title: Surgical simulation of instrumented posterior occipitocervical fusion in a child with congenital skeletal anomaly: case report.
abstract: METHODS
  Case report of a child with a congenital skeletal anomaly who underwent instrumented surgery at the craniovertebral junction (CVJ).
  
  
  OBJECTIVE
  To describe the utility of surgical simulation using three-dimensional full-scale models for preoperative planning.
  
  
  BACKGROUND
  Instrumented fusion of cervical spine with pedicle screws has several advantages compared with conventional sublaminar wiring, such as stronger fixation and reduction of malalignment. However, studies have reported a risk of injury to the vertebral artery (VA) from the insertion of screws. Especially in pediatric patients, the safety of pedicle screw insertion has not been fully established.
  
  
  METHODS
  A 7-year-old girl with a congenital skeletal anomaly presented with gait disturbance and clumsiness of her right hand. Radiographs showed dysplasia of the C1 posterior arch, leading to compression of the spinal cord posteriorly. Data from three-dimensional computed tomography (CT) angiography showed that the right VA was dominant and was shifted medially at the C2 pedicle. A surgical procedure was scheduled to resect the C1 posterior arch and perform an instrumented occiput-C2 fusion with a system of rod and screws. To evaluate the adaptation of the system to the small and deformed anatomic structure of her CVJ, we produced a three-dimensional full-scale model from CT data and performed a simulation of the scheduled surgery.
  
  
  RESULTS
  Simulation of the surgery on the model showed acceptable adaptation of the system. However, the right C2 pedicle screw penetrated the medial wall of the VA foramen. In response to these results, we altered the surgical procedure and performed occiput-C3 fixation with a system of contoured loop and wiring. Although the patient had to use a halo-vest for 2 months, no complication occurred during surgery, and she experienced relief of her myelopathy after surgery.
  
  
  CONCLUSIONS
  The three-dimensional full-scale model was useful for determining the safety of instrumented posterior occipitocervical fusion for a pediatric patient with a skeletal anomaly.
authors.affiliation: Department of Orthopaedic Surgery, Chiba University Graduate School of Medicine, Chiba, Japan. masashiy@faculty.chiba-u.jp
authors.forename: Masashi
authors.initials: M
authors.lastname: Yamazaki
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Akazawa
authors.forename: Masao
authors.initials: M
authors.lastname: Koda
authors.forename: Akihiko
authors.initials: A
authors.lastname: Okawa
mesh_terms: D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D001858:Bone Nails; D001863:Bone Screws; D001864:Bone Wires; D001915:Braces; D002574:Cervical Vertebrae / Q000601:surgery; D002648:Child; D003198:Computer Simulation; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007796:Laminectomy; D008953:Models, Anatomic; D013123:Spinal Fusion; D013131:Spine / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000601:surgery; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome