[Allofit cementless acetabular component: five-year experience].

PURPOSE OF THE STUDY: To evaluate the mid-term results of using the Allofit cementless acetabular cup for primary hip replacement.

MATERIAL AND METHOD: The Allofit cup is a cementless hemispherical acetabular component. The macrostructure on the external surface, including 1200 concentrically arranged teeth, and the rough-blasted surface of the biocompatible pure titanium provide good conditions for press-fit fixation. From 1998 to 2005 we used it in 182 cases of primary total hip replacement (THR) in 164 patients. (18 patients had bilateral THRs) The average age at the time of surgery was 58.3 years in men (range, 39-74 years) and 64.1 years in women (range, 33-80 years). We used the Bauer anterolateral approach as our standard procedure. The cup was combined with one of six types of cemented or cementless stems and a 28-mm ceramic head. At a minimum follow-up of five years, we evaluated clinical and radiological findings, i.e., the Harris hip score, radiological signs of loosening, migration and polyethylene wear. The average follow-up was 7.4 years (range, 5-11 years). For more accurate reading of X-ray films, the photographs were zoomed to 115%.

RESULTS: The final evaluation included 147 primary THRs in 129 patients. We recorded no intra-operative complications. The average Harris hip score increased from pre-operative 44 to post-operative 87 points (range, 31-100). The loosening of a cup occurred in three patients (2.1%), of which two were infected (1.4%) and one was aseptic (0.7%). We had to replace the polyethylene insert in three patients, in one for abnormally high polyethylene wear and, in two, because of a ceramic head fracture due to a fall. Cup migration was not recorded. Eight cups (5.4%) had a thin (less than 1 mm) radiolucent line without signs of loosening. Polyethylene wear indicated by an asymmetric position of the head was detected by the Dorr method in 32 cups (21.8%). A shift of the head centre towards the proximal pole of the titanium shell ranged from 0.4 to 6.0 mm. The average polyethylene wear of all cups was 0.29 mm in 5 years, which is 0.06 mm per year.

DISCUSSION: The Allofit acetabular cup is suitable for younger patients with good bone quality. In elderly patients or in those with severe osteoporosis, we preferably indicate cemented components. Press-fit cups can also be used in patients with postdysplastic osteoarthritis of the hip on condition that enough bone is left around the cup margin for press-fit fixation.

CONCLUSIONS: Cementless press-fit cups have very good outcomes, even in a long-term follow-up. Our experience gives support to these results because of a low number of hips with loosening, both septic and aseptic, or polyethylene wear of the primary implanted acetabular cup, and no cup migration in our patients. The five-year survival rate of the Allofit acetabular cup was 95.8%.