Computer-assisted surgical system - Patent Review 5682886

What is claimed is:

1. A method for planning surgery on a portion of a body with the goals of improving the accuracy of the surgery and reducing the risks associated with surgery, comprising the steps of:

gathering image data of the portion of a body using a radiant energy means for gathering image data;

storing the image data in a memory means for storing image data;

reading the stored image data into a computer interfaced to the memory means, the computer having a visual display means for visually displaying images generated in at least one process step;

generating a three-dimensional computer model of the body portion from the image data using a modeling means for creating three-dimensional computer models from the image data;

identifying anatomical features relevant to the surgery on the three-dimensional computer model of the body portion; and

using software to define at least one desired correction to the anatomical structures to be accomplished by the surgery.

2. The method for planning surgery of claim 1, wherein the radiant energy means for gathering image data is selected from a group consisting of magnetic resonance imaging devices, X-ray devices, and computed tomography imaging devices.

3. The method for planning surgery of claim 1, wherein the memory means for storing image data is selected from a group consisting of electronic media, electronically erasable media, electromagnetic media, magnetic media, optical media, and magnetic-optical media.

4. The method for planning surgery of claim 1, wherein the visual display means is selected from a group consisting of raster display means and vector display means.

5. The method of planning surgery of claim 1, wherein the image data represent discrete areas corresponding to at least one relevant anatomical structure, wherein boundaries defining each anatomical structure are determined by predefined variations in the image data, and wherein the modeling means locates the boundaries that define the anatomical structures to create the three-dimensional computer model of the body portion.

6. The method for planning surgery of claim 5, wherein the modeling means locates the boundaries that define the surfaces of the anatomical structures and defines continuous curves corresponding to those boundaries to construct the three-dimensional computer model from those continuous curves.

7. The method of planning surgery of claim 6, wherein the modeling means uses a Canny filter to define a set of edges corresponding to the boundaries that define the surfaces of the anatomical structures.

8. The method for planning surgery of claim 7, wherein the modeling means uses a snake algorithm first to form active contours, and then to adjust the sizes and shapes of the active contours to fit the set of edges.

9. The method of planning surgery of claim 8, wherein the modeling means uses points on the active contours to create surface patches.

10. The method for planning surgery of claim 9, wherein the modeling means uses a third-order polynomial equation to define the surface patches.

11. The method for planning surgery of claim 10, wherein the surface patches are Bezier patches.

12. The method for planning surgery of claim 10, wherein the modeling means tessellates the surface patches into polygonal meshes that in combination correspond to the relevant anatomical structures.

13. The method for planning surgery of claim 1, wherein the modeling means is software.

14. The method for planning surgery of claim 1, wherein the modeling means identifies the relevant anatomical structures.

15. The method for planning surgery of claim 1, wherein the three-dimensional computer model of the body portion is displayed on the visual display means.

16. The method for planning surgery of claim 1, wherein software is used to define the desired corrections.

17. The method for planning surgery of claim 1, wherein the relevant anatomical features are displayed on the visual display means.

18. The method for planning surgery of claim 1, further comprising the step of determining the size and pose of at least one prosthesis to be used in the surgery.

19. The method for planning surgery of claim 18, wherein prothesis size data is stored in a second memory means accessible by the computer, and further comprising the step of determining prosthesis size and pose by comparing the three-dimensional computer model of the body portion with the prothesis size data.

20. The method for planning surgery of claim 19, wherein the prothesis size data includes at least two three-dimensional prosthesis images of different sizes.

21. The method for planning surgery of claim 20, wherein at least two three-dimensional prothesis images of different sizes are displayed on the visual display means, superimposed on the three-dimensional computer model of the body portion, and wherein a three-dimensional prosthesis image of a particular size is chosen to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired correction.

22. The method for planning surgery of claim 21, wherein at least two three-dimensional prothesis images of different sizes are displayed on the visual display means superimposed on the three-dimensional computer model, and wherein an operator chooses the size of the three-dimensional prosthesis image to fit the three-dimensional computer model of the body portion to a degree sufficient to accomplish the defined desired correction.

23. The method for planning surgery of claim 18, wherein the pose of the three-dimensional prosthesis image is adjusted to fit the three-dimensional computer model of the body portion to a degree sufficient to accomplish file defined desired correction.

