Mobility in the lumbosacral spine after fusion studied with the aid of roentgen stereophotogrammetry.

Twelve cases operated upon with fusion in the lumbosacral spine were studied with a roentgen stereophotogrammetric method. With this method the movements in the area supposed to be fused can be studied with high accuracy in 3 dimensions. The precision is 0.3 degrees for the rotation about the x-axis (transversal axis), 0.2 degrees for the rotation about the y-axis (longitudinal axis), and 0.1 degrees for that about the z-axis (sagittal axis) and of the magnitude of 0.1 mm for the translations. It was found that the possible stabilization of a fusion takes place within 180 days. The supposed gain of internal fixation with a sacral bar device was not verified. It was recommended that the supine and erect standing positions should be investigated and compared with this method and that standing with flexion should be added as soon as the healing process is supposed not to be injured by flexion movements.