[Correlations between polyethylene wear direction and other influencing factors in total hip arthroplasty]

To explore the correlations between polyethylene wear direction and implanted parameters of prosthesis in total hip arthroplasty (THA) by computer-assisted measurement techniques.

Retrospective analyses were performed for 58 uncemented THAs from April 1997 to March 2006. The sagittal displacement of femoral head to axis of acetabulum opening plane was examined to determine the direction and degree of linear polyethylene wear. Radiographs were assessed for femoral offset, acetabular abduction, acetabular anteversion and conventional polyethylene wear. The linear polyethylene wear directions were compared between different parameter groups.

The average linear wear rate was 0.17 ± 0.08 mm/year and the angle between linear wear direction and axis of acetabulum 34.2° ( ± 29.3°) . Linear wear direction and acetabular abduction were positively relevant (r = 0.480, P = 0.000) . Linear wear direction was negatively correlated with postoperative Harris scores (r = -0.314, P = 0.016) . Compared with the acetabular abduction of < 45°, the acetabular abduction of 45° or larger was associated with greater decentralization of acetabulum opening plane (P = 0.001). As an independent variable, there were no statistically significant difference in linear wear direction between different acetabular anteversions. And femoral offset had no significant association with linear wear direction (P > 0.05).

Reasonable acetabular abduction and femoral offset may decrease linear wear rates, maintain hip stability and improve long-term putcomes.