Abstract
INTRODUCTION
Multiple video fluoroscopic analyses have been performed to determine the in vivo kinematic patterns of total knee arthroplasty (TKA) and non implanted knees. Unfortunately, many of these studies were not correlated with bearing surface forces and possible failure modes that could be detected with a sound sensor. Therefore, the objective of the present study was to conduct a comparative analysis of the kinematic data derived for all subjects having a TKA who were analyzed over the past seventeen years at our laboratory and to determine how these patterns correlate with bearing surface forces and joint sound.
METHODS
Initially, femorotibial contact positions and axial rotation magnitudes were derived for subjects having either a non implanted or implanted knee. Non implanted knees consisted of normal and anterior cruciate ligament (ACL) deficient knees (ACLD). Implanted knees consisted of posterior stabilized (PS) fixed (PSF) and mobile (PSM) bearing, posterior cruciate ligament retaining (PCR) fixed (PCRF) and mobile (PCRM) bearing, posterior cruciate sacrificing mobile (PCSM) bearing and ACL retaining fixed (ACRF) bearing TKA. Each subject, while under fluoroscopic surveillance, performed a weight-bearing deep knee bend and/or normal gait. Using a three-dimensional (3D) model fitting approach, the relative pose of knee implant components were determined in 3D from a single-perspective fluoroscopic image by manipulating a CAD model in three-dimensional space. Anterior/posterior (A/P) contact positions for both the medial and lateral condyles and axial rotation of the femoral component relative to the tibial component were assessed. Then, a subset of these subjects were further analyzed to determine their in vivo bearing surface forces and joint sound using a more recently derived protocol for analyzing audible signals.
RESULTS
During gait, subjects having a ACRF TKA experienced the most normal-like kinematic patterns, where the femoral condyles were more anterior than other TKA designs. Subjects having a PCSM TKA experienced the least amount of femoral head sliding during gait, whereas the medial and lateral condyles remained near the midline of the tibia in the sagittal plane. Subjects having a mobile bearing TKA did seem to experience axial rotation during this activity. Subjects having a normal knee experienced posterior motion of the lateral condyle from full extension to maximum knee flexion (maximum = 27 mm), while their medial condyle experienced less motion (maximum 12 mm). Similar to the subjects with a normal knee, all subjects having an ACRF TKA experienced posterior motion of their lateral condyle, albeit less than the normal knee, and less medial condyle motion. Subjects having a PCRF or PCRM TKA experienced highly variable kinematic patterns. Many of these subjects experienced an anterior sliding motion with increasing knee flexion. Subjects having either a PSF or PSM TKA experienced a higher incidence and magnitude of posterior condylar motion, but less in magnitude when compared with the normal knee. Not all PS TKA knees produced similar results and some experienced poor weight-bearing range-of-motion and more erratic kinematic patterns. Subjects having a PCSM TKA experienced a contact position that remained centralized during the deep knee bend activity, often leading to posterior impingement and less weight-bearing range-of-motion. Subjects having a mobile bearing TKA experienced greater contact area and less contact stress than subjects having a fixed bearing TKA and subjects having a high flexion TKA experienced less contact stress in deep flexion than subjects having a more traditional-type TKA design. The sound sensor revealed various sounds related to cam/post mechanism engagement, condylar lift-off, patellofemoral interaction and other sounds that at present, having not yet been correlated to identifiable mechanics parameters.
DISCUSSION
The magnitudes of posterior femoral rollback during deep flexion in all TKA designs tested were less than in the normal knee. This may explain, at least in part, why knee flexion following TKA is reduced when compared to the normal knee. During gait, PSF and PSM TKA designs experienced similar kinematic patterns as those designs that lacked a cam and post mechanism. Subjects having a TKA experienced significantly less axial rotation when compared to the normal knee (p<0.001). Reversing axial rotation patterns where of high incidence in subjects having a TKA. Additionally, it is clear that surgeon variability can play a significant role in eventual knee mechanics patterns. Bearing surface mechanics related to contact force, area and stress varied considerably between subjects and TKA designs. Bearing surface sounds may play a significant role in the future when attempting to assess failure modes as various sounds were detected for subjects having a TKA design.
