title: Free-hand placement of occipital condyle screws: a cadaveric study.
abstract: OBJECTIVE
  Cranio-vertebral junction fixation is challenging due to the complex topographical anatomy and the presence of important anatomical structures. There are several limitations to the traditional occipital squama fixation methods. The purpose of this work is to assess the safety and feasibility of a new optimum trajectory of occipital condyle (OC) screws for occipitocervical fixation via a free-hand technique.
  
  
  METHODS
  Eight different parameters of OC morphology were studied in fifty adult skulls. Free-hand placement of OC screws was performed in five cadavers using 3.5-mm titanium polyaxial screws and a 3-mm rod construct (C0-C1-C2). Postoperative computed tomography was performed to determine the success of the screw placement and their angulation, length and effect on hypoglossal canal volume.
  
  
  RESULTS
  The average length, width and height of the OC were 24.2 ± 3.6, 14.2 ± 1.9, and 10.7 ± 2 mm, respectively. The average medio-lateral, hypoglossal canal and atlanto-occipital joint angles were 38.8° medially ±5°, 7.4° rostrally ±1.9° and 23.4° caudally ±3.5°, respectively. The ten screws were successfully inserted using a free-hand technique with bicortical purchase. There was no vertebral artery injury or breach of the hypoglossal canal in any specimen. The average screw length was 22.2 ± 3.9 mm. The average medio-lateral angle was 30° medially ±6.7°. The average cranio-caudal angle was 4° caudally ±6.2°.
  
  
  CONCLUSIONS
  The free-hand technique of OC screw placement is a safe and viable option for occipitocervical fixation and may be a preferred alternative in selected cases. However, further studies are needed to compare its safety and reliability to other more established methods.
authors: Department of Neurosurgery, Faculty of Medicine, Kasr Al-Aini Medical School, Cairo University, Cairo, Egypt, mohamedelgaidi@gmail.com.
authors: Mohamed Ali
authors: MA
authors: El-Gaidi
authors: Ehab Mohamed
authors: EM
authors: Eissa
authors: Ehab A A
authors: EA
authors: El-Shaarawy
mesh_terms: D000328:Adult; D001269:Atlanto-Occipital Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D001368:Axis, Cervical Vertebra / Q000000981:diagnostic imaging / Q000601:surgery*; D001863:Bone Screws; D002102:Cadaver; D001270:Cervical Atlas / Q000000981:diagnostic imaging / Q000601:surgery*; D005260:Female; D006801:Humans; D008297:Male; D009777:Occipital Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D015203:Reproducibility of Results; D013123:Spinal Fusion / Q000295:instrumentation* / Q000379:methods* / Q000592:standards; D013124:Spinal Injuries / Q000601:surgery; D014057:Tomography, X-Ray Computed