IMPINGEMENT WEAR OF LARGE X3 BEARINGS

Abstract

Acetabular rim damge due to rim impingement is frequently found on retrievals and may be associated with increased wear and contact stresses, instability, and implant loosening of total hip replacement devices. Large X3 bearings (> 36mm) from Stryker have increased implant range of motion and improved polyethylene material (sequentially crosslinked and annealed). A hip simulator wear study was performed with and without femoral neck to acetabular rim impingement to determine the wear performance of these new bearings under aggressive impingement conditions. Two sizes of these new components were tested (36mm with 3.9mm thickness and 40mm with 3.8mm thickness) with two standard sized controls (28mm with 7.9mm thickness in X3 and conventional polyethylene. The 36mm component was chosen to be the largest component utilizing the same shell as the standard 28mm size components while the 40mm component was chosen to be the thinnest bearing currently offered.

Impingement significantly increased wear for all bearings (p< 0.05) but no cracking or failures of the rim occurred. Wear rates for all X3 bearings were statistically indifferent under each testing condition despite bearing size and thickness. Average wear rates for X3 bearings were 0.3mm3/million cycles (mc) under standard conditions and 3.5mm3/mc under impingement conditions. Average wear rates for conventional bearings were 19.5mm3/mc under standard conditions and 48.3mm3/mc under impingement conditions. Overall the X3 bearings exhibited a 93% reduction in wear under impingement conditions and 99% reduction in wear under standard conditions.

Increased bearing range of motion reduces the chance of impingement. This study shows the simulated outcome even if these larger bearings were to impinge. We conclude that these larger X3 bearings exhibits the same wear performance as standard X3 bearings and significantly superior wear performance compared to conventional polyethylene bearings under standard and impingement conditions.