Morphometric analysis of the working zone for posterolateral endoscopic lumbar discectomy based on magnetic resonance neurography.

Abstract

A magnetic resonance neurography (MRN)-based morphometric analysis of the working zone for posterolateral endoscopic lumbar discectomy (PELD) procedures on 32 health volunteers. The purpose is to utilize MRN as a noninvasive evaluation of the Kambin's working zone, and further to analyze operative safety of the PELD procedures. Intraoperative nerve root injuries of PELD procedures occur relative to the Kambin's triangular working zone, which has been described previously based on formalin-fixed cadaver studies. However, the investigation in living individuals is not known. Thus, it is necessary to evaluate the dimensions of the working zone on both coronal and sagittal plane by radiologic assessments. MRN images of 32 health volunteers (average age 26.8 y; 18 men, 14 women) were analyzed from L1-L2 to L5-S1. On the coronal plane, we measured the distance from the superior endplate to the nerve root exiting from the dura (distance a), the distance from lateral aspect of the dura to the medial aspect of the nerve root along the superior endplate (distance b), and the angle between the nerve root and plane of the corresponding disk (angle α). On the transversal plane, the vertical distance from the upper facet surface to the exiting nerve root at the lower/upper disk margin level (distance c/d) was also measured. On the coronal plane, distance a was 16.69±5.07 mm (range, 6.60-26.10 mm), distance b was 13.64±2.52 mm (range, 9.30-21.20 mm), angle α was 55.45±7.14 degrees (range, 40.00-73.00 degrees). Distance c on the transversal plane was 5.01±2.66 mm (range, 1.30-13.10 mm) and distance d was 1.99±1.26 mm (range, 0.70-7.80 mm). All these measurements increased as the spine level went down. The study indicated that MRN was a feasible noninvasive tool to evaluate the anatomic dimensions in the Kambin's working zone. Before PELD, radiologic measurements of this working zone were recommended to perform a safer procedure.