PL-TOSP, the Novel Entry Point in Transforaminal Endoscopic Spine Surgery: Radiological Analysis with Prospective Surgical Evaluation and Review of Literature of Various Skin Entry Points
Authors: Patgaonkar Prasad , Dhole Kiran , Kokate Sagar , Goyal Vaibhav , Patel Vivek , Patel Ravi 
Published: July 2024

Abstract
Objective Aim of this study was to analyze variation in angulation of trajectories of various skin entry points in transforaminal endoscopic spine surgery with change in the physical parameters, namely, weight, abdominal girth, and body mass index and to validate our hypothesis that posterolateral (PL)-tip of spinous process (TOSP) entry has minimal variation in the angle of trajectory as compared with currently available skin entry points. The study included an analysis of the functional outcomes of these patients who underwent transforaminal endoscopy using the novel PL-TOSP technique, assessing improvements in pain and disability. Entry point in transforaminal endoscopic lumbar discectomy (TELD) was taken as a rough distance of 10 to 12 cm from midline as proposed by Kambin whereas Yeung and Tsou advised entry point as distance between the center of the disc space and the posterior skin line measured on lateral. But entry points cannot be static as they tend to change according to changes in physical parameters.
Materials and Methods This study comprises of radiological analysis and a prospective evaluation of these patients operated on using the PL-TOSP entry point. Radiological analytic study was performed on 50 symptomatic preoperative patients who underwent transforaminal endoscopy using the novel PL-TOSP entry point. A lumbar spine magnetic resonance imaging (MRI) field of vision (MRI-FOV) was performed for the patients including the abdominal perimeter. Weight, height, and abdominal girth of the patients were noted prior to MRI. Angulation of trajectory made by four standard entry points used in TELD, namely, 45–45, PL, TOSP), dorsum of facet joint, and our proposed entry point PL-TOSP (which is a midpoint between PL and TOSP entry), were calculated using MRI-FOV at L45 and L5S1 level. For the functional outcome analysis of these 50 patients, preoperative Visual Analogue Score (VAS) for lower limb pain and Oswestry Disability Index (ODI) were recorded. Postoperative VAS and ODI scores were reassessed at 2, 6, and 12 weeks. Statistical analysis was conducted to evaluate the significance of changes in VAS scores and ODI preoperative versus postoperative. A p-value of < 0.05 was considered statistically significant.
Results Angle of trajectory with the horizontal for all five entry points varies with physical parameters. PL-TOSP entry point has the least variation with change in physical parameters as compared with other entry points. The range of angle for PL-TOSP entry was 21 to 29 degrees. In our study, there was improvement in postoperative VAS and ODI scoring systems which was statistically significant (p-value < 0.05). This suggests reliability of our proposed entry point with consistent postoperative improvement.
Conclusion The novel PL-TOSP entry point for transforaminal endoscopy demonstrates superior stability in trajectory angle despite variations in physical parameters, and is associated with significant improvements in functional outcomes and pain reduction for patients with lower limb radiculopathy. Angulation of PL-TOSP trajectory with horizontal also corresponds to current generation of endoscopes (25 or 30 degrees).