Comparative study of the paraspinal muscles after OVF between the insufficient union and sufficient union using MRI.

BACKGROUND: Identification of poor prognostic factors for OVF is important but has not yet been clearly established. Despite paraspinal muscles could play an important role in the etiology of OVF, what influence time-dependent changes in paraspinal muscles have after OVF, and the impact on conservative treatments for patients who have an OVF remain largely unknown. The purposes of this study were to (1) evaluate time-dependent changes of the paraspinal musculature using MRI after injury in patients with osteoporotic vertebral fractures (OVFs), and (2) compare paraspinal muscles between conservatively treated patients with OVF who have successful union and those failed to conservative treatment.

METHODS: A total of 115 consecutive patients who had sustained a recent OVF injury in the thoracolumbar region were assessed for eligibility using medical records and all required data were available from 90 patients who had been followed up for at least 6 months. Patients who needed to undergo surgery and patients who were diagnosed as having insufficient union after 6 months of follow-up were assigned to a group with insufficient union. Lumbar trunk parameters, relative cross-sectional area (rCSA) and proportion of fat infiltration (FI%) were calculated from MRI. To evaluate the time-dependent changes in the paraspinal muscle in patients after OVF injury, correlations between the timing of MRI and rCSA, FI% were determined. To clarify the impact of paraspinal muscles on the outcome of conservative treatments of patients with OVF, we compared rCSA between the groups.

RESULTS: Sixty-five patients were assigned to a group with insufficient union and 25 patients were assigned to a group with successful union. FI% of the multifidus and erector spinae in the group with insufficient union were significantly greater than in the group with union. The timing of MRI in relation to initial injury was significantly correlated with FI% of the multifidus and erector spinae. rCSA of the erector spinae was significantly larger in the group with successful union than in the group with insufficient union.

CONCLUSIONS: These findings indicated a time-dependent increase of fatty degeneration of the multifidus and erector muscles, but no change in the rCSA and larger rCSAs of spinal erectors may play a role in successful union in patients with OVF.