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.

Radiological Analysis of the Triangular Working Zone during Transforaminal Endoscopic Lumbar Discectomy

Study Design

Clinical study.

Purpose

The dimensions of the working zone for endoscopic lumbar discectomy should be evaluated by preoperative magnetic resonance images. The aim of this study was to analyze the angle of the roots, root area, and foraminal area.

Overview of Literature

Few studies have reported on the triangular working zone during transforaminal endoscopic lumbar discectomy. Many risk factors and restrictions for this procedure have been proposed.

Methods

Images of 39 patients were analyzed bilaterally at the levels of L3-L4 and L4-L5. Bilateral axial and coronal angles of the roots, root area, and foraminal area were calculated.

Results

No significant difference was observed between the axial angle of the left and right L3 root. A significant difference was found between the axial angle of right and left L4 roots. A significant difference was observed when the coronal angle of the right and left L3 roots were compared, but no significant difference was found when the coronal angle of the right and left L4 roots were compared. No significant difference was observed when the foraminal area of the right and left L3 and L4 roots were compared, but a significant difference was observed when the root area of right and left L3 and L4 roots were compared.

Conclusions

We suggest that these radiological measurements should be obtained for safety reasons before endoscopic discectomy surgery.