Longitudinal study of bone mineral content in the lumbar spine, the forearm and the lower extremities after spinal cord injury.

Bone mineral content (BMC) of the lumbar spine, femoral neck and shaft, and proximal tibia was measured by dual photon absorptiometry in six men and two women after traumatic spinal cord injuries. In six of these patients, BMC of the distal forearm was measured as well. The patients were 18-49 years old at injury and had complete motor lesions from C7 to L1. All but one had some spasticity, and they all used a wheelchair. The initial BMC measurements were carried out from 9-167 days (median 43) post-injury and followed up by 5-13 (median 8) measurements up to 31-53 months (median 41) after the injury. BMC of the lumbar spine and distal forearm remained nearly unchanged in the whole period, and the measurements were within the normal range, except for the lumbar spine when Harrington rods in the scanned area induced high BMC values. In the lower extremities the BMC decreased after injury. New steady-state levels for BMC were reached at 2 years post-injury for the proximal tibia and the femoral neck at 40-50% and 60-70% respectively of normal values. For the femoral shaft the decrease in BMC was more slow and it seems that a steady-state was not reached within our observation period for several of the patients. This longitudinal study indicates, in agreement with a previous cross-sectional study, that normal muscle function and load bearing is necessary to prevent bone loss.