three dimensional computer model of at least a portion of a joint surface of an arthroplasty implant to be used in the arthroplasty procedure; and shape match an articular joint surface of the restored bone model and a corresponding articular joint surface of the implant model.

In a third embodiment, the method may include the following: generate a bone model, wherein the bone model includes a three dimensional computer model of at least a portion of a knee joint surface of a patient femur to undergo an arthroplasty procedure; identify at least one of a most distal point and a most posterior point of a condyle articular surface of the bone model; generate an implant model, wherein the implant model includes a three dimensional computer model of at least a portion of a joint surface of a femoral arthroplasty knee implant to be used in the arthroplasty procedure; identify at least one of a most distal point and a most posterior point of a condyle articular surface of the implant model; and move at least one of the bone model and the implant model so the at least one of the most distal point and the most posterior point of the condyle articular surface of the bone model generally positionally correspond with the at least one of the most distal point and the most posterior point of the condyle articular surface of the implant model. In a variation of the third embodiment, the method may further include the following: shape match the condyle articular surface of the bone model and the articular condyle surface of the implant model.

In a fourth embodiment, the method may include the following: generate two-dimensional images of a joint surface of a patient bone; generate first data from the two-dimensional images, wherein the first data is representative of the joint surface in a deteriorated state; generate second data from the two-dimensional images, wherein the second data is representative of the joint surface in a non-deteriorated state; generate third data and fourth data positionally referenced to the third data, wherein the third data is representative of a joint surface of an arthroplasty implant and the fourth data is representative of a surgical cut plane associated with the arthroplasty implant; generate fifth data from the first data, wherein the fifth data is representative of a surface of the arthroplasty jig that will matingly receive the joint surface; generate sixth data by matching the second data and the third data, the resulting sixth data including a position of the fourth data when the second and third data are matched; generate seventh data by merging the fifth data and the sixth data; and employ the seventh data in manufacturing the arthroplasty jig from a jig blank.

An arthroplasty jig is also disclosed herein. In one embodiment, the arthroplasty jig may be for performing an arthroplasty procedure on a joint surface of a bone of a patient joint to receive an arthroplasty joint implant. In one embodiment, the arthroplasty jig may include: a mating surface configured to matingly receive the joint surface; a first saw guide oriented relative to the mating surface to result in a resection that allows the arthroplasty joint implant to restore the patient joint to a pre-degenerated alignment; and a second saw guide oriented relative to the mating surface to result in a resection that allows the arthroplasty joint implant to cause the patient joint to have an alignment approaching a zero degree mechanical axis alignment.

DETAILED DESCRIPTION

Disclosed herein are customized arthroplasty jigs2and systems4for, and methods of, producing such jigs2. The jigs2are customized to fit specific bone surfaces of specific patients. Depending on the embodiment and to a greater or lesser extent, the jigs2are automatically planned and generated and may be similar to those disclosed in these three U.S. patent applications: U.S. patent application Ser. No. 11/656,323 to Park et al., titled “Arthroplasty Devices and Related Methods” and filed Jan. 19, 2007; U.S. patent application Ser. No. 10/146,862 to Park et al., titled “Improved Total Joint Arthroplasty System” and filed May 15, 2002; and U.S. patent Ser. No. 11/642,385 to Park et al., titled “Arthroplasty Devices and Related Methods” and filed Dec. 19, 2006. The disclosures of these three U.S. patent applications are incorporated by reference in their entireties into this Detailed Description.

A. Overview of System and Method for Manufacturing Customized Arthroplasty Cutting Jigs

For an overview discussion of the systems4for, and methods of, producing the customized arthroplasty jigs2, reference is made toFIGS. 1A-1E.FIG. 1Ais a schematic diagram of a system4for employing the automated jig production method disclosed herein.FIGS. 1B-1Eare flow chart diagrams outlining the jig production method disclosed herein. The following overview discussion can be broken down into three sections.

The first section, which is discussed with respect toFIG. 1Aand [blocks100-125] ofFIGS. 1B-1E, pertains to an example method of determining, in a three-dimensional (“3D”) computer model environment, saw cut and drill hole locations30,32relative to 3D computer models that are termed restored bone models28. The resulting “saw cut and drill hole data”44is referenced to the restored bone models28to provide saw cuts and drill holes that will allow arthroplasty implants to restore the patient's joint to its pre-degenerated or natural alignment state.

The second section, which is discussed with respect toFIG. 1Aand [blocks100-105and130-145] ofFIGS. 1B-1E, pertains to an example method of importing into 3D computer generated jig models383D computer generated surface models40of arthroplasty target areas42of 3D computer generated arthritic models36of the patient's joint bones. The resulting “jig data”46is used to produce a jig customized to matingly receive the arthroplasty target areas of the respective bones of the patient's joint.

The third section, which is discussed with respect toFIG. 1Aand [blocks150-165] ofFIG. 1E, pertains to a method of combining or integrating the “saw cut and drill hole data”44with the “jig data”46to result in “integrated jig data”48. The “integrated jig data”48is provided to the CNC machine10or other rapid production machine (e.g., a stereolithography apparatus (“SLA”) machine) for the production of customized arthroplasty jigs2from jig blanks50provided to the CNC machine10. The resulting customized arthroplasty jigs2include saw cut slots and drill holes positioned in the jigs2such that when the jigs2matingly receive the arthroplasty target areas of the patient's bones, the cut slots and drill holes facilitate preparing the arthroplasty target areas in a manner that allows the arthroplasty joint implants to generally restore the patient's joint line to its pre-degenerated state or natural alignment state.

As shown inFIG. 1A, the system4includes a computer6having a CPU7, a monitor or screen9and an operator interface controls11. The computer6is linked to a medical imaging system8, such as a CT or MRI machine8, and a computer controlled machining system10, such as a CNC milling machine10.

As indicated inFIG. 1A, a patient12has a joint14(e.g., a knee, elbow, ankle, wrist, hip, shoulder, skull/vertebrae or vertebrae/vertebrae interface, etc.) to be replaced. The patient12has the joint14scanned in the imaging machine8. The imaging machine8makes a plurality of scans of the joint14, wherein each scan pertains to a thin slice of the joint14.

As can be understood fromFIG. 1B, the plurality of scans is used to generate a plurality of two-dimensional (“2D”) images16of the joint14[block100]. Where, for example, the joint14is a knee14, the 2D images will be of the femur18and tibia20. The imaging may be performed via CT or MRI. In one embodiment employing MRI, the imaging process may be as disclosed in U.S. patent application Ser. No. 11/946,002 to Park, which is entitled “Generating MRI Images Usable For The Creation Of 3D Bone Models Employed To Make Customized Arthroplasty Jigs,” was filed Nov. 27, 2007 and is incorporated by reference in its entirety into this Detailed Description.

As can be understood fromFIG. 1A, the 2D images are sent to the computer6for creating computer generated 3D models. As indicated inFIG. 1B, in one embodiment, point P is identified in the 2D images16[block105]. In one embodiment, as indicated in [block105] ofFIG. 1A, point P may be at the approximate medial-lateral and anterior-posterior center of the patient's joint14. In other embodiments, point P may be at any other location in the 2D images16, including anywhere on, near or away from the bones18,20or the joint14formed by the bones18,20.

As described later in this overview, point P may be used to locate the computer generated 3D models22,28,36created from the 2D images16and to integrate information generated via the 3D models. Depending on the embodiment, point P, which serves as a position and/or orientation reference, may be a single point, two points, three points, a point plus a plane, a vector, etc., so long as the reference P can be used to position and/or orient the 3D models22,28,36generated via the 2D images16.

As shown inFIG. 1C, the 2D images16are employed to create computer generated 3D bone-only (i.e., “bone models”)22of the bones18,20forming the patient's joint14[block110]. The bone models22are located such that point P is at coordinates (X0-j, Y0-j, Z0-j) relative to an origin (X0, Y0, Z0) of an X-Y-Z axis [block110]. The bone models22depict the bones18,20in the present deteriorated condition with their respective degenerated joint surfaces24,26, which may be a result of osteoarthritis, injury, a combination thereof, etc.

In one embodiment, the bone surface contour lines of the bones18,20depicted in the image slices16may be auto segmented via a image segmentation process as disclosed in U.S. Patent Application 61/126,102, which was filed Apr. 30, 2008, is entitled System and Method for Image Segmentation in Generating Computer Models of a Joint to Undergo Arthroplasty, and is hereby incorporated by reference into the present application in its entirety.

Computer programs for creating the 3D computer generated bone models22from the 2D images16include: Analyze from AnalyzeDirect, Inc., Overland Park, Kans.; Insight Toolkit, an open-source software available from the National Library of Medicine Insight Segmentation and Registration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-source software available from www.slicer.org; Mimics from Materialise, Ann Arbor, Mich.; and Paraview available at www.paraview.org.

As indicated inFIG. 1C, the 3D computer generated bone models22are utilized to create 3D computer generated “restored bone models” or “planning bone models”28wherein the degenerated surfaces24,26are modified or restored to approximately their respective conditions prior to degeneration [block115]. Thus, the bones18,20of the restored bone models28are reflected in approximately their condition prior to degeneration. The restored bone models28are located such that point P is at coordinates (X0-j, Y0-j, Z0-j) relative to the origin (X0, Y0, Z0). Thus, the restored bone models28share the same orientation and positioning relative to the origin (X0, Y0, Z0) as the bone models22.

In one embodiment, the restored bone models28are manually created from the bone models22by a person sitting in front of a computer6and visually observing the bone models22and their degenerated surfaces24,26as 3D computer models on a computer screen9. The person visually observes the degenerated surfaces24,26to determine how and to what extent the degenerated surfaces24,26surfaces on the 3D computer bone models22need to be modified to restore them to their pre-degenerated condition. By interacting with the computer controls11, the person then manually manipulates the 3D degenerated surfaces24,26via the 3D modeling computer program to restore the surfaces24,26to a state the person believes to represent the pre-degenerated condition. The result of this manual restoration process is the computer generated 3D restored bone models28, wherein the surfaces24′,26′ are indicated in a non-degenerated state.

In one embodiment, the above-described bone restoration process is generally or completely automated, as disclosed in U.S. patent application Ser. No. 12/111,924 to Park, which is entitled Generation of a Computerized Bone Model Representative of a Pre-Degenerated State and Usable in the Design and Manufacture of Arthroplasty Devices, was filed Apr. 29, 2008 and is incorporated by reference in its entirety into this Detailed Description. In other words, a computer program may analyze the bone models22and their degenerated surfaces24,26to determine how and to what extent the degenerated surfaces24,26surfaces on the 3D computer bone models22need to be modified to restore them to their pre-degenerated condition. The computer program then manipulates the 3D degenerated surfaces24,26to restore the surfaces24,26to a state intended to represent the pre-degenerated condition. The result of this automated restoration process is the computer generated 3D restored bone models28, wherein the surfaces24′,26′ are indicated in a non-degenerated state.

As depicted inFIG. 1C, the restored bone models28are employed in a pre-operative planning (“POP”) procedure to determine saw cut locations30and drill hole locations32in the patient's bones that will allow the arthroplasty joint implants to generally restore the patient's joint line to its pre-degenerative alignment [block120].

In one embodiment, the POP procedure is a manual process, wherein computer generated 3D implant models34(e.g., femur and tibia implants in the context of the joint being a knee) and restored bone models28are manually manipulated relative to each other by a person sitting in front of a computer6and visually observing the implant models34and restored bone models28on the computer screen9and manipulating the models28,34via the computer controls11. By superimposing the implant models34over the restored bone models28, or vice versa, the joint surfaces of the implant models34can be aligned or caused to correspond with the joint surfaces of the restored bone models28. By causing the joint surfaces of the models28,34to so align, the implant models34are positioned relative to the restored bone models28such that the saw cut locations30and drill hole locations32can be determined relative to the restored bone models28.

In one embodiment, the POP process is generally or completely automated. For example, a computer program may manipulate computer generated 3D implant models34(e.g., femur and tibia implants in the context of the joint being a knee) and restored bone models or planning bone models28relative to each other to determine the saw cut and drill hole locations30,32relative to the restored bone models28. The implant models34may be superimposed over the restored bone models28, or vice versa. In one embodiment, the implant models34are located at point P′ (X0-k, Y0-k, Z0-k) relative to the origin (X0, Y0, Z0), and the restored bone models28are located at point P (X0-j, Y0-j, Z0-j). To cause the joint surfaces of the models28,34to correspond, the computer program may move the restored bone models28from point P (X0-j, Y0-j, Z0-j) to point P′ (X0-k, Y0-k, Z0-k), or vice versa. Once the joint surfaces of the models28,34are in close proximity, the joint surfaces of the implant models34may be shape-matched to align or correspond with the joint surfaces of the restored bone models28. By causing the joint surfaces of the models28,34to so align, the implant models34are positioned relative to the restored bone models28such that the saw cut locations30and drill hole locations32can be determined relative to the restored bone models28. A discussion of various embodiments of the automated POP process is provided later in this Detailed Description.

As indicated inFIG. 1E, in one embodiment, the data44regarding the saw cut and drill hole locations30,32relative to point P′ (X0-k, Y0-k, Z0-k) is packaged or consolidated as the “saw cut and drill hole data”44[block145]. The “saw cut and drill hole data”44is then used as discussed below with respect to [block150] inFIG. 1E.

