Axial Loading during MRI Induces Lumbar Foraminal Area Changes and Has the Potential to Improve Diagnostics of Nerve Root Compromise

Abstract

Lumbar foraminal stenosis is a common cause of lumbar radiculopathy and conventionally assessed with magnetic resonance imaging (MRI) in supine-positioned patients. An MRI acquired during spine loading may unmask pathology not otherwise revealed in a relaxed position. Therefore, we investigated how spine loading during MRI affects lumbar foramina. In 89 low-back pain patients’ lumbar, MRIs were performed in a relaxed supine position and during axial loading using a Dynawell® compression device. The smallest area of all intervertebral foramina at levels L3/L4–L5/S1 (534 foramina) was determined using a freehand polygonal tool in parasagittal T2-weighted sequences. The grading system described by Lee et al. was also used to qualitatively assess foraminal stenosis. Overall, a mean reduction of 2.2% (mean −0.89 cm2 and −0.87 cm2, respectively) was observed (p = 0.002), however for individual foramina large variations, with up to about 50% increase or decrease, were seen. Stratified for lumbar level, an area reduction was found for L3/L4 and L4/L5 foramina (mean change −0.03 cm2; p = 0.036; and −0.03 cm2; p = 0.004, respectively) but not for L5/S1. When comparing the measured area changes to qualitative foraminal grading, 22% of the foramina with a measured area decrease were evaluated with a higher grading. Thus, detailed information on foraminal appearance and nerve root affection can be obtained using this method.