THE EFFECT OF THE REACTIVE ZONE ON THE MECHANICAL BEHAVIOR OF THE TRABECULAR BONE IN THE OSTEONECROSIS OF THE FEMORAL HEAD
Ye-yeon Won*, Myung-hyun Pak* and Seung-hyun Yoo**
*Dept. of Orthopaedic Surgery, School of Medicine, Ajou University, San 5 Wonchun-dong Paldal-gu, Suwon, 442-749, Korea, Tel +82-31-219-5223, E-mail: thrtkr@madang.ajou.ac.kr
**Division of Mechanical and Industrial Engineering, School of Engineering, Ajou University

The osteonecrotic femoral head has three zones (normal, reactive and necrotic zone) with different mechanical properties. We investigate the mechanical effect of the reactive zone on the adjacent trabecular bone.

After coring two cylindrical bone specimens from the normal and osteonecrotic femoral head, each specimens were scanned using a micro-CT and divided into three volumes of interest respectively. We performed a finite element analysis and a histomorphometry.

Histomorphometrically, there were an evidence for suggesting structural enhancement in the reactive zone. The stresses were concentrated in necrotic and normal zone but not in reactive zone of the necrotic head, while the stresses of the normal head were uniformly distributed.

We can hypothesize that the stress concentration by the reactive zone in the osteonecrosis of femoral head cause an adaptive remodeling of trabeculae in the normal zone, while it causes micro-fractures of trabeculae in the necrotic zone without following adaptive remodeling and decrease the stiffness of the necrotic zone by accumulation of micro-fracture and finally make a gross fracture line.