Changes in the Flexion-Relaxation Response After Percutaneous Endoscopic Lumbar Discectomy in Patients with Disc Herniation

BACKGROUND: Previous studies of percutaneous endoscopic lumbar discectomy (PELD) to treat lumbar disc herniation (LDH) have shown good clinical results. However, limited information has been reported regarding postoperative improvement in back muscle function. We aimed to determine whether changes in neuromuscular patterns, assessed using the flexion-relaxation phenomenon (FRP), could be observed after PELD. METHODS: A total of 30 patients participated in the present study. The patients' muscle functions were evaluated before and after PELD using surface electromyography and self-report measures. The evaluated action included 3 repetitions of a trunk flexion and extension movement. The association between the FRP measures and patient-reported outcomes was evaluated. RESULTS: At 4 weeks after PELD, the patients had significantly lower visual analog scale and Quebec Back Pain Disability Scale (QBPDS) scores and significantly increased gross range of motion. Also, we observed a reduction in erector spinae muscle activation at L3 in the maximum voluntary flexion phase. Normalized electromyographic root-mean-square values were significantly reduced in the maximum voluntary flexion phase and significantly increased in the extension phase. Postoperatively, 60% of the patients successfully achieved flexion-relaxation compared with 7% of the patients preoperatively. A significant correlation was found between the FRP measures and patient-reported outcomes, except for the Fear-Avoidance Beliefs Questionnaire scale. CONCLUSION: PELD for individuals with LDH appears to normalize paraspinal muscle activation during lumbar flexion-extension movement. The gross range of motion and disability-related limitations of physical activity also improved.