Computer-assisted surgical method - Patent Review 5871018

What is claimed is:

1. 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, comprising the steps of:

loading into a computer surgical plan data stored in a memory means interfaced to the computer, the computer having a visual display means for visually displaying images generated in at least one process step, wherein 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 pose relative to the body portion;

registering the three-dimensional computer model to the body portion using a registration means for registering the model and body portion;

providing at least one surgical tool having 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;

positioning the surgical tool relative to the body portion in the desired pose and performing the surgery.

2. The method of performing surgery of claim 1, wherein the memory means is selected from a group consisting of electronic media, electronically erasable media, electromagnetic media, magnetic media, optical media, and magnetic-optical media.

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

4. The method or performing surgery of claim 1, wherein the three-dimensional computer model is registered to the body portion by displaying a three-dimensional representation of the registration means relative to the three-dimensional computer model on the visual display means, aligning the registration means relative to the body portion in the same relationship as shown in the display, and signalling the computer that the registration means is in the pose shown on the display means.

5. The method of performing surgery of claim 4, wherein the registration means is a coordinate measuring device that provides pose data relative to a fixed set of spatial coordinates to the computer.

6. The method of performing surgery of claim 5, wherein the coordinate measuring device has a fixed end and a free end, and further comprises a pointer attached at the free end.

7. The method of performing surgery of claim 6, wherein the pointer comprises a transdermal means for registering the body portion without incision.

8. The method of performing surgery of claim 7, wherein the transdermal means is a percutaneous means for registering the body portion without incision.

9. The method of performing surgery of claim 8, wherein the percutaneous means is a needle.

10. The method of performing surgery of claim 6, wherein the pointer is removably attached to the coordinate measuring device.

11. The method of performing surgery of claim 1, comprising further the step of providing visual feedback on the visual display means to inform a user of the accuracy of registration.

12. The method of performing surgery of claim 1, wherein the three-dimensional computer model is registered to the body portion by touching the body portion with the registration means; signalling the computer that the registration means is located at a point on the body portion to be sampled; and, relating the sampled points to points on the three-dimensional computer model of the body portion.

13. The method of performing surgery of claim 12, wherein the registration means comprises a transdermal means for sampling points on the body portion without incision.

14. The method of performing surgery of claim 13, wherein the transdermal means is a percutaneous means for sampling points on the body portion without incision.

15. The method of performing surgery of claim 14, wherein the percutaneous means is a needle.

16. The method of performing surgery of claim 12, wherein the computer displays on the visual display means the location of predetermined points on the body portion to be sampled.

17. The method of performing surgery of claim 16, wherein the sampled points are displayed on the visual display means.

18. The method of performing surgery of claim 12, wherein the sampled points are displayed on the visual display means.

19. The method of performing surgery of claim 1, wherein the step of positioning at least one of the surgical tools relative to the body portion comprises the steps of attaching the surgical tool to the registration means; displaying a three-dimensional representation of the registration means and the attached surgical tool on the visual display means so that the representation moves in correspondence with movement of the registration means and the surgical tool; displaying a representation of the attached surgical tool in a desired pose on the three-dimensional model of the body portion; positioning the surgical tool relative to the body portion using the registration means; and providing feedback to the user when the surgical tool is in the desired pose.

20. The method of performing surgery of claim 19, further comprising the step of performing at least one resection on the body portion, wherein the resection is performed using a burring device.

21. The method of performing surgery of claim 20, further comprising the step of comparing the resection to the intended resection defined in the surgical plan data.

22. The method of performing surgery of claim 21, wherein the step of comparing the resection to an intended resection comprises the steps of sampling characteristic corners of the resection, constructing the resection on the three-dimensional computer model of the body portion using the characteristic corners by finding the plane formed by the characteristic corners, constructing an intended resection from the surgical plan data on the three-dimensional computer model, comparing the resection with the intended resection by determining variations in the pose of the resections and the pose of the intended resection and displaying the variations on the visual display means.

