Patent Application
20070179626
Not applicable
Not applicable
Not applicable
1. Field of the Invention
This invention relates to methods, software and systems to assist in the performance of reconstruction and total and partial replacement surgery for joints. More particularly this invention relates to methods, and software to assist in surgical reconstructive interventions of joints that have kinematic behavior influenced by the soft tissue apparatus surrounding it. Typical examples are surgical procedures of the knee or ankle, such as ACL repair, uni-compartmental or multi-compartmental replacement of the joint surfaces, revision surgery and the like.
2. Description of the Background of the Invention
Current joint reconstruction and replacement surgery, including ankle, knee, shoulder, or elbow arthroplasty is based in large part on standard methods and guidelines for acceptable performance. In this regard, the positioning of the implants into the joint is based on standard values for orientation relative to the biomechanical axes, such as varus/valgus, or flexion/extension, and range of motion. One surgical goal might be that the artificial components used to achieve the reconstruction of the joint should have a certain alignment relative to the load axes. These standards are based on static load analysis and therefore may not be appropriate to establish optimal joint functionality taking into account life style patterns of the individual undergoing surgery. There have been systems that look at the ipsilateral side to gage parameters for the operative joint. Also, there have been kinematic approaches that attempt to determine appropriate values for varus/valgus, flexion/extension, and range of motion. One reason for the need to properly balance unconstrained joints, like the knee, ankle and elbow, is that these joints are held together by the soft tissue, including the ligaments, that surrounds the joint The proper functioning of the joint is dependent on a combination of the proper resection of the joint to receive the implant, the proper choice of implant sizing and the proper balance of the soft tissue relative to the implants and the resection. Currently, this balancing is done by the surgeon based on experience and rule of thumb guidelines.
A computer assisted surgical navigation system normally requires a time consuming setup and registration of the patient's anatomy with either a pre-operative scan or with a three dimensional model that is constructed from reference points obtained from the patient's anatomy. Further, prior computer assisted navigation systems have not assisted the surgeon by providing step-by-step procedures to guide the surgeon in making the proper balance between bone cuts, implant size, and soft tissue constraints or balancing. The necessity of additional steps without corresponding added benefits have kept surgeons from using surgical navigation systems for orthopedic surgeries even though the increased accuracy of the surgical navigation systems could improve the end result for the patient.
One embodiment of the present comprises a method for performing arthroplasty on a joint using a surgical navigation system. The method includes the steps of locating articular anatomical structures using the surgical navigation system; determining biomechanical properties of the joint; and evaluating the soft tissue envelope properties for the joint. The method also includes the steps of displaying an interactive view of the joint, the soft tissue envelope properties, the biomechanical properties and a chosen implant to enable a surgeon to manipulate simultaneously the soft tissue envelope properties, the biomechanical properties and the chosen implant on the interactive view; preparing the joint to receive the chosen implants; and installing the implants in the prepared joint.
Referring to
In addition to the femur 102 and the tibia 104, the knee 106 has a patella 122. The location of the patella 122 can be determined by using the pointer 116. Also because the patella 122 is anatomically tied to the location of the tibia 104, the navigation system 112 can also locate the patella 122 by reference to the location of the tibia 104. Further, because the patella 122 is constrained, it is often only necessary to locate the patella 122 relative to three degrees of freedom. As is well known, the properties of the patella 122 should be considered during knee replacement surgery and any implant that replicates the patella 122 can have an impact on the post surgical functioning of the knee 106.
One relationship that can be considered in certain embodiments is a joint line between the femur 102 and the tibia 104, and the relationship of the femoral-tibial joint line to a joint line between the femur 102 and the patella 122. The joint line is the momentary rotation of the joint in space, in this case the knee 106. The joint line is different than the functional flexion axis. The functional flexion axis describes the overall flexion of the joint. In any joint are typically distinct points of contact between the bones that comprise the joint. Once the surface of one of these bones has been determined, the system can determine the contact points on one bone and link the contact points of the one bone to the contact points of the second bone at the same position of the joint. In the case of the knee, the two contact points on the first bone are related to each other on a line, the joint line. The two contact points on the second bone are also related on the same line initially. However each line can be viewed individually for each of the bones that comprise the joint. Because one or both bones may be deformed as a result of disease or injury, the optimal joint line relative to the reconstructed joint often will be offset from the initial observed joint line for one or both bones.
