ROTATIONAL STABILITY OF THE THORACOLUMBAR SPINE AFTER LAMINOTOMY FOR INTRAOPERATIVE SONOGRAPHY AND AFTER HEMILAMINECTOMY AND LAMINECTOMY - A COMPARATIVE EXPERIMENTAL-STUDY

Intraoperative spinal sonography to check whether fragments have been successfully repositioned requires enlargement of the natural interlam inar window to 8 x 10 mm. The present study was performed to measure a ny rotational instability caused by such a laminotomy and compare it w ith that resulting when the conventional methods of checking the spina l canal, e.g. hemilaminectomy and laminectomy, are applied. The invest igations were carried out in 10 human vertebral columns, in the area o f T-12, L-2 and L-4. Torsional loads of up to 20 Nm were applied to th e spines and axial rotations were recorded. Laminotomy, hemilaminectom y and laminectomy were done step by step. The loading-unloading cycles were achieved with initial axial rotation and decreasing torsional mo ment after measurement the dorsal manipulations. It was shown that int erlaminar fenestration causes a hardly measurable instability. A lamin otomy to 10 x 20 mm, allowing direct repositioning of the posterior ve rtebral surface, causes a 6% loss of stability. A significant decrease is caused by hemilaminectomy, with a 20% loss and by laminectomy, wit h 27% loss of rotational stability compared with the intact spine. Rot ational instability of the spine causes severe pain and often has to b e treated by spondylodesis. The present investigations show that the s pinal canal should not be checked by hemilaminectomy or laminectomy. F or this we now use intraoperative ultrasound.