24. The method for planning surgery of claim 23, wherein an operator adjusts the pose of the three-dimensional prosthesis image to fit the three-dimensional computer model of the body portion to a degree sufficient to accomplish the defined desired correction.

25. The method for planning surgery of claim 18, wherein the three-dimensional prothesis image is displayed on the visual display means superimposed on the three-dimensional computer model of the body portion, and wherein the size and pose of the three-dimensional prosthesis image are adjusted to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired correction.

26. The method for planning surgery of claim 25, wherein the three-dimensional prothesis image is displayed on the visual display means superimposed on the three-dimensional computer model of the body portion, and wherein an operator adjusts the size and pose of the three-dimensional prosthesis image of the prosthesis to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired correction.

27. The method for planning surgery of claim 18, further comprising the step of determining characteristics of at least one resection to be performed on the anatomical structures.

28. The method for planning surgery of claim 27, wherein the resection is shown in relation to the three-dimensional computer model and displayed on the visual display means.

29. A method for planning unicompartmental knee arthroplasty surgery with the goals of improving the accuracy of the surgery and reducing the risks associated with surgery, comprising the steps of:

gathering image data of a femur and a tibia using a radiant energy means for gathering image data;

storing the image data of the femur and tibia in a memory means for storing image data;

reading the stored image data into a computer interfaced to the memory means, the computer having a visual display means for visually displaying images generated in at least one process step;

generating a three-dimensional computer model of the femur and tibia using a modeling means for constructing three-dimensional computer models from the image data;

identifying a hip center on the three-dimensional computer model;

identifying a knee center on the three-dimensional computer model;

identifying an ankle center on the three-dimensional computer model;

defining the line from the hip; center to the knee center on the three-dimensional computer model;

defining the line from the knee center to the ankle center on the three-dimensional computer model;

determining a desired varus/valgus correction on the three-dimensional computer model;

determining the size and pose of both a femoral prosthetic component and a tibial prosthetic component to accomplish the desired correction on the three-dimensional computer model; and,

determining the size and pose characteristics of resections to be performed on the femur and the tibia as shown in the computer model.

30. The method for planning surgery of claim 29, wherein the radiant energy means for gathering image data is selected from a group consisting of magnetic resonance imaging devices, X-ray devices, and computed tomography imaging devices.

31. The method for planning surgery of claim 29, wherein the memory means for storing image data is selected from a group consisting of electronic media, electronically erasable media, electromagnetic media, magnetic media, optical media, and magnetic-optical media.

32. The method for planning surgery of claim 29, wherein the visual display means is selected from a group consisting of raster display means and vector display means.

33. The method of planning surgery of claim 29, wherein the image data represents discrete areas corresponding to each of the femur and tibia; wherein boundaries that define surfaces of each of the femur and tibia are determined by predefined variations in the image data; and, wherein the modeling means locates the boundaries that define each of the femur and tibia to create the three-dimensional computer model.

34. The method for planning surgery of claim 32, wherein the modeling means locates the boundaries that define the surfaces of each of the femur and tibia, and defines continuous curves corresponding to those boundaries to construct the three-dimensional computer model from those continuous curves.

35. The method for planning surgery of claim 33, wherein the modeling uses a Canny filter to define a set of edges corresponding to the boundaries that define the surfaces of each of the femur and tibia.

36. The method for planning surgery of claim 35, wherein the modeling means uses a snake algorithm first to form active contours, and then to adjust the sizes and shapes of the active contours to fit the set of edges.

37. The method for planning surgery of claim 36, wherein the modeling means uses points on the active contours to create surface patches.

38. The method for planning a surgery of claim 37, wherein the modeling means uses a third-order polynomial equation to define the surface patches.

39. The method for planning a surgery of claim 38, wherein the surface patches are Bezier patches.

40. The method for planning a surgery of claim 38, wherein the modeling means tessellates the surface patches into polygonal meshes that in combination correspond to surfaces of the femur and tibia.

41. The method for planning a surgery of claim 29, wherein the modeling means is software.

42. The method for planning a surgery of claim 29, wherein the image data of a femur includes data relating to a femoral head having a perimeter, and wherein the step of identifying the hip center comprises identifying at least four points on the perimeter of the femoral head on the image data, defining a sphere from these four points, and defining the center of the sphere as the hip center.

