Characterisation of spinal ligaments in the embryonic chick.

Ligaments are important connective tissues within the musculoskeletal system that connect bone to bone and provide support and stability. The spine contains a number of ligaments that predominantly function in mechanical stabilisation and allow for certain ranges of spinal motion. Establishment of mechanical stability provided by spinal ligaments has not been described, and it is not known to what extent failure or inadequate spinal ligaments contribute to spinal conditions, such as scoliosis. While there are many similarities between ligaments and tendons, there is no experimental evidence investigating the development of these stability-bearing tissues. This study uses the embryonic chick model Gallus gallus and investigates the development of spinal ligaments in the thoracic spine, examining structure and molecular expression across development. Findings show organisational changes in spinal ligaments in association with vertebral shape changes from cranial to caudal, with the anatomical identification of six vertebral ligaments in the thoracic spine. As development proceeds, the size of the anterior longitudinal ligament, on the ventral surface of the vertebral body, and the supraspinous ligament, on the dorsal side of the spine, becomes greater, with the orientation of collagen fibres in the supraspinous ligament becoming more aligned. In addition, this study demonstrates that cell density decreases and nuclei become smaller and more circular across development. This study provides evidence that the embryonic chick is an appropriate model to study spinal ligament development and has added knowledge on the structural hallmarks of embryonic vertebral ligament tissues. These findings allow for subsequent investigation of the mechanical and molecular characteristics of spinal ligament development, for example useful for determining if in utero movement is important for the establishment of spinal ligament stability. Use of this model and integration of findings with additional models will provide knowledge of the contribution of spinal ligaments in spinal failure conditions.