Transforaminal full-endoscopic lumbar surgery is widely accepted as a method of treating lumbar conditions, such as disc herniation, spinal stenosis, and lumbar foraminal stenosis (LFS). This minimally invasive approach, often performed under local anesthesia, is ideal for older patients and those with significant comorbidities. Full-endoscopic lumbar foraminotomy (FELF) has shown high success rates and notable symptom relief for LFS. However, complications including postoperative dysesthesia, dural tears, restenosis, and scoliosis progression, especially at L5–S1 due to extensive facet joint resection, remain challenges. In such cases, lumbar fusion may be more appropriate. A unique anatomical feature, the "lateral kissing spine," is characterized by contact between the L5 transverse process and the sacral ala. This feature appears to mitigate scoliosis progression, regardless of the preoperative Cobb angle or bone resection extent during FELF. We report two L5–S1 foraminal stenosis cases treated with FELF under local anesthesia: one with a lateral kissing spine, showing no scoliosis progression, and another without it, demonstrating significant progression. A review of 11 additional cases supports the protective role of the lateral kissing spine against scoliosis, even in cases with severe preoperative Cobb angles. This study reviews the complications of FELF, focusing on scoliosis progression, and proposes indications for FELF, highlighting the importance of the lateral kissing spine in surgical decision-making.