Intra-operative vs. post-operative patellofemoral mechanics in cadaveric specimens

摘要

Introduction: During knee replacement surgery, surgeons aim to optimize knee component placement for post-operative performance but can only judge patellofemoral mechanics by observing passive knee flexion intra-operatively. In particular, surgeons wish to achieve central, balanced patellar tracking within the femoral groove. To our knowledge, intra-operative joint mechanics have not been compared to post-operative joint mechanics either in vivo or ex vivo. The purpose of our study was to compare the patellar kinematics (tilt and shift) and patellofemoral forces (peak load) for cadaveric specimens in experimental preparations simulating both the passive intra-operative and loaded post-operative situations. Methods: We used Optotrak 3020 optoelectronic markers (Northern Digital, Waterloo, Canada) to record femoral, tibial and patellar kinematics, and custom-calibrated I-Scan 5051 electronic pressures sensors (Tekscan, Boston, USA) to record patellofemoral force distribution in 8 cadaveric mid-femur to mid-tibia knee joints (6F/2M, ages 51-80). Rods inserted into the femur and tibia were connected to a simulated ankle and hip joint in each rig. A five-de-gree-of-freedom custom-designed intra-operative rig allowed the hip joint to be pushed along a horizontal track, causing the knee to flex in a manner similar to passive intra-operative flexion. Passive tension in the quadriceps was produced by a spring mounted between the quadriceps tendon and the simulated hip joint. A six-degree-of-freedom Oxford-type post-operative rig, which has commonly been used in biomechanical studies, applied an 80 N vertical load to the simulated hip joint. The clamp on the quadriceps tendon was attached to a motor via a cable.