WO2007067150A1

WO2007067150A1 - Computer assisted navigation for total knee arthroplasty

Info

Publication number: WO2007067150A1
Application number: PCT/SG2006/000360
Authority: WO
Inventors: Kuang Ying Yang
Original assignee: Kuang Ying Yang
Priority date: 2005-12-05
Filing date: 2006-11-24
Publication date: 2007-06-14
Also published as: SG132557A1

Abstract

A method and apparatus for assisting total knee arthroplasty includes the use of positional tracking devices and computer calculation of the spatial relationships between the patella and the femur and/or tibia. The computer calculation ensures correct position of the femoral component of the joint during arthroplasty by software simulation so that the trochlear groove will fall under the patella bone and achieve central tracking.

Description

Computer Assisted Navigation for Total Knee Arthroplasty

Background

This invention relates to a new method and apparatus for total knee arthroplasty. It particularly includes a software control system and positional indicators but is not limited to such.

Orthopaedic implants have been used in the past to repair damage to the skeleton and related structures, and to restore mobility and function. For example, various devices, such as pins, rods, surgical meshes and screws, have been used to join fractured bones in the proper orientation for repair.

Implants that restore the function to a damaged joint have also been used. Surgery intended to restore function to a joint is referred to as arthroplasty. A successful arthroplasty may eliminate pain and prevent the degradation of adjacent tissue. Arthroplasty has been performed on knees, hips and shoulders by replacing portions of the joint with implants.

In contrast, in some instances, instead of replacing a damaged joint, the joint is merely fused in a single position. Surgery intended to fuse a joint rather than to restore mobility is referred to as arthrodesis. Arthrodesis is particularly common for the complex load-bearing joints of the spine.

In patients suffering from advanced knee arthritis, the cartilage covering the tibia, femur and patella surfaces is worn out and can be treated effectively with a total knee arthroplasty. Total knee arthroplasty can involve the replacement of portions of the patella, femur and tibia with artificial components. In particular, a portion of the tibia and an adjacent (in use) portion of the femur can be cut away (resected) and replaced with artificial components. These components need to be placed in a certain position and angle to ensure correct limb alignment and function after the surgery and this usually requires certain tools and guides. For example, US 6,595,997 discloses methods used in performing femoral and tibial resection in knee surgery there is disclosed the need for aligning a resection guide relative to a patient's bone has applications during arthroplasty. An alignment guide is coupled to a patient's bone, to which there is coupled a resection guide. The resection guide is positioned along a transactional path and a plurality of rotational paths by manipulation of the alignment guide, thereby providing three degrees of freedom of manipulation over infinitely adjustable ranges.

In US 6,080,196 there is disclosed a provisional knee implant assembly including a femoral provisional having an articulating surface and a plurality of locating openings. A patella height gauge is required having at least two projections which each engage with a corresponding locating opening in the femoral provisional. The patella height gauge includes at least one visual locating reference for a patella. The femoral provisional is located relative to the patella by placing the femoral provisional on a distal end of the femur; attaching the patella height gauge to the femoral provisional; overlying the patella onto the gauge; and repositioning the femoral provisional relative to the one or more visual locating references on the patella height gauge.

There has been use of computers in some forms of orthopaedic surgery. For example in US 6,711,432 there is disclosed devices and methods for implementing computer-aided surgical procedures and more specifically devices and methods for implementing a computer-aided orthopaedic surgery utilizing intra-operative feedback. A three-dimensional model of an area of a patient upon which a surgical procedure is to be performed is modelled using software techniques. The software model is used to generate a surgical plan, including placement of multifunctional markers, for performing the surgical procedure. After the markers are placed on the patient, an updated image of the patient is taken and used to calculate a final surgical plan for performing the remainder of the surgical procedure. The three- dimensional modelling, surgical planning, and surgery may all take place remote from each other. The various entities may communicate via an electronic

Communications network such as the Internet. However such computer use is involved in modelling and not control of the components of tibia, femur and patella in knee arthroplasty.

In US 6,685,711 there is disclosed a tool for resecting tibia and femur, which includes anchoring devices, a three-way alignment guide attachable to the anchoring devices, two embodiments of a resection guide^' attachable to the alignment guide and equipped with couplings for trackers, a plane probe for examining the resected plane, and apparatus for extra-medullary (EM) alignment of the resection guide in the event of a computer failure. The methods of the invention include operating a computer aided navigation apparatus in the conventional manner including attaching one or more trackers to the bone to be resected; choosing a location for the anchoring device with or without guidance from the computer and installing the anchoring device; attaching the three-way alignment guide to the anchoring device; attaching a resection guide to the alignment guide; attaching one or two trackers to the resection guide; locating the resection guide with the aid of the alignment guide and the computer; fixing the resection guide to the bone with pins. After the bone is resected, the resection plane probe may be attached to a tracker and moved about the resected plane to obtain feedback from the computer navigation system. In the event of computer failure, the methods include attaching the EM alignment guide to the resection guide; attaching the EM rod to the EM alignment guide; and locating the resection guide by visual location of the EM rod rather than by feedback from the computer navigation system.

