Abstract
Purpose
In general, the amount and rate of linear wear are associated with femoral head size in the conventional UHMWPE acetabular liner. The smaller the femoral head, the higher the linear wear rate. The aim of this study is to verify the relationship between wear rate and femoral head size and the polyethylene cup thickness.
Materials and Methods
We conducted a retrospective review of all patients who had undergone primary cementless total hip arthroplasty using the conventional UHMWPE (HGP2) acetabular liner between July 1992 and December 2002. 128 hips (34 hips of female, 94 hips of male) of 64 patients who had 28 mm femoral head with different polyethylene acetabular linear thickness and 102 hips (41 hips of female, 61 hips of male) of 81 patients with 22 mm femoral head were included. Patients were assessed clinically and radiographically at postop 6 weeks, 3 months, 6 months and annually thereafter. Clinical assessment was performed using Harris Hip Score. Radiographic analysis included measurement of acetabular component position, polyethylene wear using a validated radiographic technique (Dorr method). Their mean age at the time of operation was 45.3 (24–81) years old and mean follow-up period was 10.8 (96–144 months) years.
Results
At a mean of 10.8 years, clinical results as determined by Harris Hip Score did not differ in different liner thickness and head sizes. For male, the linear wear rate was 0.139 mm/y in 22 mm femoral head group, 0.137 mm/y in 28 mm femoral head group. For female, the linear wear rate was 0.136 mm/y in 22 mm femoral head group, 0.169 mm/y in 28 mm femoral head group. In 28 mm femoral head group, the each linear wear rate of 6.2, 7.2, 8.2, 9.2, 10.2, 11.2, 12.2, 13.2, 14.2, 15.2 and 16.2 mm of thickness of PE liner was 0.223, 0.197, 0.190, 0.182, 0.130, 0.104, 0.095, 0.086, 0.070, 0.064 and 0.059 mm/y, respectively. In 22 mm group, the linear wear rate of 6.1, 7.1, 9.1, 10.1, 11.1, 12.1, 13.1, 14.1 and 15.1 mm thickness of PE liner was 0.172, 0.164, 0.148, 0.139, 0.137, 0.138, 0.123, 0.122 and 0.114 mm/y, respectively. The thinner the liner, the larger the linear wear rate. If the thickness of PE liner was less than 9 mm, the larger femoral head, the higher the linear wear rate. But, if thickness of liner was more than 10 mm, the larger femoral head, the lower the linear wear rate. If the liner thickness was less than 13 mm, volumetric wear rate was larger in 28 mm than 22 mm femoral head group.
Conclusions
The linear wear rate of conventional PE liner is not high in the articulation with smaller metal head and the volumetric wear rate is not high in the articulation with larger metal head constantly. This study demonstrated that if the conventional PE liner is thin(less than 10 mm), larger metal head(28 mm) can induce higher linear wear rate than smaller metal head, and if the thickness of conventional PE is more than 13 mm, the volumetric wear rate of liner with larger metal head is lower than that of smaller head.
