METAL-ON-METAL HYBRID SURFACE ARTHROPLASTY FOR DEVELOPMENTAL DYSPLASIA OF THE HIP: 3.5 TO 6.5-YEAR FOLLOW-UP

Abstract

Introduction and Aims: To review the medium-term clinical and x-ray results of metal-on-metal Surface Arthroplasty (MMSA) in DDH, using the Conserve Plus™.

Method: Fifty hips (44 patients, avg. age 42.7 years) with DDH were treated with hybrid MMSA. Seventy-five percent were female. Ten percent had prior osteotomies. Twenty-five percent had acetabular cysts that were grafted and 64% had femoral cysts (> 1cm in size) and one was grafted. All cases were Crowe Class 1 or 2. A posterior approach was used in all but one case.

Results: Mean follow-up was 4.9 years (3.8–7.8). UCLA hip scores were 3.2, 5.9, 5.5 and 4.4 pre-op and 9.2, 9.5, 9.4 and 7.1 at last follow-up for pain, walking, function and activity. SF-12 scores normalised. Range of motion was 126.6 degrees, 80.5 degrees and 83.2 degrees at last follow-up for flexion, abduction-adduction, and rotation arcs. Four hips were converted to THA: 2 for femoral neck fracture at two and five months, one for recurrent subluxations due to poor offset and impingement due to prior multiple osteotomies, and one for femoral component aseptic loosening. Four technical complications successfully resolved: one trochanteric non-union, one post-op dislocation (closed reduction), one component mismatch (acetabular component exchange) and one femoral nerve palsy. X-ray analysis: two patients presented complete radiolucencies around the metaphyseal stem.

Conclusion: SA is stable, except for one subluxation due to impingement with poor offset compared to seven to 10% with THA. The socket fixation is secure without adjunct fixation with grafts incorporating whereas prior SA with PE were poor due primarily to socket loosening. Femoral bone preparation is critical to avoid fractures and loosening.