23. The method of performing surgery of claim 22, wherein software is used to reconstruct the actual resections, to reconstruct the intended resection, to compare the intended resection to the actual resection, and to display the variations on the visual display means.

24. The method of performing surgery of claim 19, wherein feedback is provided to indicate the movement of the surgical tool towards the desired pose and away from the desired pose.

25. The method of performing surgery of claim 19, wherein feedback is audible.

26. The method of performing surgery of claim 19, wherein the feedback is visual.

27. The method of performing surgery of claim 25, wherein the feedback also is visual.

28. The method of performing surgery of claim 1, further comprising the step of performing at least one resection on the body portion using a means for resecting bone.

29. The method of performing surgery of claim 28, wherein the means for resecting bone is a burring device.

30. A method of performing 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:

loading unicompartmental knee arthroplasty surgical plan data stored in a memory means 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, wherein the surgical plan data comprises a three-dimensional computer model of at least the femur and tibia, data relating to at least one femoral prosthetic component of defined size and pose relative to the femur, and data relating to at least one tibial prosthetic component of defined size and pose relative to the tibia;

registering the three-dimensional computer model to the femur and the tibia using a registration means for registering the model to the femur and the tibia;

providing at least one femoral jig having a defined relationship relative to the femoral prosthetic component defined in the surgical plan data, and providing at least one tibial jig having a defined relationship relative to the tibial prosthetic component defined in the surgical plan data;

positioning the femoral jig relative to the femur, and the tibial jig relative to the tibia, in the desired poses and performing the surgery.

31. The method of performing surgery of claim 30, wherein the memory means 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 of performing surgery of claim 30, wherein the visual display means is selected from a group consisting of raster display means and vector display means.

33. The method of performing surgery of claim 30, wherein the step of registering the surgical plan data to the femur and the tibia using the registration means comprises the steps of selecting a first bone to be registered from either the femur or the tibia; displaying a three-dimensional computer representation of the registration means relative to the three-dimensional computer model of the selected bone on the visual display means; aligning the registration means relative to the selected bone as shown on the display means; signalling to the computer that the registration means is aligned as shown on the display means; and repeating the sequence of displaying, aligning and signalling for the other of the femur and the tibia.

34. The method of performing surgery of claim 33, wherein the registration means is a coordinate measuring device that provides pose data relative to a fixed set of spatial coordinates to the computer.

35. The method of performing surgery of claim 34, wherein the coordinate measuring device has a fixed end and a free end, further comprising a pointer attached at the free end.

36. The method of performing surgery of claim 35, wherein the pointer comprises a transdermal means for registering the body portion without incision.

37. The method of performing surgery of claim 36, wherein the transdermal means is a percutaneous means for registering the body portion without incision.

38. The method of performing surgery of claim 37, wherein said percutaneous means is a needle.

39. The method of performing surgery of claim 35, wherein the pointer is removably attached to the coordinate measuring device.

40. The method of performing surgery of claim 30, comprising further the step of providing visual feedback on the display means to inform a user of the accuracy of the registration.

41. The method of performing surgery of claim 30, wherein the three-dimensional computer model is registered to the femur and the tibia by selecting a bone to be sampled, the bone being one of the femur or the tibia; touching the registration means to points on the selected bone; signalling to the computer each point where the registration means touches the selected bone; relating the sampled points to points on the three-dimensional computer model; and repeating the steps of selecting, touching, signalling and relating for the other of the femur and the tibia.

42. The method of performing surgery of claim 41, wherein the registration means comprises a transdermal means for sampling points on the femur and the tibia without incision.

43. The method of performing surgery of claim 42, wherein the transdermal means is a percutaneous means for sampling points on the femur and the tibia without incision.

