Digital three-dimensional reconstruction simulating anterior occipital condyle screw placement

English Keywords:Anterior occipital condyle screw  Three-dimensional reconstruction  Occipital condyle  Occipitocervical fusion  Internal fixation

English Abstract:

  【Abstract】 Objectives: To measure the related placement parameters of anterior occipital condylar screw by using digital three-dimensional reconstruction technique, and to assess the feasibility and safety of anterior occipital condylar screw placement. Methods: The spiral CT images of the upper cervical vertebrae of 50 patients with normal occipital and neck morphology in Ningbo Sixth Hospital were selected, including 30 males and 20 females with an average age of 42.2±8.6 years(ranging from 23 to 68 years). Excluding infection, tumor, anatomical deformity, fracture and dislocation, degeneration and severe osteoporosis, CT data were imported into Mimics software. After three-dimensional CT reconstruction of occipital bone and atlas, anterior occipital condylar screws with diameter of 3.5mm were placed to measure the distances from the entry point to the medial wall of occipital condyle and the atlantooccipital joint interface, the shortest vertical distance between screw and hypoglossal canal, and the length of screw trajectory entering into the bone of occipital condyle. Then, the upper tilting angle and outside tilting angle of each screw were measured by 3-matic software. The parameters of each screw placement were statistically analyzed. Results: A total of 100 anterior occipital condylar screws were successfully placed. No injury of medial and lateral wall of occipital condyle, atlantooccipital joint interface and hypoglossal canal in three-dimensional model were observed. There were no statistical differences in the placement parameters of anterior occipital condylar screw between the left and right sides(P>0.05). The horizontal distance from the entry point to the medial wall of the occipital condyle and the vertical distance from the entry point to the atlantooccipital joint interface were 3.28±0.54mm and 2.84±0.45mm, respectively. The upper tilting angle, outside tilting angle, the shortest vertical distance from the screw to the hypoglossal canal and the length of the screw trajectory were 4.07°±2.40°, 33.09°±4.37°, 4.76±0.74mm and 21.54±2.01mm, respectively. Conclusions: Simulating anterior occipital condyle screw placement by digital three-dimensional reconstruction demonstrates that normal adult occipital condyle has enough volume space to accommodate a 3.5mm diameter anterior occipital condyle screw, which will be a safe and feasible method for cranial internal fixation in the treatment of occipital cervical instability.