Total knee arthroplasty using the Stryker knee trac system

Abstract

This author was in the process of studying the effects of soft-tissue release in managing varus and valgus knee deformities when the possibility of guiding the entire total knee operation became apparent. We were using magnetic spatial tracking equipment in a first stage cadaver study of the effects of sequential soft tissue release on the achievement of proper alignment and ligament balance. The natural step after this preliminary work was to measure similar changes occurring during actual surgical cases. An Optotrak infrared tracking system was purchased (Northern Digital Corp. Ontario, Canada), which required the development of custom software for our application. In planning this software it became apparent that nearly all of the relevant anatomic landmarks for TKA could be indicated to this type of system. The single point having great importance in knee alignment which is out of the field, is the center of the femoral head. Recognizing that the motion of the femur at the hip is about a point in space which is that femoral head center, it became immediately apparent that this point could be determined mathematically simply by tracking the motion of the femur. With this determination it then followed that we could track and measure the displacements occurring during the entire total knee operation. Rather than measuring only relative movement of the tibia in relationship to the femur, similar to the cadaver study, we could determine absolute positions of the femur and tibia in the whole body. In addition to positions of the bones themselves it followed that we could determine the positions of jigs, resulting cuts, and positions of the trial and final prosthetic components. As a result of these realizations, software and hardware were developed to these ends. A study of the accuracy of the femoral head determination was undertaken in cadavers, and this very equipment was used to assist in the performance of the entire total knee procedure. The first fully navigated total knee arthroplasty was successfully done, in our first try, in August 1997. The cadaver study and that case were the subject of a publication which implicitly became the first report of a fully navigated TKR [1]. © 2007 Springer Medizin Verlag Heidelberg.