Is the Preoperative MRI Appearance of Lumbar Multifidus Prognostic for Outcomes of Lumbar Decompression?
Authors: Yoon Wai Weng , Clifton Thomas , Zotti Mario , Vilas-Boas Felipe , Piche Matthew , Freeman Brian 
Published: May 2015

Introduction

Decompressive surgery for symptomatic lumbar spinal stenosis is associated with good outcomes provided that appropriate patient selection is undertaken, which has proven critical (Aalto et al 2006). It has previously been proposed that the MRI appearance of multifidus is correlated to leg and back pain symptoms (Ali et al 2011 and Kader et al 2000). Therefore, our aim was to assess whether the preoperative MRI appearance of multifidus was predictive of outcomes for lumbar spinal stenosis surgery and could be used in patient selection. Our hypothesis was that patients with fatty atrophy on MRI would have significantly poorer clinical outcomes than those without.

Patients and Methods

A review of patients who had undergone lumbar spinal stenosis surgery in the previous 2 years (minimum 1-year follow-up) and had completed spine tango outcomes was undertaken. Exclusion criteria were additional procedures, for example, fusion and patients without MRI scans. Individual patient comorbidities and complication profiles were also assessed. The multifidus caliber was measured for each patient on MRI using a DICOM viewer by two assessors blinded to the outcome scores. In addition to the Kader et al (2000) classification, elliptical cross-sectional area mapping of multifidus was taken as an average measurement at the axial L4/5 level. Also, measured were the posterior adipose tissue layer and dimensions of the L5 vertebral body, areas of critical stenosis and psoas muscles, respectively.

Results

A total of 66 patients (41 females and 25 males) met the inclusion criteria and underwent analysis. There was a significant improvement for the cohort in ODI and COMI scores following surgical intervention and 89% of patients had improvement in ODI and COMI scores. The mean age was 67 years (range, 29–86 years). Overall, 44 patients had single level decompressions while for 2 level and 3 level decompressions; there were 16 and 6 patients, respectively. Overall, 44 (84%) of single levels involved either L4/5 or L5/S1 (37/44) with L3/4 and L2/3 involved in five and two patients, respectively. Moderate or severe fatty degenerative changes (Kader grades II or III) were noted in 71% of patients while a mean CSA (cm2) of 8.4 cm2 or less for multifidus at the measured level was noted in 71% of patients. The proportions of the cohort who improved more than 40% in their COMI and ODI when comparing the cohorts of patients with CSA < 8.5 cm2 compared with ≥ 8.5 cm2 were significantly different (47 vs. 79% [ p = 0.02] and 32 vs. 68% [ p = 0.006]). For patients with a Kader grade of 0 to 2 and CSA ≥ 8.5 cm2, there was significantly more percentage improvement with ODI/COMI (mean 84, 75) compared with Kader 2 to 3 and CSA < 8.5 cm2 (mean 28, 23) ( p = 0.05).

Conclusion

The appearance of lumbar multifidus on preoperative MRI is predictive of outcomes of lumbar spinal stenosis surgery with better results at a minimum of 1 year in patients with less fatty degenerative changes and higher cross-sectional area. This has implications for use in the perioperative setting and further research on the value of preoperative imaging for other spinal surgery is indicated.