Abstract
Introduction: Little is known about periacetabular bone remodelling and stress shielding after total hip arthroplasty.
Aim: To analyse prospectively the bone changes around an acetabular component using high resolution computerised tomography (CT).
Methods: A sequential CT scan mode was used (140kv and 206mA, table feed 10mm, slide thickness 2mm). Special software (IMPACT-HIP, VAMP, Germany) was used for bone density (BD) measurements. Parameters of the assessment were: BD of cancellous, cortical and full bone, bone-implant-contact area, bone-area. Twenty patients with degenerative osteoarthrosis (20 hips) were operated on using an uncemented, pressfit, acetabular component and alumina-alumina pairing (Cerafit, Ceraver Osteal, France). The average age of patients was 57 years. CT examinations were performed after two weeks and again one year after the operation. Measurement of BD of the contralateral hip was conducted as a control.
Results: Cancellous bone showed a decrease of BD ranging from 20% to 23% in the caudal portion of the periacetabular area and a decrease ranging from 8% to 12% in the cranial portion. The cortical BD increased 6% at the cranial portion of the periacetabular area. Only slight changes of cortical BD were observed at the caudal portion.
Conclusions: The study showed a significant atrophy of the cancellous bone around the cup, but limited changes of the cortical bone. Periacetabular stress shielding is a little recognised phenomenon which requires further investigations. The method used in the present study allowed analysis of bone changes by 3D-viewing of the acetabulum and by separation of cancellous and cortical bone.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
