Biomechanical effect of graded minimal-invasive decompression procedures on lumbar spinal stability.

INTRODUCTION: Decompression surgery represents the standard operative treatment for lumbar spinal stenosis, but this procedure is often combined with fusion surgery. It is still discussed whether minimal-invasive decompression procedures are sufficient and if they compromise spinal stability as well. The aim of this study was to analyze the effects of different minimal-invasive decompression procedures on the range of motion (ROM) of the decompressed and adjacent segments under preload conditions.

METHODS: Fourteen fresh frozen human cadaver lumbar spines (L2-L5) were tested in a spinal testing device with a moment of 7.5 N m in flexion/extension, lateral bending and rotation with and without a preload. The ROM of the decompressed segment L3/4 and the adjacent segments L2/L3 and L4/L5 was measured intact and after creating a gradual defect with resection of the interspinous ligament (ISL), bilateral undercutting decompression, detachment of the supraspinous ligament (SSL) and bilateral medial facetectomy.

RESULTS: The resection of the ISL had no significant effect on the ROM of all segments. Undercutting decompression showed a significant increase in the ROM of all segments during flexion/extension and lateral bending. The detachment of the SSL caused a significant increase of ROM during flexion/extension in the instrumented and adjacent segments. After bilateral medial facetectomy, a decrease of ROM was observed in all directions of motion except flexion/extension with preload.

CONCLUSIONS: The results support minimal-invasive procedures for the preservation of spinal stability. Therefore, surgeons can determine which grade of decompression procedure can be performed in the individual patient without requiring additional fusion to maintain spinal stability.