Fifteen-year results of the Müller CoCrNiMo Straight Stem

Abstract

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.

Subsidence of titanium straight stems in combination with highly viscous bone cement

“…In the Swedish prosthesis register, the 10-year results of the Müller straight stem prosthesis are superior to those of the Charnley prosthesis [12]. In other studies, a 15-year survival rate of 88% and a 10-year survival rate of 94% were found for the chromium-cobalt design [7,19]. Good results were also reported in other studies with shorter follow-up examination intervals [11,22,25].…”

Cemented Müller straight stem total hip replacement: 18 year survival, clinical and radiological outcomes

“…The films were rated according to the Gruen zone system for the femoral component and according to De Lee and Charnley for the acetabular component ( Figure 1) [9] . Loosening was defined as follows: potential loosening: radiolucency (linear/focal) < 2 mm; probable loosening: linear radiolucency > 2 mm; focal radiolucency > 5 mm; definitive loosening: linear radiolucency > 2 mm all around [1,9] (Table 1). Subsidence of the stem was measured as the difference between the highest point of the prosthesis shoulder and the horizontal sclerotic line above the shoulder.…”

“…The original Müller straight stem prosthesis falls into this category. The original Müller straight stem prosthesis has shown excellent results at 10 to 15 years [1][2][3][4] . The 10 year survival rate for the stem ranges from 91.2% to 98.3% [3,5] .…”

“…The Müller straight stem was designed to achieve a press fit fixation in the anteroposterior radiological view with a self-centering effect (shape-closed). A close stembone contact is established in the coronal plane, resulting in a thin or even incomplete cement mantle [1,12,13] which has been described in the literature as the "French paradox" [13] . It is well known that it is desirable to have a complete cement mantle around the stem [14] .…”

“…Radiologically, an obvious loss of mineralization of the cortex and cancellous bone has been observed in older women [25] . Räber et al [1] reported a 15 year survival rate for aseptic loosening of 88.1% with the Müller straight stem when using a first generation cementing technique, but found that about 70% of the remaining stems exhibited osteolysis or longitudinal lucencies. The incidence of osteolysis was not reported but the longitudinal lucencies might have been due to cortical atrophy.…”