Introduction The double-tapered femoral stem is recognised for its excellent long-term results. The design allows greater cement engagement by capitalising on the phenomenon of cement creep. An additional third taper is thought to provide greater stability, fixation and improved femoral neck loading. This study compares prospectively the early clinical and radiological results between triple and double-tapered stems in cemented THA.
Methods Between March 1998 and October 2002, 391 patients (405 hips) underwent primary THA and received either a triple, 192 patients (200 hips) or double 189 patients (205 hips) tapered stem. The post-operative protocol was identical and patients were followed-up clinically and radiologically at approximately three, six and 12 months and yearly thereafter. Clinical outcomes were assessed with respect to mortality, complications, Harris Hip Score (HHS) and Merle d’Aubigne and Postel score (MDA). Radiological analysis was performed looking for evidence of radiolucent lines, aseptic loosening, subsidence, endosteolysis, heterotrophic ossification, cortical hypertrophy and cement fractures. Age, sex, weight, height, indications for surgery and the distribution of right and left hips were comparable between the two groups. The average follow-up in the triple and double tapered groups was 21 and 23 months respectively.
Results Clinically, in the triple-taper group, there was a mean improvement in HHS of 44 points and MDA of 5.8. Similar improvements were seen in the double-tapered group, with increases of 45 and 5.6 points in the HHS and MDA respectively. No significant difference was noted in terms of complications. In the triple-tapered group, evidence of radiolucency between the cement-stem interface was seen in only one patient in Zone 1, and this was associated with a small cement fracture in Zone 3. Cement-bone radiolucency occurred in one hip at Zone 1. In the double-tapered group, five hips showed cement-stem radiolucency, all in Zone 1. Radiolucency between the cement-bone interface was present in two hips, one in Zone 1 and the other in Zone 7. Average subsidence of the triple-tapered stems was 0.77 mm (range 0 to 2.5), which compared to 0.82 mm (range 0 to 2.5) in the double-tapered group. No stems were considered at risk of aseptic loosening. There was no significant difference in the extent of proximal femoral resorption and heterotopic ossification.
Conclusions In our study, the triple and double-tapered components performed equally well clinically and are comparable on radiological analysis. The triple-tapered stem is safe and is not associated with increased rates of loosening, subsidence or radiolucency, compared to the double-tapered stem. There is potential to translate the promising early results of the triple-tapered design into the future and expect similar long-term success.
