Anatomical changes of the ligamentum flavum and the epidural space after spinal surgery: a retrospective magnetic resonance imaging study

BACKGROUND: Anatomical changes of the ligamentum flavum (LF) and epidural space (ES) after spinal surgery may affect the loss-of-resistance during interlaminar epidural procedure and distribution of drug administered into the ES. This study aims to investigate clinically relevant anatomical changes of the LF and ES after spinal surgery. METHODS: We reviewed pre- and postoperative lumbar magnetic resonance imaging data from 34 patients who underwent spinal surgeries at two vertebral body levels. The presence and thickness of LF (midline, right, and left) and the cross-sectional area of the ES were checked at L2, L3, L4, L5, and S1 levels. RESULTS: Intact LF was observed in only 4/34 (12%) and 9/27 (33%) patients at the upper and lower vertebral level of surgery, respectively. Intact LF was observed in 30/30 (100%), 28/33 (75%), and 2/4 (50%) patients, at two levels above, one level above, and one level below the segment level of surgery, respectively. Intact ES was observed in only 4/34 (12%) and 8/27(30%) patients at the upper and lower vertebral level of surgery, respectively. Intact ES was observed in 30/30 (100%), 29/33 (88%), and 3/4 (75%) patients, at two levels above, one level above, and one level below the segment level of surgery, respectively. The thickness of LF and the cross-sectional area of ES significantly decreased at the levels of spinal surgery. CONCLUSIONS: For epidural anesthesia in patients who have previously undergone spinal surgery, it is reasonable to select a needle insertion site other than the level of spinal surgery.