Hounsfield unit measurements to predict odontoid fracture union in elderly patients: post-hoc subgroup analysis from an international prospective comparative study

BACKGROUND CONTEXT: Decreased bone mineral density (BMD) has been associated with worse fracture healing in vertebral fractures. In the absence of dual-energy X-ray absorptiometry (DXA) scans, CT-derived Hounsfield units (HU) may serve as a surrogate marker for BMD. PURPOSE: To study whether baseline HU measurements in the C2 and C3 vertebrae could predict odontoid fracture union in elderly patients. STUDY DESIGN/SETTING: Subgroup analysis from an international prospective comparative study. PATIENT SAMPLE: A total of 142 prospectively included patients aged ≥55 years with acute (<2 weeks) type II/III odontoid fractures. OUTCOME MEASURES: Fracture union at 52 weeks. METHODS: Standardized HU measurements were obtained from baseline CT scans in both mid-sagittal and midaxial planes of C2 and C3. Fracture union at 52 weeks was compared between patients with and without union. Multivariable regression analyses with fracture union as the dependent variable adjusted for age, gender, fracture type, fracture displacement, other C1–C2 fractures, and treatment modality. RESULTS: There were no relevant differences in HU values between the union and nonunion groups. Mean (SE) C2 HU was 246 (6.3) in the union group vs 282 (33) in the nonunion group (p=.29), and mean C3 HU was 260 (6.5) vs 251 (15), respectively (p=.56). No association was found between baseline HU and fracture union (aOR 1.00 (95% CI 0.99, 1.01) per HU increase for both C2 and C3). None of the baseline characteristics were significant predictors of union at 52 weeks. Compared to control patients in the literature, both the union and nonunion groups had reduced HU (cervical HU <300), indicating osteopenia. CONCLUSIONS: Baseline HU measurements in C2 and C3 did not predict fracture union at 52 weeks. Given that both groups exhibited decreased BMD, all elderly patients with odontoid fractures should be referred for osteoporosis screening and appropriate treatment.