[Failure of acetabular cups fixed with cement and thick embedded wire mesh]

Abstract

Purpose of the study: We report our experience with the SKH(R) cemented acetabular cup, analyzing the clinical and radiographic consequences of using cement armed with a thick embedded wire mesh.

Material and methods: Between June 1990 and June 1991, 118 total hip arthroplasties (THAs) were performed in 110 patients (8 bilateral cases) using the SKH(R) cemented acetabular cup, a self-blocking cemented femoral stem with anterograde injection made of a Ti-6Al-7Nb alloy and a 28 mm ceramic polyethylene articulation. Mean follow-up for 97 implants (91 patients) was 7.1 years (3 - 9 years). Mean age at implantation was 65 years (36 - 85 years) (43 men and 48 women). THAs were performed for degenerative joint disease (n=79) including 67 cases of primary disease, necrosis (n=11), rheumatoid disease (n=6), and fracture of the femoral neck (n=1).

Results: For the 118 procedures, there were 4 complications: 2 dislocations (no revision), one failure of the ceramic head and one implant infection (with revision). As assessed by the Postel-Merle-d'Aubigné score as modified by Charnley for the mobility criterion, clinical outcome was excellent or good in 82% of the cases, fair in 11% and poor in 7%. According to the Massin criteria at last follow-up, there were 13 cup loosenings (13.4%, 10 migrations and 3 total lucent lines > 1 mm); revision procedures were performed in 6 cases. A lucent line postoperatively, observed in 51% of the cases (p=0.025) and involving all or part of zone 1 in 44% (p=0.047), was predictive of acetabular failure. Linear polyethylene wear as measured manually was 0.08 mm/year (average) for non-loosened cups and 0.2 mm/year for loosened cups; the difference was significant (p=0.001). On the contrary, the thickness of the cement, measured at the limits of the three De Lee and Charnley zones, cup tilt and size, age, weight and patient activity level had no effect on failure rate. Actuarial survival of the cup at 9 years was 86.3% taking aseptic loosening (with or without revision) as the failure criterion and 93.8% taking revision for aseptic loosening as the failure criterion.

Discussion: These results were rather disappointing. The thick layer of cement reinforced with the wire mesh produces a metal back effect with the known consequences in terms of loosening, cement-bone lucent line, and polyethylene wear. A modification is now undergoing thermal and mechanical assessment. A thinner and tighter mesh would appear to be preferable.