The prior art software programs are focused on the navigation of the tibial femoral joint. Those programs will guide the surgeon in terms of the angle and amount of resection of the lower end of the femur bone and upper end of the tibia bone. This is to facilitate correct placement of the metallic prosthesis which is shaped like the uncut bone so that after the surgery, the metallic prosthesis takes over the function of the joint and can achieve knee bending like that of a natural joint. The programs will also allow the surgeon to tighten or loosen the various ligaments around the knee joint so that the leg is straight after the surgery, as defined by so called "mechanical axis of the lower limb". However, there are 3 compartments in the knee joint - (a) medial (inner) tibio-femoral compartment (2) lateral (outer) tibiofemoral compartment and (3) patello-femoral compartment. None of the software in the market allows the navigation of the patello-femoral compartment as they cannot take into the account of the patella during the surgery.

Unfortunately, according to clinical studies, up to 20 to 30% of the failures after a total knee arthroplasty are related to the problems in the patello-femoral joint. This is despite a correct positioning and alignment in the tibio-femoral joint. Several published papers have shown that correct patello-femoral joint position is important to avoid knee pain following total knee arthroplasty surgery.

With computer assisted total knee arthroplasty, the surgeon can be guided and plan the resection of various bones correctly and accurately and avoid certain problems even before making any actual resection. This applies largely to the tibio-femoral joint. With the new concept of navigated patello-femoral resection, the inventor hopes to avoid the problems of patello-femoral joint pain or failure after surgery.

It is therefore an object of the invention to eliminate the need to rely on mechanical aids to control the relative movement of the parts of the knee structure.

It is also an object of the invention to provide an improved control over the patella.

It is still further an object of the invention to provide an improved method and apparatus for total knee arthroplasty which overcomes or at least ameliorates the problems of the prior art.

It is still further an object of the invention to provide an improved commercially useable improved method and apparatus for total knee arthroplasty. The invention involves both a concept of guiding the knee replacement in the patello-femoral joint and also an apparatus for the computer system to track the position of the patella. This will allow the navigation of the patello-femoral joint during a computer assisted total knee arthroplasty.

Summary of the invention

In accordance with the invention there is provided a method for assisting total knee arthroplasty comprising:

anchoring a first positional tracking device to the patella bone;

manipulating the unopened joint through its maximum range of movement and detecting the 3-dimensional position of the patella throughout the entire range of motion by camera tracking the tracking device; and

calculating the correct position of the femoral component of the joint by software simulation so that the trochlear groove will fall under the patella bone and achieve central tracking.

In an alternative embodiment of the method, the tracking device may be temporarily held on the surface of the patella bone; for example, by means of a clamp.

Preferably, the method includes the steps of:

anchoring a second tracking device to the femur and/or the tibia;

camera tracking the second tracking device(s); and

incorporating the added information obtained from the tracking of the second tracking devices(s) in calculating the correct position of the femoral component of the joint. In another embodiment of the invention, there is provided apparatus for assisting total knee arthroplasty comprising: ^•

(a) a positional tracking device that is adapted to be anchored to the patella bone or a positional tracking device that is temporarily held on the surface of the patella bone;

(b) a camera tracking system that will detect the 3-dimensional position of the patella throughout the entire range of motion of the knee joint; and

(c) a computer adapted to receive data from the camera tracking system for software simulation that will calculate the correct position of the femoral component so that the trochlear groove will fall under the patella bone and achieve central tracking.

Preferably, the apparatus includes:

(d) a tracking device or devices adapted to be anchored to the femur and/or tibia bone; and

(e) a camera tracking system adapted to detect the 3-dimensional positions of the patella and the femur and/or tibia.

Detailed description of a preferred embodiment of the invention

The present invention will now be described in more detail according to a preferred but non-limiting embodiment with reference to me accompanying drawings, wherein:

Figure 1 shows a dissected, anatomical view of a knee in flexion; and Figure 2 shows the knee of Figure 2 in extension.

As can be seen, the prior art was only involved in the tibio-femoral joint. However the invention also guides cutting of the patello-femoral joint by haying control of the navigation of the patella. In a normal patient, the patella tracks in the centre off a groove at the lower end of the femur called the trochlear groove. After the total knee arthroplasty, the objective is to restore the patello-femoral joint so that the patella will again track in the centre of the new trochlear groove of the prosthetic femoral component. How well the patella tracks after a knee replacement depends on several factors like rotation of the femoral component in the transverse plane, thickness of the patella, the tightness of the lateral patella fibres, etc. With the current total knee arthroplasty, with or without computer navigation, the surgeon does not know the exact 3 dimensional position of the patella tracking before the surgery and hence there is no way of predicting how well the patella tracks after the surgery until all the bone resections are made. If the patella tracking is incorrect, further soft tissue releases or further bone resections need to be performed.

