Chondrosis of the disc - risk factor for osteoporotic vertebral fractures (biomechanical analysis).

Based on biomechanical analysis, we present an until now unrecognised new view on pathological interactive relations in basic functional motor segments of the spine (vertebra - disc - vertebra), elevating the risk of osteoporotic vertebral fractures. They are classified as follows: 1. Degenerative alterations of intervertebral disc (chondrosis); 1a) decrease of intervertebral disc viscoelasticity; 1b) increase of compressive and tensile stress in the intervertebral disc. Loading the spine increases the compressive and tensile stress in the disc, afflicted by chondrosis, beyond physiological values. This increase conditions the non-physiological elevation of reaction compression forces in adjacent vertebrae, representing a fracture risk for endplates of these vertebrae. 2. Osteoporosis of vertebrae; 2a) decrease of vertebra elasticity and strength; 2b) phenomenon of local elevated compressive stress in the vertebra fracture site. In the vertebral body endplate infraction or fracture site develop a locus minoris of resistance and it contributes to the progression of breaking the vertebra and its whole compression by loading the spine with compressive force. With regard to the fact that above-mentioned risk factors are influenceable, we suggest preventive measures.