RESUMEN
The aim of the present study is to analyze the generation of osteoporotic vertebral bone induced by malnutrition during growth period and analyze its effects for disc degeneration, based on biomechanical and histomorphometrical study. Mechanical and histomorphological characteristics of lumbar vertebral bones and discs of rats with calcium free diet (CFD) were detected and tracked by using high resolution in-vivo micro-computed tomography (in-vivo micro-CT), finite element (FE) and histological analysis. Twenty female Sprague-Dawley rats (6 weeks old, approximate weight 170g) were randomly divided into two groups (CFD group: 10, NOR group: 10). The CFD group was maintained on a refined calcium-controlled semisynthetic diet without added calcium, to induce osteoporosis. All lumbars (L1~L6) were scanned by using in vivo micro-CT with 35 micrometer resolution at 0, 4, 8 weeks to track the effects of CFD on the generation of osteoporosis. The results of morphological characteristics showed that BV/TV, Tb.Th, Tb.N in CFD group were significantly decreased over time (p<0.05), while those in NOR group were statistically increased over time (p<0.05) in the most lumbars (L1~L6). We also investigated the contrary tendency in Tb.Sp and SMI, compared to the above results in each group. In the simulated compression test using FE models, the structural effective modulus of CFD group significantly decreased (p<0.05), whereas that of NOR group was statistically increased, depending on the measuring time (p<0.05). The present study observed remarkable histological changes of nucleus pulposus and annulus fibrous by water loss in CFD group, compared with NOR group. These findings indicated that calcium insufficiency was the main factor in the generation of osteoporosis and it induced lumbar vertebral disc degeneration. This study is a valuable experiment to firstly evaluate osteoporotic vertebral bone and disc degeneration induced by malnutrition during growth period from a biomechanical and histomorphometrical point of view.