For many patients, total knee replacement (TKR) provides pain relief and restores motion for many years [1]. Some patients, however, experience early failures and require revision surgery. One of the suggested contributors to early failure has been excessive wear due to malalignment [2]. Previous work has shown that varus-valgus malalignment results in extreme condylar loading and could lead to high wear [3]. The purpose of this experiment, therefore, was to evaluate medial/lateral load sharing in an in vitro wear simulation. Wear testing was conducted on midsized Attune and Sigma fixed bearing cruciate substituting TKR components (DePuy Synthes). The two systems differ in many aspects; notably, Attune employs antioxidant-stabilized moderately-crosslinked polyethylene and a gradually changing sagittal femoral curvature while Sigma uses remelted moderately-crosslinked polyethylene and a mulit-radius femoral design. Wear was evaluated across a wide range of medial/lateral (M/L) load splits: 10/90, 60/40, and 90/10 using an AMTI six-station knee simulator (Figure 1). Simulation was conducted for 3 million cycles using at 1 Hz using previously described methods [4] with ‘High Kinematic’ displacement controlled inputs in 25% bovine calf serum (Hyclone) at 37 ± 2°C supplemented with sodium azide and EDTA. Polyethylene wear was determined gravimetrically with load soak compensation every 0.5 Mcyc.Introduction
Methods
