Excellent long-term survival of an uncemented press-fit stem and screw cup in young patients: Follow-up of 75 hips for 15–18 years

BACKGROUND: The long-term results of uncemented total hip arthroplasties vary widely due to differences in design, metal alloy, coating, surface structure, and porosity. PATIENTS AND METHODS: We retrospectively studied 75 cementless Zweymuller SL stems in combination with Endler titanium-backed threaded cups (Z-E) in 70 patients. 35 patients were women, and the mean age at surgery was 52 (24-68) years. 16 patients died and 1 emigrated, 7 patients (of which 1 later died) subsequently underwent revision, and the remaining 47 patients with 50 original arthroplasties were followed up after a median of 16 (15-18) years. RESULTS: Revision of 8 hips resulted in an 18-year Kaplan-Meier estimated overall survival rate of 88% (CI: 79-96). 6 of 7 cup revisions were due to liner wear and osteolysis, and 1 was due to aseptic loosening. 2 of 3 stem revisions were due to femoral loosening and 1 was due to fracture of the neck of the stem. The clinical results were good, with a mean Harris hip score of 89 (54-100). Half of 70 hips in 65 patients had ectopic bone formation. All unrevised implants were radiographically stable, with a mean liner wear of 0.07 mm/year. INTERPRETATION: These long-term results demonstrate that the combination of a Zweymuller SL stem and an Endler titanium-backed screw cup is a good hip arthroplasty in young and active patients. A prefixed polyethylene liner is a drawback, necessitating exchange of the whole cup in cases with polyethylene wear.