Traumatic thoracic spine fracture: can we predict when MRI would modify the fracture classification or decision-making compared to CT alone?

PURPOSE

To determine the impact of magnetic resonance imaging (MRI) on fracture classification for thoracic spine fractures (TSFs) compared to computed tomography (CT) alone.

METHODS

This study was a retrospective review of 63 consecutive patients with TSFs who underwent CT and MRI within ten days of injury. Three reviewers classified all fractures according to the AOSpine Classification and the Thoracolumbar AOSpine Injury severity score (TLAOSIS). Posterior ligamentous complex (PLC) injury on MRI was defined by "black stripe discontinuity" and on CT by the presence of vertebral body translation, facet joint malalignment, horizontal laminar or spinous process fracture, and interspinous widening. The proportion of patients with AO type A/B/C and with TLAOSIS ≤ 5 and ≥ 6 was compared between CT and MRI. Classification and regression trees were used to create a series of predictive models for the probability of PLC injury in AO type A fractures.

RESULTS

AO classification using CT was as follows: type A in 35 patients (55%), type B in 18 patients (29%), and type C in 10 patients (16%). Thirty-three patients (52%) had a TLAOSIS ≤5, while the remaining 30 (48%) had TLAOSI ≥6. The addition of MRI after CT upgraded type A to type B fractures in 10 patients (16%) and changed TL AOSIS from ≤5 to ≥6 in 8 cases (12.8%). Type A fractures with load sharing score (LSC) ≥6 had a 60% chance of upgrading to type B, while LSC <6 had a 12.5% chance of upgrading to type B.

CONCLUSIONS

CT yielded (89%) accuracy in diagnosing PLC injury in TSFs. The addition of MRI after CT substantially changed the AO classification or TLAOISS, compared to CT alone, thus suggesting an added value of MRI for PLC assessment for TSFs classification.