Comprehensive Anatomic and Morphometric Analyses of Triangular Working Zone for Transforaminal Endoscopic Approach in Lumbar Spine: A Fresh Cadaveric Study

Objective: The aim of this study is to provide essential information for endoscopic transforaminal approach by performing morphometric analysis of the triangular working zone (TWZ) in fresh cadavers. Methods: Fifteen fresh human cadavers (9 women and 6 men) with no history of spinal surgery were used in this study. Anatomic dissection of 150 foraminal levels were performed. Significant surgical landmarks constructing TWZ were measured bilaterally from L1–2 to L5–S1 on 15 fresh cadavers. The relationship between traversing roots and intervertebral discs was defined. Results: Base, height, and hypotenuse measurements of TWZ were longer as the level lowered. Mean base height and hypotenuse of TWZ were 12.15 mm, 11.29 mm, and 16.69 mm (L1–2); 17.94 mm, 17.18 mm, and 28.03 mm (L5–S1), respectively. TWZ was triangular shaped at the upper lumbar levels (L1–2, L2–3, and L3–4), and trapezoid at the lower lumbar levels (L4–5 and L5–S1). Going down the levels, the exiting root angle was narrower, the mean exiting angle of the L5 root being 28.23°. All L2 and L3 traversing roots and nearly all L4 traversing roots (86.7%) originated from below the disc level. Forty percent of L5 traversing roots originated above the disc level, and 53.3% originated at the disc level. Most S1 traversing roots originated at the proximal margin of the disc level (80%). Conclusions: Our study reveals a detailed morphometric analysis of TWZ. Understanding the foraminal anatomy is crucial for safely performing transforaminal endoscopic surgery. The learning curve of transforaminal surgery can be reduced by garnering knowledge of TWZ anatomy. © 2020 Elsevier Inc.