Center of Gravity and Radiographic Posture Analysis: A Preliminary Review of Adult Volunteers and Adult Patients Affected by Scoliosis

In Brief Study Design. This is a prospective radiographic and force plate analysis involving adult volunteer and patients with scoliosis. Objective. To assess accurately the center of pressure in standing volunteers and patients with scoliosis, and correlate these finding with radiographic data. Summary of Background Data. A simple and commonly applied parameter of global balance is the plumbline offset. This radiographic measurement refers to the center of C2 (or C7) drawn vertically downward. Although this measurement is simple, it may not accurately reflect the balance of the spine. Methods. This study included adult volunteers (n = 41) and patients with scoliosis (n = 45). Full-length, freestanding spine radiographs were obtained with subjects on a force plate. Simultaneous assessment of the radiologic spinal posture and the floor projection of the center of pressure (gravity line) was possible. The latter was projected on the full spine images and correlated to common radiographic parameters. Results. The position of the gravity line differed significantly from the plumbline in frontal and sagittal planes (P < 0.001). This difference was maintained in both study populations. The mean frontal plane alignment of the gravity line was consistently to the right of the plumbline. The mean sagittal plane alignment of the gravity in relation to the plumbline revealed an offset anteriorly. Conclusions. The data analysis of offsets between the gravity line and radiographic parameters revealed a frontal plane mean displacement of the gravity line to the right. In the sagittal plane, a highly significant lack of correlation between the gravity line and plumbline was noted. The plumbline represents a common and convenient visual display of apparent sagittal plane imbalance, but its value as a marker of true postural balance must be questioned. This study involves a radiographic and center of pressure analysis in a group of volunteers and adult patients with scoliosis. The hypothesis was that the commonly used plumbline measurement does not accurately reflect the center of pressure (and, thus, center of gravity) in a standing subject. The data from this investigation confirmed a poor correlation between the plumbline (from C7) and the gravity line (obtained from force plate measurements) in frontal and sagittal planes for volunteers and scoliotic groups. The center of the femoral heads had a significantly better correlation with the gravity line. Significant age-related changes in radiographic-gravity line offsets were noted.