As set out in
Control then passes to a block 202 where the biomechanical properties for the femur 102, the tibia 104, the knee 106, and optionally the patella 122 are determined. Some of the biomechanical properties can be determined before the actual incision is made. For instance, after the tracking device 108 is attached to or associated with the femur 102, the location of the femoral head can be determined by manipulating the femur 102 to rotate about the hip socket. In addition, an initial functional flexion axis analysis and a range of motion analysis can be performed by manipulating the knee 106 through the entire range of motion of the knee 106. Also, the location of the lateral malleolus and medial malleolus can be determined using the pointer 116 and touching the pointer tip 118 to the appropriate bony landmarks on the ankle. The navigation system 112 can display a series of screens on the display 114 of the type as shown in
Traditionally knee replacement has had enormous focus around the tibio-femoral joint. Nevertheless the knee is a tri-compartmental joint with the patella gliding in the femoral trochlear groove transmitting quadriceps forces onto the tibia. Failing to re-establish proper patello-femoral kinematics often yields to unsatisfactory pain levels after implantation. One of the most important parameters to take into consideration in order to re-establish proper operation of the quadriceps mechanism is the distance of the patella to the functional flexion axis. If the distance is increased, so called overstuffing of the patella occurs that leads to a limited range of motion and pain. If the distance is decreased, the efficacy of the quadriceps mechanism is compromised and mal-tracking of the patella may occur. Medial-lateral displacement of the patella is in turn influenced by internal-external rotation of the implant. If there is a gross mismatch of the natural track of the patella and the reconstructed trochlear groove of the implant, dislocation and pain may occur. The rotational degrees of freedom of the patella, namely tilt, rotation and flexion, are coupled to the above parameters and are of secondary importance.
Tracking only the trajectory of the patella simplifies the needed devices by not having to implement all 6 degrees of freedom. This is important because the patella is relatively small structure and the kinematics of the patella can be altered if a foreign object attached to the patella. Furthermore, the patella has a constant relationship to the tibia. It is attached by a tendon to the proximal spine of the tibia where the forces from the quadriceps mechanism are received and passed on to the foot. This relationship is seldom affected and represents a very faithful landmark intrinsically describing some of kinematic parameters of the knee joint. These parameters are very helpful while re-establishing the function of the knee but are especially helpful in cases where no other references may be available as for example in revision surgery where the tibio-femoral joint has been replaced.
After the closed knee biomechanical data has been determined and recorded, the initial incision is made to the knee 106 to expose the distal portion of the femur 102, the patella, and the proximal portion of the tibia 104. The surgeon can then determine other landmarks using the pointer 116 as guided by the navigation system 112 through the various screens displayed on display 114. Typical landmarks include the surface of the lateral and medial condyles, the tibial plateau dishes, and other landmarks.
Certain landmarks can be inferred from the digitization of other landmarks. For instance the surfaces of the femoral condyles can be determined by assessing the location of the surface of the tibial plateau throughout the range of motion. Because of the envelope constraints on the knee joint, the surface of the femoral condyles will sweep the tibial plateau as the knee joint is flexed throughout the range of motion and can be computed once these two properties or landmark locations are known. While there can be a lift off situation, this still does not have a significant impact on the computation because the femur can not penetrate into the tibia. Also, the center of the knee can be computed as the most distant point of the groove from the center of the femoral head.
In addition through further geometrical analysis of the obtained surfaces fundamental properties can be derived, such as radiuses of curvature or axes of rotation. For example in a knee 106 the internal/external rotation of the femur 102 can be computed by a cone or cylinder fitted to the geometry of the posterior condyles, which are usually unaffected by the disease condition of the knee 106. The femoral-tibial joint line is constructed by joining the two points of contact of the tibial dishes with the femoral condyles. Because one of the condyles is normally eroded, due to the disease condition, the joint line is affected and reflects the varus or valgus deformation. The varus/valgus deformation has been determined during the closed knee range of motion analysis and the surgical navigation system 112 can compute the current joint line and also the system can propose a restored joint line that will reflect the knee in a repaired state. The restored joint line can be used as a target by the surgeon during the balancing of the knee soft tissue, the implants and the modifications made to the bones to receive the implants.