As can be understood fromFIG. 1D, the 2D images16employed to generate the bone models22discussed above with respect to [block110] ofFIG. 1Care also used to create computer generated 3D bone and cartilage models (i.e., “arthritic models”)36of the bones18,20forming the patient's joint14[block130]. Like the above-discussed bone models22, the arthritic models36are located such that point P is at coordinates (X0-j, Y0-j, Z0-j) relative to the origin (X0, Y0, Z0) of the X-Y-Z axis [block130]. Thus, the bone and arthritic models22,36share the same location and orientation relative to the origin (X0, Y0, Z0). This position/orientation relationship is generally maintained throughout the process discussed with respect toFIGS. 1B-1E. Accordingly, movements relative to the origin (X0, Y0, Z0) of the bone models22and the various descendants thereof (i.e., the restored bone models28, bone cut locations30and drill hole locations32) are also applied to the arthritic models36and the various descendants thereof (i.e., the jig models38). Maintaining the position/orientation relationship between the bone models22and arthritic models36and their respective descendants allows the “saw cut and drill hole data”44to be integrated into the “jig data”46to form the “integrated jig data”48employed by the CNC machine10to manufacture the customized arthroplasty jigs2.

Computer programs for creating the 3D computer generated arthritic models36from the 2D images16include: Analyze from AnalyzeDirect, Inc., Overland Park, Kans.; Insight Toolkit, an open-source software available from the National Library of Medicine Insight Segmentation and Registration Toolkit (“ITK”), www.itk.org; 3D Slicer, an open-source software available from www.slicer.org; Mimics from Materialise, Ann Arbor, Mich.; and Paraview available at www.paraview.org.

Similar to the bone models22, the arthritic models36depict the bones18,20in the present deteriorated condition with their respective degenerated joint surfaces24,26, which may be a result of osteoarthritis, injury, a combination thereof, etc. However, unlike the bone models22, the arthritic models36are not bone-only models, but include cartilage in addition to bone. Accordingly, the arthritic models36depict the arthroplasty target areas42generally as they will exist when the customized arthroplasty jigs2matingly receive the arthroplasty target areas42during the arthroplasty surgical procedure.

As indicated inFIG. 1Dand already mentioned above, to coordinate the positions/orientations of the bone and arthritic models22,36and their respective descendants, any movement of the restored bone models28from point P to point P′ is tracked to cause a generally identical displacement for the “arthritic models”36[block135].

As depicted inFIG. 1D, computer generated 3D surface models40of the arthroplasty target areas42of the arthritic models36are imported into computer generated 3D arthroplasty jig models38[block140]. Thus, the jig models38are configured or indexed to matingly receive the arthroplasty target areas42of the arthritic models36. Jigs 2 manufactured to match such jig models38will then matingly receive the arthroplasty target areas of the actual joint bones during the arthroplasty surgical procedure.

In one embodiment, the procedure for indexing the jig models38to the arthroplasty target areas42is a manual process. The 3D computer generated models36,38are manually manipulated relative to each other by a person sitting in front of a computer6and visually observing the jig models38and arthritic models36on the computer screen9and manipulating the models36,38by interacting with the computer controls11. In one embodiment, by superimposing the jig models38(e.g., femur and tibia arthroplasty jigs in the context of the joint being a knee) over the arthroplasty target areas42of the arthritic models36, or vice versa, the surface models40of the arthroplasty target areas42can be imported into the jig models38, resulting in jig models38indexed to matingly receive the arthroplasty target areas42of the arthritic models36. Point P′ (X0-k, Y0-k, Z0-k) can also be imported into the jig models38, resulting in jig models38positioned and oriented relative to point P′ (X0-k, Y0-k, Z0-k) to allow their integration with the bone cut and drill hole data44of [block125].

In one embodiment, the procedure for indexing the jig models38to the arthroplasty target areas42is generally or completely automated, as disclosed in U.S. patent application Ser. No. 11/959,344 to Park, which is entitled System and Method for Manufacturing Arthroplasty Jigs, was filed Dec. 18, 2007 and is incorporated by reference in its entirety into this Detailed Description. For example, a computer program may create 3D computer generated surface models40of the arthroplasty target areas42of the arthritic models36. The computer program may then import the surface models40and point P′ (X0-k, Y0-k, Z0-k) into the jig models38, resulting in the jig models38being indexed to matingly receive the arthroplasty target areas42of the arthritic models36. The resulting jig models38are also positioned and oriented relative to point P′ (X0-k, Y0-k, Z0-k) to allow their integration with the bone cut and drill hole data44of [block125].

In one embodiment, the arthritic models36may be 3D volumetric models as generated from the closed-loop process discussed in U.S. patent application Ser. No. 11/959,344 filed by Park. In other embodiments, the arthritic models36may be 3D surface models as generated from the open-loop process discussed in U.S. patent application Ser. No. 11/959,344 filed by Park.

In one embodiment, the models40of the arthroplasty target areas42of the arthritic models36may be generated via an overestimation process as disclosed in U.S. Provisional Patent Application 61/083,053, which is entitled System and Method for Manufacturing Arthroplasty Jigs Having Improved Mating Accuracy, was filed by Park Jul. 23, 2008, and is hereby incorporated by reference in its entirety into this Detailed Description.

As indicated inFIG. 1E, in one embodiment, the data regarding the jig models38and surface models40relative to point P′ (X0-k, Y0-k, Z0-k) is packaged or consolidated as the “jig data”46[block145]. The “jig data”46is then used as discussed below with respect to [block150] inFIG. 1E.

As can be understood fromFIG. 1E, the “saw cut and drill hole data”44is integrated with the “jig data”46to result in the “integrated jig data”48[block150].

As explained above, since the “saw cut and drill hole data”44, “jig data”46and their various ancestors (e.g., models22,28,36,38) are matched to each other for position and orientation relative to point P and P′, the “saw cut and drill hole data”44is properly positioned and oriented relative to the “jig data”46for proper integration into the “jig data”46. The resulting “integrated jig data”48, when provided to the CNC machine10, results in jigs2: (1) configured to matingly receive the arthroplasty target areas of the patient's bones; and (2) having cut slots and drill holes that facilitate preparing the arthroplasty target areas in a manner that allows the arthroplasty joint implants to generally restore the patient's joint line to its pre-degenerated state or natural alignment state.

As can be understood fromFIGS. 1A and 1E, the “integrated jig data”48is transferred from the computer6to the CNC machine10[block155]. Jig blanks50are provided to the CNC machine10[block160], and the CNC machine10employs the “integrated jig data” to machine the arthroplasty jigs2from the jig blanks50.

For a discussion of example customized arthroplasty cutting jigs2capable of being manufactured via the above-discussed process, reference is made toFIGS. 1F-1I. While, as pointed out above, the above-discussed process may be employed to manufacture jigs2configured for arthroplasty procedures involving knees, elbows, ankles, wrists, hips, shoulders, vertebra interfaces, etc., the jig examples depicted inFIGS. 1F-1Iare for total knee replacement (“TKR”) or partial knee (“uni-knee”) replacement procedures. Thus,FIGS. 1F and 1Gare, respectively, bottom and top perspective views of an example customized arthroplasty femur jig2A, andFIGS. 1H and 1Iare, respectively, bottom and top perspective views of an example customized arthroplasty tibia jig2B.

As indicated inFIGS. 1F and 1G, a femur arthroplasty jig2A may include an interior side or portion100and an exterior side or portion102. When the femur cutting jig2A is used in a TKR procedure, the interior side or portion100faces and matingly receives the arthroplasty target area42of the femur lower end, and the exterior side or portion102is on the opposite side of the femur cutting jig2A from the interior portion100.

The interior portion100of the femur jig2A is configured to match the surface features of the damaged lower end (i.e., the arthroplasty target area42) of the patient's femur18. Thus, when the target area42is received in the interior portion100of the femur jig2A during the TKR surgery, the surfaces of the target area42and the interior portion100match.

The surface of the interior portion100of the femur cutting jig2A is machined or otherwise formed into a selected femur jig blank50A and is based or defined off of a 3D surface model40of a target area42of the damaged lower end or target area42of the patient's femur18.

As indicated inFIGS. 1H and 1I, a tibia arthroplasty jig2B may include an interior side or portion104and an exterior side or portion106. When the tibia cutting jig2B is used in a TKR procedure, the interior side or portion104faces and matingly receives the arthroplasty target area42of the tibia upper end, and the exterior side or portion106is on the opposite side of the tibia cutting jig2B from the interior portion104.

The interior portion104of the tibia jig2B is configured to match the surface features of the damaged upper end (i.e., the arthroplasty target area42) of the patient's tibia20. Thus, when the target area42is received in the interior portion104of the tibia jig2B during the TKR surgery, the surfaces of the target area42and the interior portion104match.

The surface of the interior portion104of the tibia cutting jig2B is machined or otherwise formed into a selected tibia jig blank50B and is based or defined off of a 3D surface model40of a target area42of the damaged upper end or target area42of the patient's tibia20.

While the discussion provided herein is given in the context of TKR and TKR jigs and the generation thereof. However, the disclosure provided herein is readily applicable to uni-compartmental or partial arthroplasty procedures in the knee or other joint contexts. Thus, the disclosure provided herein should be considered as encompassing jigs and the generation thereof for both total and uni-compartmental arthroplasty procedures.

The remainder of this Detailed Discussion will now focus on various embodiments for performing POP.

B. Overview of Preoperative Planning (“POP”) Procedure

In one embodiment, as can be understood from [blocks100-120] ofFIGS. 1B-1Cand fromFIGS. 1J and 1K, which contain portions of a flow chart illustrating an overview of the POP system and method disclosed herein, medical images16of the femur and tibia18,20are generated and formed into three dimensional (“3D”) bone models22, which are then restored or modified into restored bone models28′,28″ to represent the patient's femur and tibia18,20prior to injury or degeneration [block171]. Three dimensional computer models34′,34″ of the femur and tibia implants are generated from engineering drawings of the implants and may be generated via any of the above-referenced 3D modeling programs [block172]. The sizes of the implant models34′,34″ are selected relative to the femur and tibia restored bone models28′,28″ [block173]. The femur and tibia restored bone models28′,28″ are moved towards the implant models34′,34″ to superimpose the femur and tibia restored bone models28′,28″ over the implant models34′,34″ [block174]. Landmark reference lines for the femur restored bone model28′ are determined [block175]. The elliptical contours of the femoral condyles430,445are determined from the landmark reference lines [block125]. The elliptical contours505,510for the lateral and medial condyles515,520of the femur implant model34′ are determined [block176]. The lateral and medial condyles515,520of the femur implant model34′ are aligned with the lateral and medial condyles430,445of the femur restored bone model28′ [block177]. The superposing of the femur restored bone model28′ with the implant model34′ is refined by aligning the condyles of the of the femur restored bone model28′ with the condyles of the implant model34′ [block178]. An asymmetrical or symmetrical femoral implant model34′ is selected for the shape matching process [block179]. An adjustment value tr is determined to account for cartilage thickness or joint gap of a restored joint [block180]. The implant model34′ is modified according to the adjustment value tr [block181]. The shape matching process takes place where the articular condylar surfaces of the modified implant model34′ are shape matched to the articular condylar surfaces of the restored bone model28′. The process then continues as indicated in [block125] ofFIG. 1E.

As indicated inFIG. 1Jwith respect to the tibia, areas of interest are identified for the tibia restored model [block183]. Reference points are identified for the tibia restored bone model and the tibia implant model [block184]. An adjustment value tr is determined for the tibia implant model [block185]. Slope vectors are identified for the tibia restored bone model [block186] and the tibia implant model [block187]. Potential IR/ER misalignment is addressed [block188]. The tibia implant model is modified according to the adjustment value tr [block189]. The condylar articular surfaces of tibia implant model are shape matched to those of the tibia restored bone model [block190].

This ends the overview of the POP process. The following discussions will address each of the aspects of the POP process in detail.

C. Computer Modeling Femur and Tibia

FIG. 2Adepicts 3D computer generated restored bone models28′,28″ of the femur and tibia18,20generated from medical imaging scans16and representing the patient's femur18and tibia20prior to injury or degeneration [see block171ofFIG. 1J]. More specifically,FIG. 2Ais an isometric view of a 3D computer model28′ of a femur lower end200and a 3D computer model28″ of a tibia upper end205representative of the corresponding patient bones18,20in a non-deteriorated state and in position relative to each to form a knee joint14. The femur lower end200includes condyles215, and the tibia upper end205includes a plateau220. The models28′,28″ are positioned relative to each other such that the curved articular surfaces of the condyles215, which would normally mate with complementary articular surfaces of the plateau220, are instead not mating, but roughly positioned relative to each other to generally for the knee joint14.

As generally discussed above with respect toFIGS. 1A-1C, the POP begins by using a medical imaging process, such as magnetic resonance imaging (MRI), computed tomography (CT), and/or another other medical imaging process, to generate imaging data of the patient's knee. The generated 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 images16) into 3D anatomical computer bone models22of the knee joint14with the aid of a medical imaging conversion computer program, the bone models22being representative of the patient's bones18,20in the current deteriorated state. 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.

As provided in U.S. patent application Ser. No. 12/111,924 to Park, which is entitled Generation of a Computerized Bone Model Representative of a Pre-Degenerated State and Usable in the Design and Manufacture of Arthroplasty Devices, was filed Apr. 29, 2008 and is incorporated by reference in its entirety into this Detailed Description, specialized medical converging software recognizes the anatomy of the knee and shapes the bone models22using mathematical algorithms, such as sequences of nthorder polynomials, where n is greater than or equal to 3. A technique such as surface-rendering is then used to construct 3D restored bone models28′,28″ of the knee joint14from the bone models22. Examples of medical imaging computer programs that may be used here include Analyze (from AnalyzeDirect, Inc., Overland Park, Kans.), open-source software such as the Insight Toolkit (ITK, www.itk.org) and 3D Slicer (www.slicer.org), and Mimics (from Materialise, Ann Arbor, Mich.).

In one embodiment, the resulting 3D restored bone models28′,28″ of the femur portion200and tibia portion205forming the knee joint14include the cortical bone of the femur18and the tibia20. Depending on the embodiment, the restored bone models28′,28″ may includes articular cartilage attached to the distal region of the femur18and the proximal region of the tibia20. The computer program may automatically exclude the rest of the soft tissue, as well as the cancellous bone, from the 3D computer models28′,28″, although in some variations the computer program may not automatically exclude the rest of the soft tissue and/or the cancellous bone.

