[Analysis of the migration of cementless all-metal hip endoprosthesis]

Since September 1997, 58 patients have received a newly developed all-metal hip prosthesis at the department of orthopaedic surgery, University Hospital Vienna. In a retrospective study, the migration profile of 26 acetabular components of these prostheses with all-metal cups was evaluated. A total of 25 patients (10 men, 15 women, mean age 61 years) who had been operated on earlier than 11 months previously were studied. Indications included coxarthrosis (15), congenital dysplasia of the hip (7), post-traumatic coxarthrosis (3), and change of the implant due to infection (1). Twenty-three patients (7 men, 16 women; mean age 63 years) with 25 metal-backed polyethylene implants and matched demographic data, indications and cup size, served as the group for comparison. The mean duration of follow-up for both groups was 14 months. For analysis of migration a modified version of Dickob's method for digital measurement of comparative hip radiographs was used. Measurements were performed three times by one examiner. Migration values of more than 2.0 mm were regarded as a sign of possible cup loosening. After 13 to 20 months the average migration was -0.10 mm in horizontal and 0.18 mm in vertical direction for all-metal prostheses, and -0.20 mm horizontally and 0.47 mm vertically for the other group. Mean migration values exceeded the critical limit of 2.0 mm in two patients in the all-metal group, one of whom also had clinical signs of cup loosening. The covariance analysis of the highest migration levels of each patient revealed no significant differences between the groups; the postoperative Harris hip score was 98 points (range, 93-100) in the all-metal group and 97 (range, 92-100) in the other. Provided metal is carefully processed and cups are initially stable, the all-metal implants have equivalent in-growth as expressed by the migration analysis, and thus constitute an alternative therapeutic modality without polyethylene components.