FAILURE OF AUSTIN MOORE HEMIARTHROPLASTY: IS FEMORAL MORPHOLOGY A RISK FACTOR?

Abstract

The aim of our study was to determine if the canal flare index of the proximal femur is a dependent factor in prosthetic failure after Austin Moore hemiarthroplasty.

We measured the canal flare index on A-P hip X-rays of 100 and 100 patients with failed and successful Austin Moore hemiarthroplasty respectively. We also measured the canal flare index of a control group of 100 patients without hip fractures. The canal flare index (CFI) is defined as the ratio of the width of the femoral canal at two levels: 20mm proximal to the centre of the lesser trochanter and the canal isthmus. Overall we reviewed 300 radiographs. The study group consisted of 68 males and 232 females. In the failed Austin Moore group there were 62 patients (62%) with loosening, 28 patients (28%) with dislocations and 10 patients (10%) with periprosthetic fractures. The canal flare index of the proximal femur was significantly higher in patients who had persistent thigh pain with radiological loosening in comparison the successful and control groups. (3.3 vs 2.6; 3.2 vs 2.7 respectively: p< 0.001). On the other hand patients with periprosthetic fractures had a lower canal flare index in comparison with the successful and control groups (2.1 vs 2.6; 2.1 vs 2.7 respectively: p< 0.001). However there was no differences in the CFI of patients with dislocations compared with successful (2.4 vs 2.6;p=0.1) and control groups (2.4 vs 2.7;p=0.2). This remained the same when controlled for age and sex in a logistic regression analysis.

Conclusion: The CFI can identify patients prone to persistent thigh pain who present as radiological loosening and to periprosthetic fractures and an alternative cemented prosthesis should be considered in this group of patients