Radiological anatomy and posterior screw placement strategy on C1 pedicle

English Keywords:Atlas  Pedicle  Screw  Image  Anatomy

English Abstract:

  【Abstract】 Objectives: To investigate the strategy and safety of posterior screw fixation on C1 pedicle. Methods: From January 2005 to January 2011, 28 cases suffering from upper cervical spine instability as well as C1 pedicle variation treated surgically in our hospital were reviewed retrospectively. There were 11 males and 17 females, with age ranging from 18 to 75 years old. Based on the height of medial and lateral part at 3 sections on C1 posterior arch, the vertebral artery groove and the boundary between pedicle and lateral mass, the atlas with variation were divided. Each category underwent specific strategy: Type Ⅰ(height of posterior arch of atlas less than 3.5mm and vertebral artery groove more than 3.5mm) had anchoring point inferior to the posterior arch; Type Ⅱ(both data less than 3.5mm) had anchoring point between pedicle and lateral mass; Type Ⅲ(height of posterior arch of atlas more than 3.5mm and vertebral artery groove less than 3.5mm) underwent in-out-in technique. The accuracy and complication of screw fixation were evaluated in each category. Results: All the 56 pedicles included 34 Type Ⅰ, 18 Type Ⅱ and 4 Type Ⅲ. In all atlas, the height of pedicle adjacent to lateral mass was more than 5.0mm, and no statistical difference between lateral and medial region was noted. The height of vertebral artery groove at the lateral part was significantly larger than the medial part（t=13.07, P＜0.01）, with 60% of the lateral region higher than 3.5mm. The height of almost all posterior arch was less than 3.0mm, and no difference between lateral and medial region was noted. 54 screws were successfully placed into the atlas(96.4%). Post-operative CT scan showed 52 screws as ideal or acceptable(96.3%) and 2 as unacceptable(3.7%). There were no complications such as hemorrhea, injury to vertebral artery and nerve root, fracture on the posterior arch. 2 patients complained of the symptom of greater occipital nerve irritation. Conclusions: Different fixation strategy should be considered on C1 pedicle with varied type. It is reliable to place the screw on C1 lateral part.