The Anatomical Study And Possible Clinical Significance Of Cervical Meningovertebral Ligaments And Extraforaminal Ligaments

Background and purpose:Cervical Laminoplasty is a common procedure for the treatment of ossification of the posterior longitudinal ligament and multilevel cervical spondylotic myelopathy,but about 4.4%to 17.3%of patients could develop shoulder muscle weakness after laminoplasty.This post-operative symptoms are associated with C5 palsy.Previous studies have suggested that the unique anatomical features of C5 nerve root,such as its shorter length than other segments and the C5 vertebral body is located at the apex of physiological cervical lordosis,are the important causes of this condition.In addition,the ligaments structure in cervical intervertebral foramen and spinal canal have been studied,which may be related to the occurrence of C5 palsy.The purpose.of this study was to study the anatomic structure of the ligaments associated with cervical laminoplasty,and to help clinicians open their minds and explore methods to reduce the occurrence of C5 palsy.Methods:8 normal whole cervical embalmed specimens(54 to 78 years old,average age 66 years old).Removed the soft tissues in the foramina from the lateral side along the nerve root,to identify and preserve all ligamentous structures at exit zone of the foramina.Expose the cervical vertebral lamina to the zygapophysial joints on both sides of the vertebral lamina,and make a bone gutter on both sides at the medial border of zygapophysial joints,reserve the bone cortex of one side of the inner cortex,and the other side should penetrated the inner bone cortex.Periosteal elevator was used to open the lamina and remove the fat tissue in the spinal canal to preserve all the ligamentous structures between the dura sac and the posterior wall of the spinal canal.The ligaments were observed under the microscope.The length,width,and diameter of the ligaments were measured with a Vernier scale under the operating microscope.Compare and observe the position and morphology of spinal cord,nerve roots and ligaments in the spinal canal when the lamina was opened and closed.In addition,the most cranial and caudal lengths C4～C8 intradural ventral branches were measured.Results:A total of 177 foraminal ligaments were found in the exit zone of 64 cervical foramina in 8 adult cadaveric cervical specimens(C3～7 segments).There were 166(93.8%)radiating ligaments connecting nerve roots with surrounding structures.According to the different attachment sites,it can be divided into four types:superior,inferior,anterior and posterior types.The most numerous type was inferior ligaments(105,63.3%).Connecting the cranial transverse process and the caudal transverse process,11(6.2%)transforaminal ligaments that crossed the nerve roots.Among them,the transforaminal ligaments were the most common in the C4-5 segment(6,54.5%)of the cervical spine.A total of 37 meningovertebral ligaments were found.The meningovertebral ligaments originated from the the ligamentum flavum or the inner surface of the lamina and inserted into the posterior wall of the dural sac,and the strip type was the most numerous one.The distribution of meningovertebral ligaments was gradually decreasing from C3 to C7 level.The meningovertebral ligaments are more common at the C3-C4 segments of the spinal cord.After cervical laminoplasty surgery,it can be observed that the meningovertebral ligaments were tighted,the shape of dural sac was changed,and movement of spinal cord and nerve root was observed.Compared with other segments vulnerable to neurological symptoms,the length of the most cranial(13.18±1.12 mm)and caudal(8.07±1.11 mm)border of the C5 intradural ventral branch is the shortest.Conclusions:The occurrence of C5 nerve palsy may be related to the nerve tethering effect and the nerve injury caused by the extraforaminal ligaments.After laminoplasty,the strained meningovertebral ligaments could further increase displacement of spinal cord,deformation of dural sac and internal displacement of nerve root,magnifying the tethering effect of nerve root,and then cause nerve injury.The extraforaminal ligaments at exit zone of intervertebral foramen of the cervical spine is a normal physiological anatomical structure.After laminoplasty,the nerve roots may be compressed by the transforaminal ligaments or pulled by the radial ligaments,resulting in nerve injury.