Long-term Results and Bone Remodeling After THA With a Short, Metaphyseal-fitting Anatomic Cementless Stem

Abstract

Long-term results of standard total hip arthroplasty (THA) in young patients were not optimal. There are a number of reported disadvantages to longer cementless stems in THA including thigh pain and proximal stress shielding. However, it is unknown whether a short, metaphyseal-fitting anatomic stem without diaphyseal fixation, which represents a possible alternative, will maintain fixation over the longer term. We therefore evaluated long-term (1) clinical results using validated scoring instruments; (2) osseointegration and bone remodeling; (3) complications; and (4) rates of revision and osteolysis in patients younger than 65years who underwent THA with a short, metaphyseal-fitting anatomic cementless stem. We reviewed 500 patients (630 hips) younger than 65years (mean age at surgery, 52.7years) who underwent THA with the Immediate Postoperative Stability stem (IPS; DePuy, Leeds, UK) by one surgeon (Y-HK) from January 1995 to March 2002. Demographic data, Harris hip score, WOMAC score, UCLA activity score, and radiographic data were recorded. All patients underwent dual-energy x-ray absorptiometry scanning of the acetabulum and proximal femur at 2weeks after the operation and at final followup to determine stress shielding. Thigh pain was specifically investigated and scored by patients on a visual analog scale. Other complications were recorded. We determined component survival rates at 15years using revision and aseptic loosening as end points. Minimum followup was 11years (mean, 15.8years; range, 11-18years). The clinical and functional results improved significantly for the Harris hip score, WOMAC, and UCLA activity scores (p<0.001). At latest followup, mean Harris hip, WOMAC, and UCLA activity scores were 94 (range, 71-100), 15 (range, 5-29), and 7.9 (range, 6-9) points, respectively. All hips had osseous integration of the acetabular and femoral components. No patients had thigh pain. Four hips (0.6%) had deep infection and four (0.6%) had a recurrent dislocation. No patients had Grade 3 stress shielding. Fifteen-year survival rates were 98.7% (95% confidence interval [CI], 0.95-1.00) for the acetabular component and 99.4% (95% CI, 0.97-1.00) for the femoral component with revision as the end point and 100% (95% CI, 0.98-1.00) for both components with aseptic loosening as the end point. The short, metaphyseal-fitting anatomic cementless femoral stem provided stable fixation without relying on diaphyseal fixation in younger patients, suggesting metaphyseal fitting alone is sufficient in young patients who have good bone quality. Because we observed no thigh pain and little stress shielding in our patients, modifying the distal stem design as is done with this implant might be advantageous, but this would need to be determined in future comparative studies. Level IV, therapeutic study. See Instructions for Authors for a complete description of levels of evidence.