Dual energy X-ray absorptiometry analysis of femoral remodelling after Exeter total hip replacement

We report a 2 to 6-year cross sectional study using dual energy X-ray absorptiometry (DXA) to evaluate femoral bone mineral density (BMD) Changes after Exeter total hip arthroplasty (THA). A coordinate technique was used to precisely position regions of interest within the bone cortex and corresponding to periprosthetic Gruen zones. 18 patients (2-4 year N= 9; 5-6 year N=9) were analysed. Ten contralateral hips were analysed forming the control group. At 2 to 4 years after surgery, a relative loss of 13% BMD was observed in Gruen zones 1 and 7, increasing to 22.5% loss at 5 to 6 years. In the middle and distal Gruen zones at 2 to 4 years, relatively less bone was lost, and by 5 to 6 years a 10% relative increase in BMD had occurred compared to the control group. This study of the Exeter stem indicated that stress shielding and loss of BMD continued in the proximal femur in the medium term, but positive bone remodelling occurred in the middle and distal Gruen zones. This study therefore supports the design rationale of the Exeter stem and confirms the favourable effects on bone loading observed in radiographic studies. Longitudinal densitometric studies are indicated to confirm the remodelling characteristics of the Exeter stem and enable comparison with other stem designs. The investigation was performed at the Department of Orthopaedic Surgery, Royal Adelaide Hospital, North Terrace, Adelaide, SA 5000, Australia.