44. The method of performing surgery of claim 43, wherein the percutaneous means is a needle.

45. The method of performing surgery of claim 41, wherein the computer displays on the visual display means the location of the predetermined points on the body portion to be sampled.

46. The method of performing surgery of claim 45, wherein the sampled points are displayed on the visual display means.

47. The method of performing surgery of claim 41, wherein the sampled points are displayed on the visual display means.

48. The method of performing surgery of claim 30, wherein the step of positioning the femoral jig relative to the femur and the tibial jig relative to the tibia, comprises the steps of selecting a first jig to be positioned from either the femoral jig or the tibial jig; attaching the selected jig to the registration means; displaying a three-dimensional representation of the registration means and the attached selected jig on the visual display means so that the representation moves in correspondence with movement of the registration means and the selected jig; displaying a representation of the selected jig in a desired pose; positioning the selected jig relative to the bone corresponding to the selected jig using the registration means; providing feedback to the user when the selected jig is in the desired pose; and repeating the sequence of attaching displaying, positioning, and providing feedback for the other of the femoral jig and the tibial jig.

49. The method of performing surgery of claim 48, wherein feedback is provided to indicate the movement of the selected jig towards the desired pose and away from the desired pose.

50. The method of performing surgery of claim 48, wherein the feedback is audible.

51. The method of performing surgery of claim 50, wherein the feedback is also visual.

52. The method of performing surgery of claim 48, wherein the feedback is visual.

53. The method of performing surgery of claim 48, further comprising the steps of performing at least one resection on the femur, and performing at least one resection on the tibia using a means for resecting bone.

54. The method of performing surgery of claim 53, wherein the means for resecting bone is a burring device.

55. The method of performing surgery of claim 54, further comprising the steps of comparing the resection on the femur to an intended resection on the femur defined in the surgical plan data, and comparing the resection on the tibia to an intended resection on the tibia defined in the surgical plan data.

56. The method of performing surgery of claim 55, wherein the steps of comparing the resection on the femur to an intended resection on the femur, and comparing the resection of the tibia to an intended resection on the tibia, each comprises the steps of selecting a bone to be checked, sampling characteristic corners of the resection on that bone, constructing the resection on the three-dimensional computer model using the characteristic corners by finding the plane formed by the characteristic corners, constructing an intended resection from the surgical plan data on the three-dimensional computer model, comparing the intended resection with the actual resection by determining variations in the pose of the resections and the pose of the intended resection, displaying the variations on the visual display means, and repeating the steps of sampling, reconstructing, comparing, and displaying for the other of the femur and the tibia.

57. The method of performing surgery of claim 56 wherein software is used to reconstruct the actual resections, to reconstruct the intended resections, to compare the intended resections to the actual resections, and to display the variations on the visual display means.

58. The method of performing surgery of claim 30, further comprising the steps of performing at least one resection on the femur, and performing at least one resection on the tibia, wherein the resections are performed using a burring device.

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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 plane. 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 misalignment 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 than is used by current methods.

Another object of the invention is to provide a method of registering a computer model and surgical plan to a patient's body using a coordinate measuring machine.

Another object of the invention is to provide a method of registering a computer model and surgical plan to a patient without the need for an additional surgical procedure.

Still another object of the invention is to provide cutting jigs that are smaller than current cutting jigs, thereby requiring smaller incisions for placement.

Another object of the invention is to provide cutting jigs each of which can guide multiple bone resections necessary for UKAs, thereby reducing the number of cutting jigs required to perform UKAs.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front plan view of a femur.

FIG. 2 is a front plan view of a tibia.

FIG. 3 is a front elevational view of the knee joint, showing the bottom of a femur, with the patella deleted to expose the femur, tibia, and ligaments.

FIG. 4 is a functional block diagram of the planning computer and associated hardware used in the invention.

FIG. 5 is a flow chart illustrating one sequence of steps that is useful in the invention to generate a three-dimensional computer model of a patient's anatomy.