Further to the geometrical analysis of the pairing surfaces of a joint, its functional kinematic data can be analyzed to derive momentary or instantaneous axes of rotation or overall axes of rotation by analyzing portions or all of the instantaneous axes. One of the best known and most widely used techniques is the helical axis computation which is said to describe the home-screw mechanism of unconstrained joints. In the case of the knee, the flexion axis of the patello-femoral joint as well as the tibio-femoral joint can be computed by passively moving the joint throughout its range of motion. The so derived flexion axis of a diseased joint will undoubtedly reflect the diseased kinematics of the joint. Partial correction of some of its degrees of freedom will be necessary before it is used as a guide for the surgical measure. The corrections may be derived by combining information or constraints given by the biomechanical axes of the joint and/or by dynamic load transfer patterns while ranging the joint. Another alternative is by combination of information provided by unaffected degrees of freedom of other pairing surfaces of the joint. In the case of the knee 106, a possible combination could be perpendicularity of the derived functional flexion axis to the biomechanical axis, translational constraints given by the patello-femoral flexion axis and its internal/external rotation dictated by the conical fit axis of the posterior condyles of the femur.
Another method to re-establish normal kinematics of the affected joint is to assess the kinematics of the non-affected ipsilateral side. These parameters can be extracted by the same methods and are expressed preferably in terms of local non-affected anatomical structures to enable its transfer to the affected site after identification of the corresponding anatomical structures. In the case of the knee 106, a local reference can be established by the intercondylar notch and the anterior cortex of the femur 102. The identification of these structures can be done intra- but preferably preoperatively with any non-invasive imaging technology. In the case where the functional analysis is not done with the same modality as the one used for the identification of the reference structures the registration of both modalities is necessary. A preferred embodiment uses ultrasound as imaging modality. This coupled with tracking technology relates kinematic information to the underlying reference structures and minimally invasive tracking devices as described in published U.S. Patent application No. 2005/199,250, published Sep. 15, 2005, the disclosure of which is hereby incorporated by reference.
The computed kinematics information in form of restored functional axes and joint lines of the joint surfaces may not only be used as a guide for driving the position of prosthetic components but also for establishing an optimum between the kinematics constraints of the individual's joint and the prosthetic system being used. In a scenario where multiple prosthetic systems or surgical techniques are available the computer system may choose the optimal implant and propose an optimized position to best fit constraints given by the function of joint and those of the implant. A further example of an optimization criterion could be optimal performance for a given activity of the individual that best restore his or her quality of life.
A block 204 evaluates the soft tissue surrounding the joint. The soft tissue can be evaluated by further manipulating the knee 106 and also by the use of strain gauges or similar devices. The knee includes four main ligaments that interact with the tibia 104 and the femur 102 to form a stable knee 106. The tension on these ligaments must be properly balanced to provide stability to the knee 106. The surgical navigation system 112 can also guide the surgeon through the soft tissue analysis and based on the particular manipulation that is performed record values for the tension of the various ligaments and muscles of the knee 106. Other methods of acquiring the soft tissue tension values can also be used.
Particularly useful are the in-situ devices of the type shown in
Another benefit of in-situ devices is the ability to iteratively establish or capture the functional parameters, as the functional flexion axis of the joint that exactly describes the actual state of the soft tissue envelope of the joint. Through instant assessment of the effect of a given soft tissue measure are important to precisely drive the desired soft tissue correction.
The usage of more sophisticated distraction devices in which force or pressure sensing elements have been incorporated can yield precise information on loading pattern characteristics for the joint throughout range of motion. These in turn can be used to establish a certain soft tissue management strategy in which specific group or bundles of bands are selectively targeted to affect the load or force pattern at a specific flexion or kinematic state of the joint. These devices can transmit wirelessly in a real time fashion the information to the computer system for on the fly analysis. The information can then be displayed numerically or graphically in relationship to the established model of the joint. Using this information the computer system can also deliver the most likely soft tissue management strategy based on e.g. an underlying expert system.
The surgical navigation system 112 will also include a database 206 of implant components in digitized form. A block 208 takes the values from the location analysis 200 of the femur 102 and the tibia 104, the biomechanical properties analysis 202, the soft tissue evaluation 204, and the database 206. Using all these values, as well as other criteria including but not limited to gender, age, race, life style, and the like, the block 208 simultaneously solves for the functional goal and displays the calculated result, including a suggested implant from the database of implants 206, on an interactive screen on the display 114. One possible element of the functional goal in one embodiment of the present invention can be the restored joint line. This can be shown on the interactive screen along with other values relative to restoring the joint. Control passes to a block 210 that enables the surgeon to manually adjust the chosen functional goal and other values if necessary to reflect the surgeon's experience with the procedure. If the surgeon determines that the solution shown by the block 208 is not optimum, control will pass via a NO branch to a block 212 that allows the surgeon to digitally manipulate the joint and possibly change the suggested implant or other parameters as shown on the interactive screen. After the changes are made, the navigation system 112 will recalculate the result and the block 208 will display the updated result. If at this point, the surgeon believes that the proposed solution meets the surgical objective, then control will pass via a YES branch to a block 214 that asks for confirmation and recording of the choice of implant and other parameters. At this point, the surgeon in a block 216 will prepare the joint to match the chosen solution. The navigation system 112 can guide the surgeon through the procedure and make suggestions of modifications necessary to achieve the desired outcome or the surgeon can proceed in a conventional fashion to prepare the joint without the navigation system 112. After the joint is prepared in the block 216, the implant is installed in a block 218. Again, if the surgeon chooses, the navigation system 112 can guide the surgeon through this procedure as well. As will be discussed later, the installing of the implants can also include the use of trial implants that replicate the final implants and allow the surgeon to test the configuration of the joint before the final implants are permanently placed in the joint.
