Changes of ultrasound velocity in children's tibial bone due to hypodynamia

Abstract

The ultrasound propagation velocity was measured in the medial surface of tibial bone of 58 children's shins, ages 3 to 16 years. The children had uninterrupted bed rest from 1 to 52 months because of osteochondropathies of femoral head. The average ultrasound velocity in tibia decreased with the term of hypodynamia, due to diminishing of the amount of hydroxyapatite in the bone. This insignificant relationship could not completely charaterize pathological changes in the bone. Therefore 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 (maximal 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 gave evidence about beginning bone adaption to the hypodynamia. Type 3 (maximal velocity in the distal epiphysis) was revealed for children after long term bed rest. Distribution of the velocity for type 4 (maximal velocity in the proximal epiphysis) was characteristic for sensible osteoporosis and indicated pathological changes in children's bones after very long term hypodynamia (from 3 to 4 years). The investigations 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 adaption, reversible, and pathological nonreversible changes. Such approach improves the results of ultrasound diagnostics of the bone tissue state.