O1342 THE LONG TERM CLINICAL RELEVANCE OF CALCAR ATROPHY DUE TO STRESS SHIELDING IN THA. A TEN YEAR PROSPECTIVE RANDOMISED STUDY

Aim: To evaluate long term effects of stress shieldieng phenomenon after cementless total hip arthroplasty. Materials-Methods: 80 female pts with OA were randomly allocated in 4 groups according to the type of the cementless stem which was primarily implanted (A-Zwey-Muller,B-Corail,C- Optifix,DAutophor900S). BMD changes of the operated hip (in seven zones), of the operated, contralateral normal hip and of the Lumbar spine were measured pre-op, at 2, 8 and 12 months and every year thereafter. Results: At ten years, 72 pts were available for follow up, all with satisfactory clinical and radiological results with no evidence of polyethylene wear or endosteal lysis. In all groups, the greatest reduction of BMD (calcar atrophyzone 7) was observed at the 2nd post-op year (A:24%, B:8%, C:14.8%, D:18.5%). In all groups, the greatest increase (zone 4) of BMD was also observed at the 2nd post-op year (A7%, B2%, C2.5%, D6.3%). In all groups a similar pattern of slow but progressive recovery of bone mineral density changes after the 3rd year was observed in both zones, approaching baseline values at 10 years in all groups. Preoperative lumbar BMD (osteopenia), body weight, sex and height were not statisticaly correlated to calcar atrophy. Conclusions: We suggest that the clinical and theoretical relevance of stress shielding phenomenon in total hip replacement has been overestimated in the literature