SAGGITAL FEMORAL COMPONENT ALIGNMENT IN TOTAL HIP ARTHROPLASTY: A PROSPECTIVE STUDY COMPARING POSTERIOR AND DIRECT LATERAL APPROACHES.

Abstract

Introduction: There is an increased risk of revision for aseptic loosening with a transgluteal approach as described in the Swedish Hip Register. Femoral component malpositioning is itself associated with a poor outcome. A cuff of posteriorly situated glutei during the direct lateral approach may result in levering the proximal stem anteriorly and the tip of the stem posteriorly and does not allow the entry point of the stem to be placed posteriorly at the level of neck resection resulting in possible malpositioning.

The purpose of this study was to determine whether there is a significant difference in femoral component alignment when the posterior and direct lateral approaches are compared.

Materials and methods: Forty patients underwent a direct lateral approach and forty a posterior approach (n = 80). Inclusion criteria included primary hip arthroplasty using a cemented Exeter femoral component. At 6 weeks a standard AP and a modified lateral radiograph were taken. Measurements were taken from digitized radiographs as follows:

1. AP radiograph

   • Tip of stem to outer medial cortex.

   • Tip of stem to outer lateral cortex.

2. Lateral radiograph

   • C Tip of stem to anterior outer cortex

   • D Tip of stem to posterior outer cortex.

Component alignment was defined as A – B and C – D.

Results: A–B was 0.71 for the modified direct lateral approach and 2.56 for the posterior approach. C–D was 1.47 for the direct lateral approach and 1.21 for the posterior approach. This difference was not statistically different using paired t tests as p > 0.05(P=0.69) for lateral views measurements.

Discussion: This study demonstrates that there is no significant difference between direct lateral and posterior approaches as far as femoral component alignment is concerned. The increased revision rate noted by the Swedish Hip Register when a transgluteal approach is likely to be multifactorial, but not likely to be due to femoral component malalignment.