Postoperative Paraspinal Muscles Assessment After Endoscopic Stenosis Lumbar Decompression: Magnetic Resonance Imaging Study

Background Context Conventional open lumbar decompression is a widely accepted procedure for degenerative lumbar disease. However, it is associated with morbidity due to damage to the paraspinal muscles and posterior ligamentous complex. Endoscopic spine surgery (ESS) is considered the least invasive type of spine surgery in modern times and was developed to minimize the iatrogenic injury to the paraspinal muscles.

Purpose Many studies are reported to estimate the paraspinal muscle damage after an open or minimal invasive spine surgery by radiological methods (magnetic resonance imaging [MRI] and computed tomography], biochemistry (creatinine phosphokinase level), or electrophysiology (electoneuromyography). The objectives of this study were to assess paraspinal muscles changes after lumbar endoscopic unilateral laminotomy with bilateral decompression (LE-ULBD) based on preoperative and 6-month postoperative MRIs.

Patient Sample We studied 159 consecutive patients with lumbar degenerative disease who underwent LE-ULBD at a spine specialty hospital from 2018 to 2019.

Study Design The current study was a single-center, single-surgeon, retrospective case study.

Outcome Measures Changes of paraspinal muscles after LE-ULBD measured on lumbar MRI.

Methods Postoperative paraspinal muscles changes are evaluated on a picture archiving and communication system by measuring the cross-sectional area (CSA) of multifidus and erector spinae muscles along with the fatty infiltration of muscle on Kjaer’s scale at the level of surgery on the ipsilateral and contralateral sides on T1W image. Correlations between imaging and visual analog scale (VAS) score for back, Oswestry Disability Index (ODI), and MacNab’s criteria were examined in the preoperative and postoperative periods.

Results Of the 159 patients included, 120 underwent a single level procedure and 39 a multilevel procedure. For single-level LE-ULBD group, mean (SD) preoperative, postoperative, and final follow-up VAS score (7.83 [1.37], 3.15 [0.67] and 2.19 [0.88]; P < 0.001) and ODI (74.09 [7.18], 27.88 [4.40], and 23.88 [4.56]; P < 0.001) improved significantly. Based on MacNab’s criteria, the clinical result was excellent in 37 patients, good in 78 patients, and fair in 5 patients. For the multilevel LE-ULBD group, the mean (SD) preoperative, postoperative, and final follow-up VAS score (7.84 [1.38], 3.50 [0.60],and 2.44 [0.79]; P < 0.001) and ODI (74.1 [7.72], 31.30 [4.46], and 24.90 [4.75]; P < 0.001) also improved significantly . Based on MacNab’s criteria, the clinical result was excellent in 6 patients, good in 31 patients, and fair in 2 patients.

The functional CSA of paraspinal muscles for both groups showed no significant difference in the 6-month follow-up MRI. The fatty infiltration of paraspinal muscles significantly improved from 0.77 to 0.59 (P < 0.05) for the single level LE-ULBD group but not for the multilevel LE-ULBD group (P = 0.320). The mean dural sac CSA increased significantly for both groups (P < 0.001).

Conclusion Adequate neural decompression can be achieved with the preservation of paraspinal muscles after an ESS. Preservation of the paraspinal muscles along with the posterior ligamentous complex improves the stability of motion segment in the postoperative period, which ultimately results in better patient outcomes in related to postoperative pain and rehabilitation.

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