The CT scanning and clinical application of axis pedicle screw placement guided by the morphology of C2 interarticularis

English Keywords:Axis  Interarticularis  Pedicle screw  Three-dimensional CT

English Abstract:

  【Abstract】　Objectives:　To evaluate the feasibility and reliability of axis pedicle screw placement guided by the morphology of interarticularis. Methods:　C2 three-dimensional CT reconstruction was performed in 57 normal adults.　The cross-sectional images were used for study. The width of the central(L1) and the height(L2) at left and right side were measured. The distances from the interarticularis to the outer anchoring point B and the most medial point A were used as anatomical sign in C2 interarticularis.The distances from the interarticularis to the best anchoring point S(the intersection between vertebral pedicle central line and interarticularis rear cortex), and the maximum safety for screw placement at cross-sectional plane through A, B and S point respectively were measured. The distance from the interarticularis to the best point S at coronal plane was measured, and the best introversion and uptroversion angle at point S was measured. From October 2007 to July 2011, 33 cases underwent posterior atlantoaxial pedicle screw fixation guided by this method. Of these, there were 13 with new odontoid fracture,　10 with old odontoid process fracture,　7 with transverse ligment rupture and 3 with Jefferson fractrue.　Intraoperative and postoperative complications associated with instrumentation were evaluated. Screw position was also determined under three-dimensional CT scan after operation. Results:　The distance between point A, B, S to interarticularis on CT coronal plane was 1.75mm,　9.01±0.62mm,　5.77±0.53mm respectively. There were statistical differences between piont S and A, B with respect to safety instrumentation(P＜0.05).　 The distance from point S to the superomedial part of C2 interarticularis at coronal plane was 4.30±0.49mm, with an introversion of 30° and uptroversion of 26°. A total of 66 C2 pedicle screws was placed. There was no neurovascular complication noted.　Postoperative three-dimensional CT scan showed no screw into spine canal and transverse foramen. The distance between the entry point to the medial border of C2 interarticularis was 5.44±0.72mm,　the distance from point S to the superomedial part of C2 interarticularis on coronal plane was 4.50±0.52mm, which showed no significant difference with point S of preoperation. Conclusions:　There is constant relationship between C2 pedicle and its isthmus.　Screw placement at superomedial part of C2 isthmus is safe and reliable.