The shape of vertebral bodies and femoral necks in relation to activity.

Abstract

The shape of children's bones is affected by the stress of muscular activity and weight-bearing. In children unable to walk, Gooding and Neuhauser (6) described increased height of the vertebral bodies, while others (1, 9–11, 13) reported coxa valga. Girdany and Danowski (5) described both features in children with advanced muscular dystrophy. The purpose of the present study has been to quantitate the above features and assess their probable relationship to physical activity in a group of mentally retarded children. Material and Methods One of us (W. A. Z.) selected a group of physically inactive mentally retarded children and matched them as closely as possible with physically active mentally retarded children of the same age. For the purposes of this study, anteroposterior and lateral films of the lumbar spine and anteroposterior films of the pelvis were obtained in 129 patients aged three to eighteen years. Lateral radiographs of the pelvis allowed an approximate calculation of the degree of ante version of the femoral neck in 55 patients. Measurements were made by one of us (C. S. H.) prior to any knowledge of the clinical diagnosis or degree of physical activity of these children. There was no concern about the possible genetic effects of the x radiation since none of these patients are expected to reproduce. All films were taken at a standard 40-inch distance, since available equipment did not allow a greater tube-film distance. Geometric distortion thus was present, yet constant. Since the retarded patients were unable to co-operate and difficult to position, true lateral films of the spine and true anatomical positioning of the extremities were not always obtained. Diameters of each lumbar vertebral body were measured in both anteroposterior and lateral projections. In the lateral view, the superoinferior diameter was measured midway between the anterior and posterior margins of the vertebral body, except in a few cases where the vertebral plates “peaked” posterior to this point; in these cases, the maximum measurement was used. The anteroposterior diameter was measured midway between and parallel to the superior and inferior vertebral plates. When necessary, approximate correction for angulation in the lateral film was made, as shown in Figures 1, A and B, allowing an accuracy within 1 mm of the true figure. The ratio of Superoinferior Diameter/ Anteroposterior Diameter provided a height index (H.I.) for each vertebral body, calculated to two decimal places. (For simplicity, in the accompanying figures this ratio is shown to only one decimal point.) The mean height index was then obtained from the average of the five lumbar vertebrae. The angle between the femoral neck and shaft was measured at the intersection of a line drawn through the axis of the femoral shaft and another line through the axis of the femoral neck. If the femoral head was at all eccentric in position, this line did not pass through the center of the femoral head.