[Total hip replacement in osteoarthritis with acetabular protrusion].

PURPOSE OF THE STUDY: The acetabular protrusion changes anatomical conditions for implantation of a cup in total hip replacement. The aim of this study was to evaluate different approaches to implantation of acetabular components in patients with this condition.

MATERIAL: A total of 50 hips in 33 patients who had surgery for osteoarthritis with acetabular protrusion between 1992 and 2000 were evaluated. Their initial diagnoses were: idiopathic rotrusio acetabuli in 20 patients, rheumatoid arthritis in nine, arthropathy due to psoriasis in two and Bekhterev's disease in two patients. The average age of the patients was 64.1 years (range, 27 to 74 years). In group I including 18 hips, cemented polythylene cups were used (11 Poldi, 5 Ultima and 2 Weber prostheses). In group II involving 32 hips, uncemented cups were employed (29 CLS, 2 Morscher and 1 Balgrist prostheses). Bone grafts inserted in the acetabular bottom were used in eight and 25 cases of groups I and II, respectively. The mean follow-up was 7.1 years.

METHODS: The following parameters were evaluated: Wiberg's angle, protrusion grades according to Sotelo-Garzy, Charnley scores, teardrop collapse, angle of acetabular inclination, approximate femoral head center and center of the femoral prosthesis head, and the distance between them in both horizontal and vertical directions, deviation of the center of the femoral component head from the anatomical center of rotation in horizontal and vertical directions, radiolucent zones according to de Lee and Charnley, position of the femoral head center inside or outside the TAR triangle and aseptic loosening of the acetabular component.

RESULTS: At a follow-up of 7.1 years in group I, 10 hips showed full osteointegration, five underwent revision arthroplasty for aseptic loosening and three showed some degree of aseptic loosening. All failures occurred in the acetabular cups implanted without bone grafting of the acetabular bottom. In group II, 29 hips showed full clinical survival with complete osteointegration of the acetabular cup and three were found to have a radiolucent zone of 1 mm in width.

DISCUSSION: The complete osteointegration of a cemented acetabular cup was achieved in 10 out of 18 hips, with eight having spongioplasty of the acetabular bottom. The use of uncemented cup resulted in full clinical survival and complete osteointegration in 29 cases out of 32. The best outcome was achieved with the use of an expansion, uncemented CLS cup. This is designed for peripheral fixation, which is useful in the protrusion of an acetabulum with a thin bottom and permits acetabular bottom grafting and positioning of the femoral component head in the center of hip rotation. It provides full osteointegration even with low bone quality.

CONCLUSION: Prerequisites for successful arthroplasty in hips with acetabular protrusion include the firm implantation of an acetabular component, placement of the femur lateral to Köchler's line, location of the center of the femoral component head inside the TAR triangle and an agreement between the approximate center of the femoral head and the center of the femoral component head. The firm and lasting implantation of a cemented cup requires spongioplasty of the acetabular bottom. At an average of 7.1 years after surgery, uncemented cups in conjunction with bone grafting of the acetabular bottom showed better outcomes than cemented acetabular components.