title: A clivus plate fixation for reconstruction of ventral defect of the craniovertebral junction: a novel fixation device for craniovertebral instability.
abstract: OBJECTIVE
  A fabricated mesh cage and/or posterior occipitocervical instrumentation alone has been used for reconstruction of ventral defect of the upper cervical spine. However, using a trimmed mesh cage it was hard to achieve optimal clival screw purchase and it migrated or broke. A specific instrumentation at the craniovertebral junction (CVJ) should incorporate the morphology of the CVJ and biomechanical validation. The purpose of the present study was to develop an innovative clivus plate integrated with the clinical anatomy of CVJ and to evaluate the stability of the clivus plate fixation (CPF), stand-alone or combined with a posterior occipitocervical fixation (POCF).
  
  
  METHODS
  Dimensions relevant to the clivus plate were measured on 40 adult dry bones and CT images of 30 patients. The CPF was composed of the clivus plate and a titanium mesh cage. The clivus plate was anchored to the clivus, atlas and C3 body and connected to the mesh cage. Six fresh cadaveric head-neck specimens (Oc-C4) were used in this study (46 ± 15 years old, 2 F/4 M). A continuous pure moment of ±1.5 Nm was applied to the specimen in flexion, extension, lateral bending and axial rotation. The status of intact, CPF alone, and CPF plus POCF was tested on each specimen. The CPF was implanted to the specimen following resection of the C1 anterior arch, C2 vertebral body, C2-C3 disc and atlantoaxial ligaments. The POCF was applied with screws anchoring at the occiput, C1, C3 and C4. The range of motion (ROM) and neutral zone (NZ) from the occiput to C3 were calculated.
  
  
  RESULTS
  The clivus plate was developed based on measurements of 40 adult dry bones and CT images of 30 patients. The plates were successfully applied to all specimens. No obvious loosening or mismatch was observed. The mean clival length and widest and narrowest diameter of the clivus were 26, 33 and 19 mm, respectively. The clivus screw length was 8 mm for the caudal holes and 10 mm for the cephalad hole. The CPF reduced ROMs to 3.9° in flexion, 2.8° in extension, 4.2° in lateral bending and 6.8° in axial rotation. The combined CPF and POCF constrained motion within 0.6° in all directions and more than the CPF (P < 0.05). NZs after the CPF were 1.0° in flexion-extension, 2.1° in lateral bending and 2.2° in axial rotation, respectively. NZs after the CPF plus POCF were within 0.2° in all directions and less than the CPF (P < 0.05).
  
  
  CONCLUSIONS
  This study demonstrated screw purchase in the adult clivus and developed an innovative clivus plate fixation for reconstructing an extensive ventral defect in the upper cervical spine. The clivus plate fixation combined a posterior instrumentation ensuring reliable upper cervical stability.
authors.affiliation: Department of Spinal Surgery, Nanfang Hospital, Southern Medical University, 1838 North Guangzhou Avenue, Guangzhou, China.
authors.forename: Wei
authors.initials: W
authors.lastname: Ji
authors.forename: Jie
authors.initials: J
authors.lastname: Tong
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Huang
authors.forename: Minghui
authors.initials: M
authors.lastname: Zheng
authors.forename: Xiuhua
authors.initials: X
authors.lastname: Wu
authors.forename: Jianting
authors.initials: J
authors.lastname: Chen
authors.forename: Qingan
authors.initials: Q
authors.lastname: Zhu
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D001270:Cervical Atlas / Q000601:surgery*; D003388:Cranial Fossa, Posterior / Q000601:surgery*; D005260:Female; D006801:Humans; D007593:Joint Instability / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods