Introduction: The original Müller straight stem (MSS, Zimmer^®; Winterthur, Switzerland) is made out of CoNiCr and showed excellent 20 year results but later modifications of the stem proved to be inferior. Aim of this study was to analyse the effect of shape, material and surface roughness on aseptic loosening of cemented Müller type straight stems.

Materials and patients: Between 1984 and 1996 a total of 926 THR were operated with four different versions of cemented Müller type straight stems and followed prospectively in the in-house register at our institution. Two different shapes of cemented Müller type straight stems (MSS and SL), both made out of two different alloys (CoNiCr and TiAl), were included in this study. All four versions differed in surface roughness (MSS CoNiCr Ra 1.0μm (satin); SL CoNiCr Ra 1.2μm (satin); MSS TiAl Ra 2.0μm (rough); SL TiAl Ra > 2.0μm (rough)). Survival analysis was done using Kaplan-Meier curves with aseptic loosening as endpoint, risk factors were tested with regression analysis.

Results: The 4 groups did not differ in age, gender and diagnosis, the mean follow up was 11.4 (0.1 to 23.0) years. Survival with aseptic loosening as endpoint was 97.7% (MSS CoNiCr), 96.4% (SL CoNiCr), 82.5% (MSS TiAl) and 67.4% (SL TiAl), respectively, at ten years. At final follow up all four groups differed significantly (p=0.044 Log rank test). Increasing roughness increased the risk for aseptic loosening and the harder CoCr had better survival than TiAl. results were significantly worse for the combination of the soft TiAl with a rough surface (SL TiAL, Ra > 2.0μm). For both stem designs the MSS shape had better survival than the SL shape (p=0.001)

Discussion: Wear modalities (abrasion vs. fretting) in the cement-stem interface are directly correlated with surface roughness, the amount of the released particles correlates with loosening. All examined stems had a roughness exceeding the limit of Ra =0.4 μm, producing abrasive wear with a higher volume of wear particles as compared to established polished stems which show fretting wear. Stem roughness and hardness are more important for long-term survival than some modifications in the shape.

Conclusion: Cemented Müller type straight stems should have a polished surface (Ra < 0.4 μm) and be made out of a hard material (CoNiCr) to minimize surface wear. This might be true for all types of cemented stems.

Introduction: Since its introduction in 1977 the Müller straight stem and its various copies have become one of the most often used cemented stems worldwide (about 1.1 million stems, figure quoted by manufacturer). Though, there is still a lack of long-term follow-up data.

Material/Methods: A consecutive series of 165 primary hip replacements (161 patients) with the original forged Müller straight stem (CoNiCr) was operated between July 1984 and June 1987 and followed prospectively. Mean age at operation was 68.9 years (25.6 to 86.3 years). 70 stems were implanted in female patients. Operation was done in supine position through a transgluteal approach with no trochanteric osteotomy. All stems were cemented with a second-generation technique (distal plug, cement syringe). The head diameter was 32 mm diameter, 134 heads were out of metal, 31 out of ceramic. 151 hips had a cemented polyethylene cup (52 with armament screws). 13 were combined with an acetabular reinforcement ring (Müller ring) and one with an anti-protrusion cage (Burch-Schneider).

Clinical and radiological follow-up was planned at 4 months 1, 2, 5, 10, 15 and 20 years. Clinical follow-up included a standardised examination and the completion of an IDES form. Cumulative survival rates were calculated by Kaplan-Meier analysis. Radiographs were analysed for osteolysis according to Gruen et al. (zones 1–7) and radiolucent lines.

Results: 3 patients (3 stems) were lost to follow-up (two postoperative and one after 16.8 years), 103 patients (with 106 hips) had died without revision and 55 patients (56 hips) remained for follow-up. 15 stems were revised, 11 for aseptic loosening (9 in combination with the cup), two for infection and two for other reasons. 13 further patients had isolated cup revision. Survival with aseptic loosening of the stem as endpoint was 86% (95%-CI: 82 to 90%) at 20 years.

The median HHS at the last follow-up was 80 points (range 30–98 points).

31% of the non-revised 41 stems showed osteolysis, most of them in zone 7 (21.9%). Two stems with isolated cup revision had a continuous radiolucent line. Incomplete radiolucent lines appeared most frequently in zone 1. Cup revision was associated with increased radiological changes on the femoral side (p=0.094, Mann-Whitney U-test).

Conclusion: The Müller straight stem shows excellent clinical and radiological results in the long-term, comparable to those achieved with other well established cemented and non-cemented stems. From our data further clinical use of the Muller straight stem can highly be recommended.

Introduction: The Acetabular Reinforcement Ring (ARR) (ME Müller®) was introduced in 1977 as successor of the Endler ring, especially to allow total hip replacement (THR) in patients with congenital hip dislocation, serious dysplasia and revision of loose cups. The Polyethylen (PE)-inlay can be freely oriented in the fixed ARR. It is the first implant with screws having angular stability as the screw-heads are blocked when cementing the inlay in the ring.

Patients and Methods: Out of 2251 primary THR performed between 1984 and 2005 at our hospital the ARR was used in 399 hips (363 patients). The indication for a THR with ARR was mainly a deficient acetabular bone stock as judged by the operating surgeon. 51 % of the patients had osteoarthritis, 22% dysplasia, 7% fractures, 6,5% osteonecrosis, 5% protrusion acetabuli, 4% rheumatoid arthritis and 4,5% other diagnosis. The mean age at operation was 66.4 years, 64% were females.

Intraoperatively, the ARR was placed with its medial border adjacent to the tear drop figure. The weight bearing area was fixed with 3–4 cancellous screws in the acetabular bone stock. Regular clinical and radiological follow-up 3months, 1, 2, 5, 10,15 and 20 years was planned. The radiographs were assessed for osteolysis, radiolucent lines and screw breakage after 15 years. Survival for revision due to aseptic loosening was calculated by Kaplan Meier.

Results: The overall survival regarding aseptic loosening of the cup was 100% after 10 years, 97,2% after 15 and 93,2% after 20 years.

Of the 96 patients (104 rings) operated at least 15 years ago, one was lost for follow-up. Three rings were revised due to aseptic loosening (11, 12, 16 years after implantation) and one was removed due to infection (1,8 years after implantation). 54 patients (with 56 rings) died before they reached the 15 years control. None of them was revised for aseptic loosening of the ring. 37 patients (43 hips) remained for 15-years control, six of them refused to come and were contacted by questionnaire or phone. Two cups were radiologically loose with broken screws but not symptomatic. The mean HHS after 15 years was 80.1.

Conclusion: The ARR shows a very good long term survival even in patients with difficult acetabular situations such as deficient bone stock. The design allows an application in a variety of positions. Even at a teaching hospital good long term results could be reached with this implant.