CHANGES OF ULTRASOUND VELOCITY IN CHILDRENS TIBIAL BONE DUE TO HYPODYNAMIA

The ultrasound propagation velocity was measured in the medial surface of tibial bone of 58 children's shins, ages 3 to 16 years. The childr en had uninterrupted bed rest from 1 to 52 months because of osteochon dropathies of femoral head. The average ultrasound velocity in tibia d ecreased with the term of hypodynamia, due to diminishing of the amoun t of hydroxyapatite in the bone. This insignificant relationship could not completely characterize pathological changes in the bone. Therefo re the bone acoustical nonuniformity was analyzed by approximation of the experimental data by polynomial equations. Four different types of ultrasound velocity distribution along the bone were found. Type 1 (m aximal velocity in the midpart of diaphysis) was characteristic after short term hypodynamia, when the adaption of the bone remained to the normal loading conditions. For type 2 a characteristic diminishing of the ultrasound velocity in the midpart of diaphysis was found, which g ave evidence about beginning bone adaption ro the hypodynamia. Type 3 (maximal velocity in the distal epiphysis) was revealed for children a fter long term bed rest. Distribution of the velocity for type 4 (maxi mal velocity in the proximal epiphysis) was characteristic for sensibl e osteoporosis and indicated pathological changes in children's bones after very long term hypodynamia (from 3 to 4 years). The investigatio ns of the ultrasound velocity distribution nonuniformity in tibia from the point of view of functional adaptation showed that there were at least three stages of response of bone tissue to hypodynamia: normal a daption, reversible, and pathological nonreversible changes. Such appr oach improves the results of ultrasound diagnostics of the bone tissue state.