Ultrasound sector scanning used to define changes in muscle configuration

Dynamic configurational changes in the rectus femoris muscle were examined using a real time ultrasound sector scanner in ten normal subjects. The angle of passive knee flexion was varied as transverse ultrasound scanning was performed at the mid-transverse thigh. Configurational changes in the rectus femoris were computed from a traced outline of the muscle and the geometric center of the mass was calculated at all degrees of knee flexion. The geometric center of the mass varied with knee position. The anterioposterior dimensions and cross sectional areas of the rectus femoris and vastus intermedius remained constant, however, despite changes in knee position. The pattern of change observed was reproducible and reflects consistent changes in muscle configuration. The technique and instrumentation should have value for non-invasive dynamic and static observation of individual muscles.