Abstract
Introduction
Malalignment of some designs of stem is associated with an increased risk of aseptic loosening and revision. We investigated whether the alignment of the cemented polished, double-taper design adversely affected outcome, in a multicentre prospective study.
Methods
A multicentre prospective study of 1189 total hip replacements was undertaken to investigate whether there is an association between surgical outcome and femoral stem alignment. All patients underwent a primary THR with the Exeter femoral stem (Stryker Howmedica Osteonics, Mahwah, NJ) and a variety of acetabular components. The primary outcome measure was the Oxford hip score (OHS) and change in OHS at five years. Secondary outcomes included rate of dislocation and revision. Radiographic evaluation of the femoral component was also undertaken. The long axis of the Exeter femoral component and the long axis of the femoral canal were located, and the angle at the point of intersection measured. The cementing quality was determined as defined by Barrack et al. Radiolucent lines at the cement-stem and cement-bone interface in the five year radiographs were defined using the zones described by Gruen et al. Subsidence was measured as the vertical dimension of the radiolucency craniolateral to the shoulder of the stem in Gruen zone 1 as described by Fowler et al. Cement fractures were recorded.
Results
The incidence of varus (>5 ° to the femoral axis), and valgus (>5 °) malignment were 3.7% and 0.8% respectively. Pre-operative demographics and OHS were similar in all groups (p > 0.4). There was no significant difference in OHS or change in OHS between neutral and malaligned groups at 5 years (neutral, mean=40.1, change=23.1; varus, mean=40.1, change=23.7; valgus, mean=42.0, change=26.6; p=0.46 and p=0.45 respectively). There was no significant difference in dislocation rate between the groups (p=0.66). There was also no significant difference in revision rate (p=0.34). There were no statistically significant differences in the incidence of femoral radiolucency, stem subsidence or cement fracture (p > 0.1).
Conclusion
This study provides evidence that both varus and valgus implantation does not compromise the short to medium term clinical results of the cemented, polished, double-taper stems. Longer follow-up is required to establish the influence of stem alignment on the incidence of aseptic loosening and revision.