The 3D computer generated femur and tibia restored bone models28′,28″ are repaired versions of the patient's femur18and tibia20as these bones are believed to have existed before degenerating into their current existing date, the current state of the patient's femur18and tibia20being represented by the 3D bone models22. In other words, the femur and tibia computer generated bone models22resulting from the MRI scans depict the femur18and tibia20in the current deteriorated state. These models22are then modified or restored into restored bone models28′,28″ to represent the femur18and tibia20as they likely appeared before beginning to degenerate. The resulting modified or restored models28′,28″ can then be used for planning purposes, as described later in this Detailed Description.

For greater detail regarding the methods and systems for computer modeling joint bones, such as the femur and tibia bones forming the knee, please see the following U.S. patent applications, which are all incorporated herein in their entireties: U.S. patent application Ser. No. 11/656,323 to Park et al., titled “Arthroplasty Devices and Related Methods” and filed Jan. 19, 2007; U.S. patent application Ser. No. 10/146,862 to Park et al., titled “Improved Total Joint Arthroplasty System” and filed May 15, 2002; U.S. patent Ser. No. 11/642,385 to Park et al., titled “Arthroplasty Devices and Related Methods” and filed Dec. 19, 2006; and U.S. patent application Ser. No. 12/111,924 to Park, titled “Generation of a Computerized Bone Model Representative of a Pre-Degenerated State and Usable in the Design and Manufacture of Arthroplasty Devices” and filed Apr. 29, 2008.

FIG. 2Bis an isometric view of a computer model of a femur implant34′ and a computer model of a tibia implant34″ in position relative to each to form an artificial knee joint14. The computer models34′,34″ may be formed, for example, via computer aided drafting or 3D modeling programs [see block172ofFIG. 1J].

The femur implant model34′ will have a joint side240and a bone engaging side245. The joint side240will have a condoyle-like surface for engaging a complementary surface of the tibia implant model34″. The bone engaging side245will have surfaces and engagement features250for engaging the prepared (i.e., sawed to shape) lower end of the femur18.

The tibia implant model34″ will have a joint side255and a bone engaging side260. The joint side255will have a plateau-like surface configured to engage the condoyle-like surface of the femur implant model34′. The bone engaging side260will have an engagement feature265for engaging the prepared (i.e., sawed to shape) upper end of the tibia20.

As discussed in the next subsection of this Detailed Description, the femur and tibia restored bone models28′,28″ may be used in conjunction with the implant models34′,34″ to select the appropriate sizing for the implants actually to be used for the patient.

D. Selecting the Sizes for the Femoral and Tibial Implants

FIG. 3Ais a plan view of the joint side240of the femur implant model34′ depicted inFIG. 2B.FIG. 3Bis an axial end view of the femur lower end200of the femur restored bone model28′ depicted inFIG. 2Aand showing the condoyle surfaces215. The views depicted inFIGS. 3A and 3Bare used to select the proper size for the femoral implant model34′ [see block173ofFIG. 1J].

As can be understood fromFIG. 3A, each femoral implant available via the various implant manufactures may be represented by a specific femoral implant 3D computer model34′ having a size and dimensions specific to the actual femoral implant. Thus, the representative implant model34′ ofFIG. 3Amay have an associated size and associated dimensions in the form of, for example, an anterior-posterior extent iAP and medial-lateral extent iML. These implant extents iAP, iML may be compared to the dimensions of the femur restored bone model28′ that represents the patient's femur18as it may have existed prior to degeneration or injury. For example, the femur restored bone model28′ may have dimensions such as, for example, an anterior-posterior extent bAP and a medial-lateral extent bML, as shown inFIG. 3B. InFIG. 3A, the anterior-posterior extent iAP of the femoral implant model34′ is measured from the anterior edge270to the posterior edge275of the femoral implant model34′, and the medial-lateral extent iML is measured from the medial edge280to the lateral edge285of the femoral implant model34′.

Each patient has femurs that are unique in size and configuration from the femurs of other patients. Accordingly, each femur restored bone model28′ will be unique in size and configuration to match the size and configuration of the femur medically imaged. As can be understood fromFIG. 3B, the femoral anterior-posterior length bAP is measured from the anterior edge290of the patellofemoral groove to the posterior edge295of the femoral condyle, and the femoral medial-lateral length bML is measured from the medial edge300of the medial condyle to the lateral edge305of the lateral condyle.

As can be understood fromFIG. 3C, which is a flow chart depicting the process undertaken by the system4when selecting the femur implant model34′ corresponding to the appropriate femur implant size to be used in the actual arthroplasty procedure, the system4determines the femoral anterior-posterior length bAP and the femoral medial-lateral length bML for the femur restored bone model28′ [block1000].

In one embodiment, there is a limited number of sizes of a candidate femoral implant. For example, one manufacturer may supply six sizes of femoral implants and another manufacturer may supply eight or another number of femoral implants. The iAP and iML dimensions of these candidate implants may be stored in a database. The bAP and bML are compared to the iAP and iML of candidate femoral implants stored in the database [block1005]. The system4selects a femoral implant model34′ corresponding to a candidate femoral implant having iAP and iML that satisfies the following two relationships: bML≧iML+ε, wherein −2 mm<ε<5 mm; and bAP≧iAP+σ, where −4 mm<σ<4 mm [block1010]. As an alternative to [block1010], in one embodiment, instead of selecting from a limited number of candidate femoral implants, these two relationships are used to manufacture a custom sized femoral implant.

Still referring toFIG. 3Cand continuing from [block1010], the system4provides the computer modeled femoral implant34′ corresponding to the selected candidate femoral implant [block1015]. This computer modeled femoral implant34′, which corresponds to the selected candidate femoral implant, is used with the computer modeled femur restored bone model28′ in computer modeling a femoral arthroplasty jig, as discussed later in this Detailed Description.

FIG. 3Dis a plan view of the joint side255of the tibia implant model34″ depicted inFIG. 2B.FIG. 3Eis an axial end view of the tibia upper end205of the tibia restored bone model28″ ofFIG. 2Aand showing the plateau220. The views depicted inFIGS. 3D and 3Eare used to select the proper size for the tibial implant model34″.

As can be understood fromFIG. 3D, each tibial implant available via the various implant manufactures may be represented by a specific tibia implant 3D computer model34″ having a size and dimensions specific to the actual tibia implant. Thus, the representative implant model34″ ofFIG. 3Dmay have an associated size and associated dimensions in the form of, for example, anterior-posterior extent cAP and the medial-lateral extent cML of the tibia model34″, as shown inFIG. 3E. InFIG. 3D, the anterior-posterior extent jAP of the tibia implant model34″ is measured from the anterior edge310to the posterior edge315of the tibial implant model34″, and the medial-lateral extent jML is measured from the medial edge320to the lateral edge325of the tibial implant model34″.

Each patient has tibias that are unique in size and configuration from the tibias of other patients. Accordingly, each tibia restored bone model28″ will be unique in size and configuration to match the size and configuration of the tibia medically imaged. As can be understood fromFIG. 3E, the tibial anterior-posterior length cAP is measured from the anterior edge330of the of the tibial restored bone model28″ to the posterior edge335of the tibial restored bone model28″, and the tibial medial-lateral length cML is measured from the medial edge340of the medial plateau of the tibia restored bone model28″ to the lateral edge345of the lateral plateau of the tibia restored bone model28″.

As can be understood fromFIG. 3F, which is a flow chart depicting the process undertaken by the system4when selecting the tibia implant model34″ corresponding to the appropriate tibia implant size to be used in the actual arthroplasty procedure, the system4determines the tibial anterior-posterior length cAP and the tibial medial-lateral length cML [block1020].

In one embodiment, there is a limited number of sizes of a candidate tibia implant. For example, one manufacturer may supply six sizes of tibia implants and another manufacturer may supply eight or another number of tibia implants. The jAP and jML dimensions of these candidate implants may be stored in a database. The cAP and cML are compared to the jAP and jML of candidate tibia implants stored in the database [block1025]. The system4selects a tibia implant model34″ corresponding to a candidate tibia implant having jAP and jML that satisfies the following two relationships: cML≧jML+ω, wherein −2 mm<ω<4 mm; and cAP≧jAP+0, where −2 mm<θ<4 mm [block1030]. As an alternative to [block1030], in one embodiment, instead of selecting from a limited number of candidate tibia implants, these two relationships are used to manufacture a custom sized tibia implant.

Still referring toFIG. 3Fand continuing from [block1030], the system4provides the computer modeled tibia implant34″ corresponding to the selected candidate tibia implant [block1035]. This computer modeled tibia implant34″, which corresponds to the selected candidate tibia implant, is used with the computer modeled tibia restored bone model28″ in computer modeling a tibia arthroplasty jig, as discussed later in this Detailed Description.

Femoral and tibial implants represented by the implant models34′,34″, such as those depicted inFIG. 2B, are commercially available. Examples of commercially available implants include the Vanguard™ prosthetic femoral arthroplasty implants (manufactured by Biomet, Inc.), the Triathlon® Knee System (from Stryker® Orthopedics), and the P.F.C.® Sigma Knee System (from Depuy).

E. Moving Femur and Tibia Models Towards Corresponding Implant Models Such that Femur and Tibia Models are Superimposed Over the Implant Models.

As explained above with respect to [blocks100-115] ofFIGS. 1A-1C, the restored bone models28′,28″ can be reconstructed from bone models22generated from the plurality of MRI image slices16, which are scanned around a live patient's knee14. As can be understood from [blocks100-115] ofFIGS. 1A-1C, the image slices16, bone models22and restored bone models28may be positioned at a coordinate point P (X0-j, Y0-j, Z0-j) relative to an origin X0, Y0, Z0of an X-Y-Z axis throughout their respective generations and existences. Similarly, the implant models34may be positioned at a coordinate point P (X0-k, Y0-k, Z0-k) relative to the origin X0, Y0, Z0of the X-Y-Z axis throughout their existence. Thus, as indicated inFIG. 4A, which is an isometric view of the restored bone models28and implant models34, the restored bone models28may be positioned such that a point PRBMassociated with the restored bone models28occupies coordinate point P (X0-j, Y0-j, Z0-j) relative the origin X0, Y0, Z0of the X-Y-Z axis, and the implant models34may be positioned such that a point PIMassociated with the implant models34occupies coordinate point P (X0-k, Y0-k, Z0-k) relative the origin X0, Y0, Z0of the X-Y-Z axis.

As indicated by arrows A inFIG. 4A, the restored bone models28and implant models34may be moved together to superimpose one type of model over the other type of model. For example, in one embodiment, the implant models34are held stationary at coordinate point P (X0-k, Y0-k, Z0-k) and, as indicated by arrows A, the restored bone models28are moved from coordinate point P (X0-j, Y0-j, Z0-j) to coordinate point (X0-k, Y0-k, Z0-k) such that point PRBMof the restored bone models28moves from coordinate point P (X0-j, Y0-j, Z0-j) to coordinate point (X0-k, Y0-k, Z0-k). As a result and as indicated inFIG. 4B, which is an isometric view of the restored bone models28superimposed over the implant models34, points PRBMand PIMend up both being generally occupying coordinate point (X0-k, Y0-k, Z0-k) such that the models28,34are superimposed.

As mentioned above with respect to the discussion of [block135] ofFIG. 1D, movement of the restored bone models28during the POP or other process from coordinate point P (X0-j, Y0-j, Z0-j) to another coordinate point, such as, coordinate point (X0-k, Y0-k, Z0-k), is reflected or mimicked by the arthritic models36such that the location and orientation of the arthritic models36matches those of the restored bone models28, thereby facilitating the combining of the data types44,46into the integrated jig data48, as discussed in [block150] ofFIG. 1E.

In one embodiment, the point PIMassociated with the implant models34is located between the implant models34′,34″ close to their centers, near the intercondylar notch of the femur implant model34′, and the point PRBMassociated with the restored bone models28is located between the restored bone models28′,28″ close to their centers, near the intercondylar notch of the femur restored bone model28′. Of course, depending on the embodiment, the points PIM, PRBMmay be located at other locations relative to their respective models34,28as long as the locations of the points PIM, PRBMrelative to their respective models34,28are generally coordinated with each other. For example, points PIM, PRBMcould be positioned relative to their respective models34,28such that the points PIM, PRBMare generally centered at the most distal point of the medial articular condylar surface of each respective model34,28.

The preceding example is given in the context of holding the implant models34in place and moving the restored bone models28to the implant models34to superimpose the restored bone models28over the implant models34. However, in other embodiments, the reverse situation may be the case, wherein the restored bone models28are held in place and the implant models34are moved to the restored bone models28to superimpose the implant models34over the restored bone models28.

In summary, as can be understood fromFIGS. 4A-4BandFIG. 4C, which is a flow chart summarizing the process of superimposing the models28,34over each other as mention in [block174] ofFIG. 1J, the implant reference point PIMis designated as coordinate point (X0-k, Y0-k, Z0-k) with respect to an X-Y-Z coordinate system having an origin at coordinate point (X0, Y0, Z0) [block1035]. The implant reference point PIMmay be located between the implants models34′,34″, close to their centers, near the intercondylar notch of the femur implant model34′. The restored, bone model reference point PRBMis designated as coordinate point (X0-j, Y0-j, Z0-j) with respect to the X-Y-Z coordinate system having its origin at coordinate point (X0, Y0, Z0) [block1040]. The restored bone model reference point PRBMmay be located between the restored bone models28′,28″, close to their centers, near the intercondylar notch of the femur restored bone model28′.