43. The method for planning a surgery of claim 42, wherein the four points, the computer image of the sphere, and the image data of the femoral head are displayed on the visual display means.

44. The method for planning a surgery of claim 42, wherein the four points are automatically identified by software programmed to find the four points.

45. The method for planning a surgery of claim 29, wherein the step of identifying a knee center comprises the steps of identifying epicondyle points on each of a femoral lateral epicondyle and a femoral medial epicondyle, defining a line segment connecting the epicondyle points, and defining the midpoint of that line segment as the knee center.

46. The method for planning a surgery of claim 29, wherein the step of identifying an ankle center comprises the steps of identifying malleoli points on each of a medial malleoli and a lateral malleoli on the three-dimensional computer model, defining a line segment connecting the malleoli points, and defining the midpoint of that line segment as the ankle center.

47. The method of planning surgery of claim 29, wherein the hip center, knee center, ankle center are displayed on the visual display means.

48. The method for planning surgery of claim 47, wherein the lines from the hip center to the knee center, and from the knee center to the ankle center, are displayed on the visual display means.

49. The method for planning surgery of claim 45, further comprising the steps (a) identifying on the three-dimensional computer model the femoral condyle on which the arthroplasty is to be performed; (b) translating the knee center to the origin of a Cartesian coordinate system; (c) rotating the three-dimensional computer model until the hip center lies on a coordinate axis; (d) rotating the three-dimensional computer model about the selected coordinate axis until the plane formed by the hip center and the epicondyle points is parallel to a coordinate plane formed using the selected coordinate axis, so that the line from the hip center to the knee center is aligned with the selected coordinate axis; (e) selecting a vertex on the three-dimensional computer model of the opposite femoral condyle that has the lowest value along the selected coordinate axis; (f) defining a rotation axis as the line perpendicular to the selected coordinate plane through the selected point; and, (g) rotating the three-dimensional computer model of the tibia about the rotation axis until the alignment has been accomplished.

50. The method of planning surgery of claim 49, wherein the selected point, the rotation axis, and the varus/valgus correction are identified by software stored in the computer.

51. The method for planning surgery of claim 29, wherein size and three-dimensional image data for each of the femoral and tibial prosthetic components is stored in a second memory means accessible by the computer, and further comprising the step of determining the size and pose of the prosthesis components by comparing the three-dimensional computer model of the femur and tibia with the prothesis size and image data.

52. The method for planning surgery of claim 51, wherein the three-dimensional prothesis image data is displayed on the visual display means superimposed on the three-dimensional computer model of the femur and tibia, and wherein the size and pose of the three-dimensional prosthesis image are adjusted to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired varus/valgus correction.

53. The method for planning surgery of claim 52, wherein at least two three-dimensional images of different sizes of the femoral prosthetic component and the tibial prosthetic component are displayed on the visual display means superimposed on the three-dimensional computer model of the femur and the tibia, and wherein a three-dimensional image of the femoral prosthetic component of a particular size, and a three-dimensional image of the tibial prosthetic component of a particular size, are chosen to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired varus/valgus correction.

54. The method for planning surgery of claim 53, wherein at least two three-dimensional images of different sizes of the femoral prosthetic component and the tibial prosthetic component are displayed on the visual display means superimposed on the three-dimensional computer model of the femur and the tibia, and wherein an operator chooses a three-dimensional image of the femoral prosthetic component of a particular size, and a three-dimensional image of the tibial prosthetic component of a particular size, to fit the three-dimensional computer model to a degree sufficient to accomplish the defined desired varus/valgus correction.

55. The method for planning surgery of claim 29, wherein the resections of each of the femur and tibia are shown in relation to the three-dimensional computer model of the femur and tibia and displayed on the visual display means.

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BACKGROUND OF THE INVENTION

This invention relates generally to computer-assisted surgical systems, and in particular to a computer-assisted knee replacement system used to achieve accurate limb alignment with minimal surgical invasiveness.

