P35. Transforaminal full-endoscopic lumbar discectomy at the L5-S1 disc level: anatomical considerations and operability

Abstract

BACKGROUND CONTEXT Transforaminal full-endoscopic lumbar discectomy (TELD) is a minimally invasive procedure for the surgical treatment of lumbar disc herniation (LDH). It can be performed under local anesthesia and requires a skin incision of only 8 mm, with minimal disruption of the spinal structures including ligaments and muscles. However, performing TELD for the lower lumbar spine is associated with some anatomical problems, such as interference with the iliac crest. This study sought to assess the operability of TELD at the L5-S1 disc level. PURPOSE The purpose of this study is to assess a three-dimensional relationship between the trajectory of TELD and the iliac crest, and the operability of TELD at the L5-S1 disc level compared with the L4-L5 disc level using CT images. STUDY DESIGN/SETTING This is a retrospective study using 323 multiplanar abdominal computed tomography (CT) scans. PATIENT SAMPLE We retrospectively reviewed multiplanar abdominal CT scans of 323 consecutive patients (203 male and 120 female) in our hospital from April 2009 to March 2013. The mean age was 66.5 (range 15-89) years old. OUTCOME MEASURES The operability of the TELD at the L5-S1 disc level was the outcome measure. METHODS We defined the tangent line in the iliac crest and the superior articular process of the caudal spine as the trajectory line of TELD, and evaluated the maximum inclination angle of the trajectory of the TELD (α angle) at the L4–L5 and the L5-S1 disc levels. Assuming the use of an oblique viewing endoscope at 25°, we defined α angle≥65° as the operability of TELD. RESULTS (1) The relationship between the iliac crest and disc level: The trajectory of the TELD interfered with the iliac crest at L4-L5 in 40.2% (right) and 54.5% (left) of the subjects, and at L5-S1 in 99.7% and 100% of the subjects. (2) The maximum inclination angle of the trajectory of TELD: the α angles were 84.3° and 82.3° at the L4-L5, and 56.8° and 55.2° at L5-S1. (3) Operability of TELD: At L4-L5, TELD could be performed in 94.4% and 90.4% of the subjects. In contrast, at L5-S1 the procedure could be performed in 24.1% and 19.2% of the subjects (male: 15.8% and 10.8%, female: 38.3% and 33.3%). CONCLUSIONS From the results of this study, the trajectory of TELD can be limited by the surrounding anatomical structure. The maximum inclination angle indicates that TELD for the central type of LDH at the L5-S1 disc level is more technically demanding than TELD at the L4-L5 disc level because of the interference of the iliac crest. However, in the clinical setting, such anatomical particularities can be overcome by using a hand-down technique with the possible addition of a foraminoplasty when we perform TELD at the L5-S1 disc level. Because the maximum inclination angle is defined by the iliac crest and ventrolateral aspect of the superior articular process, it makes sense that we remove the superior articular process partially. After widening the neural foramen after foraminoplasty, the working cannula could easily and safely pass through the foramen without touching the exiting nerve root, and be close to the herniated disc. FDA DEVICE/DRUG STATUS This abstract does not discuss or include any applicable devices or drugs.