[The cemented Müller straight stem total hip prosthesis with polyethylene cup and 28 mm head: ten-year results]

The purpose of this study was to evaluate the 10-year results of the cemented Müller straight stem total hip prosthesis with polyethylene cup and 28 mm head.

From May 1988 to May 1990, 187 cemented prostheses (second-generation technique) were implanted via a transgluteal approach for degenerative hip disease. A Protasul 10 straight stem with a 28 mm modular head and a gamma ray sterilized polyethylene cup was used in all cases. At ten years, the follow-up of the 187 implants was: 60 implants in deceased patients, 24 implants in patients contacted by telephone (all with implants in place), 90 implants in 82 patients seen for review. The series thus included 40 women and 42 men, mean age 65 years. The clinical outcome was assessed with the Postel Merle d'Aubigné (PMA) score. Radiographic assessment noted lucent lines, granulomas, implant migration, polyethylene wear, and ossifications. Survival curves were established with the actuarial method.

Among the 187 implants, two patients required revision: one for sepsis and the other for posttraumatic dislocation. Among the 82 patients reviewed at 10 year, the PMA score was 16.8 (92% good and very good results). Radiographically, assessment of the acetabular component demonstrated three probable and one certain loosening, four cases of polyethylene wear greater than 2 mm. At the femoral level, osteolysis was noted in zones 1, 3, and 7 and rarified bone in zone 7 in four patients. Linear penetration of the stem into the cup was 0.09 mm/yr, corresponding to a volumetric wear of 55, 35 mm3/year. Brooker grade 3 ossification was observed in 27% of men and 14% of women.

The clinical results were comparable to other series of cemented prostheses. At ten years, acetabular loosening was more frequent with active radiolucent lines present from the fifth year. It would thus appear that better results could be achieved by optimizing the bearing. Furthermore, there was no parallelism between the clinical and anatomic observations, cup loosening and femoral osteolysis were well tolerated. The prevention of ossification appears to be an important point, particularly in men.