An Intraoperative Pressure-Measuring Device Used in Total Knee Arthroplasties and Its Kinematics Correlations

Fluoroscopic and retrieval analyses of knee implants show considerable variability even for the same implant design, and implicate the possible importance of surgical technique and compartment pressure balance in total knee arthroplasties. This study was done to correlate intraoperative computer-assessed compartment pressure measurements with postoperative kinematics to explain these variations. Thirty-eight patients had posterior cruciate-sacrificing low-contact stress total knee arthroplasties using a balanced gap technique. At trial reduction, an instrumented tibial insert designed to record the magnitude, location, and dynamic imprint of the pressures in the medial and lateral compartments was placed into the knee. Pressures were recorded electronically for a range of motion from 0°–120°. Sixteen of the 38 patients agreed to do successive weightbearing deep knee bends under fluoroscopic surveillance. Only three of the 16 patients had condylar lift-off, but all experienced lift-off at a single flexion angle. In the three patients who had condylar lift-off, a compartment pressure imbalance, as measured by the intraoperative pressure sensor, occurred at the same flexion angle of lift-off. These data suggest that although a given implant design may have inherent kinematic tendencies, surgical technique and compartment pressure balance significantly impact kinematic performance.