The Müller self-locking cemented total hip prosthesis with polyethylene liner: After twentyyears, what did they become?

Abstract

The M.E. Müller (MEM) prosthesis is a self-locking straight stem. Although this prosthesis is widely used, few outcomes have been published thus far. We examined long-term outcomes with the MEM cemented self-locking total hip arthroplasty (THA) with a polyethylene liner and 28-mm head. Between 1993 and 1994, 167 patients (173 hips) underwent primary THA implantation and were invited for clinical and radiological review a mean of 20.6(20.1 - 21.7)years later; 111 patients had a metal and 62 a ceramic head. Hip function was assessed using the Postel Merle d'Aubigné Score. Overall, 121 patients died and six were lost to follow-up. Forty patients (41 hips) were reviewed. Five patients required revision, of whom two were due to acetabular loosening, one to premature haematoma, one to recurrent dislocation and one to femoral fracture. Wear levels were significantly lower with ceramic than metal heads. The majority of radiological or clinical failures were acetabular (7.3% versus 2.4% femoral). At the femoral level, osteolysis was observed in seven patients (17%). Twenty-year survival was 88.67 ± 6.61% using an endpoint of all-cause revision and 97.9 ± 2.1% using femoral failure as the endpoint. Our retrospective analysis confirms the good results seen with the MEM stem in the literature and support the "French paradox" concept. Failures of these prostheses with a cemented polyethylene cup are largely on the acetabular side and, as such, the cup is the weak link. Improvements in survival will require optimisation of cup fixation and the use of a ceramic head to reduce wear in patients with a long life expectancy.