Risk Factors of Nonunion After Anterior Screw Fixation of Anderson and D'Alonzo Type II Odontoid Fractures

Anderson-D'Alonzo Type II odontoid fractures are common in the elderly and often treated surgically due to high nonunion rates and increased morbidity and mortality associated with conservative treatment. However, high rates of nonunion still occur with surgical treatment and specific fracture characteristics predicting nonunion remain unclear. This study aimed to identify morphological fracture features associated with nonunion in patients undergoing anterior screw osteosynthesis for Type II odontoid fractures.

In this retrospective study, 60 adult patients treated with two anterior fixations for Anderson-D'Alonzo Type II odontoid fractures at a Level 1 trauma center (2011-2019) were analyzed. Demographic, clinical, and radiographic data (time to surgery, use of 3D imaging, implant loosening, ASA class, age, sex, BMI, smoking status, Grauer classification, fracture angle, fracture dislocation angle, dislocation direction, dislocation distance, comminution, periarticular ossification or ankylosing spondilitis) were collected. Pre- and postoperative computed tomography (CT) scans were evaluated. Bony union status was determined at a minimum of six months follow-up. Statistical significance was set at α=0.05.

Of the 60 patients (median age 80 years), 36 (60%) achieved bony union while 24 (40%) developed nonunion. Fracture angle was the only parameter significantly associated with nonunion (union median 27 vs. nonunion 40, p=0.049). No associations were found for age, sex, BMI, ASA class, smoking, surgical delay, Grauer type, displacement, comminution, or use of 3D imaging.

Fracture angle is a significant predictor of nonunion in Type II odontoid fractures treated with anterior screw fixation. Preoperative assessment of fracture angle may aid in surgical decision-making and to optimize outcomes.