Thoracic and lumbar laminoplasty using a translaminar screw: morphometric study and technique

Abstract

The aim of this study was to describe a novel technique for laminoplasty in which translaminar screws are used in the thoracic and lumbar spine. The authors first performed a morphometric study in 20 control individuals using 3D reconstructed CT scans and spine simulation software to measure the lengths and diameters of the spaces available for translaminar screw placement from the T-1 to S-1. Based on the results of the morphometric study, the authors then attempted translaminar screw fixation in 5 patients (April 2007-July 2007) after en bloc laminectomy in the thoracic and lumbar regions. All patients had intradural lesions: 3 schwannomas, 1 cavernoma, and 1 arachnoid cyst. The morphometric study in control individuals revealed that the safe trajectories for simulated screws measured 25-30 mm in length and 8-11 mm in diameter in the thoracic region (T1-12) and 26-34 mm in length and 6-7 mm in diameter in the lumbosacral region (L1-S1). This morphometric and simulation study showed that translaminar screw placement would be possible in practice. Five patients underwent en bloc laminoplasty and translaminar screw fixation in which the screws measured 2.7 mm in diameter and 24 or 26 mm in length. Sixteen attempts at translaminar fixation were made in 8 vertebrae. Fourteen translaminar screws were successfully placed at the thoracic and lumbar levels. Two microplates had to be used because the laminae were too thin and narrow after further laminectomy with undercutting. There were no complications associated with the translaminar screws. The mean follow-up period was 14.5 months. There was no screw breakage or displacement. Solid osseous fusion was documented in 2 patients who underwent CT scanning 15 months postoperatively. The authors found that the laminoplasty and translaminar screw technique is feasible in the thoracic and lumbar regions, but further studies are needed to analyze the biomechanical effects and long-term outcomes in a large number of patients.