Mobility of the lower lumbar spine after posterolateral fusion determined by roentgen stereophotogrammetric analysis.

To determine the time-table for intervertebral stabilization after posterolateral fusion without osteosynthesis in the lower lumbar spine, 11 patients with no previous spinal surgery and with fusion due to spondylolysisolisthesis Grade 1 to 2 or lumbar disc disorder/facet joint arthrosis were examined by roentgen stereophotogrammetric analysis (RSA) in supine and erect positions, and by conventional radiography for 1 year after surgery. In eight patients with osseous fusion radiographically, the sagittal and the vertical translations between the fused vertebral segments began to decrease after 3 to 6 months. However, the time for rigid fusion as defined by RSA varied between 3 months and 1 year, and in four patients sagittal/vertical translations of mostly less than 1 mm still persisted at 1 year postoperatively. In three patients with poor fusion radiographically, no rigid fusion as defined by RSA was obtained. Sagittal/vertical translations of 1 to 10 mm persisted at 1 year postoperatively in these patients. The preoperative pain disappeared in all patients except in one who had osseous fusion radiographically but persisting translations after 1 year.