Quantitative MRI comparison of multifidus muscle degeneration in thoracolumbar fractures treated with open and minimally invasive approach

Abstract

Background: Minimally invasive pedicle screw fixation has less approach-related morbidity than open screw placement and is allegedly less traumatizing on paravertebral muscles, as there is no requirement to mobilize and retract the adjacent muscle portion. The approach-related long-term effects to the morphology of the paravertebral muscles are unknown. The purpose of this study was to compare the long-term amount of fatty degeneration of the multifidus muscle in patients treated with a classical open or a minimally invasive approach.

Methods: Fourteen Patients meeting inclusion criteria were selected. In all patients a singular fracture of the thoracolumbar spine with a two-level posterior instrumentation was treated, either using an open approach or a minimally invasive approach. All patients underwent quantitative MRI spectroscopy for quantification of the fatty degeneration in the multifidus muscle as a long-term proof for muscle loss after minimum 4-year follow-up. Clinical outcome was assessed using Oswestry Low Back Pain Disability Questionnaire, SF-36 and VA-scale for pain.

Results: The minimally invasive approach group failed to show less muscle degeneration in comparison to the open group. Total amount of fatty degeneration was 14.22% in the MIS group and 12.60% in the open group (p = 0.64). In accordance to MRI quantitative results there was no difference in the clinical outcome after a mean follow up of 5.9 years (±1.8).

Conclusion: As short-term advantages of minimal invasive screw placement have been widely demonstrated, no advantage of the MIS, displaying a significant difference in the amount of fatty degeneration and resulting in a better clinical outcome could be found. Besides the well-known short-term advantage of minimally invasive pedicle screw placement, a long-term advantage, such as less muscle degeneration and thus superior clinical results, compared to the open approach could not be shown.

Keywords: Dorsal instrumentation; Minimal invasive surgery; Muscle degeneration; Spine trauma.

Fig. 1

A quantitative MR-spectroscopy was performed and the fat amount in the multifidus muscle was measured at the fracture level and the adjacent vetebrae

Fig. 2

MR-spectroscopy revealed a fat amount of 12.6% (±6.3) for the open and a amount 14.2% (±5.3) for the MIS group. The upper and the lower whisker of boxplots represent the standard deviation. The heights of box represents the interquartile range (25% and 75% quartile). The line in the middle represents the median

Fig. 3

Open approach (a) for pedicle screw placement and Minimal invasive approach (b)

Fig. 4

T1-weighted transversal imagfe of the paravertebral muscles. MR spectroscopy reveald a fat amount of 26.5% for the multifidus muscle in a and an amount of 5.6% in b