A biomechanical study.Objective:
How much of the facet joint and the pars interarticularis (PI) can be removed in microendoscopic lateral decompression (MELD) for lumbar foraminal stenosis (LFS)?Summary of Background Data:
MELD is a surgical modality for patients with LFS. In severe degenerative cases, unilateral facet joint resection or unilateral removal of the lateral part of the PI are sometimes needed to decompress the nerve root adequately.Methods:
Twelve human lumbar motion segments were tested according to the following loading protocol: axial compression, flexion, extension, lateral bending to the right and left, and axial rotation to the right and left. This loading protocol was applied to each motion segment after MELD in 2 experiments: (1) unilateral graded facetectomy was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1; (2) unilateral removal of the lateral part of the PI was performed in stages of 25%, 50%, 75%, and 100% using 3 segments of L3/L4 and 3 segments of L5/S1. The relative stiffness of each motion segments was determined each time.Results:
(1) Unilateral facet joint resection of >75% can lead to a significant reduction in stiffness in axial rotation at both L3/L4 and L5/S1. (2) Unilateral removal of 75% of the lateral part of the PI can lead to significant reduction in stiffness in right and left rotation at L3/L4 and in left rotation at L5/S1. (3) Unilateral removal of 100% of the lateral part of the PI can lead to a significant reduction in stiffness in right axial rotation at L5/S1.Conclusions:
It would seem judicious to remove no >50% of the facet joint or the lateral part of the PI in order to prevent postoperative instability when using MELD for LFS.