In Vitro Knee Wear, Kinematics, and Particle Morphology Among Different Bearing Geometries in a Mobile Bearing Knee System

Abstract

Excellent clinical long term results were reported from individual clinical centers for both of the two fundamental design principles—fixed and mobile bearing knee designs. Several pre-clinical studies are dealing with a direct comparison between fixed and mobile bearing knee replacements, but to our knowledge there is no published data comparing the in vitro wear and kinematic behaviour of mobile bearing designs with floating, rotating and posterior stabilized gliding surfaces. The objective of our study was to evaluate the influence of the tibio-femoral bearing type on abrasive wear, tibio-femoral kinematics and particle release for a mobile bearing knee system with three different design alternatives. Wear simulator testing on 12 e.motion® TKA devices (Aesculap, Germany) was performed according to ISO 14243-1. The knee replacements were tested for 5 million cycles on a customized 4 station knee wear simulator (Endolab, Germany) in the bearing configurations floating platform (FP), ultra-concruent rotating platform (UC) and posterior stabilized (PS). The amount of wear in the polyethylene gliding surfaces was estimated to 4.4±0.9 mg/million cycles (FP design) to 2.3±0.1 mg/million cycles (UC) and 5.2±1.0 mg/million cycles (PS). The amplitudes of A/P displacement during 5 million cycles showed a mean value of 3.7±0.33 mm (FP design), 2.3±0.14 mm (UC) and 2.9±0.26 mm (PS). For the I/E rotation angle, the amplitudes of the recorded mean values were 6.3°±0.82° (FP design), 3.7±0.41° (UC) and 4.9°±0.48° (PS). The polyethylene particle release (mean size and morphology) is comparable for the mobile bearing articulations FP, UC, and PS. The present study demonstrates the influence of different mobile bearing types on abrasive wear, tibio-femoral kinematics, and particle release under elimination of bearing material influences.

Functionality and Safety of an Ultra-Congruent Rotating Platform Knee Prosthesis at 5.6 Years: More than 5- Year Follow-Up of the e.motion® UC-TKA

“…Several factors may have contributed to the relatively low rate of complications in this pilot study: the surgical technique with attention to soft tissue balancing [3], the innovative design of the prosthesis, and the computer-assisted navigation system [22]. Biomechanical investigations conducted in vitro showed that the gravimetric wear rate for the e.motion ® UC prosthesis was 2.3 mg/106 cycles [4], which is relatively low compared with the wear rates of mobile-bearing designs with good long-term clinical outcome (6.6 to 16 mg/106 cycles) [1, 23, 24]. This is a promising result for the e.motion ® UC prosthesis, considering the long-term survivorship of an implant is related to the wear of the bearing surface [25].…”

“…The objectives of this new implant are to avoid contact stress peaks while providing good stability and mobility also in the absence of a posterior cruciate ligament. More specifically, the constant distal radius from -5° to 90° of flexion allows high stability in the midstance phase through a constant ligament tension, thereby reducing the incidence of paradox movement [4]. The primary objective of this pilot study was to assess the general functionality of the e.motion ® UC prosthesis in daily life activities, 5.6 years after the TKA index surgery.…”

Single-radius, multidirectional total knee replacement

“…It might be argued that multidirectional mobility has been associated with higher risk of PE wear [23]. However, this design has shown to decrease the PE wear in in vitro simulation [14, 30]. Other authors observed no significant osteolysis after implantation of either unidirectional or multidirectional mobile‐bearing TKR [25, 26].…”