Unilateral Biportal Endoscopy for L5-S1 Extraforaminal Stenosis (Far Out Syndrome) – Technical note With Literature Review

Introduction: Extraforaminal stenosis in L5–S1, or far-out syndrome (FOS), is defined as L5 nerve compression by the transverse process (TP) of the L5 and the ala of the sacrum and disc bulging with/without osteophytes and/or the thickened lumbosacral and extraforaminal ligament. This study aims to describe the unilateral biportal endoscopic (UBE) decompression technique for extraforaminal stenosis at L5–S1 or far-out syndrome and evaluate its clinical results with a literature review. Case Report: A 44-year-old male presented with severe right sharp shooting pain in the buttock, thigh, leg, foot, and/or toes with numbness in the foot and toes (Visual Analog Scale [VAS] 8/10) for six months. Her pain aggravated when bending forward and performing daily routine activities. He also complained of exaggeration of pain in daily regular activities. On physical examination, power in the right lower limbs was 5/5 as per the Medical Research Council grading, and deep tendon reflexes were normal. Pre-operative X-ray and CT scan showed no instability or calcified disc osteophyte, and magnetic resonance imaging showed extraforaminal stenosis due to disc herniation at L5–S1 (Fig. 1). We performed UBE-assisted extraforaminal discectomy on L5-S1 to resolve his symptoms. The operative time was 38 min; blood loss was less than 30 mL (total saline intake volume – corrected fluid output volume). After surgery, the patient was able to be discharged on postoperative day (POD) 3 and followed up at one week, six weeks, three months, six months, 12 months, and two years. The pain and tingling sensation in the legs improved at the 1-week follow-up, with a VAS back/buttock pain score improved to 1/10 and VAS leg pain improved from 8 preoperatively to 0. The preoperative mean ODI score decreased from 70% to 10% at 2 years following surgery. Patient satisfaction was surveyed using Macnab’s criteria at the final follow-up visit of 2 years and was found to be excellent. Post-operative imaging showed a good extraforaminal decompression at L5-S1 Conclusion: The unilateral biportal endoscopic is an advanced technique in treating spinal pathologies and has served as another treatment option for the past 10-15 years. The UBE decompression technique for extraforaminal stenosis at L5–S1 has the advantages of minimally invasive spine surgery; it is a safe and effective treatment option for treating extraforaminal stenosis at L5–S1. Keywords: Unilateral biportal endoscopy, L5–S1 Extraforaminal stenosis, far-out syndrome, minimally invasive spine surgery, lumbar spine