In one embodiment, in the image analysis of the POP, the restored bone models28′,28″ may be translated to near the corresponding implants models34′,34″ through a distance (α, β, γ) by f (x−α, y−β, z−γ), where a=X0-k−X0-j; β=Y0-k−Y0-j; and y=Z0-k−Z0-j[block1045]. In other words, the restored bone models28′,28″ are moved to the implant models34′,34″ such that the two reference points PRBM, PIMare generally in the same location. Therefore, the restored bone models28′,28″ and the implants models34′,34″ are closely superimposed to provide the starting reference points for translational and rotational positioning of the femoral and tibial implants models34′,34″ with respect to the femur and tibia restored bone models28′,28″ for the shape matching process discussed in the following subsections of this Detailed Discussion. In other words, the above-described superimposing of the models28,34may act as an initial rough positioning of the models in preparation for the following shape matching process.

F. Refining Positioning Between Bone and Implant Models

Once the bone and implant models28,34are roughly positioned relative to each other via the above-described superimposing process, the positioning of the bone and implant models28,34relative to each other is further refined prior to the shape matching process. The position refining process first entails the identification of landmark reference planes for the femur model, the utilization of the landmark reference planes to identify the elliptical contours of the femur restored bone model, and then the correlation of the femur elliptical contours to corresponding elliptical contours of the implant model in an approximate manner.

1. Determining Landmark Reference Planes for Femur Model.

The determination of the landmark reference planes for the femur model may be made via at least two methods. For example, a first method entails employing asymptotic lines to identify the landmark reference planes. In a second method, the landmark reference planes are identified via their relationship to a trochlear groove plane.

i. Landmark Reference Planes Identified Via Asymptotic Lines

FIGS. 5A-5Cillustrate a process in the POP wherein the system4determines landmark reference planes via asymptotic lines for the femur restored bone model28′ (seeFIG. 1J[block175]) relative to a coordinate system axis410.FIG. 5Cis a flow chart illustrating the process for determining the landmark references.FIG. 5Ais a view of the lateral side of the lower or distal portion of the femur restored bone model28′ illustrating how to determine landmark reference planes for the posterior and anterior sides415,420of the femur planning model, which is also known as the femur restored bone model28′. As indicated inFIGS. 5A and 5C, an asymptotic line-cd can be obtained by the exponential function, y=α+β EXP (−μ (x−ω)), from the anterior-distal femur along the anterior side420of the femoral shaft423[block1050]. To obtain the tangent contact spot425representing the posterior extremity of lateral femoral condyle430, the line-ab along the curvature of femoral condyle can be identified by using the asymptotic line-cd, where lines-cd, ab are parallel to each other, or where line-ab is substantially parallel to line-cd such that the acute angle between lines-cd, ab is less than approximately five degrees [block1055]. In some embodiments, line-ab may represent a plane-ab that includes line-ab and is generally perpendicular to the sagittal image slice planes16used to form the restored bone model, as discussed with respect toFIGS. 1B-1C.

FIG. 5Bis an anterior or coronal view ofFIG. 5Aillustrating how to determine landmark reference planes for the medial and lateral sides435,440of the femur planning model28′. As indicated inFIGS. 5B and 5C, the asymptotic line-ah can be obtained by the asymptotic distribution, y=α+βEXP(−μ(x−ω)), along the curvature of the lateral epicondyle430up to the lateral edge of femoral shaft423[block1060]. Similarly, the asymptotic line-bj can be obtained by the asymptotic distribution, y=α+βEXP(−μ(x−ω)), along the curvature of the medial epicondyle445up to the medial edge of femoral shaft423[block1065].

As indicated inFIG. 5B, the point-k represents the center of the distal femur shaft423, the lowermost point in the patellofemoral surface450. The point-i is located approximately at the midpoint between point-h and point-j. The lines-ik, ah are parallel, and line-ik defines the femoral anatomical axis (FAA)455[block1070]. The lowest extremity of the medial epicondyle445is a tangent contact spot460that can be obtained inFIG. 5Bby a line-ef extending across tangent contact spot460, as line-ef is perpendicular to line-ik [block1075]. InFIG. 5B, line-hi is related to line-ij by the equation: hi=ij+m, where −3 mm<m<3 mm [block1080]. In some embodiments, line-ef may represent a plane-ef that includes line-ef and is generally perpendicular to the sagittal image slice planes16used to form the restored bone model, as discussed with respect toFIGS. 1B-1C.

ii. Landmark Reference Lines Identified Via Trochlear Groove Plane.

FIGS. 5D-5Gillustrate a process in the POP wherein the system4determines landmark reference planes via their relationship to the trochlear groove plane-GHO of the femur restored bone model28′ (seeFIG. 1J[block175]).FIG. 5Dis a sagittal view of a femur restored bone model28′ illustrating the orders and orientations of imaging slices16(e.g., MRI slices, CT slices, etc.) forming the femur restored bone model28′.FIG. 5Eis the distal images slices1-5taken along section lines1-5of the femur restored bone model28′ inFIG. 5D.FIG. 5Fis the coronal images slices6-8taken along section lines6-8of the femur restored bone model28′ inFIG. 5D.FIG. 5Gis a perspective view of the distal end of the femur restored bone model28′.

In one embodiment, the identification of the trochlear groove plane-GHO may be made during the verification of the accuracy of the bone restoration process as disclosed in U.S. patent application Ser. No. 12/111,924 to Park, which is entitled Generation of a Computerized Bone Model Representative of a Pre-Degenerated State and Usable in the Design and Manufacture of Arthroplasty Devices, was filed Apr. 29, 2008 and is incorporated by reference in its entirety into this Detailed Description.

As shown inFIG. 5D, a multitude of image slices are compiled into the femur restored bone model28′ from the image slices originally forming the femur bone model22′ (seeFIG. 1C[block110]) and those restored image slices are modified via the methods disclosed in U.S. patent application Ser. No. 12/111,924. Image slices may extend medial-lateral in planes that would be normal to the longitudinal axis of the femur, such as image slices1-5. Image slices may extend medial-lateral in planes that would be parallel to the longitudinal axis of the femur, such as image slices6-8. The number of image slices may vary from 1-50 and may be spaced apart in a 2 mm spacing.

As shown inFIG. 5E, each of the slices1-5can be aligned vertically along the trochlear groove, wherein points-G1, G2, G3, G4, G5respectively represent the lowest extremity of trochlear groove for each slice1-5. By connecting the various points G1, G2, G3, G4, G5, a point-O can be obtained. As can be understood fromFIG. 5G, resulting line-GO, is perpendicular or nearly perpendicular to tangent line-AC. In a 90° knee extension, line-GO is perpendicular or nearly perpendicular to the joint line of the knee and line-AC. As can be understood fromFIGS. 6A and 6B, points-A and C represent the most posterior contact points on the femoral condylar surfaces.

As shown inFIG. 5F, each of the slices6-8can be aligned vertically along the trochlear groove, wherein points-H6, H7, H8respectively represent the lowest extremity of the trochlear groove for each slice6-8. By connecting the various points-H6, H7, H8, the point-O can again be obtained. As can be understood from5G, resulting line HO is perpendicular or nearly perpendicular to tangent line-BD. In a 0° knee extension, line HO is perpendicular or nearly perpendicular to the joint line of the knee and line BD. As can be understood fromFIGS. 6A and 6B, points-B and D represent the most distal contact points on the femoral condylar surfaces.

As illustrated inFIG. 5G, the trochlear grove plane-GHO, as the reference across the most distal extremity of the trochlear groove of the femur and in a 90° knee extension, should be perpendicular to tangent line AC. The line-HO, as the reference across the most posterior extremity of trochlear groove of the femur and in a 0° knee extension, should be perpendicular to tangent line AC.

Line HO and line AC may form a plane S, and lines GO and line BD may form a plane P that is perpendicular to plane S and forms line SR therewith. Line HO and line GO are parallel or nearly parallel to each other. Lines AC, BD and SR are parallel or nearly parallel to each other. Lines AC, BD and SR are perpendicular or nearly perpendicular to lines HO and GO and the trochlear plane GHO.

2. Determine Elliptical Contours for Condyles of Femur Restored Bone Model.

FIGS. 6A and 6Bare respective sagittal views of the lateral and medial condyles430,445of the distal femur restored bone model28′ depicted inFIGS. 5B and 5G, wherein elliptical contours of the condyles430,445have been determined from the landmark reference lines depicted inFIG. 5BorFIG. 5G(seeFIG. 1J[block176]).FIG. 6Cis a flow chart illustrating the process of determining the elliptical contours of the condyles430,445from the landmark reference lines depicted inFIG. 5BorFIG. 5G.

Based on plane-ef fromFIG. 5Band plane-ab fromFIG. 5A, or, alternatively, from plane-p fromFIG. 5Gand plane-s fromFIG. 5G, the related reference landmarks can be obtained on the sagittal views of lateral condyle430and medial condyle445inFIGS. 6A and 6B. As can be understood from a comparison ofFIGS. 5A and 5GtoFIGS. 6A and 6B, reference lines or planes-AE, CF are parallel to plane-ab and plane-s and respectively intersect the posterior extremity of the lateral femoral condyle430and the medial femoral condyle445at respective tangent spots A, C [block1085]. As can be understood from a comparison ofFIGS. 5B and 5GtoFIGS. 6A and 6B, reference planes-EB, DF are parallel to plane-ef and plane-p and respectively intersect the distal or bottom most extremity of the lateral femoral condyle430and the medial femoral condyle445at respective tangent spots B, D [block1090]. In one embodiment, in addition to being employed to identify the most distal extremities B, D and most posterior extremities A, C of the elliptical shape of the condyles, the planes-EB, DF, AE, CF may be used to define the major elliptical axes470,485and minor elliptical axes475,490of the elliptical shape of the condyle surfaces. These axes and points may be corresponded to similar axes and points of the implant models34′, as described below.

As indicated inFIG. 6A, plane-AE represents the tangent of the lateral condylar curve at the most proximal point-A, and plane-EB represents the tangent of the lateral condylar curve at the most distal point-B. The respective tangent contact spots A, B of the planes-AE, EB define the major axis470and minor axis475of the lateral ellipse contour465[block1095].

As indicated inFIG. 6B, plane-CF represents the tangent of the medial condylar curve at the most proximal point-C, and plane-DF represents the tangent of the medial condylar curve at the most distal point-D. The respective tangent contact spots C, D of the planes-CF, DF define the major axis485and minor axis490of the medial ellipse contour480[block1100].

3. Determine Elliptical Contours for Condyles of Femur Implant and Align in an Approximate Manner Implant Condyles to Femur Model Condyles.

FIG. 7Ashows an isometric bottom view of the conventional femoral implant model34′ depicted inFIG. 2B. As can be understood from the following discussion, the elliptical contours505,510for the lateral and medial condyles515,520of the femur implant model34′ are determined (seeFIG. 1K[block177]). The lateral and medial condyles515,520of the femur implant model34′ are then aligned in an approximate or rough manner with the lateral and medial condyles430,445of the femur restored bone model28′ (seeFIG. 1K[block178]).

FIGS. 7B and 7Care, respectively, side views of the lateral and medial sides525,530of the femur implant model34′ depicted inFIG. 7A.FIG. 7Dis a flow chart illustrating the method of determining elliptical contours505,510and approximately or roughly aligning the respective condyles430,445,515,520of the restored bone model28′ with the implant model34′.

As indicated inFIG. 7B, the lateral femur implant condyle515includes an elliptical contour505corresponding with the outer condyle surface535. Plane-PS is tangential to the most posterior point P on the lateral outer condyle surface535, and plane-SQ is tangential to the most distal or bottom point Q on the lateral outer condyle surface535[block1105]. Planes-PS, SQ, which may also be considered vectors or lines, intersect each other at point-S and are perpendicular to each other.

As indicated inFIG. 7C, the medial femur implant condyle520includes an elliptical contour510corresponding with the outer condyle surface540. Plane-RT is tangential to the most posterior point R on the medial outer condyle surface540, and plane-UT is tangential to the most distal or bottom point U on the medial outer condyle surface540[block1110]. Planes-RT, UT, which may also be considered lines or vectors, intersect each other at point T and are perpendicular to each other.

As indicated inFIGS. 7B and 7C, points-P, R define the major axes545,550of the respective elliptical contours505,510and minor axes555,560of the respective elliptical contours505,510[block1115]. Thus, planes-PS, SQ identify respectively the most posterior and distal points on the lateral outer surface535, and planes-RT, UT identify respectively the most posterior and distal points on the medial outer surface540. Because the major and minor axes and the most distal and posterior points on the elliptical contour of the condylar surfaces can be determined, the elliptical shape of the condylar surfaces can be measured and obtained.

In case of a femoral implant model34′ with symmetric condyles515,520, both ellipse505,510on the medial side520and lateral side515are the same where plane-PS equals plane-RT and plane-SQ equals plane-UT. By the application of these planes-PS, RT, SQ, UT of the femoral implant model34′, the femoral model condyles430,445can be aligned to the proximity of the corresponding femoral implant condyles515,520where plane-AE is parallel to plane-PS, plane-EB is parallel to plane-SQ, plane-CF is parallel to plane-RT, and plane-DF is parallel to plane-UT [block1120].

In one embodiment, where the trochlear groove plane is determined with respect to the restored bone model28′, as discussed above with respect toFIGS. 5D-5G, a similar process may be employed to find the trochlear groove plane for the femoral implant model34′. Thus, each of the bone model planes-EB and DF will be perpendicular to the bone model trochlear groove plane, and each of the implant model planes-SQ and UT will be perpendicular to the implant model trochlear groove plane. In such an embodiment, plane-AE is parallel to plane-PS, plane-EB is parallel to plane-SQ, plane-CF is parallel to plane-RT, and plane-DF is parallel to plane-UT.

