Keywords:
Surgery, Ablation procedures, MR, Neuroradiology spine, Musculoskeletal spine, Arthritides
Authors:
M. Bonython1, T. Nottage2, L. Xu2, M. Zotti2, T. Fisher2, M. Selby2; 1NT/AU, 2SA/AU
DOI:
10.26044/ranzcr2019/R-0092
Methods and materials
This was a prospective study of adult patients enrolled from a single practice over a 2 year period with confirmed facetogenic chronic lower back pain, who had undergone successful bilateral L4/5 and L5/S1 RFJD. Success was defined as an improvement in VAS pain scores of 3 points or greater, or patient satisfaction at 6 weeks post-op. Those patients who had had spinal surgery in the 6 months prior, or who had contra-indications for MRI were excluded from participation.
MRIs were performed pre-operatively and at 6 and 24 weeks post-op. For each scan, seven T2-weighted slices were de-identified, de-temporised and randomised before being presented to 2 independent, blinded observers for analysis. The seven slices consisted of axial slices at the levels of the L4/5 and L5/S1 intervertebral discs and facet joints, and sagittal slices in mid-line and paracentrally to best demonstrate the left and right neural exit foramina.
In axial, freehand tracings of the outlines of MM, erector spinae (ES) and intervertebral discs were recorded using tablet computer and stylus Fig. 1.
Post-processing gave a measure of the total cross-sectional area of each muscle in pixels. Further processing to determine lean or fat subtracted muscle cross-sectional area was possible by setting a grayscale cut-off and was standardised for each image Fig. 2.
Tracings of the intervertebral discs at each level also allowed calculation of antero-posterior and lateral distances and provided a constant in order to account for any scaling or rotational variation across each patient's MRI scans.
Assessment of the degree of facet joint degeneration was made by each observer using the Weishaupt lumbar facet joint disease severity grading scale7.
In sagittal, freehand tracings of the anterior and posterior boundaries of the spinal canal between L4 and S1 were made in the mid-line slice which allowed calculation of the minimum diameter and therefore degree of central canal stenosis Fig. 3. Assessment of the degree of intervertebral disc degeneration was made by each observer using the Pfirrmann grading scale8. L4 and L5 neural exit foramina were also traced in left and right paracentral slices to calculate diameter and stenosis Fig. 4.