One application for computer-assisted surgical systems is in the field of knee arthroplasty. Knee arthroplasty is a surgical procedure in which the articular surfaces of the femur and tibia (and the patella, in the case of tricompartmental knee arthroplasty) are cut away and replaced by metal and/or plastic prosthetic components. The goals of knee arthroplasty are to resurface the bones in the knee joint and to reposition the joint center on the mechanical axis of the leg. Knee arthroplasty is performed to relieve pain and stiffness in patients suffering from joint damage caused by osteo-, rheumatoid, or post-traumatic arthritis. In 1993, approximately 189,000 knee arthroplasties were performed in the United States, and this number is expected to increase over the next decade as the U.S. population ages.

More than 95% of knee arthroplasties performed in the U.S. are tricompartmental. Tricompartmental knee arthroplasty ("TKA") involves the replacement of all the articular surfaces of the knee joint, and is performed when arthritis is present in two or more of the three compartments of the knee: medial (toward the body's central axis), lateral (away from the body's central axis), and patello-femoral (frontal).

The remaining knee arthroplasties are unicompartmental knee arthroplasties ("UKA"). UKAs involve the replacement of the articular surfaces of only one knee compartment, usually the medial. UKAs are indicated when arthritis is present in only one compartment and when the patellar surface appears healthy.

UKAs have several advantages over TKAs. These include the preservation of more patient anatomy, increased knee stability, less complicated revision surgery, and the potential for installation through a smaller incision, as compared with a TKA. A TKA requires the resection of the entire tibial plateau, both condyles of the femur, and the posterior side of the patella, because all compartments of the knee are replaced. As a result, in TKAs, the anterior cruciate ligament, which is attached to the front of the tibial plateau, usually is removed, severely reducing the stability of the knee after the operation. In contrast, during UKAs, only one compartment is replaced, and thus only one side of the tibial plateau is removed. As a result, the anterior cruciate ligament may be preserved, allowing for increased knee stability. In addition, if a revision surgery is required, more natural bone stock is present on which to place the revision components. Finally, since the resections and components used in UKAs are smaller, minimally-invasive surgical procedures may be applied.

In the late 1970s, there were reports of high failure rates for UKAs due to problems such as improper alignment. One study, for example, reported that 10% of UKA patients needed revision surgery because one or both of the other knee compartments degenerated due to the presence of polyethylene particles that flaked off the prosthetic components. Overcorrection of the varus/valgus deformity, which is the angle between the mechanical axis of the femur and the mechanical axis of the tibia in the anterior/posterior ("A/P") plane, was one suspected cause of the excessive component wear.

In contrast, many recent studies have indicated high success rates for UKAs. These studies report that the incidence of failure for UKAs is comparable to or less than that for TKAs. The higher success rates for UKAs are likely due to the use of thicker tibial components than used in earlier UKAs, the use of component materials that are less susceptible to wear than earlier materials, and better alignment of the components by the surgeon so as to not overcorrect varus/valgus deformity.

Despite those recent studies, in many cases where UKAs are indicated, orthopaedic surgeons in the U.S. still perform TKAs. This conservative attitude towards UKAs is believed to be the result of several factors, such as the use of poor instrumentation to install the implants, concern over arthritis spreading to other compartments, and the early mixed reviews of UKA outcomes in the literature. Because of this conservative attitude, the benefits of UKAs are not realized by many patients.

Although UKA success rates are higher than they were 20 years ago, there are still important problems in UKA and TKA performance. For example, alignment of the femoral and tibial prosthetic components with respect to the bones and to each other currently involves the use of purely mechanical instrumentation systems. Typical femoral instrumentation consists of an intramedullary rod (a metal rod that is aligned with the femoral shaft via insertion into the medullary canal of the femur) and several slotted cutting jigs for guiding a saw blade used to resect the bone. The surgeon aligns the jigs first by drilling a hole through the center of the distal end of the femur into the medullary canal, which runs the length of the femoral shaft, and then inserts the intramedullary rod into the canal. Thereafter, the surgeon removes the rod from the femur, and slides a cutting guide onto the rod. The surgeon next reintroduces the rod into the medullary canal, and positions the cutting guide against the distal end of the femur. To account for the fact that the rod is oriented along the femoral shaft, which does not correspond to the mechanical axis of the femur, the cutting guide is usually offset by a predetermined and fixed distance from the rod in the A/P pirate. The offset is provided to allow a distal cut to be made that is perpendicular to the mechanical axis of the femur, thus correcting any varus/valgus deformity. The depth of the distal cut is usually adjustable in discrete intervals: some systems have cutting blocks with slots at multiple depths, while others have cutting blocks with pin holes at multiple depths allowing the entire block to be moved up or down on a set of parallel pins. The remaining cuts vary depending on the geometry of the implant being installed. The depth and orientation of all these cuts, however, are determined by the cuts already made and/or by visual means.

