Biomechanical comparison of cemented versus non-cemented anterior screw fixation in type II odontoid fractures in the elderly: a cadaveric study.

BACKGROUND CONTEXT:Odontoid process fractures are the most common injuries of the cervical spine in the elderly. Anterior screw stabilization of type II odontoid process fractures improves survival and function in these patients but may be complicated by failure of fixation. PURPOSE:The present study aimed to determine whether cement augmentation of a standard anterior screw provides biomechanically superior fixation of type II odontoid fractures in comparison with a non-cemented standard screw. STUDY DESIGN:Twenty human cadaveric C2 vertebrae from elderly donors (mean age 83 years) were obtained. METHODS:Anderson and D'Alonzo type IIa odontoid fracture was created by transverse osteotomy, and fluoroscopy-guided anterior screw fixation was performed. The specimens were divided into two matched groups. The cemented group (n=10) had radiopaque high viscosity polymethylmethacrylate cement injected via Jamshidi needle into the base of the odontoid process. The other group was not augmented. A V-shaped punch was used for loading the odontoid in an anteroposterior direction until failure. The failure state was defined as screw cutout or 5% force decrease. Mean failure load and bending stiffness were calculated. RESULTS:The mean failure load for the cemented group was 352±12 N compared with 168±23 N for the non-cemented group (p<.001). The mean initial stiffness of the non-cemented group was 153±19 N/mm compared with 195±29 N/mm for the cemented group (p<.001) CONCLUSIONS: Cement augmentation of an anterior standard screw fixation of type II odontoid process fractures in elderly patients significantly increased load to failure under anteroposterior load in comparison with non-augmented fixation. This may be a valuable technique to reduce failure of fixation.