Background: Disuse induces a rapid bone loss in adults; sedentarity is now recognised as a risk factor for osteoporosis. Hypoactivity or confinement also decrease bone mass in adults but their effects are largely unknown and only few animal models have been described. The hypodynamic chick confined in small cages has been recognised as a suitable model of bone loss during growth. However, the effects on the quality of the bone matrix have not been studied.
Methods: We have used 10 chickens of the rapidly growing strain 857K bred in a large enclosure (FREE group); 10 others were confined in small cages with little space to move around (HYPO group). They were sacrificed at 53 days and femurs and tibias were evaluated by microcomputed tomography (microCT) and histomorphometry on undecalcified bone sections. Sections (4 μm thick) were analysed by FTIR to see the effects on mineralisation and collagen.
Results: Hypoactivity had no effect on the length and diameter of the bones. Bone mass measured by microCT (trabecular bone volume and trabecular microarchitecture) was significantly reduced in the animals of the HYPO group. An increase in osteoid volume and surfaces was noted in the HYPO group. However, there was no alteration of the calcified volume as the osteoid thickness did not differ from control animals. FTIR showed a significant reduction of the mineral to matrix ratio (band 9001200 cm−1/Amides I band at 15901720 cm-1) in the HYPO group associated with an increase in the carbonate content and an increase in crystallinity indicating a poor quality of the mineral when compared with the FREE group. Collagen maturity (calculated from the ratio of intensity sub-bands ratio at 1660 and 1690 cm−1) was significantly reduced in the HYPO group.
Conclusions: The confined chicken represents a new method for the study of hypodynamia since disuse is not created by a surgical lesion nor a traumatic method such as bandaging or special cages. Animals have a reduced bone mass but also present an altered quality of the bone matrix which appears less mineralised and whose collagen contains less cross-links than control chicken as evidenced by FTIR.
Disclosure: The authors declared no competing interests.