Biomechanical performance of weight-bearing bone after remodeling in a rabbit model of disuse osteoporosis / 中国组织工程研究

ABSTRACT

BACKGROUND: Disuse osteoporosis is bone mass loss caused by muscular inactivity and reduced weight bearing. OBJECTIVE: To observe bone structure and mineral matter content as well as bone biomechanicai performance change at different time points during the development of disuse osteoporosis. DESIGN, TIME AND SETTING: The present randomized, controlled, and self-controlled animal experimental was performed in the General Hospital of Tianjin Medical University between September and November 2003. MATERIALS A total of 55 male Japanese rabbits, aged 8 months, weighing 2.5-3.0 kg were enrolled for this study. METHODS: The right hind limbs of 50 randomly selected rabbits were immobilized by cast (experimental sides). The corresponding left hind limbs were untouched (control sides). The remaining 5 rabbits were raised for 3 months, and their bilateral hind limbs were used for controls. Ten rabbits were sacrificed by intravenous injection of air at each time point (2, 4, 6, 8, and 12 weeks after immobilization). MAIN OUTCOME MEASURES: Mechanical test was performed on bilateral tibiofibula for determination of calcium content. Hematoxylin-eosin staining and Masson staining of bilateral metatarsal bones were performed for histological observation. RESULTS: There was significant difference in indices of tibiofibula on the experimental sides, including maximum loading, elastic modulus, and calcium content among different time points, while significant difference also existed between the experimental side and the blank controls (P＜0.05). There was no significant difference in above-mentioned indices between the control side and blank controls as well as between control sides (P＞0.05). The experimental side limbs exhibited thinned cortical bone, increased pores, sparse and fine trabecular bone with several fragmentations, expanded medullary cavity, and increased osteoblasts. Masson staining results demonstrated that with disuse time going, collagen was decreasingly formed. The control side and blank control limbs showed thickened metatarsal bone and cortical bone, a few pores, and compactly arranged trabecular bone with normal structure. CONCLUSION: During the development of disuse osteoporosis, calcium content and the entire biomechanical performance are gradually and slowly decreased to accommodate the stress environment and functional status.