Cementless endoprostheses include the Zweymüller endoprosthesis. Extensive clinical and radiological investigations were carried out in the Department of Orthopaedics and Traumatology of the University of Medical Sciences in Poznań in 180 patients who had received this endoprosthesis between 1995 and 2004.
The study group was composed of 180 patients (252 hips), out of whom 138 patients (193 hips) had been operated on due to primary (idiopathic) degenerative changes and 42 patients (59 hips) had needed treatment on account of degenerative changes secondary to developmental hip dysplasia and hip joint dislocation. The mean duration of post-operative follow-up was 6 years in patients with primary degenerative changes and 7 years in patients with secondary degenerative changes. The patients were also divided into two groups according to the length of post-operative follow-up. The first group, evaluated after a follow-up of more than 10 years, was composed of 31 hips, whereas the second group, with a follow-up of up to 10 years after the surgery, comprised of 221 hips. We evaluated anteroposterior hip joint radiographs taken before the surgery, during the follow-up and at the final examination and, additionally, axial hip radiographs taken on the first post-operative day and lateral radiographs of the femur and the hip joint taken at the final examination. The radiographic evaluation was carried out according to the recommendations of the Hip Society.
There was no radiographic evidence of implant loosening among the 180 patients. In the group of post-dysplastic hips, the inclination angle of the acetabular component was 29-52 ° (mean: 40.2 °) and the acetabular opening angle was 0-21 ° (mean: 7.9 °). The stem was valgus-oriented in 9 hips, varus-oriented in 11 hips and neutral-oriented in 39 hips. In the group of patients with primary degenerative changes the inclination angle of the acetabular component was 29-65 ° (mean: 42.5 °) and the opening angle was 0-32 ° (mean: 8.9 °). The stem was valgus-oriented in 12 cases (6.3 %), varus-oriented in 43 cases (22.6%) and neutral-oriented in 138 cases (71%).There were no statistically significant differences between the group of patients treated due to idiopathic degenerative changes and those treated on account of post-dysplastic patients as well as between the groups divided according to the length of the follow-up as regards the position, the inclination and opening angle of the acetabular component, and the position of the stem.
The Zweymüller Alloclassic endoprosthesis provides good stability of the acetabular component and the stem in the treatment of both primary and post-dysplastic degenerative changes. The Zweymüller stem provides good conditions for the integration of bone surface with the endoprosthesis, while the acetabular component facilitates the remodelling of the bone surrounding the implant.