[Comparative study on association between femoral head size and linear wear rate of highly cross-linked polyethylene liner].

OBJECTIVE: To investigate the effects of the femoral head size on the linear wear rate of highly cross-linked polyethylene (HXLPE) liner in total hip arthroplasty (THA).

METHODS: A retrospective analysis was performed on the clinical data of 41 patients (43 hips) who underwent primary THA with HXLPE liner and different sizes of femoral heads between January 2004 and December 2007 for hip diseases. There were 22 males (23 hips) and 19 females (20 hips) with a mean age of 60.2 years (range, 35-89 years), including femoral neck fracture (26 hips), avascular necrosis of femoral head (8 hips), osteoarthritis (5 hips), rheumatoid arthritis (2 hips), and congenital hip dysplasia (2 hips). According to the size of the femoral head, the patients were divided into 2 groups: standard head size (26 and 28 mm) was used in 25 cases (26 hips, group A) and big head size (32, 36, and 40 mm) in 16 cases (17 hips, group B). The cumulative penetration of the femoral head, linear wear rate, and effectiveness were evaluated and compared between 2 groups.

RESULTS: All the incisions healed by first intention, no complications of infection, deep vein thrombosis, or nerve injury occurred. The patients were followed up 5-9 years (mean, 5.7 years). No two-stage revision was needed. Harris score was significantly improved at 3 months, 6 months, and 1, 2, 3, 4, and 5 years after operation when compared with preoperative score in each group (P < 0.05), but no significant difference was found between different time points after operation in 2 groups (P > 0.05), and between 2 groups at each time point (P > 0.05). Acetabular abduction angle was (31.4 ± 3.8)° in group A and (32.3 ± 4.1)° in group B, showing no significant difference (t = 0.482, P = 0.621). At last follow-up, no radiographic or clinical loosening was observed in each group. At 5 years after operation, X-ray results of acetabular components showed radiolucent line (< 1 mm) in 1 case (1 hip) and 1 case (1 hip) of 2 groups respectively; but X-ray results of femoral components showed no radiolucent line. There was no significant difference in the cumulative penetration of the femoral head between 2 groups at 1, 2, 3, 4, and 5 years after operation (P > 0.05). The linear wear rate was (0.026 ± 0.007) mm/year in group A and (0.025 ± 0.007) mm/year in group B, showing no significant difference between 2 groups (t = -0.708, P = 0.483).

CONCLUSION: No association is found between femoral head size and the linear wear rate of HXLPE liner. It is an ideal interface of THA because of its low linear wear rate.