The relationships between the planes-AE, EB, CF and DF of the restored bone model28′ can be positionally correlated with the respective corresponding planes-PS, SQ, RT and UT of the femur implant model34′ to refine the initial superimposing of the femur restored bone model28′ over the implant model34′ such that the condylar surfaces465,480of the bone model28′ are approximately aligned with the respective condylar surfaces535,540of the implant model34′ prior to the shape matching process described below in this Detailed Description.

G. Shape Matching Condylar Surfaces of Restored Bone Model to Condylar Surfaces of Femoral Implant Model.

In one embodiment, the POP system and method, once the position of the bone model and implant model is refined as described immediately above, then employs a shape match technique to match a model34′ of an available femoral implant to the femoral planning or restored bone model28′. Before employing the shape match technique, it is determined if an asymmetrically modified femoral implant is selected for the POP process, or is a symmetric femoral implant is selected for the POP process (seeFIG. 1K[block179]).

1. Asymmetrically Modified Femoral Implant Model

For a discussion regarding a POP design employing an asymmetrically modified femoral implant model34′, reference is made toFIGS. 8A-10.FIG. 8Bshows a coronal view of a distal femur restored bone model28′ having symmetrical femoral condyles430′,445′. The FAA455′ extends through the center of the femur restored bone model28′. A rotation reference line600′ connects the lowest extremities of the two femoral condyles430′,445′.

FIG. 8Bdepicts a joint where the size of lateral condyle430′ is substantially equal to the size of medial condyle445′. In this situation, the FAA455′ is perpendicular or substantially perpendicular to the reference line600′, where the offset distance td′ between the reference line600′ and the lateral condyle430′ is zero (i.e., td′=0) or nearly so. The offset distance td′ is the difference between the medial condyle445′ and the lateral condyle430′ of distal femur restored bone model28′.

FIG. 8Ashows a coronal view of a distal femur restored bone model28′ having an asymmetrical relationship between its condyles430,445. The asymmetrical relationship can be the result of the femur naturally having one condyle larger than the other condyle, and depending on which condyle is larger, the knee will be varus or valgus. For example, it is common for the medial condyle445to be larger than the lateral condyle430. As a result, the alignment of the rotation reference line600″ relative to the FAA455tilts from the medial condyle445towards the lateral condyle430, when the rotation reference line600″ is not held perpendicular to the FAA455. Where the rotation reference line600is held perpendicular to the FAA455, an offset distance td is indicated, wherein the offset distance is the difference between the sizes of the medial and lateral condyles445,430.

As shown inFIG. 8A, with respect to FAA455, the lateral condyle430is smaller than the medial condyle445, leaving an offset distance td when reference line600is maintained perpendicular to the FAA455, as opposed to tilting against the surfaces of both condyles430,445, as depicted by reference line600″. The offset distance td is the difference between the medial condyle445and lateral condyle430of the distal femur model28′. Depending on the direction of the tilt and which condyle430,445is smaller, the result is a varus deformity or a valgus deformity. The femoral condyle or offset difference td inFIG. 8Avaries depending on the amount natural difference between the medial and lateral condyles445,430.

As can be understood fromFIG. 8AandFIG. 9C, which is a flow chart depicting the method of shape fitting with an asymmetrically modified implant model34′, where the system4determines the femur model28′ has asymmetrical condyles430,445, the system4will determine the offset difference td between the condyles430,445[block1125].

FIGS. 9A and 9Bare, respectively, an isometric view of a symmetric implant model34′ and a lateral side view of the implant model34′ after being asymmetrically modified. As indicated inFIG. 9A, prior to being asymmetrically modified, the symmetric implant model34′ has symmetrical lateral and medial condyles515,520with articulating surfaces535,540that are nearly the same size. In order to modify the symmetric implant model34′ to fit the asymmetrical nature of bone model28′, the lateral condylar articulating surface535of the symmetrical implant model34′ is moved proximally, as indicated by arrow605, along the FAA455the offset distance td measured on the femur model34′ inFIG. 8A[block1130].

FIG. 10is a coronal view of the femur model28′ and the asymmetrical implant model34′ aligned along the FAA455, which serves as the reference axis for rotational and translation alignment between the femur and implant models28′,34′. As shown inFIG. 10, due to the asymmetric condyle configuration depicted inFIG. 8A, the femoral condyle difference td inFIGS. 8A and 9Bis shown in each of the femur model28′ and the correspondingly asymmetrically modified implant model34′. The lowest extremity of tangent contact spots A′ and B′ are know from the tangent plane procedures described above in this Detailed Description. Also, the information pertaining to FAA and td are known from the above described procedures.

As can be understood fromFIG. 10, the lowest extremity of tangent contact spots A and B for the implant model34′ can be identified in each of the distal medial condylar articulating surface540and the distal lateral condylar articulating surface535, respectively [block1135]. The FAA and td for the implant model34′ are determined from the bone model28′, and the lowest extremities A and B of the implant model condylar surfaces may be measured.

Because the line-AB connecting point-A and point-B is titled relative to the reference line600, an angle θ can be obtained where θ=tan−1(td/L) and L is the distance along the reference line600between points A and B [block1140]. The value for angle θ can be stored in a database15of the system4and further applied to a symmetric femoral implant alignment after the shape matching technique described below with respect toFIGS. 16-19in this Detailed Description [block1145]. After the shape matching technique, in order to achieve accurate alignment and rotation between the femur model28′ and a symmetric implant model34′ representative of an actual implant provided by an implant manufacturer, the femur model28′ ofFIG. 10will be superposed to the symmetric implant model34′ with a rotation of angle θ with respect to point B inFIG. 10[block1150].

For a discussion regarding a POP design employing an symmetrical femoral implant model34′, reference is made toFIGS. 11A and 11B.FIG. 11Ais a coronal view of the asymmetrical femur model28′ and the symmetrical implant model34′.FIG. 11Bis a flow chart illustrating the method of shape fitting with the symmetrical implant model34′.

As indicated inFIGS. 11A and 11B, the lowest extremity of tangent contact spots B and A are identified on each of the medial condyle445and lateral condyle430, respectively [block1155]. The line-MN extends across the two lowest extremity points-A, B and is presumed to be parallel to the joint line of the knee in a knee kinetics study. In one embodiment, the line455may represent the trochlear groove axis (plane, line or vector direction OP) reference. The line-MN may be perpendicular or generally perpendicular to the trochlear groove axis-455. Similarly, in the symmetrical femoral implant model34′, the lowest extremity of tangent contact spots D and C can be identified in each of the distal medial condylar articulating surface540and the distal lateral condylar articulating surface535, respectively [block1160]. With reference to the trochlear groove axis455(i.e., plane, line or vector direction OQ), the line across points-C, D and perpendicular to reference line455is defined as line or plane RS. To rotationally and translationally align the femur model28′ and the symmetric implant model34′, place the femur model28′ onto the symmetric implant model34′ such that plane MN is parallel to plane RS and plane OP is parallel to plane OQ [block1165].

3. Determining Joint Line and Adjustment to Surface Matching that Allows Surface Matching of Implant Model Condylar Surfaces to Restored Bone Model Condylar Surfaces to Restore Joint to Natural Configuration.

In order to allow an actual physical arthroplasty implant to restore the patient's knee to the knee's pre-degenerated or natural configuration with the its natural alignment and natural tensioning in the ligaments, the condylar surfaces of the actual physical implant generally replicate the condylar surfaces of the pre-degenerated joint bone. In one embodiment of the systems and methods disclosed herein, condylar surfaces of the restored bone model28′ are surface matched to the condylar surfaces of the implant model34′. However, because the restored bone model28′ may be bone only and not reflect the presence of the cartilage that actually extends over the pre-degenerated condylar surfaces, the surface matching of the modeled condylar surfaces may be adjusted to account for cartilage or proper spacing between the condylar surfaces of the cooperating actual physical implants (e.g., an actual physical femoral implant and an actual physical tibia implant) used to restore the joint such that the actual physical condylar surfaces of the actual physical cooperating implants will generally contact and interact in a manner substantially similar to the way the cartilage covered condylar surfaces of the pre-degenerated femur and tibia contacted and interacted.

Thus, in one embodiment, the implant model is modified or positionally adjusted to achieve the proper spacing between the femur and tibia implants. To achieve the correct adjustment, an adjustment value tr may be determined (seeFIG. 1K[block180]). In one embodiment, the adjustment value tr that is used to adjust the surface matching may be based off of an analysis associated with cartilage thickness. In another embodiment, the adjustment value tr used to adjust the surface matching may be based off of an analysis of proper joint gap spacing. Both of the methods are discussed below in turn.

i. Determining Cartilage Thickness and Joint Line

FIG. 12shows the sagittal view MRI slice of the femoral condyle615and the proximal tibia of the knee in a MRI image slice. The distal femur620is surrounded by the thin black rim of cortical bone. Due to the nature of irregular bone and cartilage loss in OA patients, it can be difficult to find the proper joint line reference for the models used during the POP.

The space between the elliptical outlining625′,625″ along the cortical bone represents the cartilage thickness of the femoral condyle615. The ellipse contour of the femoral condyle615can be seen on the MRI slice shown inFIG. 12and obtained by a three-point tangent contact spot (i.e., point t1, t2, t3) method. This three-point contact spot method is illustrated with respect toFIGS. 14A-14D, and its purpose is to “restore” the joint line reference. In a normal, healthy knee, the bone joint surface is surrounded by a layer of cartilage. Because the cartilage is generally worn-out in OA and the level of cartilage loss varies from patient to patient, it may be difficult to accurately account for the cartilage loss in OA patients when trying to restore the joint via TKA surgery. Therefore, in one embodiment of the methodology and system disclosed herein, a minimum thickness of cartilage is obtained based on medical imaging scans (e.g., MRI, etc.) of the undamaged condyle. Based on the cartilage information, the joint line reference can be restored. For example, the joint line MN identified above may be line630inFIG. 13.

The system and method disclosed herein provides a POP method to substantially restore the joint line back to a “normal or natural knee” status (i.e., the joint line of the knee before OA occurred) and preserves ligaments in TKA surgery (e.g., for a total knee arthroplasty implant) or partial knee arthroplasty surgery (e.g., for a uni-knee implant).

FIG. 13is a coronal view of a knee model in extension. As depicted inFIG. 13, there are essentially four separate ligaments that stabilize the knee joint, which are the medial collateral ligament (MCL), anterior cruciate ligament (ACL), lateral collateral ligament (LCL), and posterior cruciate ligament (PCL). The MCL and LCL lie on the sides of the joint lie and serve as stabilizers for the side-to-side stability of the knee joint. The MCL is a broader ligament, whereas the LCL is a distinct cord-like structure.

The ACL is located in the front part of the center of the joint. The ACL is a very important stabilizer of the femur on the tibia and serves to prevent the tibia from rotating and sliding forward during agility, jumping, and deceleration activities. The PCL is located directly behind the ACL and the tibia from sliding to the rear. The system and method disclosed herein provides POP that allows the preservation of the existing ligaments without ligament release during TKA surgery. Also, the POP method provides ligament balance, simplifying TKA surgery procedures and reducing pain and trauma for OA patients.

As indicated inFIG. 13, the joint line reference630is defined between the two femoral condyles430,445and their corresponding tibia plateau regions635,640. Area A illustrates a portion of the lateral femoral condyle430and a portion of the corresponding lateral plateau635of tibia205. Area B illustrates the area of interest showing a portion of the medial femoral condyle445and a portion of the corresponding medial plateau640of tibia205.

FIGS. 14A,14B and14D illustrate MRI segmentation slices for joint line assessment.FIG. 14Cis a flow chart illustrating the method for determining cartilage thickness used to determine proper joint line. The distal femur200is surrounded by the thin blank rim of cortical bone645. The cancellous bone (also called trabecular bone)650is an inner spongy structure. An area of cartilage loss655can be seen at the posterior distal femur. For OA patients, the degenerative cartilage process typically leads to an asymmetric wear pattern that results one femoral condyle with significantly less articulating cartilage than the other femoral condyle. This occurs when one femoral condyle is overloaded as compared to the other femoral condyle.

As can be understood fromFIGS. 14A and 14C, the minimum cartilage thickness is observed and measured for the undamaged and damaged femoral condyle430,445[block1170]. If the greatest cartilage loss is identified on the surface of medial condyle445, for example, then the lateral condyle430can be used as the cartilage thickness reference for purposes of POP. Similarly, if the greatest cartilage loss is identified on the lateral condyle430, then the medial condyle445can be used as the cartilage thickness reference for purposes of POP. In other words, use the cartilage thickness measured for the least damaged condyle cartilage as the cartilage thickness reference for POP [block1175].

As indicated inFIG. 14B, the thickness of cartilage can be analyzed in order to restore the damaged knee compartment back to its pre-OA status. In each of the MRI slices taken in regions A and B inFIG. 13, the reference lines as well as the major and minor axes485,490of ellipse contours480′,480″ in one femoral condyle445can be obtained.

As shown inFIG. 14D, for the three-point method, the tangents are drawn on the condylar curve at zero degrees and 90 degrees articular contact points. The corresponding tangent contact spots t1′ and t2′ are obtained from the tangents. The line1450perpendicular to the line1455determines the center of the ellipse curve, giving the origin of (0, 0). A third tangent contact spot t3′ can be obtained at any point along the ellipse contour between the 90 degree, t1point and the zero degree, t2′ point. This third spot t3′ can be defined as k, where k=1 to n points.

The three-point tangent contact spot analysis may be employed to configure the size and radius of the condyle445of the femur restored bone model28′. This provides the “x” coordinate and “y” coordinate, as the (x, y) origin (0, 0) shown inFIG. 14B. The inner ellipse model480′ of femoral condyle shows the femoral condyle surrounded by cortical bone without the cartilage attached. The minimum cartilage thickness tmminoutside the inner ellipse contour480′ is measured. Based on the analysis of the inner ellipse contour480′ (i.e., the bone surface) and outer ellipse contour480″ (i.e., the cartilage surface) of the one non-damaged condyle of the femur restored bone model28′, the inner ellipse contour480′ (i.e., the bone surface) and the outer ellipse contour480″ (i.e., the cartilage surface) of the other condyle (i.e., the damage or deteriorated condyle) may be determined.