The present invention is performed with a computer assisted total knee arthroplasty. At the beginning of the surgery before opening the joint, the surgeon will perform a registration of the patella tracking. This is achieved by inserting a tracking device or holding a tracking device on the surface of the patella. The surgeon will then bend the knee to a maximum degree of knee flexion to find out the 3-dimensional position of the patella relative to the femoral and tibial bone. Then the surgery will proceed as with any computer assisted knee replacement. However, during the resection of the femur, the software will take into the account of the patella tracking position and position the femoral prosthesis to ensure the patella tracks centrally after the surgery. If necessary, the software will also guide the surgery to resect the patella accurately to a certain thickness and also guide the surgeon in correct placement of the patella button prosthesis so as to achieve a central patella tracking.

Detailed procedure of the surgery, referring to Figures 1 and 2.

Before the skin incision, two separate positional trackers 1, 2 are inserted

percutaenously (through the skin) into the femur 3 and tibia 4 bone respectively. This will allow the tracking of the motion between the femur and tibia. The skin incision is made over the patella and the soft tissue over the patella dissected off so that the patella can glide and not remain tethered to the skin layer. Depending on the patella tracking device 5 used, it may be fixed onto the patella 6 with a drill hole in the bone or clamped around the patella with multiple claws. As the patella tracking is influenced significantly once the muscles around the knee joint are cut and dissected, the registration of the patella tracking has to be performed at this stage before the arthrotomy (cutting the muscle to enter the knee joint). The critical area that determines the patella tracking is on the posterior (back) side of the patella which moves in the trochlear groove (not shown in the drawings). This, obviously, is not accessible before the knee is opened (arthrotomy) as the muscles around the knee joint are still intact (not cut yet). The surgeon will then register the motion of the anterior (front) side of the patella during the bending of the knee. Then the knee is opened with an arthrotomy. The surgeon can now register the relative distance and location of the posterior (back) side of the patella. By knowing this relative location, the computer software can translate and project the motion on the posterior (back) side of the patella. This data from the motion and tracking is then used as a reference for determining the femoral cuts required to ensure a good central patella tracking after the surgery. The surgery of the replacement of the femur and tibial component continues as with conventional computer assisted total knee arthroplasty. However, the computer data can be used to guide the surgeon in deciding on the medial-lateral location of the femoral prosthesis, the internal and external rotation of the femoral component and whether the patella needs to be re_surfaced ^₀ further enhance the tracking.

The main technical difficulty in the patellar tracking is the development of the appropriate tracking device that is suitable for the patella. The patella is a much smaller and mobile bone in comparison with the femur or tibia. The femur and tibia average diameter (thickness) is about 36-40mm and the trackers are much larger and more robust. Using these trackers on the patella will likely to result in a fracture of the patella as a large hole is required. However, if the trackers are too small, they are difficult to anchor sufficiently onto the patella bone which is usually about 18 to 24mm thick in the Asian population. Hence such trackers have to be small enough to require minimal drilling of the patella bone or to be capable of being clamped around the entire intact patella with good stability. Yet the tracker has to be large enough for the computer camera to detect the motion accurately as the knee goes through from full extension into full flexion. The designed tracker has to be light enough so that the weight of the tracker will not change the tracking of the patella, resulting in a-mal-alignment or mal-rotation.

It will be recognized by persons skilled in the art that numerous variations and modifications may be made to the invention as broadly described and exemplified herein without departing from the spirit and scope of the invention.

Claims

1. A method for assisting total knee arthroplasty comprising:

anchoring a first positional tracking device to the patella bone;

2. A method according to claim lwhich includes the steps of:

anchoring a second tracking device to the femur and/or the tibia; camera tracking the second tracking device(s); and

incorporating the added information obtained from the tracking of the second tracking devices(s) in calculating the correct position of the femoral component of the joint.

3. A method according to claim 1 or 2 in which the tracking device is

temporarily held on the surface of the patella bone.

4. A method according to claim 4 in which the tracking device is held by means of a clamp.

5. Apparatus for assisting total knee arthroplasty comprising:

(a) a tracking device that is adapted to be anchored to the patella bone or a tracking device that is temporarily held on the surface of the patella bone;

(b) a camera tracking system that will detect the 3-dimensional position of the patella throughout the entire range of motion of the knee joint; and (c) a computer adapted to receive data from, the camera tracking system for software simulation that will calculate the correct position of the femoral component so that the trochlear groove will fall under the patella bone and achieve central tracking.

6. Apparatus according to claim 4 which includes: