Reliability of the STIR sequence for acute type II odontoid fractures.

BACKGROUND AND PURPOSE The STIR sequence is routinely used to assess acute traumatic osseous injury. Because the composition of the odontoid in older individuals may be altered with osteopenia and decreased vascularity, the STIR sequence may not accurately depict the acuity of an odontoid fracture. The purpose of this study was to evaluate the reliability of the STIR sequence to differentiate acute-versus-chronic type II odontoid fractures in older patients, particularly those with osteopenia. MATERIALS AND METHODS A retrospective review was performed for patients with type II odontoid fractures during a 10-year period with both CT and MR imaging performed within 24 hours of injury. Patients were paired with controls of similar ages and were grouped by age. The STIR images were evaluated in a blinded fashion for the presence of hyperintensity in the odontoid. Demographic and clinical characteristics were also recorded. RESULTS Seventy-five patients with type II odontoid fracture and 75 healthy controls (mean and median age of 57 years) were identified. The sensitivity of STIR to detect fracture in the age group 57 years and older was significantly worse than that in the age group younger than 57 years (54% and 82%, respectively; P = .018). CONCLUSIONS Older patients, particularly those with osteopenia, may have acute odontoid injuries without corresponding STIR hyperintensity. Additionally, interobserver agreement in STIR interpretation decreases with increasing patient age. As such, in this patient population, in which the presence of bone marrow edema as an indicator of fracture acuity may impact therapeutic decisions, correlation with CT findings and clinical history is crucial.