Performance of thin Vivacit-E hip liners: no relevant wear during ex vivo testing at high acetabular inclination angle.

BACKGROUND AND PURPOSE: There is concern among clinicians regarding the performance of thin, highly cross-linked polyethylene acetabular liners at high inclination angles that cause edge contact and high contact stresses. We studied ex vivo wear performance of thin, vitamin-E grafted, highly cross-linked polyethylene (Vivacit-E) liners in relation to high acetabular inclination angle.

MATERIALS AND METHODS: Wear of Vivacit-E acetabular liners (thickness 4.0-5.7 mm) was studied with a validated hip joint simulator at 2 different acetabular inclination angles, 40° (optimal) and 65° (high). The test simulated walking. Wear was evaluated gravimetrically and dimensionally.

RESULTS: At the optimal inclination angle, slight weight gain occurred. At the high angle, the liners lost weight slightly. Due to the minimal weight loss, gravimetric wear rates were difficult to determine. Linear wear was below the detection limit of 0.01 mm.

CONCLUSION: Even with the high acetabular inclination angle, the prostheses performed well in the present test conditions. The wear rates of the liners were estimated to be clearly below the osteolysis threshold of 0.05 mm/year, below which osteolysis is absent. Since the present hip joint simulator has been shown to produce clinically relevant wear, these ex vivo results are likely to reflect the in vivo behavior of the design.