Tibial instrumentation consists of an extramedullary rod (a metal rod that the surgeon aligns with the tibial shaft via external anatomical landmarks) and a slotted cutting guide. The mechanical axis of the tibia is assumed to run along the tibial shaft. The surgeon places the cutting jig at the top of the rod, with the cutting surface perpendicular to the rod. The depth of the cut is adjusted by moving the jig along the rod. The surgeon clamps the bottom of the rod around the ankle, just proximal to the malleoli (which form the distal portion of the tibia and fibula).

The instrumentation systems just described suffer from certain problems. Femoral varus/valgus alignment, for example, is determined by a discrete and predefined offset from the femoral shaft, which may not result in the desired angular correction. The amount of bone resected is adjustable, but only through slots positioned at discrete intervals of about two millimeters. Other parameters, such as rotation around the axis of the limb, must be determined visually. The tibial jig is aligned almost entirely by the surgeon's visual judgment.

Discretely adjustable alignment systems can introduce inaccuracies when an optimal resection falls between or outside of the range of predefined alternatives. The surgeon in such circumstances must decide which of the available alternatives is closest to the optimal resection. Moreover, the accuracy of visual alignment is primarily the product of the surgeon's experience in performing TKAs and UKAs. The accuracy needed in alignment of the prosthetic components with respect to the bones is still being debated, but it has been shown that misaligmnent of the components can cause excessive component wear. As a result, revision surgery often is necessary.

Moreover, because current UKA instrumentation systems are, for the most part, modified TKA instrumentation systems, some of the possible benefits unique to UKAs have not been realized. For example, because UKA components are less than half the size of TKA components, they can be implanted using a smaller surgical incision. However, many of the instrumentation sets for UKAs still require full exposure of the knee, and the use of an intramedullary rod, which can be a source of complications. Thus, the benefits of limited exposure, such as shorter operating room ("OR") time, decreased healing time, and less morbidity, have not been realized with current UKA techniques.

New technologies, in addition, reveal that existing procedures may be improved. Recent advances in medical imaging technology, such as computed tomography ("CT") and magnetic resonance ("MR") imaging, have made it possible to display and manipulate realistic computer-generated images of anatomical structures. These advances have had immediate practical applications to surgery simulation, i.e., computer-modeled surgical procedures used to plan, teach, or aid surgery. Many of the early simulations are related to planning and evaluating neurosurgery. More recently, three-dimensional reconstructions from CT data have been used to plan total hip reconstructions, osteotomies (a removal of a piece of bone to correct a deformity), and allograft procedures (tissue graft), and to design custom prostheses. Such surgical planning systems can be used to develop three-dimensional models, which help surgeons properly size and "pose" surgical tools and prosthetic components in the body. (As used herein, "pose" refers to the position and the orientation of a structure, and may be used as a noun or as a verb.) Most systems, however, have no way of transferring this information into the operating room. The computer assists in the planning, but not in the implementation, of the procedure. For the computer to assist in the implementation of the surgical plan, the models used in the surgical planning procedure must be "registered" to the patient intraoperatively. Registration is the process of defining a geometric transform between the physical world and a computer model. In this way, the computer can direct the placement of the tools and prosthetic components relative to the patient.

Some computer-assisted surgery systems combine surgical planning software with a registration method to implement surgical plans. These systems have been applied to the planning and implementation of orthopaedic procedures. For example, the "Robodoc" hip replacement system from Integrated Surgical Systems (Sacramento, Calif.) uses a computer-based surgical plan with a robotic manipulator to perform intraoperative registration and some of the bone resections needed for hip replacement. The Robodoc system has been tested in the operating room and has produced accurate bone resections, but the system has several important limitations. It is expensive, for example, and must be operated by a specially-trained technician. It also adds substantially to OR time, increasing the cost of using the system. Another problem is that the Robodoc system uses a pin-based registration method. The pins, called "fiducials," are inserted into the patient's bones prior to imaging. Registration is achieved by aligning the fiducials in the image data with the fiducials on the patient. Pin-based registration requires an additional surgical procedure to insert the pins, causing additional pain to the patient, and lengthening the patient's rehabilitation time.

