Biomechanical evaluation of destabilization following minimally invasive decompression for lumbar spinal canal stenosis
Authors: Hasegawa Kazuhiro , Kitahara Ko , Shimoda Haruka , Hara Toshiaki 
Published: March 2013

Object
This study aimed to clarify changes in segmental instability following a unilateral approach for microendoscopic posterior decompression and muscle-preserving interlaminar decompression compared with traditional procedures and destabilized models.

Methods
An ex vivo experiment was performed using 30 fresh frozen porcine functional spinal units (FSUs). Each intact specimen was initially tested for flexion-extension, lateral bending, and torsion up to 1.5° using a material testing system at an angular velocity of 0.1°/second under a preload of 70 N. Microendoscopic posterior decompression, muscle-preserving interlaminar decompression, bilateral medial facetectomy, left unilateral total facetectomy, and bilateral total facetectomy were then performed, followed by mechanical testing with the same loading conditions, in 6 randomized FSUs from each group. Stiffness and neutral zone were standardized by dividing the experimental values by the baseline values and were then compared among groups.

Results
Mean standardized stiffness values for all loading modes tended to decrease in the order of muscle-preserving interlaminar decompression, microendoscopic posterior decompression, bilateral medial facetectomy, left unilateral total facetectomy, and bilateral total facetectomy. In contrast, mean standardized neutral zone values tended to increase in the order of muscle-preserving interlaminar decompression, microendoscopic posterior decompression, bilateral medial facetectomy, left unilateral total facetectomy, and bilateral total facetectomy. In flexion, values for standardized stiffness following microendoscopic posterior decompression and muscle-preserving interlaminar decompression were higher and standardized neutral zone following microendoscopic posterior decompression and muscle-preserving interlaminar decompression were lower than the values following left unilateral total facetectomy and bilateral total facetectomy while there was no significant difference among bilateral medial facetectomy, left unilateral total facetectomy, and bilateral total facetectomy. Values of standardized stiffness and standardized neutral zone in left torsion following microendoscopic posterior decompression, muscle-preserving interlaminar decompression, and bilateral medial facetectomy were equally superior to values of the destabilization models (left unilateral total facetectomy and bilateral total facetectomy). Except for standardized stiffness in left bending, the values of the parameters for each bending tended to be the same as in the other loading modes.

Conclusions
The present biomechanical study showed that overall stability of the FSUs was maintained following microendoscopic posterior decompression, muscle-preserving interlaminar decompression, and bilateral medial facetectomy compared with the destabilization models of left unilateral total facetectomy or bilateral total facetectomy. Comparison of the postoperative stability following microendoscopic posterior decompression, muscle-preserving interlaminar decompression, and bilateral medial facetectomy revealed that muscle-preserving interlaminar decompression tended to be superior, followed by microendoscopic posterior decompression and bilateral medial facetectomy.