The Uncemented, Titanium-Coated RM Cup: Survival and Analyses of Failures

This study evaluates the incidence of revision of the monoblock, uncemented, titanium-coated RM (Robert Mathys) cup (Mathys Medical, Bettlach, Switzerland) in primary total hip arthroplasty. Between 1991 and 1995 a total of 630 RM cups were implanted in 462 patients. A Kaplan-Meier survival analysis was performed with failure defined as acetabular revision for any reason. The mean follow-up was 8.2 years. A total of 34 acetabular revisions (5%) were carried out: 15 for recurrent dislocation due to cup malposition, nine for wear caused by impingement of a loose femoral component, five for aseptic loosening, only one cup was revised for articular polyethylene wear, and four for other causes. The cumulative survival rate of the RM cup is 91% at 10.7 years, with a worst case scenario of 87%. The cumulative survival rate for aseptic loosening was calculated: 99% at 10.7 years. The titanium-coated RM cup shows an impressive survival rate with revision for aseptic loosening as endpoint. Correct cup positioning is the key to success and requires experience and meticulous surgical technique.