TEN-YEAR RESULTS OF A COMPOSITE TOTAL HIP REPLACEMENT STEM IN YOUNG PATIENTS.

Abstract

Introduction: A composite femoral stem was introduced with a structural stiffness similar to that of the native femur to promote proximal load transfer. This consisted of a cobalt-chromium alloy core surrounded by an injection-moulded layer of polyaryletherketone covered with a porous titanium mesh.

Materials and Method : 31 primary total hip replacement stems were implanted in 26 patients with an average age of 37 years (range 17–57) using the Epoch Stem (Zimmer, Warsaw, IN) as part of a prospective multicentre trial. A cementless Harris-Galante I acetabular component with a 28mm polyethylene insert was used in 28 cases, a Plasma cup (Aesculap) in 1 case and a bipolar head in 2 cases. Annual follow-up using Harris Hip Scores and radiographic evaluation was performed for a mean of 10.1 years.

Results: Harris Hip Scores improved from a mean of 56 points preoperatively to 90 at the time of last follow-up. Radiographs showed no stem migration or loosening. 4 cases with polyethylene wear showed trochanteric osteolysis. Specific radiographic features noted were calcar rounding in 10 cases and improvement in calcar appearance with squaring in 4 cases. Calcar resorption was seen in 1 case associated with polyethylene wear. There have been 9 instances of revision of the head or acetabular component – 3 liner exchanges for polyethylene wear, 3 liner exchanges for dissociation, 1 acetabular component revision for infection and 2 bipolar heads revised to unipolar heads with cementless acetabular component for pain. No stem has required or requires revision.

Discussion: The Epoch stem resulted in an excellent clinical outcome, with evidence of radiographic stability and proximal bone preservation, and no cases of stem revision in a small cohort of young patients at 10-year follow-up. The limitation of reconstruction in this cohort of young patients has been the acetabular component.