Fibres of the myodural bridge

The myodural bridge (MDB) is a fibrous network of connective tissue between the suboccipital musculature and cervical spinal dura mater in the atlanto-occipital and/or atlanto-axial interspaces.

It was first described in 1995 from human cadavers by Hack et al. as a dense band of tissue connecting the rectus capitis posterior minor and the posterior atlanto-occipital   membrane. The PAO membrane was connected to the spinal dura mater by many fine connective tissue bands. So the termed myodural bridge. Subsequent studies showed that this connective tissue also exists between the rectus capitis posterior major (RCPma), the oblique capitis inferior (OCI), the nuchal ligament and the spinal dura mater through the posterior atlanto-axial interspace in humans

MDB has been assumed to play important functions, including sensorimotor control, cervicocephalic pain, and stabilization of the spinal cord. MDB was hypothesised to play a role in proprioception, keeping the subarachnoid space and the cerebellomedullary cistern unobstructed, and affecting the dynamic circulation of the cerebrospinal fluid (CSF). In addition, clinicians have found that the pathologic change of the MDB might cause cervicogenic or chronic tension-type headache.

A study from China recently published in Spine Journal used histological staining methods to reveal the various origin and fibre properties of the MDB.  The results of this study show that the MDB fibres transversing the atlanto-occipital interspace originated from the Rectus Capitis Posterior Minor (RCPmi). The MDB transversing the atlanto-axial interspace originate mainly from the RCPmi, Rectus Capitis Posterior Major (RCPma) and Obliques Capitis Inferior(OCI). These fibres form the Vertebral Dural Ligament in the atlanto-axial interspace, and connect with SDM. The MDB is mainly formed by parallel running collagen I fibers thus, suboccipital muscle could pull SDM strongly through the effective force propagated by the MDB during head movement.

The authors concluded that MDB is mainly formed by parallel running collagen I fibres thus, it can transmit the strong pull from the diverse suboccipital muscles or ligaments during head movement.

In another study, the authors found similar MDB in other mammals, letting them to hypothesise that it can be an evolutionally conserved structure which plays an important role on integration of the sub-occipital muscular system and the central nervous and CSF circulation.