Patent Application
20080071195
The following detailed description primarily uses the foot as an example of a distal end of an extremity. The present invention can also be used with other extremities.
The boot 10 also can have one or more straps 22 that can be used to firmly affix the boot 10 to the leg 14. Other types of closures for the boot 10 can be used in place of straps 22 so long as the boot 10 can be firmly placed on the foot and lower lag 14 of the patient 12. These closures include clamps, buckles, adhesive tape, and the like. A tracking device 24 is attached or associated to the body 16 using a coupling 26. The particular tracking device can be any of the known types of tracking devices, including active optical devices that have emitters such as LEDS that send a signal to a locating device, passive optical devices that reflect light back to a locating device, magnetic devices, acoustic devices or inertial sensor devices. Any known tracking technology can be used as tracking device 24. The tracking device should be attached to the body 16 in such a way that there is no relative movement between the body 16 and the tracking device 24. The particular nature and structure of the coupling 26 is not important so long as there is no relative movement between the body 16 and the tracking device 24. If the tracking device 24 is an optical tracking device, the tracking device 24 will communicate with a locating camera 28 that communicates with a diagnostic or therapeutic system 30. If the tracking devise 24 is an inertial tracking device, the tracking device 24 will directly communicate with the diagnostic or therapeutic system 30.
As shown in
With reference to
The first parameter to be acquired is the hip center 80 as one of the points with which the mechanical axis of the femur 82 is constructed. For this the knee 84 is held in full extension to make sure that there is a constant transformation between the tibia 86 and the femur 82 of the patient 12. Here the ligaments and other structures prevent the limb from hyperextending. This creates a reproducible constraint of all six degrees of freedom between tibia 86 and femur 82. This relationship enables a surgeon to derive structures pertaining to the femur 82 relative to the tibia 86. The hip center 80 is calculated by circumflexing the hip with the knee 84 in full extension. Typically the surgeon will support the calf 90 with their hand while this is being done. The hip center 80 is stored by the diagnostic or therapeutic system 30 in both the boot coordinate system and the camera coordinate system.
Depending on the training and the preferences of the surgical team, there are different methods to determine the knee center. Some of these methods can be performed in a non-invasive manner. Other methods involve opening the knee capsule to directly digitize points. One invasive method is the direct digitization of the knee center using a tracked pointer device that traces the surfaces of the knee structure after the knee capsule has been opened. An alternate or supplemental method, locates the epicondyles of the femur 82 using a pointer. This can be done either invasively with the knee opened or using the surface of the skin with the knee closed. The knee center is considered as the mid-point of the epicondyles.
A third method uses motion recording of the knee flexion in order to calculate the flexion axis plus digitizing the tibial tuberosita. The digitized tibial tuberosita are projected onto the flexion axis to define the knee center. This method can be done with the knee 84 opened or with the knee 84 closed. A fourth method also uses motion recoding of the knee flexion to calculate the flexion axis plus digitizing the epicondyles. The mid-point of the epicondyles is projected onto the flexion axis to define the knee center. This fourth method can be done with the knee 84 open or with the knee 84 closed.
Next, the ankle center is located using the medial and lateral malleolus in a typical manner well know to those skilled in the art. An alternative method would be to use the well known transformation between the boot tracker reference frame and the ankle center position of the boot. This method does not require the step of maleoli digitization but does require a constant relationship between the boot tracker and the ankle center location within the boot.
If a non-invasive technique has been used as noted above, it is only at this point that any invasion of the body occurs. Here, the surgeon will make an incision at the knee to open the knee compartment and begin the replacement procedure. If either the knee center or the AP axis or the epicondyles have not been determined non-invasively as described above, direct digitization of corresponding knee landmarks in a known manner can be used to determine them.
