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

Abstract

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.

Keywords: Cross sectional area; Fat infiltration rate; Insufficient bone union; Magnetic resonance imaging; Osteoporotic vertebral fractures; Paraspinal muscles.

Fig. 1

Flow diagram showing the enrollment and assignment of patients

Fig. 2

Measurement of the cross-sectional area on T1 axial image (a) and fatty infiltration of paraspinal muscles using Image J (b). A = multifidi; B = erector spinae C = psoas; D = quadratus lumborum. c Correlation between rCSA of total paraspinal muscles and BMD (YAM%)

Fig. 3

a Correlation between the timing of MRI after the initial OVF injury and the FI% of the (a) multifidus muscle, (b) erector spinae, (c) psoas lumborum, and (d) quadratus

Fig. 4

a Correlation between the timing of MRI after the initial OVF injury and the rCSA of the (a) multifidus muscle, (b) erector spinae, (c) psoas lumborum, and (d) quadratus. e Representative images of the time-dependent increase in FI%, but no change in rCSA of the multifidus and erector muscles

Fig. 5

Graph comparing rCSA of the multifidus (a), erector spinae (b), psoas lumborum (c), and quadratus (d) between the groups (*P < 0.05, **P < 0.005, ****P < 0.0001, NS denotes no significant difference). e Representative images of paraspinal muscles of patients in both groups