Predisposing Factors of Fracture Nonunion After Posterior C1 Lateral Mass Screws Combined with C2 Pedicle/Laminar Screw Fixation for Type II Odontoid Fracture.

INTRODUCTION

The aim of this study was to explore the predisposing factors for fracture nonunion after a lateral screw was combined with C2 pedicle/laminar screw for a type II odontoid fracture and hopefully provide references in decision making and surgical planning for spinal surgeons.

METHODS

This is a retrospective study. By retrieving the medical records from January 2010 to July 2015 in our hospital, 117 type II odontoid fracture patients were reviewed. According to the occurrence of fracture union at the final follow-up, patients were divided into 2 groups: union and nonunion. To investigate the predisposing factors for fracture nonunion, 3 categorized factors were analyzed statistically: patient characteristics-age, sex, body mass index, preoperative Japanese Orthopaedic Association (JOA) scores, duration, comorbidity, and complicated injuries; surgical variables-surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2; radiographic parameters-preoperative and immediate postoperative data of C curvature, C curvature, C sagittal vertical axis, C7 slope, fracture classification, congenital hypoplastic vertebral artery, and the separation and displacement of the odontoid fracture. Other variables including JOA and visual analog scale scores for neck pain, neck stiffness, and patient satisfaction at final follow-up were recorded and compared between the 2 groups.

RESULTS

Postoperative fracture nonunion was detected in 76 of 117 patients (65%) at final follow-up. There was no statistically significant difference between the 2 groups in patient characteristics of sex, body mass index, JOA score, comorbidity, and complicated injuries. The mean age at operation was younger in the union group than in the nonunion group, and the mean duration was shorter in the union group than in the nonunion group. There was no difference in surgical variables of surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2. There was no difference in radiographic parameters of fracture classification, congenital hypoplastic vertebral artery, preoperative and immediate postoperative C curvature, C curvature, C SVA, and C7 slope. No difference was found in preoperative and immediate postoperative displacement of the odontoid fracture or immediate postoperative separation of the odontoid fracture, while the preoperative separation of the odontoid fracture was shorter in the union group than in the nonunion group. The logistic regression analysis revealed that advanced age (>45 years), long duration (>2 months), and preoperative separation of the odontoid fracture (>4 mm) were independently associated with the postoperative fracture nonunion. There were no differences between the 2 groups in JOA, neck pain, neck stiffness, and patient satisfaction at final follow-up.

CONCLUSIONS

Advanced age, long duration, and preoperative separation of odontoid fracture >4 mm are predisposing factors for fracture nonunion after posterior C1 lateral screw combined with C2 pedicle/laminar screw fixation for type II odontoid fracture. Our findings did not demonstrate any evidence of lower functional outcome and patients satisfaction for those patients who had odontoid nonunion.