The present invention is intended to overcome the disadvantages associated with current knee arthroplasty procedures, surgical planning systems, and computer-assisted surgery systems. The present invention determines optimal alignment of resections preoperatively, and uses computer modeling techniques to help the surgeon achieve that alignment. Moreover, smaller jigs are used in the present invention, and therefore, smaller incisions are made in the patient's leg. The present invention also plans the surgical procedure preoperatively, and assists in implementing the plan. Further, the present invention is less expensive than many prior art systems, and makes it possible to use pinless registration methods. Thus, the present invention represents a significant solution to many problems experienced in the field.

SUMMARY OF THE INVENTION

The invention is embodied in a method for planning surgery on a portion of a body with the goals of improving the accuracy of the surgery and reducing the risks associated with surgery. This method comprises the steps of gathering image data of the portion of a body using a radiant energy means for gathering image data. The image data is stored in a memory means. The stored image data then is read into a computer having a visual display for displaying images generated in at least one process step. The system uses the image data to generate a three-dimensional computer model of the body portion using a modeling means, and identifies anatomical features relevant to the surgery on the three-dimensional computer model. Finally, the system defines at least one desired correction to the anatomical structures to be accomplished by the surgery. In one embodiment of the invention, the method for planning surgery is used to plan unicompartmental knee arthroplasty surgery.

The invention further is embodied in a method of performing surgery on a portion of a body with the goals of improving the accuracy of the surgery and reducing the risks associated with surgery. The method comprises the steps of loading surgical plan data stored in a memory means into a computer having a visual display for displaying images generated in at least one process step. The surgical plan data comprises a three-dimensional computer model of a body portion, and data relating to at least one prosthesis of defined size and position relative to the body portion. The system then registers the three-dimensional computer model of the body portion to the actual body portion using a registration means. The system next provides at least one surgical tool that has a defined relationship relative to the prosthesis defined in the surgical plan data, the relationship defining a desired pose for the surgical tool relative to the body portion. Finally, the system allows the user to pose the surgical tool relative to the body portion in the desired pose, and the surgery is performed. In one embodiment of the invention, the method for performing surgery is used to perform unicompartmental knee arthroplasty. In another embodiment of the invention, the method for performing surgery further comprises the step of performing at least one resection on the body portion, wherein the resection is performed using a burring device.

The invention also is found in a jig assembly for guiding a device used to resect a femur and a tibia. The jig assembly comprises a femoral docking jig having a body, and a first aperture for receiving a positioning device. The jig assembly also comprises a femoral contouring jig that has a second aperture for receiving the femoral docking jig and at least one surface for guiding a device used to resect the femur and the tibia. Finally, the jig assembly comprises a tibial jig having a horizontal cutting guide surface and a vertical cutting guide surface to guide the device used to resect the femur and the tibia, and a docking hole for receiving a positioning device. In another embodiment where the tibial prosthesis employs a fixation post, a tibial post hole jig also is positioned.

It is an object of the invention to provide a computer-assisted surgical system that costs substantially less than current systems.

It is another object of the invention to provide a computer-assisted surgical system that requires shorter OR time than current systems.

Another object of the invention is to provide a computer-assisted surgical system method that decreases patient complications.

It is another object of this invention to provide a computer-assisted surgical system that decreases the length of a patient's hospital stay.

Another object of the invention is to provide a computer-assisted surgical system that decreases a patient's rehabilitation time.

Another object of the invention to provide a computer-assisted surgical system that allows surgeons to install unicompartmental knee implants more accurately and less invasively than is possible with current systems, thereby increasing implant longevity and improving knee function.

Still another object of the invention is to provide a method of performing knee arthroplasty that allows for more accurate alignment of the prosthetic components with respect to the bones than is currently available using mechanical instruments with slots distanced at discrete intervals.

Another object of the invention is to provide a method of performing knee arthroplasty that does not require the use of an intramedullary rod in the femur.

Another object of the invention is to provide a method for implanting unicompartmental knee arthroplasty components using a smaller surgical incision t