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The myodural bridge (MDB) complex are fibrous bridges that functionally connect the spinal dura mater to the suboccipital musculature. Previously, we described the maturational sequence of the MDB within the posterior atlanto-occipital interspace of the rat. The present paper describes the morphology and developmental maturation of the MDB within the posterior atlanto-axial interspace of the rat. In the present study, E18 embryonic rats, newborn rats, and adult rats were selected to evaluate the development and growth of the MDB. Within the posterior atlanto-axial interspace of the rat, the fibers of the MDB and its associated muscles, in the embryonic rat, were observed to be scarce and lightly stained. In contrast, these same structures observed in the postnatal rat were quite apparent and robustly stained. After birth, it was observed that MDB originated from the rectus capitis dorsal major muscle, extended forward and downward, and finally merged with the posterior atlanto-axial membrane. As the rats developed and matured, the observed MDB fibers passing through the posterior atlanto-axial interspace appeared denser and more organized. This study evidenced that the MDB fibers within the posterior atlanto-axial interspace were primarily composed of type I collagen fibers in the postnatal rat. By observing the suboccipital region, we are able to hypothesize that the MDB complex plays a key role in maintaining the subdural space located within the upper cervical segment during growth and development. This study provides a morphological basis for future research on the function of the MDB complex.

The myodural bridge (MDB) is a dense connective tissue structure between the suboccipital musculature and the spinal dura mater (SDM). However, few reports on the development and maturation of the human MDB. 30 head and neck specimens from human fetuses (F) from 12–40 weeks (W) were made into histological sections. The F12W sections evidenced that the SDM dominated by fibroblasts, attached to the posterior atlantoaxial membrane (PAAM) which completely sealed the atlantoaxial space. In the F13W stage, myofibrils of the suboccipital muscle fibers increased significantly in number. At the F14W stage, a gap was observed at the caudal end of the PAAM. Numerous myodural bridge-like structures were observed blending into the SDM through the gap. At the F15W stage, the MDB fibers originated between the posterior arch of atlas (C1) and the obliquus capitis inferior muscle, and extended forward and downward into the spinal canal through the atlantoaxial gap. Starting at the F21W stage, the MDB fibers were observed to pass through the atlantoaxial interspace and radially attach to the SDM. The present study adds to the knowledge base of developmental morphology research of the human embryonic MDB and provides a developmental morphological basis for its potential functionality.