Anatomic Variations of Cervical and High Thoracic Ligamentum Flavum

BACKGROUND Epidural blocks are widely used for the management of acute and chronic pain. The technique of loss of resistance is frequently adopted to determine the epidural space. A discontinuity of the ligamentum flavum may increase the risk of failure to identify the epidural space. The purpose of this study was to investigate the anatomic variations of the cervical and high thoracic ligamentum flavum in embalmed cadavers. METHODS Vertebral column specimens of 15 human cadavers were obtained. After vertebral arches were detached from pedicles, the dural sac and epidural connective tissue were removed. The ligamentum flavum from C3 to T6 was directly examined anteriorly. RESULTS The incidence of midline gaps in the ligamentum flavum was 87%-100% between C3 and T2. The incidence decreased below this level and was the lowest at T4-T5 (8%). Among the levels with a gap, the location of a gap in the caudal third of the ligamentum flavum was more frequent than in the middle or cephalic portion of the ligamentum flavum. CONCLUSIONS The cervical and high thoracic ligamentum flavum frequently has midline intervals with various features, especially in the caudal portion of the intervertebral space. Therefore, the ligamentum flavum is not always reliable as a perceptible barrier to identify the epidural space at these vertebral levels. Additionally, it may be more useful to insert the needle into the cephalic portion of the intervertebral space than in the caudal portion.