Fifteen-year results of the Müller CoCrNiMo Straight Stem

Between September 1980 and May 1982, 112 primary unilateral total hip arthroplasties with the original cemented M. E. Müller Straight stem (manufactured from Protasul-10, a CoCrNiMo alloy) were inserted in 109 consecutive patients, all combined with non-cemented, non-coated polyethylene RM cups. Forty-three patients (40%) died during the follow-up period, all with the implant in place. Of the 66 surviving patients, 2 (1.8%) were lost to follow-up, and 7 (6.3%) were unable to attend the 15-year clinical and radiological follow-up. Eight stems (7.3%) had to be revised for aseptic loosening and 3 stems (2.7%), for septic loosening. The 15-year survivorship of the Müller Straight stem regarding aseptic loosening is, therefore, 92.7%. Forty-six patients with 49 total hip replacements could be evaluated clinically and radiologically after 15 years. The mean duration of clinical follow-up for these 46 patients (42.2%) was 14.8 years (range 12.8– 16.5 years). There were 22 women (48%) and 24 men (52%). The mean age at the time of the operation was 62 years (range 38–80 years), and 78 years (range 59– 93 years) at the time of the latest follow-up. The mean Harris Hip Score at the latest follow-up evaluation of the 49 hip joints was 85 points (range 34–100 points). Of the 46 patients, 39 (85%) had a good or excellent clinical result. Radiographic follow-up was performed for 49 hips: 35 (70%) had linear or focal osteolysis in one or more zones of the stem, but only 4 (8%) had evidence of definitive loosening (linear radiolucency of over 2 mm all around the stem). Subsidence of over 2 mm was found in 20 hips (41%), 6 of them within the cement mantle. There was no correlation between subsidence and pain. The cause for the poor results is primarily the high rate of aseptic loosening of the non-coated, non-cemented all-polyethylene RM cups, with a loosening rate of 63% and a revision rate of 25% after 15 years.