As can be understood fromFIGS. 13 and 14B, ellipse contours480′,480″ are determined in areas A and B for the condyles430,445of the femur restored bone model28′. The inner ellipse contour480′, representing the bone-only surface, and the outer ellipse contour480″, representing the bone-and-cartilage surface, can be obtained. The minimum cartilage thickness tmminis measured based on the cartilage thickness tr between the inner ellipse480′ and outer ellipse480″. MRI slices of the two condyles430,445of the femur restored bone model28′ in areas A and B are taken to compare the respective ellipse contours in areas A and B. If the cartilage loss is greatest for at the medial condyle445in the MRI slices, the minimum thickness tmminfor the cartilage can be obtained from the lateral condyle430. Similarly, if the lateral condyle430has the greatest cartilage loss, the cartilage thickness tmmincan be obtained from undamaged medial condyle445of the femur restored bone model28′. The minimum cartilage can be illustrated in the formula, tmmin=MIN (ti), where i=1 to k.

ii. Determining Joint Gap

As mentioned above, in one embodiment, the adjustment value tr may be determined via a joint line gap assessment. The gap assessment may serve as a primary estimation of the gap between the distal femur and proximal tibia of the restored bone model. The gap assessment may help achieve proper ligament balancing.

In one embodiment, an appropriate ligament length and joint gap may not be known from the restored bone models28′,28″ (seeFIG. 2A) as the restored bone models may be oriented relative to each other in a fashion that reflects their deteriorated state. For example, as depicted inFIG. 14H, which is a coronal view of restored bone models28′,28″ oriented (e.g., tilted) relative to each other in a deteriorated state orientation, the lateral side1487was the side of the deterioration and, as a result, has a greater joint gap between the distal femur and the proximal tibia than the medial side1485, which was the non-deteriorated side of the joint in this example.

In one embodiment, ligament balancing may also be considered as a factor for selecting the appropriate implant size. As can be understood fromFIG. 14H, because of the big joint gap in the lateral side1487, the presumed lateral ligament length (L1+L2+L3) may not be reliable to determine proper ligament balancing. However, the undamaged side, which inFIG. 14His the medial side1485, may be used in some embodiments as the data reference for a ligament balancing approach. For example, the medial ligament length (M1+M2+M3) of the undamaged medial side1485may be the reference ligament length used for the ligament balancing approach for implant size selection.

In one embodiment of the implant size selection process, it may be assumed that the non-deteriorated side (i.e., the medial side1485inFIG. 14Hin this example) may have the correct ligament length for proper ligament balancing, which may be the ligament length of (M1+M2+M3). When the associated ligament length (“ALL”) associated with a selected implant size equals the correct ligament length of (M1+M2+M3), then the correct ligament balance is achieved, and the appropriate implant size has been selected. However, when the ALL ends up being greater than the correct ligament length (M1+M2+M3), the implant size associated with the ALL may be incorrect and the next larger implant size may need to be selected for the design of the arthroplasty jig2.

For a discussion regarding the gap assessment, which may also be based on ligament balance off of a non-deteriorated side of the joint, reference is made toFIGS. 14D and 14F.FIGS. 14E and 14Fillustrate coronal views of the restored bone models28′,28″ in their post-degeneration alignment relative to each as a result of OA or injury. As shown inFIG. 14E, the restored tibia model28″ is titled away from the lateral side1487of the knee1486such that the joint gap between the femoral condylar surfaces1490and the tibia condylar surfaces1491on the lateral side1487is greater than the joint gap on the medial side1485.

As indicated inFIG. 14F, which illustrates the tibia in a coronal cross section, the line1495may be employed to restore the joint line of the knee1486. The line1495may be caused to extend across each of lowest extremity points1496,1497of the respective femoral lateral and medial condyles1498,1499. In this femur restored bone model28′, line1495may be presumed to be parallel or nearly parallel to the joint line of the knee1486.

As illustrated inFIG. 14F, the medial gap Gp2represents the distance between the distal femoral medial condyle1499and the proximal tibia medial plateau1477. The lateral gap Gp1represents the distance between the distal femoral lateral condyle1498and the proximal tibia lateral plateau1478. In this example illustrated inFIG. 14F, the lateral gap Gp1is significantly larger than the medial gap Gp2due to degeneration caused by injury, OA, or etc. that occurred in the lateral side1487of the knee1486. It should be noted that while the bone models28′,28″ have surface configurations that have been restored such that the bone models28′,28″ are restored bone models28′,28″, the alignment of the bone models28′,28″ relative to each other for the example illustrated in FIGS.14E and14F depict the alignment the actual bones have relative to each other in a deteriorated state. To restore the joint line reference and maintain ligament balancing for the medial collateral ligament (MCL) and lateral collateral ligament (LCL), the joint line gap Gp3that is depicted inFIG. 14G, which is the same view asFIG. 14E, except with the joint line gap Gp3in a restored state, may be used for the shape matching adjustment as described below. As illustrated inFIG. 14G, the lines1495and1476respectively extend across the most distal contact points1496,1497of the femur condyles1498,1499and the most proximal contact points1466,1467of the tibia plateau condyles1477,1478.

For calculation purposes, the restored joint line gap Gp3may be which ever of Gp1and Gp2has the minimum value. In other words, the restored joint line gap Gp3may be as follows: Gp3=MIN (Gp1, Gp2). For purposes of the adjustment to the shape matching, the adjustment value tr may be calculated as being half of the value for Gp3, or in other words, tr=Gp3/2. As can be understood fromFIGS. 14E-14Fand14H, in this example, the non-deteriorated side1485has Gp2, which is the smallest joint line gap and, therefore, Gp3=Gp2in the example depicted inFIG. 14E-14H, and tr=Gp2/2.

In one embodiment, the joint line gap assessment may be at least a part of a primary assessment of the geometry relationship between the distal femur and proximal tibia. In such an embodiment, the joint gap assessment step may occur between [block173] and [block174] ofFIG. 1J. However, in other embodiments, the joint line gap assessment may occur at other points along the overall POP process.

4. Adjust Femoral Implant to Account for Joint Gap or Cartilage Thickness.

Once the adjustment value tr is determined based off of cartilage thickness or joint line gap Gp3, the femoral implant model34′ can be modified or adjusted to account for cartilage thickness to restore the joint line (seeFIG. 1K[block181].FIGS. 15A and 15Bare, respectively, an isometric view and a lateral side view of the modified femoral implant model34′.

As can be understood fromFIGS. 15A and 15B, the modification of femoral implant model34′ occurs below line KJ inFIG. 15B. The inner elliptical bone surface model480′ and the outer elliptical cartilage surface model480″ inFIG. 14Bcan be illustrated in the each of formula (1) and formula (2), respectively:

where P=wr, q=ws, and 0<w<1, wherein when p=q the result is a circle curve and when p≠q the result is an ellipse curve. Via the adjustment value tr, a restored condylar shape may be obtained by using the ellipse model and the mathematical information described above. The outer ellipse480″ may be attached with the adjustment value tr, which may be representative of cartilage thickness or half of the restored joint gap Gp3, and the inner ellipse480′ may be the bone contour without cartilage extending about the bone contour. The inner and outer ellipse480′,480″ may differ in a ratio of w factor, where 0<w<1. Based on the w factor, the p radius is smaller than radius r in a ratio of w. A similar analogy applies for radius q, where q is smaller than s in a ratio of w.

As best illustrated inFIG. 15B, the femoral implant model34′ includes an upper or distal-anterior part670and a lower or distal-posterior part675separated by the line KJ. The upper or distal-anterior part670of femoral implant model34′ comprises an external anterior-distal articular surface680and a multi-faced interior anterior-distal non-articular surface685. The interior anterior-distal non-articular surface685includes an anterior non-articular surface690and a distal-anterior non-articular surface695.

A distal portion696of the distal-anterior non-articular surface695may be a plane generally perpendicular to a natural alignment vertically extending axis when the actual physical implant is mounted on the distal femur end as part of an arthroplasty procedure. An anterior chamfered portion697of the distal-anterior non-articular surface695may be a plane having a generally chamfered relationship to the distal portion696.

The distal portion696of the distal-anterior non-articular surface695may abut against the first distal planar resection formed in the distal femur end during the arthroplasty procedure. The first distal planar resection may act as a guide from which other resections (e.g., the posterior and anterior chamfer resections) are referenced. The anterior chamfered portion697of the distal-anterior non-articular surface695may abut against the anterior planar resection formed in the distal femur end during the arthroplasty procedure. Thus, the interior anterior-distal non-articular surface685is adapted to receive the anterior flange of a resected distal femur.

The lower or distal-posterior part675of femoral implant model34′ includes an external posterior-distal articular surface700and a multi-faced interior posterior-distal non-articular surface705. The external posterior-distal articular surface700includes the medial distal-posterior condylar articulating surface540and the lateral distal-posterior condylar articulating surface535. The lower or distal-posterior part675of femoral implant model34′ is modified to account for the adjustment value tr, which may be based on the cartilage thickness or half of the restored joint gap Gp3. In one embodiment, the adjustment value tr is applied in both a posterior-anterior direction and a distal-proximal direction to the lower or distal-posterior portion675of the implant model34′.

As can be understood fromFIGS. 15A and 15B, the condyle surface535modified to account for the damaged bone and cartilage loss is dimensioned smaller than the condyle surface540for the non-damaged bone by a factor w in both the distal and posterior portions, wherein w equals the adjustment thickness tr. With the study of the cartilage thickness or restored joint gap Gp3, the system4can provide the restoration of cartilage and therefore assess the joint line for the distal femur model28′.

5. Shape Matching of Condyle Surfaces of Restored Femoral Bone Model to Condyle Surfaces of Femoral Implant Model.

FIG. 16is an isometric view of a femoral implant model34′ being shape matched to a femur planning model28′ (seeFIG. 1K[block182]). As shown inFIG. 16, the femur implant model34′ is direct surface matched onto the surface of the restored femur bone model28′ such that the articular surface profile of the femoral implant model34′ is matched to the articular surface profile of the femoral condyles430,445of the femur restored bone model28′. The function s (x, y, z) represents the surface profiles720,725for each of the exterior distal-posterior articular surfaces700of the lower or distal-posterior part675of the implant model34′ inFIG. 15B. The function h (x, y, z) represents the articular surface profile of a femoral condyle430,445of the lower or distal-posterior part of a femur restored bone model28′ as it would be if line KJ ofFIG. 15Bwere applied to a femur restored bone model28′ situated similar to the implant model34′ inFIG. 15B.

In one embodiment, the surface models720,725may displace medial-lateral relative to each other, but are constrained to move with each other in all other directions. For example the surface models720,725may displace closer or further apart to each other along the x-axis, but are matched to displace along the y-axis and z-axis as a set and fixed relative to each other.

The function ē(x,y,z) represents a true vector assuming that template noise is independent of the implant surface profile noise. The problem is estimating the parameters of a 3D transformation that satisfies the least squares fit surface matching of the implant condyle articular surface profile s (x, y, z) to the femoral condyle articular surface profile h (x, y, z). This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between these two surface profiles, represented by ē(x,y,z)=h(x,y,z)=s(x,y,z). For greater detail regarding this operation, see the following publications, which are incorporated by reference in their entireties into this Detailed Description: D. Akca,Matching of3D Surfaces and Their Intensities, ISPRS Journal of Photogrammetry & Remote Sensing, 62 (2007), 112-121; and Gruen A. et al.,Least Squares3D surface and Curve Matching, ISPRS Journal of Photogrammetry & Remote Sensing 59 (2005), 151-174.

As an option to the process discussed with respect toFIGS. 15A16, the femur implant model34′ can be directly shape matched onto the femur restored bone model28′ as described in the following discussion.FIGS. 17A and 17Bare isometric views of an ellipsoid model730of a femoral condyle430,445obtained through a plurality of MRI slices taken in a manner similar to the MRI slice depicted inFIG. 12and from areas A and B inFIG. 13. Each of the femoral condyles430,445inFIG. 13consists of a series of ellipses in areas A and B. Therefore, the 3D ellipsoid model730of the condyles430,445can be reconstructed by repetitive image analysis through a plurality of MRI slices taken through areas A and B inFIG. 13in a manner similar to the MRI slice depicted inFIG. 12. As shown inFIG. 17B, a portion735of the femoral condyle model730can be segmented and removed from the rest of the model730.

FIG. 18is an isometric view depicting the 3D surface matching using the condyle models730ofFIGS. 17A and 17B. The surface matching technique provides varus/valgus and information for the femoral implant planning design. The drilling hole of the femur implant model34′ and the surgical cut plane SCP of the femur implant model34′ provide the information for the IR/ER rotation. InFIG. 18, each of the ellipsoid model735,735′ represents the femoral condyles430,445of the distal femur restored bone model28′. The ellipsoid condylar portions735,735′ are each taken out from the 3D models730,730′. The ellipsoid equation in model730′ can be illustrated as

(x-x)2p22+(y-y)2q22+(z-z)2r22=1.
The ellipsoid equation in model in730can be illustrated as

(x-x)2p12+(y-y)2q12+(z-z)2r12=1.
The surface models of ellipsoid condylar portions735,735′ can be obtained from these two ellipsoid equations. These two portions735,735′ correspond to the distal-posterior portions of each condyle430,445of the distal femur surface model28′. In the femur model28′, the function f (x, y, z) represents a portion of ellipsoid surface of model portion735, approximately describing the distal-posterior bone surface of the medial condyle445. Similarly, the function f′ (x, y, z) represents a portion of ellipsoid surface of model portion735′, approximately describing the distal-posterior bone surface of the lateral condyle430.

