The impact of immobilization and strength exercise strategy to bone change: An animal study

The impact of immobilization and strength exercise strategy to bone change: An animal study

S116 ABSTRACTS / Bone 43 (2008) S111–S126 S16 The impact of immobilization and strength exercise strategy to bone change: An animal study Tachung Le...

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ABSTRACTS / Bone 43 (2008) S111–S126

S16 The impact of immobilization and strength exercise strategy to bone change: An animal study Tachung Lee 1, Chingyen Lin 2, Teenmeei Wang 3 1 Department of Rehabilitation, Chaili General Hospital, Tainan, Taiwan 2 Department of Dentistry, Yong-Kang Veterans Hospital, Tainan, Taiwan 3 Department of Dental Laboratory Technology, Central Taiwan University of Science and Technology, Taichung, Taiwan Objective: The aim of this study is to evaluate whether an immobilization model can be used in studies of the mechanism of structural adaptation to mechanical usage. Methods: Six-week-old male rats were subjected to right hindlimb immobilization or served as control for 0, 4, 6, 8, 12 or 24 weeks. They were double-labeled with bone markers prior to sacrifice. The right hindlimb was immobilized by sciatic nerve denervation and considered unloaded, while the left hindlimb was overloaded during ambulation, such as strengthening exercise. Static and dynamic histormorphometric studies were performed on 20-μm-thick Villanueva stained, undercalcified sections of the proximal tibia metaphysis and the tibia shaft. Results: In the unloaded limb, immobilization induced cancellous and cortical bone loss. The bone loss was accompanied by poorer trabecular architecture. Unloading shut off nearly both peri-osteal bone formation and accelerated bone marrow expansion. In the overloaded limb, significant changes occurred in proximal tibial metaphyses: trabecular area increased, trabecular number increased, and trabecular separation decreased. A significant increase in mineral apposition rate was found only at 4 weeks of overloading. Significant decrease in both eroded and labeled bone surfaces occurred at all time periods. These histomorphometric changes indicated that increased cancellous bone mass was caused by an increase in bone formation activity (i.e., increase in mineral apposition rate) and a decrease in remodeling space (i.e., decrease in bone eroded surface). Although cortical bone mass was unchanged, increased peri-osteal bone formation activity (i.e., increases in mineral apposition and bone formation rates) was detectable. Conclusions: These findings indicate that the rat skeleton can quickly adapt to mechanical usage. Therefore, the one-legged immobilization model can be used in studies of the mechanism of structural adaptation to mechanical usage. doi:10.1016/j.bone.2008.07.147

S17 Torsional properties of cortical bone in longitudinal and transverse directions Mohsen Sadeghi-Mehr, Ahmad Partovi-Miran Mechanical Engineering Department, Engineering Faculty, Bu-ali Sina University, Hamedan, Iran Objective: This study was conducted in order to investigate the effect of direction on the torsional properties of the cortical bone. Methods: Sixty femoral bovine bone specimens in transverse (n = 30) and longitudinal (n = 30) directions were prepared from the medial part of the fresh femoral shaft of 20 cows which were nearly at the age of 18 months and weight range of 500 kg–600 kg at the time of massacre. All specimens throughout preparation were kept moist with normal saline solution and both ends of specimens were potted in a low melting polyester resin into holding cups. After preparation each specimen was wrapped in normal saline soaked gauze and stored in the freezer at −20 °C prior to testing. Twenty-four h before testing specimens in transverse and longitudinal directions, they were thawed at room temperature in saline solution and were divided in four

groups, separately. During testing the specimens were kept wet using normal saline solution. Torsion tests were conducted on all specimens with angular speeds equal to 1°S− 1, 1.5°S− 1, 1.75°S− 1 and 2°S− 1. Results: Statistical analysis (Duncans method) showed that there is no significant difference in fracture torque, twisting angle and shear modulus of elasticity with the angular speed (p b 0.05) but significant difference exists in torsional strength between longitudinal and transverse specimens (p b 0.05). Imposed torque vs. angle of rotation at the time of fracture showed that the cortical bone is approximately 25% stronger in longitudinal direction for the same angle of rotation than transverse direction. The mean fracture torque were 1.38 (S.D. = 0.37) N-m and 0.863 (S.D. = 0.153) N-m for longitudinal and transverse specimens, respectively. And also the mean twisting angles at the time of fracture were 16 (S.D. = 3.07) and 9.3 (S.D. = 2.15) for longitudinal and transverse specimens respectively. The mean modulus of elasticity in shear for longitudinal specimens was 5.384 (S.D. = 0.225) GPa and for transverse specimens was 3.915 (S.D. = 0.00). Conclusion: This orthotropic property of the cortical bone can be explained by the direction of collagen fibers in the bone matrix, which is almost in the longitudinal direction. The shape of the fractured section showed that the fibers are broken due to tensile stress induced by torsion. doi:10.1016/j.bone.2008.07.148

S18 Osteoporotic change in subchondral bone in pMNX guinea pig OA model Susanne Wang 1, Mircia Dumitriu 2, Ryan H. Tam 3, Marc D. Grynpas 1 1 MDS Pharma Services, Bothell, USA 2 University of Toronto, Toronto, Canada 3 Shiley Center for Orthopaedic Research and Education, La Jolla, USA Objective: The present study investigates osteoporotic changes in guinea pig OA model from time 0 to 10, 20, 30, 90, and 180 days after surgery. Key bone characteristics such as bone density, sub-chondral trabecular bone architecture, bone turnover, mechanical and material properties of bone, and bone mineralization are tracked and correlated to cartilage and its biochemistry changes. Methods: Sixty guinea pigs were used in this study. Fifty 3-month old male Dunkin Hartley guinea pigs underwent partial medial meniscectomy (pMNX) in the right knee. Ten animals were euthanized at 0, 10 and 20 days, 1, 3, and 6 months time points post-surgery. OA cartilage morphological changes were evaluated by Mankin grading. Cartilage biochemistry, bone mineral density (BMD), subchondral bone plate thickness, bone histomorphometry and osteophyte formation were studied. Results: The animals underwent partial medial meniscectomy displayed significantly higher degree of cartilage degeneration, increased subchondral bone turnover, early decrease followed by an increase in bone mineral density and bone volume. Subchondral bone changes include: calcified cartilage thickening, changes in subchondral bone plate thickness and mineralization, and changes in trabecular bone remodeling. Conclusion: Significant osteoporotic changes in the subchondral bone are observed in the early stage of the OA development in a pMNX guinea pig model. This close correlation between subchondral bone changes and arthritic progression in the joint suggests that osteoporotic changes play a key and integral part in the early stage of OA pathogenesis. doi:10.1016/j.bone.2008.07.149