LONG- TERM BONE REMODELING AROUND STABLE UNCEMENTED STEMS:A PROSPECTIVE DEXA STUDY 12 TO 22 YEARS POSTOPERATIVELY

Abstract

Introduction: Continous periprosthetic bone loss after uncemented THA may lead to proximal femoral atrophy and increase the risk for aseptic loosening or peripros-thetic femoral fracture in the long-term. Little is known about the extent and the pattern of bone remodeling around stable, straight uncemented stems after 15 years.

Patients and Methods: In a prospective longitudinal study, bone mineral density (BMD) was measured in 131 patients with 146 stable, uncemented, double- tapered, grit- blasted stems (CLS Spotorno, Zimmer, Warsaw, USA) using dual- energy x-ray absorptiometry (DEXA) after a mean of 12 years (range:10–15, t1) postoperatively. Patients were followed with radiographs and Harris hip scores (HHS), and a second and third DEXA were performed at a mean follow-up of 17 years (range: 15–20, t2) and 22 years (range: 20–25, t3) using the identical protocol.

Results: We obtained a complete prospective set of data of three consecutive DEXA measurements for 37 hips (32 patients, 14 male, 18 female). In all cases regular bone ongrowth did occur and on radiographic evaluation there were no signs of loosening and no significant change in periprosthetic bone formation. There was no case of severe bone loss and no case of diaphyseal cortical hypertrophy. We analyzed the differences in overall femoral BMD (netavg) and in BMD in zones 1–7 according Gruen. There was no significant change in overall netavg BMD for both male and female patients (p> 0,05) comparing t1 and t3. We found a significant change in periprosthetic BMD in zone 7 (−6,62%, p< 0,05) in male patients and in zones 1, 6 and 7 (−8,7%/−5,1%/−14,2%, p< 0,01/0,05/0,01) in female patients.

Discussion and Conclusion: The results of our study suggest that there are no clinically relevant changes in overall periprosthetic BMD around stable, uncemented straight stems in the long- term. However, continuous bone remodeling with slow but steady proximal bone loss occurs, predominantly in female patients. Once osseous integration is observed, stress shielding remains moderate and changes in periprosthetic BMD are limited to the metaphyseal region.