Microscopic extra-laminar sequestrectomy (MELS) for the treatment of hidden zone lumbar disc herniation: report of the surgical technique, patient selection, and clinical outcomes

Background The area which located at the medial pedicle, posterior vertebral body and ventral hemilamina is defined as the hidden zone. Surgical management of hidden zone lumbar disc herniation (HZLDH) is technically challenging due to its difficult surgical exposure. The conventional interlaminar approach harbors the potential risk of post-surgical instability, while other approaches consist of complicated procedures with a steep learning curve and prolonged operation time. Objective To introduce microscopic extra-laminar sequestrectomy (MELS) technique for treatment of hidden zone lumbar disc herniation and present clinical outcomes. Methods Between Jan 2016 to Jan 2018, twenty one patients (13 males) with HZLDH were enrolled in this study. All patients underwent MELS (19 patients underwent sequestrectomy only, 2 patients underwent an additional inferior discectomy). The nerve root and fragment were visually exposed using MELS. The operation duration, blood loss, intra- and postoperative complications, and recurrences were recorded. The Visual Analog Scale (VAS), Oswestry Disability Index (ODI), and the modified MacNab criteria were used to evaluate clinical outcomes. Postoperative stability was evaluated both radiologically and clinically. Results The mean follow-up period was 20.95 [+ or -] 2.09 (18-24) months. The mean operation time was 32.43 [+ or -] 7.19 min and the mean blood loss was 25.52 [+ or -] 5.37 ml. All patients showed complete neurological symptom relief after surgery. The VAS and ODI score were significantly improved at the final follow-up compared to those before operation (7.88 [+ or -] 0.70 vs 0.10 [+ or -] 0.30, 59.24 [+ or -] 10.83 vs 11.29 [+ or -] 3.59, respectively, p < 0.05). Seventeen patients (81%) obtained an "excellent" outcome and the remaining four (19%) patients obtained a "good" outcome based the MacNab criteria. One patient suffered reherniation at the same level one year after the initial surgery and underwent a transforaminal endoscopic discectomy. No major complications and postoperative instability were observed. Conclusions Our observation suggest that MELS is safe and effective in the management of HZLDH. Due to its relative simplicity, it comprises a flat surgical learning curve and shorter operation duration, and overall results in reduced disturbance to lumbar stability. Keywords: Hidden zone, Lumbar disc herniation, Microscopic sequestrectomy, Extra-laminar approach