Clinical and Radiographic Results Associated with a Modern, Cementless Modular Cup Design in Total Hip Arthroplasty

Background: First-generation cementless modular cups reproducibly achieved fixation to bone but were associated with unacceptable rates of pelvic osteolysis and mechanical failure. Consequently, second-generation cups were developed with shells that had a limited number of holes (or no holes) as well as improved locking mechanisms, a polished inner surface, and increased conformity with the liner. The purpose of the present study was to evaluate the clinical and radiographic results associated with the use of a second-generation acetabular component for primary total hip arthroplasty.

Methods: Two hundred and ninety-seven patients underwent 335 consecutive primary total hip arthroplasties that were performed by a single surgeon with a second-generation modular acetabular component. All cups were implanted with a press-fit technique. Ten patients were lost to follow-up, and sixteen died from unrelated causes. The remaining 271 patients (308 hips) were followed clinically (with the Hospital for Special Surgery hip-scoring system) and radiographically for four to seven years.

Results: One cup was revised because of aseptic loosening. There were seven additional revisions: five were performed because of aseptic loosening of the stem with a well-fixed cup, and two were performed because of deep infection. Among the 271 patients who were alive at the time of the last follow-up, 266 (98%) had retention of the cup and 264 (97%) had retention of both components with a good or excellent clinical result. In the group of 229 patients (262 hips) with complete radiographic follow-up, 259 cups were well fixed and the average wear rate (for the 246 hips for which this rate could be calculated) was 0.09 mm/yr. Osteolysis was detected in twelve hips (5%) and was associated with male gender (p = 0.001) and the annual wear rate (p = 0.004). The extent of calcar resorption was also associated with the annual wear rate (p < 0.001).

Conclusions: This second-generation acetabular cup design predictably achieved bone fixation and was associated with low rates of revision for loosening and osteolysis after intermediate-term follow-up.

Level of Evidence: Therapeutic study, Level IV (case series [no, or historical, control group]). See Instructions to Authors for a complete description of levels of evidence.