The preparation of the joint according to the established goal can be performed manually with the aid of navigation but also with any type of passive, semi-active or active envelope constraining devices, with master-slave manipulators or with autonomous in-situ mounted or external manipulators, including telemanipulators.
Other biomechanical properties and landmarks can be determined by the navigation system 112 by indirect digitization using combinations of the above determined landmarks as noted above. The surface of the femoral condyles can be determined by combining the range of motion analysis with digital location of the tibial plateau.
The internal/external rotation of the femur 102 can also be determined by a variety of methods. For instance the internal/external rotation can be derived from the early, 0° to 45°, flexion. There are a number of well known algorithms that can make this calculation including helical axis, residual minimization and other similar geometrical optimization techniques. Alternatively the internal/external rotation can be derived from the shape of the posterior condyles. Normally the shape of the condyles in deep flexion, greater than 90°, are unaffected by a possible disease condition of the joint. The internal/external rotation is determined by fitting a cone or cylinder to the femur 102 as the knee 106 is flexed relative to the femur 102.
In the block 204, the soft tissue envelope is evaluated. One method of conducting this evaluation is to flex the open knee joint throughout the range of motion while at the same time applying a varus or valgus load to the knee joint. The surgeon will manipulate the knee joint by flexing the knee and press on either the lateral surface to apply a varus load or the medial surface to apply a valgus load.
As an initial aspect of the step of the block 208, a screen shot 340 similar to
The analysis of the soft tissue can be done by manipulation of the knee 106 or it can alternatively be done by making a perpendicular cut to the tibial plateau to provide space for an in-situ, patella in place balancer device. The device can be of any suitable construction so long as the device will enable the surgeon to tense the knee joint 106 against the soft tissue. One suitable balancing device is shown in
As shown in
Visualization of the above disclosed information as, flexion axis, joint line, alignment, load distribution through out range of motion, implant size and position, etc. is challenging and can be sometimes overwhelming. An effective and above all ergonomic method to convey this complex context is by virtue of augmented reality techniques where through projection techniques the graphical information can be overlaid onto the anatomical structures being addressed. This results in an intuitive context oriented visualization of the required information. For instance the chosen implant can be superimposed at the correct position directly on the anatomical structure giving the surgeon the opportunity to assess the overall fit and required preparation of an intact joint.
The system and methods of the present invention have been described using the knee 106 as an example joint. It should be understood that the knee 106 is the most complicated unconstrained type joint. As such, the methods of the present invention can be applied to other unconstrained joints in the body such as the ankle, shoulder or the elbow. It should also be understood that any type of surgical measure throughout the continuum of care of said joints will profit from the here described methods. The various surgical implants can range from autologous tissue for focal repair to structured load bearing biomaterials to replacement surfaces of inert materials to revision type prosthetic implant. It should also be understood that the methods of the present invention can be accomplished by the surgical navigation system 112 that has software loaded into random-access memory in the form of machine-readable code, such code being executable by an array of logic elements such as a microprocessor or other digital signal processing unit contained within the surgical navigation system 112 or within any standard computer system.
The computer software can be stored in any convenient format usable by computers that can be found within surgical operating rooms. Often, the software will be made available on media such as CD-ROM, DVD-ROM or similar data storage media. In addition, the software can be made available for download though an Internet connection.
Numerous modifications to the present invention will be apparent to those skilled in the art in view of the foregoing description. Accordingly, this description is to be construed as illustrative only and is presented for the purpose of enabling those skilled in the art to make and use the invention and to teach the best mode of carrying out same. The exclusive rights to all modifications which come within the scope of the appended claims are reserved.