FIG. 6 is a top plan view of a CT image slice outlined by an active contour.

FIG. 7 is a side view of a three-dimensional computer model, based in part on the active contour shown in FIG. 6, of the top of a femur lying horizontally.

FIG. 8 is a flow chart illustrating one sequence of steps that is useful in the invention to find a hip center, a knee center, and an ankle center.

FIG. 9 is a plan view of a femur and a tibia, and their mechanical axes.

FIG. 10 is a flow chart illustrating one sequence of steps that is useful in the invention to position and align a patient's leg.

FIG. 11 is a side view of a femoral prosthetic component.

FIG. 12 is a bottom view of a femoral prosthetic component.

FIG. 13 is a side view of a tibial prosthetic component.

FIG. 14 is a bottom view of a tibial prosthetic component.

FIG. 15 is a flow chart illustrating one sequence of steps that is useful in the invention to size and select a prosthetic component.

FIG. 16 is a flow chart illustrating one sequence of steps that is useful in the invention to pose a prosthetic component.

FIG. 17 is a functional block diagram of the procedure computer and associated hardware used in the invention.

FIG. 18 is a side view of a coordinate measuring machine and a pointer useful in the invention.

FIG. 19 is a flow chart illustrating one sequence of steps that is useful in the invention to prepare the patient's leg for surgery.

FIG. 20 is a perspective view of a pointer and a transdermal means for registering points underneath a patient's skin useful in the invention.

FIG. 21 is a flow chart illustrating one sequence of steps that is useful in the invention to register a femur to a computer model using suggested pose registration.

FIG. 22 is a flow chart illustrating one sequence of steps that is useful in the invention to register a femur to a computer model using multi-point optimization registration.

FIG. 23 is a top view of a femoral docking jig.

FIG. 24 is a side view of a femoral docking jig.

FIG. 25 is a top view of a femoral contouring jig.

FIG. 26 is a side view of a femoral contouring jig.

FIG. 27 is a perspective view of a CMM tool mount useful in the invention.

FIG. 28 is a flow chart illustrating one sequence of steps that is useful in the invention to place femoral jigs onto a femur.

FIG. 29 is a top view of a tibial cutting jig.

FIG. 30 is a rear view of a tibial cutting jig.

FIG. 31 is a flow chart illustrating one sequence of steps that is useful in the invention to resect a tibia and to resect a femur.

FIG. 32 is a flow chart illustrating one sequence of steps that is useful as an alternative embodiment of the invention to determine how close actual resections are to intended resections.

FIG. 33 is a flow chart illustrating one sequence of steps that is useful as an alternative embodiment of the invention to determine placement error of a prosthetic component.

FIG. 34 is a flow chart illustrating one sequence of steps that is useful as an alternative embodiment of the invention to perform a trial reduction, to cement prosthetic components into place, to close an incision, to display the amount of time a surgeon took to complete the process steps, and to provide an inventory control for devices used in surgery.

DETAILED DESCRIPTION OF THE INVENTION

While the invention will be described in connection with a system for performing UKAs, this description is not intended to limit the invention to that application. Rather, it is intended to cover other surgeries and applications to which the technology may be beneficially applied. For example, the invention can be used in connection with TKAs, revision knee surgery, and other surgeries. Likewise, the invention can be used for other joint replacements that involve placing a rigid prosthetic component, or surgical instrumentation, on a bone. The invention also may be used in surgeries to install screws into broken hips or to correct other bone injuries. Persons skilled in the art will be able to adapt the invention to other applications with ready facility. Moreover, the invention need not be limited to the exact order of the steps specified herein, except to the extent that a step requires information that is obtained in a previous step. For example, in the case of UKA surgery described herein, steps that are to be performed on the tibia may occur before steps to be performed on the femur, notwithstanding the ordering of steps that follows below.