In one embodiment, the surface models720,725may displace medial-lateral relative to each other, but are constrained to move with each other in all other directions. For example the surface models720,725may displace closer or further apart to each other along the x-axis, but are matched to displace along the y-axis and z-axis as a set and fixed relative to each other.

The function e(x, y, z) represents a true vector assuming that template noise is independent of the implant surface profile noise. The parameters of a 3D transformation satisfy the least squares matching of the interior surface profile s (x, y, z) of the implant to the ellipsoid potions surface profile f (x, y, z) of the femoral condyle. Similarly, the e(x, y, z) represents the least squares matching of the interior surface profile s′ (x, y, z) of the implant to the ellipsoid potions surface profile f′(x, y, z) of the femoral condyle. This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between the two surface profiles, represented by e(x,y,z)=f(x,y,z)−s(x,y,z), and e′(x,y,z)=f′(x,y,z)−s′(x,y,z), where J=MIN (e(x,y,z)), and J′=MIN (e′(x,y,z)). See D. Akca (supra). The valgus/varus and IR/ER of the original joint line has now been restored.

6. Aligning with Respect to Rotation and Translation the Modified Femoral Implant Model to the Femur Model

FIG. 19Ashows the sagittal view of inaccurate rotation alignment between the anterior flange750of a modified femoral implant model34′ and the anterior distal femur restored bone model28′.FIG. 19Bshows the sagittal view of correct rotation alignment between the anterior flange750of the modified femoral implant model34′ and the anterior distal femur restored bone model28′.

As previously discussed with respect toFIGS. 15A and 15B, the distal-anterior part670of the modified femoral implant model34′ includes an external anterior-distal articular surface680and an interior anterior-distal non-articular surface685. The interior anterior-distal non-articular surface685includes the anterior non-articular surface690and the distal anterior non-articular surface695. The sizes of distal-anterior part670of the modified femoral implant model34′ are selected from the femoral implants currently available from implant manufactures and according to the method discussed with respect to the bAP and bML extents of femur planning model28′ inFIGS. 3A-3C.

As can be understood from a comparison ofFIG. 19AtoFIG. 19B, the distal femur restored bone model28′ is rotated a certain number of degrees so the interior anterior-distal non-articular surface685can be adapted to meet the anterior cortex of distal femur restored bone model28′, while points M and N are preserved as much as possible to minimize error. The extent to which the femur model restored bone model28′ is rotated relative to the implant model34′ can be understood from a comparison of the FAA455inFIGS. 19A and 19B.

By employing the three-point tangent contact spot method (i.e., points M, N, and any points between M and N), the minimum degree of error A° is achieved. The degree of error A° is based on the limitation of available sizes of commercial implants, where 0<A°<20°. For example, some implant manufacturers only make available eight sizes of femoral implants. If the patient's femur bAP extent is greater than the iAP extent of the selected implant size, while the bML is approximately equal to iML, then applying the model34′ of the selected implant to align with the patient's femur restored bone model28′ will cause an error of degree A° that is larger than a 20° rotation alignment range. In this case it is suggested to choose the next bigger size of implant to minimize the degree of error.

As can be understood fromFIGS. 7A,7B,15B and19B, once the distal-posterior articular surfaces700of the implant model34′ are shape matched to the corresponding distal-posterior articular surfaces of the restored femur bone model28′, the distal portion696of the distal-anterior non-articular surface695will be superposed in the femur restored bone model28′ to indicate a location of a distal surgical cut plane or distal resection plane SCP that will correspond to a saw cut slot123(seeFIGS. 1F and 1G) in the femur arthroplasty jig2A that can be used to create the first distal planar resection formed in the distal femur end during the arthroplasty procedure. As the posterior-distal articular surface700is adjusted for the adjustment value tr for the shape matching process, the SCP ends up being located distally further by the amount of the adjustment value tr than it would otherwise be, resulting in the actual physical implant when mounted on the actual distal femur end providing articular surfaces that are positioned and oriented so as to allow the patient's knee to assume a natural or non-degenerated configuration.

The orientation and location of the implant's mounting post P (seeFIG. 7B) may also be determined once the implant model34′ and restored bone model28′ are superposed. Also, the locations and orientations of the drill holes124(seeFIGS. 1F and 1G) of the arthroplasty jig2A may be determined from the implant model34′ and restored bone model28′ being superposed.

Once the shape match process (seeFIG. 1K[block182] andFIG. 1C[block120]) is complete, the information regarding the locations and orientations for the saw cut slot123and drill holes124may be packaged as saw cut and drill hole data44(seeFIG. 1E[block125]) and the process goes forward as outlined inFIG. 1E.

H. Determining Areas of Interest A, B for Tibia Plateau Corresponding to Areas of Interest A, B for the Femoral Condyles

FIG. 20is a plan or top view of the plateau of the tibia restored bone model28″. As shown inFIG. 20, areas of interest A and B, which are similar to those depicted on the femur condyles430,445inFIG. 13, are identified on the surface of lateral plateau760and medial plateau765of tibia restored bone model28″ (seeFIG. 1J[block183]). The surface shape of the medial plateau765is incongruent with the lateral plateau760. The lateral plateau760shows a roughly flat surface. The medial plateau765shows a roughly concaved recess. The areas A and B of focus on portions of the medial and lateral plateau surfaces765,760. The areas A and B represent the contact areas around the joint line for articulatingly receiving the corresponding respective distal surfaces of the femoral medial and lateral condyles445,430identified inFIG. 13.

I. Determining Reference Points for Tibia Plateau

As with the identification of the distal reference points at the most distal points of the femoral condyle articular surfaces, as discussed above, corresponding reference points are identified on the tibia plateaus (seeFIG. 1J[block184]). As may be understood from the following discussion, the reference points for the tibia plateaus may be located at the lowest or most distally recessed points in each respective plateau.

FIG. 21Bis a MRI image slice16of the lateral portion760of the proximal tibia used to form the tibia restored bone model28″. The surface contour of lateral plateau760is outlined along the tibia meniscus starting from a portion of the anterior lateral surface to the posterior lateral surface. The reference spot V is selected and located approximately in the midpoint of the surface contour of the tibia lateral plateau760. The reference spot V is located within the area of interest A inFIG. 20and may be the most distally recessed point within area A.

In each of the MRI slices16, the landmarks as well as the origin O of the medial and lateral tibia plateaus765,760for IR/ER rotation and alignment of the tibia implant model34″ can be obtained. A medial-lateral extending line connecting both spots S, V can be made which is parallel to the joint line or parallel to a reference Z-axis of the X-Y axis indicated inFIGS. 21A and 21B. In the slices16depicted inFIGS. 21A and 21B, the length of line I1equals the length of line I2. In other words, the respective distances of each point S and V from the origin O along the y-axis are equal. This provides an “x” coordinate and a “y” coordinate, as the (x, y) origin O has a coordinate of (0, 0), as shown inFIGS. 21A and 21B. The plane formed by the x-axis and z-axis (i.e., the plane perpendicular to the x-y plane) is parallel to the joint line. Corresponding reference points S′, V′ are indicated on the lateral and medial plateaus770,775of the implant model34″, which is depicted inFIG. 21Cas an isometric view.

InFIG. 21C, the tangent or reference points S′, V′ represent the midpoints of the respective surfaces of the medial tibia plateau775and the lateral tibia plateau770. These two points S′, V′ are located in the respective areas of interest described inFIG. 20. Also, each point S′, V′ may represent the most distally recessed point in the respective tibia plateau775,770. A vector direction line-212extends across point-S′ in medial tibia plateau775. A vector direction line-216extends across point-V′ in the lateral tibia plateau770. The vector-212is parallel or generally parallel to vector-216, and is about the same height with vector-216. The line-S′V′ extends across points-S′ and V′ and can be obtained. This line-S′V′ is parallel or generally parallel to the joint line of the knee.

As can be understood fromFIGS. 21A-21C, the midpoints S, V in the medial plateau765and lateral plateau760of tibia205coincide with the points S′, V′ located approximately at the centre of the medial and lateral bearing surfaces775,770of the tibia implant model34″. As indicated inFIG. 21C, the tibia implant34″ includes a base member780for being secured to the proximal tibia28″. The line across the points S′, V′ of tibia implant34″ is parallel to the joint line and, parallel to the X-axis of the MRI slices ofFIGS. 21A and 21B.

J. Determining Joint Line and Adjustment to Surface Matching That Allows Surface Matching of Implant Model Condylar Surfaces to Restored Bone Model Condylar Surfaces to Restore Joint to Natural Configuration.

In order to allow an actual physical arthroplasty implant to restore the patient's knee to the knee's pre-degenerated or natural configuration with its natural alignment and natural tensioning in the ligaments, the condylar surfaces of the actual physical implant generally replicate the condylar surfaces of the pre-degenerated joint bone. In one embodiment of the systems and methods disclosed herein, condylar surfaces of the restored bone model28″ are surface matched to the condylar surfaces of the implant model34″. However, because the restored bone model28″ may be bone only and not reflect the presence of the cartilage that actually extends over the pre-degenerated condylar surfaces, the surface matching of the modeled condylar surfaces may be adjusted to account for cartilage or proper spacing between the condylar surfaces of the cooperating actual physical implants (e.g., an actual physical femoral implant and an actual physical tibia implant) used to restore the joint such that the actual physical condylar surfaces of the actual physical cooperating implants will generally contact and interact in a manner substantially similar to the way the cartilage covered condylar surfaces of the pre-degenerated femur and tibia contacted and interacted.

Thus, in one embodiment, the implant model is modified or positionally adjusted to achieve the proper spacing between the femur and tibia implants. To achieve the correct adjustment, an adjustment value tr may be determined (seeFIG. 1J[block185]). In one embodiment, the adjustment value tr that is used to adjust the surface matching may be based off of an analysis associated with cartilage thickness. In another embodiment, the adjustment value tr used to adjust the surface matching may be based off of an analysis of proper joint gap spacing, as described above with respect toFIGS. 14E and 14F. Both of the methods are discussed below in turn.

The wm inFIG. 21Arepresents the cartilage thickness of the medial tibia meniscus, and the wl inFIG. 21Brepresents the cartilage thickness of the lateral tibia meniscus. In one embodiment, the cartilage thicknesses wl and wm are measured for tibia meniscus for both the lateral and medial plateaus760,765via the MRI slices depicted inFIGS. 21A and 21B. The measured thicknesses may be compared. If the cartilage loss is observed for the medial plateau765, then the wlminof lateral plateau760is selected as the minimum cartilage thickness. Similarly, if the lateral plateau760is damaged due to cartilage loss, then the wmminof medial plateau765is selected as the minimum cartilage thickness. The minimum cartilage wr may be illustrated in the formula, wr=min (wm, wl). In one embodiment, for purposes of the adjustment to the tibia shape matching, the adjustment value tr may be may be equal to the minimum cartilage value wr.

ii. Determining Joint Gap

In one embodiment, the joint gap is analyzed as discussed above with respect toFIGS. 14E and 14Fto determine the restored joint line gap Gp3. In one embodiment, for purposes of the adjustment to the tibia shape matching, the adjustment value tr may be calculated as being half of the value for Gp3, or in other words, tr=Gp3/2.

K. Determine Slope Vectors for Tibia Plateau

The slope vectors for the plateau of the tibia restored bone model28″ are determined (seeFIG. 1J[block186]), as will be discussed with respect toFIGS. 22A and 22B. The sagittal view ofFIGS. 22A and 22Bare, respectively, lateral and medial sagittal MRI views of the plateau of the tibia restored bone model28″.FIG. 22Ashows the lateral tibial plateau760for establishing the anterior-posterior landmark references in the tibia plateau.FIG. 22Bshows the medial tibial plateau765for establishing the anterior-posterior landmark references in the tibia plateau. The anterior-posterior references can apply to both the tibia restored bone model28″, as can be understood from the MRI slices ofFIGS. 22A and 22Band the tibial implant model34″ ofFIGS. 23A-23C.

As indicated inFIG. 22A, points P, Q represent the highest of the anterior and posterior portions of lateral plateau surface760. The direction vector PQ inFIG. 22Arepresents the anterior-posterior slope of the lateral plateau760of tibia restored bone model28″.

As indicated inFIG. 22B, points R, S represent the highest of the anterior and posterior portions of medial plateau surface765. The direction vector RS inFIG. 22Brepresents the anterior-posterior slope of the medial plateau765of tibia restored bone model28″. For these vectors, it can be said that vector PQ is equal to vector t, vector RS is equal to vector z, and vector t is parallel to vector z or substantially parallel such that the acute angle between vectors z and t is less than five degrees.

L. Determine Slope Vectors for Tibia Implant

The of slope vectors for the plateau of the tibia implant model34″ are determined (seeFIG. 1J[block187]), as will be discussed with respect toFIGS. 23A-23C. The same analogy described with respect to finding the slope vectors for the tibia plateaus of the tibia restored bone model28″ applies to the tibia implant model34″ ofFIGS. 23A-23C.FIGS. 23A-23Care, respectively, two isometric views and a side view of the tibia implant model34″. Because the tibia implant model34″ is a symmetric design, the anterior-posterior slope in both the medial and lateral plateaus775,770of the implant model34″ are parallel to each other. The information regarding direction vector t in the lateral side and direction vector z in the medial side of tibia restored bone model28″ applies to the anterior-posterior slopes of tibia implant model34″. In the case when vectors t and z are within a five degree difference, an average value is provided by α, where

FIGS. 23A-23Cdepict a left knee tibia implant model34″. As can be understood fromFIG. 23A, the plateaus770,775of the tibia implant model34″ are symmetrical as viewed normal to the plateaus. As indicated inFIG. 23B, the lateral bearing surface770is quite close to being a flat surface as compared to the medial surface775.

