Background: Modern hip resurfacing implants may increase stability and preserve bone compared to conventional total hip arthroplasty. The purpose of this retrospective study was to analyze the mid-term results of a consecutive series of middle-aged patients with developmental dysplasia of the hip treated by hybrid resurfacing joint arthroplasty.  

Materials and Methods: Conserve? Plus Metal-on-metal resurfacing was performed in 54 patients (59 hips), 43 females and 11 males.  The average age at the time of surgery was 43.7 years.  Radiographic and clinical data were collected at 3 months and at yearly follow-up. Seven hips had Crowe class type II and fifty-two had type I developmental dysplasia of the hip. 

Results: The follow-up period ranged from 4.2 years to 9.5 years (average 6.0 years). Initial stability was achieved in all but 3 patients.  Clinical outcome using the UCLA hip scores showed significant improvement from pre-operative ratings.  Pain ratings improved from 3.2 to 9.3, walking from 6.0 to 9.8, function from 5.7 to 9.7, and activity from 4.6 to 7.5 (all, p<0.0001).  SF-12 mental scores increased from 46.6 to 53.4 and physical scores from 31.7 to 52.0 (all, p<0.0001).  The mean post-operative Harris hip score was 93.0. Range of motion improved in flexion from106.5? to 129.4?, the abduction-adduction arc from 41.9? to 77.5?, and the rotation arc in extension from 32.1? to 85.4? (all, p<0.0001). Four patients have delivered six healthy babies since implantation. Radiographic analysis showed a decrease in body weight lever arm from 118.5 mm pre-op to 103.9 mm post-op (p=0.007).  There were 5 femoral failures requiring conversion to a total hip arthroplasty One hip showed a femoral radiolucency around the metaphyseal stem. There were no complete acetabular radiolucencies and all sockets remained well fixed.

Conclusions: The mid-term results of metal-on-metal resurfacing in Crowe type I and II developmental dysplasia of the hip were disappointing, with respect to the durability of the femoral component. The more recent results with meticulous bone preparation have been effective in eliminating femoral neck fractures and loosening in the past 6 years.  The fixation of the Conserve? Plus porous coated acetabular components without adjuvant fixation has been excellent from the beginning of implantations despite incomplete lateral acetabular coverage of the socket. (See Abstract “The Effects of Technique Changes on Aseptic Loosening of the Femoral Component in Hip Resurfacing. Results of 600 Conserve? Plus With a 3 to 9 Year Follow-up”)