UKA surgery involves two bones shown in FIGS. 1 and 2: the femur 10 and the tibia 20. As shown in FIG. 1, the femur 10 extends from the hip (not shown) to the tibia 20, and has a top 30 and bottom 40 separated by a long shaft 50. The top 30 of the femur 10 is dominated by a femoral head 60, which is nearly spherical, and which extends at an angle of about 135 degrees from the shaft 50 of the femur 10 towards the center of the body, to fit within a hip socket. The bottom 40 of the femur 10 consists of a medial condyle 70 and a lateral condyle 80, which are rounded knobs separated by a smooth depression in front, called the trochlea 90, and a large notch in the rear (not shown), called the intercondylar notch. The medial condyle 70 is the condyle that is closest to the center axis of the body, and the lateral condyle 80 is the furthest from the center axis of the body.

Turning now to FIGS. 2 and 3, the tibia 20 extends from the femur 10 to the ankle (not shown), and has a top 100 and bottom 110 separated by a long shaft 120. The top 100 of the tibia 20, known as the tibial plateau 130, consists of a medial condyle 140 and lateral condyle 150, which are concave, and separated by a small ridge, called the tibial spine 160. The tibial medial condyle 140 and lateral condyle 150 articulate with the corresponding femoral medial condyle 70 and lateral condyle 80 of the femur 10. Several centimeters below the tibial plateau 130 is the tibial tuberosity 170, which is a mass that protrudes slightly from the tibia's anterior surface down from the top portion 100 of the tibia 20. The bottom 110 of the tibia 20 consists of a medial malleolus 180. which is a bony protuberance that protects the joint between the tibia 20 and the talus (not shown), a small bone just below the tibia 20. The anterior cruciate ligament 190 connects the lateral condyle 80 of the femur 10 and the anterior part of the tibial plateau 130, and provides stability to the knee.

The system of the present invention can be described as two subsystems: (1) a planning subsystem and (2) a procedure subsystem. The planning subsystem hardware, as shown in FIG. 4, first is composed of a planning workstation 200, which is a computer 210 interfaced with a memory means 220 for storing image data so that the image data may be read into the computer 210. The memory means 220 is of any suitable form, such as electronic storage media, electronically erasable storage media, electromagnetic storage media, magnetic storage media, optical storage media, or magnetic-optical storage media. The computer 210 also includes a visual display means 230 for visually displaying images generated in at least one process step, but preferably displays images generated in more than one process steps. The visual display means 230 is preferably a raster display means; however, other visual display means 230 (such as a vector display means) may be used without departing from the instant invention. An embodiment of the instant invention uses a Silicon Graphics Indigo 2 workstation as the computer 210; however, other computers having adequate graphics and processing capability may be used without departing from the invention. The planning subsystem also is composed of preoperative planning software used to process medical image data, build a three-dimensional computer model of the patient's leg from that data, align the model of the limb, and size and place the representations of prosthetic components.

Turning now to FIG. 5, in the first step of the planning subsystem, the operator gathers image data of the patient's leg using a radiant energy means for gathering image data, as reflected by block 240. The radiant energy means is preferably a CT device well-known in the art; however, other radiant energy means, such as MR imaging devices and X-ray devices, may be used without departing from the instant invention. When using the preferred CT device, a conventional scanning protocol is employed to collect image data. Thus, in one embodiment, the protocol collects the following image data with the knee in full extension to create a three-dimensional computer model of the patient's bones: ten 1.5 mm CT image "slices" (or, in other words, ten slices 1.5 mm apart) at the hip, several 50 mm slices through the shaft 50 of the femur 10, seventy 1.5 mm slices at the knee, several 50 mm slices through the shaft 120 of the tibia 20, and ten 1.5 mm slices at the ankle. A "slice" is a two-dimensional image of a body portion taken in the transverse plane (as seen looking down from above the head) by an imaging means, preferably an X-ray. The number of slices that are taken for the femur 10 and tibia 20 will depend on the length of those bones, but enough slices must be taken to create an accurate three-dimensional computer model of those bones. For a normal-sized leg, the operator will take approximately fifty slices for each of the femur 10 and tibia 20. As already noted, image data collection using other imaging techniques, for the purpose of developing three-dimensional computer models of the imaged body, is well-known in the field. The collected image data then is stored on the memory means 220.