As shown inFIGS. 23B and 23C, the direction vector h represents the anterior-posterior slope of tibia implant model34″. A process similar to that employed to determine the anterior-posterior slope for the tibia restored bone model28″ inFIGS. 22A and 22B, wherein the tibia plateau MRI slices were used to determine direction vectors t and z, can be applied to the tibia implant model34″ where vector h is parallel to vector z, which is parallel to vector t. Therefore, the anterior-posterior slope information for the lateral plateau can be obtained in tibia implant model34″ inFIG. 23C. The same analogy applies to the tibia implant model34″ of the right knee, where the implant is a symmetric design. The lateral surface profile of a right knee tibia implant is close to a flat surface. The anterior-posterior slope information for the lateral plateau of the planning model of the right knee can apply to the lateral surface profile of the tibial implant of the right knee.

M. Addressing Possible IR/ER Misalignment for the Tibial Implant

The possible IR/ER misalignment issue for the design of tibial implant model34″ can be assessed (seeFIG. 1J[block188]), as depicted inFIGS. 24A and 24B, which are, respectively, a plan or top view of the tibia plateau and a side medial side view of the tibia restored bone model28″. The medial plateau765of tibia restored bone model28″ inFIGS. 24A and 24Bshows the elliptical concavity786. The direction vector m inFIG. 24Bshows a rolling or sliding movement of the medial condyle445of the femur restored bone model28′. InFIG. 24A, the tangential line m along the medial plateau765of the tibia restored bone model28″ can be obtained. The elliptical shape786(shown in dashed lines) in the medial plateau765is identified, as indicated inFIG. 24A. The major axis (i.e., vector m) of the ellipse786provides the IR/ER alignment information to the location of tibial implant model34″.

The above described landmark references and the IR/ER alignment of the tibial restored bone model28″ provides the proximity information of the landmarks and IR/ER alignment to the tibial implant model34″.

N. Modifying the Tibial Implant Model to Account for the Adjustment Value tr

FIG. 25is an isometric view of the tibia implant model34″ as it is compensated to account for the adjustment value tr, which depending on the embodiment, may be a function of cartilage thickness or restored joint gap. As shown inFIG. 25, the tibia implant model34″ can be compensated with respect to the adjustment value tr in the medial and lateral sides775,770of the articular bearing member785of tibial implant model34″ (seeFIG. 1J[block189]).

The adjustment value tr may be determined via any of the above-described embodiments. Having determined the adjustment value tr, the compensation of the tibial implant model34″ for the adjustment value tr can be achieved by lowering the mid-portions of each tibial plateau770,775a tr distance. For example, the mid-portions of the medial side775will be lowered to achieve the adjustment value tr. Similarly, the mid-portions of the lateral side770of the articular bearing member785will be lowered to achieve the adjustment value tr.

O. Surface Matching for Tibia Implant

FIG. 26is an isometric view of the tibia implant model34″ being surface matched relative to the tibia restored bone model28″ (seeFIG. 1J[block190]). As shown inFIG. 26, direct surface matching occurs from the plateau surfaces760,765of tibia bone restored bone model28″. The modeling of surface profiles800,805of the lateral and medial plateau770,775of the tibial implant model34″ are based from each of the portions of lateral and medial plateau760,765of tibia restored bone model28″, respectively.

For example, based on the surface profile q (x, y, z) of the medial plateau765of the restored bone model28″, the surface profile805(i.e., p (x, y, z)) of medial portion775of the implant model34″ can be obtained. The function e(x, y, z) represents a true vector assuming that template noise is independent of the implant medial surface profile noise. The problem is estimating the parameters of a 3D transformation which satisfies the least squares fit 3D surface matching of the tibial medial surface profile805(i.e., p (x, y, z)) of the tibial implant model34″ to the medial plateau surface profile q (x, y, z) of restored bone model28″. This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between these two surface profiles, represented by e(x,y,z)=q(x,y,z)−p(x,y,z).

The same rationale applies to the surface profile modeling of the lateral compartment800of implant model34″. Based on the surface profile q′ (x, y, z) of lateral plateau760in restored bone model28″, the surface profile800(i.e., p′ (x, y, z) of the lateral compartment770of the implant model34″ can be obtained. The e′(x, y, z) represents a true vector assuming that template noise is independent of the implant medial surface profile noise. Again, the problem is estimating the parameters of a 3D transformation which satisfies the least squares fit 3D surface matching the lateral surface profile800(i.e., p′ (x, y, z)) of the tibial implant model34″ to the lateral plateau surface profile q (x, y, z) of the tibial restored bone model28″. This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between these two surface profiles, represented by e′(x,y,z)=q′(x,y,z)−p′(x,y,z). See D. Akca (supra).

Surface modeling, as described in the following discussion, can be utilized as an option to the surface matching process discussed with respect toFIG. 26.FIGS. 27A and 27Bare, respectively, medial and lateral sagittal MRI views of the tibia.FIG. 28is an isometric view of the tibia restored bone model28″ and tibia implant model34″ being used in the surface matching process.

FIG. 27Ashows the elliptical concavity outline810in as viewed via a medial MRI slice. Each of the medial plateau MRI slices shows an ellipse shape in Area A ofFIG. 20. The major axis and radius of the ellipse can be obtained inFIGS. 24A and 24B. A 3D ellipsoid model815from medial tibia plateau765inFIG. 28can then be reconstructed by computer software through a plurality of MRI slices similar to the MRI slice depicted inFIG. 27A.

FIG. 27Bshows the rectangle shape outline820in a lateral MRI slice. Each of the lateral plateau MRI slices shows a rectangle shape820in Area B ofFIG. 20. The 3D rectangle block model825from the lateral tibia plateau760inFIG. 28can then be reconstructed by computer software through a plurality of MRI slices similar to the MRI slice depicted inFIG. 27B.

FIG. 28shows a representation of 3D surface matching that can be employed with the process discussed with respect toFIGS. 27A and 27B. As described above, the ellipsoid model815is reconstructed from the medial plateau MRI slices. The surface profile of this ellipsoid model815can be represented as k(x,y,z). The medial concavity830matches the ellipsoid model815.

The surface profile805(i.e., p(x,y,z)), representing the medial compartment775of the articular bearing member785, can be obtained either through the surface profile of the ellipsoid model815or the medial concavity830of the tibial restored bone model28″, as shown inFIG. 28. The function e(x, y, z) represents a true vector assuming that template noise is independent of the implant surface profile noise. The parameters of a 3D transformation satisfy the least squares fit 3D surface matching so as to match the surface profile805(i.e., p (x, y, z)) of the medial compartment775to the surface profile k (x, y, z) of ellipsoid model815. This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between these two surface profiles, represented by e(x,y,z)=k(x,y,z)−p(x,y,z). See D. Akca (supra).

The rectangle block model825is reconstructed from the lateral plateau MRI slices. The surface profile of this rectangle block model825can be represented as k′(x,y,z). The lateral concavity835matches the rectangle block model825. In one embodiment, the surface profile800(i.e., p′(x,y,z)), representing the lateral compartment760of the articular bearing member785, can be obtained either through the surface profile of the rectangle block model825or the lateral concavity835of the tibial restored bone model28″ as shown inFIG. 28. The function e′(x, y, z) represents a true vector assuming that template noise is independent of the implant surface profile noise. The parameters of a 3D transformation satisfy the least squares fit 3D surface matching the surface profile800(i.e., p′ (x, y, z)) of the lateral compartment760to the surface profile k′ (x, y, z) of rectangle block model825. This can be achieved by minimizing a goal function, which measures the sum of squares of the Euclidean distances between these two surface profiles, represented by e′(x,y,z)=k′(x,y,z)−p′(x,y,z). See D. Akca (supra).

P. Determining Surgical Cut Plane for Tibia

FIG. 29Ais an isometric view of the tibia restored bone model28″ showing the surgical cut plane SCP design.FIGS. 29B and 29Care sagittal MRI views of the surgical tibia cut plane SCP design with the PCL.

As can be understood fromFIGS. 29A-29C, the surgical cut plane SCP850is designed in the tibial planning model of the POP procedure. During the TKA surgery, the damaged bone surface portions of the proximal tibia will be resected from the cut plane level850and be removed by the surgeon. As shown inFIGS. 29B and 29C, the surgical tibial cut plane850may be positioned above the surface where PCL is attached. Therefore, the system disclosed herein provides the maintenance of the PCL ligament during TKA surgery. In the POP planning, if the cut plane is below the surface plane of PCL, the revaluation of the tibial implant size is conducted. In such a case, a one-size smaller implant is selected for the implant model design.

In a manner similar to that depicted inFIG. 19B, when the tibia implant model34″, which was modified according to the adjustment value tr as indicated inFIG. 25, is shape fit to the tibia restored bone model28″, the surgical cut plane SCP (seeFIG. 23C) ends up being located proximally further by the amount of the adjustment value tr than it would otherwise be, resulting in the actual physical implant when mounted on the actual proximal tibia end providing articular surfaces that are positioned and oriented so as to allow the patient's knee to assume a natural or non-degenerated configuration.

The orientation and location of the implant's mounting post780may also be determined once the implant model34″ and restored bone model28″ are superposed. Also, the locations and orientations of the drill holes124(seeFIGS. 1H and 1I) of the arthroplasty jig2A may be determined from the implant model34″ and restored bone model28″ being superposed.

Once the shape match process (seeFIG. 1J[block195] andFIG. 1C[block120]) is complete, the information regarding the locations and orientations for the saw cut slot123and drill holes124may be packaged as saw cut and drill hole data44(seeFIG. 1E[block125]) and the process goes forward as outlined inFIG. 1E.

R. Verification of Implant Planning Models and Generation of Surgical Jigs Based of Planning Model Information

FIGS. 30A-30Care various views of the implant models34′,34″ superimposed on the bone models28′,28″.FIG. 30Dis a coronal view of the restored bone models28′,28″.

FIGS. 30A-30Cshow an embodiment of the POP system disclosed herein. The alignment of the implants models34′,34″ with the restored bone models28′,28″ is checked in both the anterior view (FIG. 30A) and the posterior view (not shown) and the lateral view (FIG. 30B) and the medial view (FIG. 30C).

The IR/ER rotation between the implants34′,34″ and the femur and tibia restored bone models28′,28″ is examined in both the medial view and the lateral view. For example,FIG. 30Bshows the lateral view showing the IR/ER rotation between no flexion and high flexion, andFIG. 30Cshows the medial view showing the IR/ER rotation between no flexion and high flexion. The stem of the tibia implant model34″ and the surgical cut plane SCP of the tibia implant model34″ provide the information for the IR/ER rotation.

FIG. 30Dshows the varus/valgus alignment of the knee model28′,28″ with the absence of the implants34′,34″. The gaps g1, g2between the lowermost portions of distal femoral condyles430,445and the lowermost portions of the tibia plateau760,765will be measured in the femoral and tibia restored bone models28′,28″″. Gap g1represents the distance between the distal lateral femoral condyle430and the lateral tibial plateau760. Gap g2represents distance between the distal medial femoral condyle445and the medial tibial plateau765. In the varus/valgus rotation and alignment, g1is substantially equal to g2, or |g1−g2|<<1 mm.

FIG. 30Dshows the knee model28′,28″ that is intended to restore the patient's knee back to his pre-OA stage. The knee model28′,28″ and associated implant models34′,34″ developed through the above-discussed processes include dimensions, features and orientations that the system4depicted inFIG. 1Acan utilize to generate 3D models of femur and tibia cutting jigs2. The 3D model information regarding the cutting jigs can the be provided to a CNC machine10to machine the jigs2from a polymer or other material.

S. Mechanical Axis Alignment

While much of the preceding disclosure is provided in the context of achieving natural alignment for the patient's knee post implantation of the actual physical femur and tibia implants, it should be noted that the systems and methods disclosed herein can be readily modified to produce an arthroplasty jig2that would achieve a zero degree mechanical axis alignment for the patient's knee post implantation.

For example, in one embodiment, the surgeon utilizes a natural alignment femoral arthroplasty jig2A as depicted inFIGS. 1F and 1Gto complete the first distal resection in the patient's femoral condylar region. Instead of utilizing a natural alignment tibia arthroplasty jig2B as depicted inFIGS. 1H and 1I, the surgeon instead completes the first proximal resection in the patient's tibia plateau region via free hand or a mechanical axis guide to cause the patient's tibia implant to result in a mechanical axis alignment or an alignment based off of the mechanical axis (e.g., an alignment that is approximately one to approximately three degrees varus or valgus relative to zero degree mechanical axis).

In one embodiment, as indicated inFIGS. 31A-32B, the arthroplasty jigs2AM and2BM may be configured to provide bone resections that lead to natural alignment, mechanical axis alignment or alignments in between the two. For example, the jigs2AM and2BM may have a natural alignment saw slot123and one or more non-natural alignment saw slots123′,123″ and123′″ that may, for example, be one degree, two degrees, three degrees or some other incremental measurement away from natural alignment and towards zero degree mechanical axis alignment. The surgeon may select a two degree deviation slot123″ based on a physical inspection and surgical experience.

In one embodiment of the POP systems and methods disclosed herein, instead of superposing and shape matching the restored bone models28′,28″ to the implant models34′,34″ in a manner that results in the saw cut and drill hole data44that leads to the production of natural alignment arthroplasty jigs2A,2B, the superposing and shape matching of the bone and implant models28,34may be conducted such that the resulting saw cut and drill hole data44leads to the production of zero degree mechanical axis alignment arthroplasty jigs or some other type of arthroplasty jig deviating in a desired manner from zero degree mechanical axis.

Thus, depending on the type of arthroplasty jig desired, the systems and methods disclosed herein may be applied to both the production of natural alignment arthroplasty jigs, zero degree mechanical axis alignment jigs, or arthroplasty jigs configured to provide a result that is somewhere between natural alignment and zero degree mechanical axis alignment.