Exiting root injury in transforaminal endoscopic discectomy: preoperative image considerations for safety

To evaluate the clinical and radiological risk factors for exiting root injuries during transforaminal endoscopic discectomy. We retrospectively examined cohort data from 233 patients who underwent percutaneous endoscopic lumbar discectomy for lumbar disc herniation between January 1st, 2010 and December 31st, 2011. We divided the patients into the two groups: those who presented a postoperative exiting root injury, such as postoperative dysesthesia or motor weakness (Group A, n = 20), and those who did not suffer from a root injury (Group B, n = 213). We examined the clinical and radiological factors relating exiting root injuries. We measured the active working zone with the exiting root to the upper facet distance (Distance A), the exiting root to disc surface distance at the lower facet line (Distance B) and the exiting root to the lower facet distance (Distance C) in magnetic resonance imaging (MRI). Group A exhibited a shorter Distance C (6.4 +/- A 1.5 versus 4.4 +/- A 0.8 mm, p < 0.001) and a longer operation time (67.9 +/- A 21.8 versus 80.3 +/- A 23.7 min, p = 0.017) relative to Group B. The complication rate decreased by 23 % per each 1-mm increase in Distance C (p = 0.000). In addition, the complication rate increased 1.027-fold per each 1-min increase in the operation time (p = 0.027). We recommend measuring the distance from the exiting root to the facet at the lower disc level according to a preoperative MRI scan. If the distance is narrow, an alternative surgical method, such as microdiscectomy or conventional open discectomy, should be considered.