After the image data is collected, the system uses the data to generate a three-dimensional computer model of the bones. First, an operator interfaces the memory means 220 to the computer 210, and locates the image data in the memory means 220. The planning software then, as reflected by block 250, reads the image data into the planning computer 210. After the image data has been loaded, the operator may view the image data to confirm its quality and accuracy. The operator then, as reflected by block 260, directs the use of a modeling means for creating three-dimensional anatomical models from image data. The image data represent discrete areas corresponding to the relevant anatomical structures (for UKAs, those anatomical structures are the femur 10 and tibia 20), wherein boundaries defining each anatomical structure are determined by variations in the image data such as color or brightness gradients (variations in color or light-to-dark changes) The operator uses the modeling means to locate the boundaries that define the surfaces of the anatomical structure, and to define continuous curves (or, in other words, outlines) corresponding to those boundaries, to create the three-dimensional computer model of the anatomy from those continuous curves. The operator also may locate anatomical landmarks in the image data for use in surgical planning.

(As used in this application, the term "three-dimensional model," whether applied to a bone model or to images corresponding to other structures, means a set of relevant coordinates in three-dimensional space. Thus, a three-dimensional model of a body portion may be a surface reconstruction of the relevant anatomical structures (such as bones), or relevant portions of those structures where less than the entire structure is relevant to the surgical procedure, or a selection of critical and/or noncritical points in space that may be used to define the surgical procedure. A three-dimensional model of a prothesis may be a surface reconstruction of the actual prothesis, or a selection of critical points on the prosthesis useful to determine required dimensions and geometry.)

In the preferred embodiment, the modeling means first uses two algorithms to define a set of edges in the image data, and to create active contours that fit those edges. The first algorithm is the Canny edge filter, which is well known in the art, and which is described in Canny, J., "A Computational Approach to Edge Detection," IEEE Transactions on Pattern Analysis and Machine Intelligence, PAMI 8(6), pp. 679-698 (1986). First, as reflected by block 265, a slice is displayed on the visual display means 230. As reflected by block 270, the Canny edge filter then defines edges in the image data by comparing variations in the image data with a reference value that is preselected to correspond to the edge of an anatomical structure. Preferably, the variations in the image data are variations in brightness; however, other variations from which the Canny edge filter can define a set of edges may be used without departing from the instant invention. In a particularly preferred embodiment, the operator can adjust the reference value to adjust for imaging variations.

Turning now to FIGS. 5 and 6, the second algorithm is the "snake" algorithm, which also is well known in the art, and is described in Kass, M., Witkin, A., & Terzopoulos, D., "Active Contour Models," International Journal of Computer Vision, pp. 321-331 (1988). As reflected by block 280, the "snake" algorithm first forms a continuous boundary, called an active contour 290, which consists of a series of points 300 connected by straight lines 310. For the first slice of image data, the operator specifies the positions of these points on the image data using a pointer, such as a mouse. For each subsequent slice, the algorithm uses the points from the previous slice to define the initial position of the active contours 290. The algorithm then adjusts the sizes and shapes of the active contours 290 to fit the set of edges defined above. The active contours 290 are analogous to a closed loop of springs connected at these points 300. If a spring is near an edge in the image data, the snake algorithm moves the spring close to the edge, which also causes associated springs to move. This process continues until a best fit of the active contours 290 to the edges in the image data is obtained, as reflected by block 320.

Preferably, the snake algorithm uses two parameters to limit the movement of the active contours 290. The first parameter is a bending factor that limits how much the active contours 290 can curve in a small region. The lower the bending f