Analysis of Risk Factors Associated With Fusion Failure After Anterior Odontoid Screw Fixation

STUDY DESIGN: Retrospective study. OBJECTIVE: To evaluate the incidence of fusion failure after anterior screw fixation of type II and rostral shallow type III fractures and to identify related risk factors. SUMMARY OF BACKGROUND DATA: Although several studies have reported fusion rates after anterior odontoid screw fixation of type II and rostral shallow type III fractures, few reports have analyzed in detail the risk factors associated with fusion failure. METHODS: Forty-one patients with a type II and rostral shallow type III odontoid fracture were treated using anterior screw fixation. The patients were 33 men and 8 women mean age = 46.6 years; age range = 15-79 years. Range of follow-up was 7 to 48 months. RESULTS: Anterior odontoid screw fixation resulted in solid bony union in 33 patients (80.5%), fibrous union in 3 (7.3%), and nonunion in 5 (12.2%). When surgery was delayed for more than 1 week, the incidence of fusion failure significantly increased (P = 0.0051). Furthermore, a fracture gap of 2 mm or more was found to be significantly associated with fusion failure (P = 0.0172). However, patient age and fracture displacement were not found to be significantly associated with fusion failure (P = 0.8236 and P = 0.5762, respectively). CONCLUSION: Our study of anterior odontoid screw fixation reveals that the risk of fusion failure is 37.5 times greater in patients with a delay of more than 1 week before operation, and 21 times greater in patients with a fracture gap of greater than 2 mm.