A short-term comparison of metal-on-metal and metal-on-polyethylene bearing surfaces in total hip replacement

Abstract

Objective To compare the short-term results of metal-on-metal (MOM) and metal-on-polyethylene (MOP) bearing surfaces in total hip replacement (THR). Methods Thirty cases, 12 males and 18 females, received MOM THR through a posterolateral surgical approach from June 2007 to December 2008. Their mean age was 60.3 years, mean body mass index (BMI) was 23.7 g/m2 and mean Harris score was 36 ± 15 preoperatively. For comparison, another 30 cases, 9 males and 21 females, received MOP THR through the same approach at the same period. Their mean age was 62.4 years, mean BMI was 23.4 kg/m2 and mean Harris score was 34 ± 17 preoperatively. The 2 groups were compared in terms of hip functional recovery and radiographic examination. Results All patients obtained an average follow-up of 14.4 months (range, 12 to 18 months) . No infection, fracture or neurovascular injury occurred in either group. There were one deep venous thrombosis and one dislocation in the MOP group. The average Harris scores at 1, 3, 6, 12 months postoperatively were respectively 78 ±4, 84 ±4, 90 ±3, 92 ±4 for the MOP group and 86 ± 3, 90 ± 3, 95 ± 4, 95 ± 3 for the MOM group. The differences between the 2 groups were significant at 1, 3, 6 months ( P ＜ 0.05) but insignificant at 12 months ( P ＞ 0.05). In the MOM group,the total range of hip motion averaged 239.2°± 21.9° and the hip inflexion averaged 135.4°± 10.9°. In the MOP group, the total range of hip motion averaged 190.1°± 16.7° and the hip inflexion averaged 95.3°± 11.3°. The differences between the 2 groups were significant ( P ＜ 0.05). Conclusion On a short-term basis, MOM THR may be better than MOP THR, but the medium and long-term results of MOM bearing surfaces still need further investigation. Key words: Arthroplasty, replacement, hip; Prostheses and implants; Treatment outcome