At this point, all of the relevant alignment parameters and relationship between the tibia and femur are either known or can be determined by the diagnostic or therapeutic system 30. These parameters are typically varus/valgus alignment, internal/external rotation and flexion range. Optionally, varus/valgus laxity in extension can be determined if desired. Additional recordings are needed to determine this parameter. One method involves digitizing the boot tracker when applying varus stress to the knee and digitizing the boot tracker when applying valgus stress to the knee. The knee must be in full extension during this determination. A further optional parameter would be range of motion of the knee joint. This parameter is either directly determined by flexing and extending the knee to the maximum while keeping the hip stable and recoding the movement, or by recording the hip center with motion analysis first with the knee in full extension and then with the knee in full flexion.
The balance of the replacement procedure will proceed in a known manner using the approach with which the surgeon is most familiar. In one method, the surgical instruments, such as guides, jigs and cutting blocks, can be tracked and navigated in a non-invasive or minimally invasive manner using methods disclosed in co-pending application Ser. No. 11/251,044. Filed Oct. 14, 2005, entitled, system and method for bone resection, the disclosure of which is hereby incorporated by reference. After implantation of the prosthetic components the same methods as disclosed above can be used to obtain the newly installed biomechanical configuration of the limb. The diagnostic or therapeutic system 30 will be able to calculate the final varus/valgus alignment, internal/external rotation as well as flexion range of motion of the pre-operative or the post-operative situation.
In another embodiment as shown in
One advantage in using the boot of the present invention, is that the opposite side (non-operative) leg can also be evaluated in a noninvasive manner for comparison purposes during the replacement procedure. The same non-invasive procedure as described above is repeated for the non-operative leg. This is also outside joint arthroplasty of immense value as e.g. in trauma and reconstructive surgery where natural biomechanics of the contralateral side are often otherwise impossible to reproduce intra-operatively without significant technical and logistical efforts such as intra-operative CT scans.
In a similar manner, the necessary anatomical locations can be determined for hip replacement surgery. In this case the main parameter of interest is leg length. After attaching the boot, the hip center is determined by circumflexing the hip with the knee in full extension. The ankle center is then digitized as described above relative to determination of the knee center. The distance between ankle center and hip center 80 serves as the initial leg length. The procedure is repeated after the hip implant procedure has been complete to calculate the final leg length as the distance between the hip center 80 and the ankle center in the final alignment. Alternatively to the ankle center, any other anatomical point on the femur or tibia can be used as the distal reference. Optionally, the procedure can also be applied to the opposite leg to use the leg length of the opposite leg as a reference for the leg length of the treated leg.
A further application at the lower extremities is the treatment of femoral or tibia fractures. In these procedures a major difficulty is restoration of the correct leg length after fracture reduction and implant fixation. A boot is attached to the non-fractured leg. By motion analysis with the knee in full extension the hip center 80 is determined and stored in the coordinate system of the boot tracker. The distance between the hip center 80 and the boot is used as the reference for leg length. Alternatively, the ankle center can be determined as described above to calculate leg length as the distance between the hip center and the ankle center. At this point in the procedure, the boot is attached to the fractured leg. After nail insertion and preliminary reduction, a motion analysis with the knee in full extension is performed in the same manner as for the non-fractured leg to calculate the leg length for the leg with the fracture. The leg length is compared to the length of the opposite non-fractured leg. The surgeon can then make adjustments to the reduction to obtain matching leg lengths.
Also, using a suitable shell that is shaped to be placed around the forearm, the same technique as described above can be used for shoulder surgery as well. In general, the stabilization method of the tracker to the anatomy is an encapsulating conforming shell with or without active or passive layers that conform preferably around the metaphysical aspects of the members of a limb. These anatomical regions usually possess enough local geometrical irregularities that allow the shell device to lock onto the underlying anatomical structures so that there is no translational or rotational movement between the shell and the underlying anatomical structures. Even if adipose tissue attenuates the geometric metaphysical irregularities so that the shell can not be properly locked onto the underlying anatomical structure, it is possible to create a pseudo constraint by flexing the joint onto which the shell will be attached. The flexed joint now provides enough conforming areas to provide a stable and rigid configuration.
This invention is usable to assist in joint replacement surgeries without adding to the necessary invasion of the body.
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.
