C1:C2 ratio is a potential tool assessing atlas fracture displacement and transverse ligament injury.

OBJECTIVES

The aim of this study was to determine the reliability of a C1:C2 ratio in a cohort of patients with atlas fractures. Second, we aimed to consider the utility of the C1:C2 ratio with regard to diagnosis of transverse ligament (TL) injury.

DESIGN

This is a retrospective analysis.

METHODS

Patients with atlas fractures in the Waikato region between 2008 and 2010 were identified retrospectively through clinical coding and collated radiology trauma database.

MAIN OUTCOME MEASUREMENTS

The maximal width of C1 and C2 was measured using the first-taken trauma radiograph series. Combined overhang of lateral masses (△mm) and a C1:C2 ratio was then calculated. Final ratio and atlanto-dens interval (ADI) were measured at the last clinical follow-up.

RESULTS

A total of 24 patients with full radiographic records were included. Of these, five patients (21%) had TL injuries confirmed on computed tomography or magnetic resonance imaging. No patient with a ratio 1.15 had an intact TL, whereas a ratio of >1.10 captured 80% of TL injuries. The ratio ( < 0.001) and delta values ( < 0.001) were statistically significantly different between TL-injured and TL-intact cohorts. Two patients in the TL injury group demonstrated increased ADI on final follow-up with a ratio of >1.10.

CONCLUSIONS

A C1:C2 ratio >1.10 on plain radiographs showed a sensitivity of 80% in detecting atlas fractures with associated TL injury. All patients with a ratio of ≥1.15 had TL rupture subsequently confirmed by an advanced modality. A ratio calculation on radiographs is a potentially useful method of describing atlas lateral mass displacement.

LEVEL OF EVIDENCE

Level III.