CT analysis of deformity and injury affecting posterior C1 to C3 pedicle screw fixation for Hangman fracture

English Keywords:Hangman fracture  Posterior approach  Screw trajectory  Pedicle screw

English Abstract:

  【Abstract】 Objectives: To evaluate the presence of regional deformities and injuries in patients with Hangman fracture that affected the placement of C1 to C3 pedicle screws. Methods: Seventy-eight patients with Hangman fracture, including 67 males and 11 females, were treated in our hospital during May 2004 and May 2012. The mean age was 37.7(17 to 73)years. The interval from trauma to surgery was 3 hours to 18 days. Incomplete spinal cord injury was documented in 20 patients. According to Edward-Levine′s classification, 11 patients were type Ⅰ, 48 were type Ⅱ, 13 were type ⅡA and 6 were type Ⅲ fractures. They were evaluated by three-dimensional computed tomography preoperatively. The pedicle screw trajectories from C1 to C3 were specifically assessed to identify the presence of any deformity or injury that would preclude safe pedicle screw placement in these segments. The height of posterior arch of C1 and the width of pars interarticularis of C2 and pedicle of C3 were measured. It was considered highly risky to place a pedicle screw in one segment when its value was less than 4mm. Results: It was found 45% of type Ⅰ fractures, 23% of type Ⅱ, 38% of type ⅡA, 66% of type Ⅲ and 27% of all types complicated with injury or deformity that affected the placement of pedicle screws. Six(7.6%) cases were not fit for C1 posterior arch screw fixation, including small size of posterior arch in 2 cases and fractures of C1 posterior arch in 4. Ten(13%) cases were precluded from C2 trans-pedicle screw placement, including small pedicle size and high riding of vertebral artery and fractured fragment encased into vertebral canal or transverse process foramen. Nine(12%) cases were precluded from C3 trans-pedicle screw fixation due to small pedicle size, sclerotic pedicle and pedicle fracture or vertebral body fracture. Four patients had 2 or more types of such injuries or deformities concomitantly. Anterior approach was adopted in 17 patients, including 15 cases of C2-C3 discetomy and fusion and 2 cases of C3 corpectomy and C2-C4 fusion. Posterior approach was adopted in 55 patients, including 5 cases of C1-C3 pedicle screw fixation, 5 cases of mono-segmental C2 lag screw fixation and 45 cases of C2-C3 pedicle screw fixation. 6 patients were managed conservatively. No iatrogenic vascular or neurological injury occurred. Conclusions: There is a high incidence of regional deformity and injury in the C1 to C3 region after Hangman fracture that affects the placement of posterior screws. These factors include hypoplasia of C1 and C3 pedicles and hypoplasia of C2 pars interarticularis, pedicle sclerosis of C3, encasement of fractured segment into spinal canal or transverse process and high riding of vertebral artery.