Biomechanical effects of the cephalad extent of laminotomy

The superior aspect of the unilateral laminotomy for bilateral decompression (ULb) typically corresponds with the superior ligamentum flavum attachment. Unlike lateral expansion, cranial expansion is considered a viable option to ensure sufficient decompression. The aim of this study was to investigate how cranial expansion affects the biomechanical stability in the lumbar spine.

Range of motion of eight fresh-frozen human cadaveric L1-L5 specimens was assessed in flexion-extension, lateral bending (LB), and axial rotation (AR). The workflow comprised testing in the intact state and after L3-4 ULb with sequential increase of the cephalad extent over 4 steps: (1)25% of the lamina height = insertion of Ligamentum Flavum, (2)50%, (3)75%, and (4)100%. Throughout all steps, constant mediolateral and caudal dimensions were maintained.

Even though within the tested sequences of the workflow an overall significant change was eminent for extension (p = 0.002), right LB (p = 0.030), and left AR (p = 0.009), no significant differences was detected when comparing their five different states pairwise. At L2-3, no overall significant changes were detected for all six motion directions (p ≥ 0.107).

ULb induced minor instabilities to the operated segment and no instability to the cranial adjacent segment. However, the absolute increase remained small under the tested conditions, suggesting that unilateral laminotomy is a safe technique at all cranial extents. With a bone-sparing laminotomy preferred, extending cranially appears to be a viable option to achieve sufficient decompression.