[Thirteen-year results for the CLS expansion cup in primary hip arthroplasty]

Clinical studies of the CLS expansion cup in hybrid hip arthroplasty generally show good results. However, follow-up times are limited to between 5 and 10 years. The aim of our study was to assess the clinical and radiological outcome of the CLS cup after more than 10 years.

After a follow-up of 13 years (10-15 years), 41 of 186 patients with a total of 41 CLS cups were available for clinical and radiological evaluation. In addition, a digital analysis of all radiographs was done. This included measurement of the migration, inclination, polyethylene wear, shaft subsidence, and osteolytic lesions.

The average preoperative Harris hip score was 48, which increased to 81 at final follow-up. No acetabular loosening was found. Two cups (5%) showed osteolytic lesions not exceeding 50% of the specific zone according to DeLee and Charnley and were considered stable. There was no migration or inclination of the cups. The average polyethylene wear corresponded to 0.1 mm/year. Sixteen patients (39%) showed osteolyses around the stem and were considered loose.

The CLS expansion cup provides excellent clinical results after 13 years in hybrid total hip arthroplasty. Time-correlative polyethylene wear and the extremely high rate of stem loosening have no consequences for the cup stability in our patient group. Acetabular osteolysis is rare.