Effect Of Posterior Fossa Decompression On Craniovertebral Junction Stability And Related Factors In The Treatment Of Chiari Type Ⅰ Malformation

Objective: Chiari malformation type Ⅰ,also known as subcerebellar tonsillar hernia malformation type Ⅰ,is a common malformation in the craniovertebral junction.Posterior fossa decompression is the preferred treatment for Chiari malformation type Ⅰ.Etiology is not clear at present,some scholars speculate Chiari malformation of atlantoaxial vertebral instability in the process of the nature of a form,The purpose of this study was to investigate whether the destruction of the posterior arch of the atlas and the foramen magnum by posterior fossa decompression will affect the stability of the cranialcervical junction and cause the atlantoaxial or atlantooccipital joint instability,and to further analyze the cranialcervical junction after surgery The influencing factors of regional stability changes,to confirm the necessity of occipitocervical fusion for the treatment of CM-ⅠMethods: From January 2015 to January 2020,the date of 89 cases with CM-Ⅰwho had complete preoperative imaging data and were treated with atlantooccipital decompression+ enlarged duraplasty were retrospectively collected.Sort out the relevant information: gender,age,hometown,disease course;Preoperative and postoperative measurements:Atlanto-dental interval(ADI),Basion-dental interval(BDI),Basion-axis interval(BAI),Odontoid-Wackenheim line interval,Clivus canal angle,cerebellar tonsil hernia length,posterior fossa volume and syringomyelia volume;Follow-up.According to the modified Japanese Orthopaedic Association(mJOA) scoring system and the Chicago Chiari Outcome Scale(CCOS),the postoperative symptoms and functional improvement were evaluated.Patients were included in the instability group when craniocervical junction diameter measurements during followup suggested craniocervical junction instability,and finally statistical analysis is performed.Result: Of the 89 subjects included,4 patients had no raniovertebral junction instability before surgery but atlantooccipital joint instability and atlantoaxial joint stability at 3 or 4 years postoperatively,with an incidence of 4.49%.Instable group of4 people,stable group of 85 people,posterior fossa volume statistical differences between the two groups(p = 0.00034),gender,age,disease course,cervicomedullary angle,cerebellar tonsil hernia length,syringomyelia volume in there is no statistically significant difference between the two groups(p > 0.05),No independent influencing factors of craniocervical junction instability have been found.Conclusion: The treatment of Chiari malformation type Ⅰ by posterior fossa decompression is safe and effective.There is no obvious impact on the stability of t craniocervical junction.The volume of the posterior fossa is correlated with the instable group.For patients with small posterior fossa volume indicated by preoperative imaging measurement,the posterior fossa decompression should avoid biting too much of the occipital bone and protect the structures of the occipital condyle and ligaments,and strictly follow up to observe the stability of the cranial-cervical junction after surgery.