INTRODUCTION: Load and activity induced neurogenic claudication is typical for spinal stenosis. A constriction of the cauda equine (< 75 mm2) (Schönström et al 1984) is in most subjects a prerequisite for this claudication. Separately both the epidural fat and the yellow ligament have been shown to contribute to the constriction of the cauda. The aim of this study was to evaluate the interference between the fat and the ligament in load and position induced cauda equine constrictions.
METHODS: The lumbar spines in 24 men and women with non specific LBP were examined with MRI; in a supine position with and without an axial loading (+50 % of the body weight) applied through a nonmagnetic loading device. The changes of the cross sectional areas of the flavum, the epidural fat, the dural sac, the spinal canal and also the posterior bulge of the intervertebral disc were determined and compared in the unloaded and loaded spines.
RESULTS: The structure showing the largest expansion inwards the spinal canal during axial loading was the ligamentum flavum. On both the L3/L4 and L4/L5 levels flavum contributed to more than 50% of the reduction of the size of the spinal canal. The posterior bulging of the disc when loaded was quite small while the loading caused a statistically significant inward expansion of the epidural fat. This expansion occurred as a consequence of the bulging flavum, compressing and pushing the epidural fat towards the dural sac.
DISCUSSION: It is likely that the effects the load induced bulging of the ligamentum flavum (Hansson et al 2009) has on the epidural fat is a consequence of “functional compartments” within the spinal canal formed by the meningo‐vertebral ligaments (Geers et al 2003). These “compartments” will allow axial sliding motions but also transversal expansion of the epidural fat.