A morphological comparison of the extraforaminal ligament between the cervical and thoracic regions.

Purpose: The current study was conducted to clarify the morphology of the extraforaminal ligament (EFL) at the cervicothoracic junction and to compare the attachment of the EFL and the positional relation between the EFL and the spinal nerves, additionally to clarify the details within the connecting bundles at the cervicothoracic junction.

Materials And Methods: The EFLs from the 4th cervical to the 4th thoracic vertebrae were dissected in 56 sides of 28 Japanese cadavers (11 males, 17 females). The range of age was 62.0-99.0 years. In addition, connecting bundles were analyzed by histological examination.

Results: Ventral to the spinal nerve, the capsulotransverse ligament (CTL), transforaminal ligament (TFL) and the ligament between the 7th cervical vertebra and the 1st rib were attached to the transverse process and rib. The EFL ventral to the 1st thoracic nerve was not observed in all sides. Dorsal to the spinal nerve, the anterior part of the superior costotransverse ligament (ASCL) and the ligament homologous to the ASCL were attached to the transverse process and rib. The superior radiating ligament (SRL) and the ligament homologous to the SRL were identified. The connecting bundles identified between the 7th cervical and the 1st thoracic nerve were histologically confirmed to consist of nerves and vessels.

Conclusions: The EFLs at the cervicothoracic junction were found to be homologous. The connecting bundles were observed between the 7th cervical and the 1st thoracic nerve. Interestingly, the 1st thoracic level alone might be a unique level at the cervicothoracic junction.