[Metal-metal-backed polyethylene cemented hip arthroplasty: mid-term results]

Metal-on-metal bearings in total hip arthroplasty may, in theory, provide an effective answer to osteolysis in active patients. The purpose of this retrospective study was to evaluate the results of a consecutive series of Metasul total hip arthroplasties with a cemented socket.

The series was composed of 28 total hip arthroplasties in 23 patients (13 women and 10 men). The mean age at operation was 44 +/- 8.3 years (range 22-59 years). The initial diagnosis was osteoarthritis (14 hips), osteonecrosis of the femoral head (11 hips) and rheumatoid arthritis (3 hips). Cemented cups with a metal articulation surface molded into the polyethylene were used. The cup was articulated with a 28-mm metallic head. Cemented stems were used in 27 hips, whereas a hydroxyapatite coated stem was implanted in one hip.

One hip required revision for deep infection five months postoperatively. One patient (one hip) was lost to follow-up. Twenty-six hips were evaluated at an average 31-month follow-up (range 12-47 months). All hips were rated excellent or very good. Radiographically, seven hips (27%) had a progressive acetabular radiolucent line, including three complete radiolucent lines. The latter always were located at the bone-cement interface. No implant migration was noted. In these cases, the mean socket diameter was lower than for the rest of the cohort (p < 0.001).

Progression of acetabular radiolucent lines remains of concern in this series of Metasul artificial hips. It is hypothesized that the diminution of polyethylene thickness has led to an increased rigidity of the socket, resulting in a higher rate of constraints at the bone-cement interface. Special attention must be given to these hips.