Study On Structure And Function Of Canine Myodural Bridge

Objective: To reveal the morphology and functions of the myodural bridge in dog models.Materials and methods: Seventy adult beagles were used in this experiment regardless of gender.The morphology and function of suboccipital myodural bridge were found by gross anatomy dissection,tissue section,scanning electron microscopy and in vivo physiology.Firstly,the structural connectional relationship between the post-occipital muscles and the spinal dura mater(SDM)in dorsal atlanto-occipital and atlanto-axial interspaces was observed by gross anatomy.Then the continuous tissue blocks including occipital bone,atlas,axis,RCDmi,short head of RCDma,OCP and SDM were prepared for HE staining,Masson staining and scanning electron microscopy.The connections between post-occipital muscles and SDM and their morphological characteristics were observed under microscope and scanning electron microscopy respectively,and the results were recorded by photos.On the basis of morphological study,passive head movement and electrical stimulation of post-occipital muscles were performed on dogs under anesthesia.The changes of cerebrospinal fluid pressure in the spinal canal were monitored simultaneously to explore the physiological function of the myodural bridge.The experimental results were recorded as average ±standard deviation.Paired t test was used for statistical analysis,it had statistical significance when P < 0.05.Results:1.There were the rectus capitis dorsal minor(RCDmi),RCDma(short and long heads)and OCP in the canine post-occipital region.The RCPmi,the RCPma and the OCI of human were corresponding to RCDmi,RCDma(short head)and OCP of dogs.2.The parallel dense collagen fibers originating from the ventral muscular fibers of the RCDmi in direction parallel with them were participated in the formation of the DAOM,the dense collagen fibers originating from the ventral side of DAOM were connected with the SDM.There were multiple collagen fibers between DAOM and SDM,and the two ends of them were fused tightly with DAOM and SDM respectively.The dense collagen fibers sending out from the caudal end of the short head of the RCDma and the ventral side of the OCP were involved in the formation of the dense part of the dorsal atlantoaxial membrane(DAAM).The dense collagen fibers from the ventral side of DAAM were closely connected with the SDM and make the SDM thicker.Scanning electron microscopy showed that the collagen fiber bundles from DAAM are woven into the SDM.3.The cerebrospinal fluid(CSF)pressure was(12.407±4.584)mm Hg before the electrical stimulation of the OCP,and became(13.453±5.164)mm Hg during its electrical stimulation with significant increase(P=0.001).There was no significant change in CSF pressure after the OCP was separated from its deep tissues.There was no significant change in the pressure of CSF when the electrical stimulation was performed on the long and short head of the RCDmi.The cerebrospinal fluid pressure before head passive lateral flexion was(11.077±4.209)mm Hg,while during lateral flexion it was(12.135±4.107)mm Hg with a significant increase(P=0.001);the CSF pressure before head passive rotation was(10.728±3.829)mm Hg,while during rotation it was(11.828±3.876)mm Hg with a significant increase(P=0.000);the CSF pressure before head passive flexion and extension exercise was(11.245±3.944)mm Hg,while during head passive flexion and extension exercise it was(12.480±4.079)mm Hg with an significant increase(P=0.002).Conclusions: The myodural bridges existed in Dogs,and they were originated from the RCDmi,the short head of the RCDma and the OCP respectively.The myodural bridge was composed of dense collagen bundles,which was closely connected with the SDM.Head movements had significant effects on CSF pressure.Myodural bridge may be the morphological mechanism of the significant increase of CSF pressure caused by head movement.Myodural bridge may play an important physiological role in providing power for CSF circulation.