Does knee implant size affect wear variability?

Small and large sized-mobile inserts (i.e. size #2 and size #6) were tested on a knee wear simulator for 2 million cycles, using bovine calf serum as lubricant. Gravimetric and micro-Raman spectroscopic analyses were performed on polyethylene inserts. Roughness analysis was performed on the metallic components. The larger size, i.e. #6, had almost twice weight loss with respect to the smaller one, i.e. #2 (37.8±2.8 mg and 19.46±0.93 mg, respectively). Significant statistical differences were observed in wear rates (p=0.001, Kolmogorov-Smirnov test for two samples). Raman spectroscopy showed a greater increase in crystallinity for the smaller inserts: upon wear, the orthorhombic content (α_o) significantly increased at the expense of the third phase content (α_b).