Modular neck prostheses in DDH patients: 11-year results

Total hip replacement in developmental dysplasia of the hip is a demanding procedure and usually requires dedicated devices and special surgical techniques. Nevertheless, the described techniques have shown variable outcomes. The aim of this study was to assess the 11-year outcomes of an off-the-shelf modular neck prosthesis in dysplastic patients and to evaluate the ability of the modular neck system to adequately restore femoral offset, abductor muscles lever arm and leg length. We retrospectively evaluated 61 modular neck prostheses implanted in 47 patients between June 1995 and March 2004. The preoperative diagnosis was developmental dysplasia of the hip in all cases. The clinical outcomes were assessed using the Harris hip score and the Western Ontario and McMaster Universities score. The femoral offset, abductor muscles lever arm, height and medialization of the hip center of rotation, and differences in leg length were evaluated on postoperative radiographs. Prosthesis survival was calculated according to the Kaplan-Meier method considering any reason for revision as failure. The average follow-up was 117.2 months (range 57-162 months). The cumulative survival at 11 years was 97.5%. One prosthesis failed 5 years after surgery because of a ceramic liner fracture due to an inappropriate obstetric maneuver during labour. At the latest follow-up the mean Harris hip score was 74.7 (range 23-91). Leg length discrepancy was avoided in the majority of cases; femoral offset was almost always restored. The results of this series support the use of modular neck prostheses as an effective alternative in the treatment of developmental dysplasia of the hip. The modularity was very efficient in restoring offset, leg length and maintaining stability with a good mid-long-term follow-up. Unlike other proposed surgical techniques, these good results are achievable by a standard surgical technique and with an off-the-shelf prosthesis.