The glasgow lumbar spinal stenosis scale: an individualised measurement formula for the radiological assessment of lumbar spinal stenosis.

Background: Lumbar spinal stenosis (LSS) is a common and important spinal surgical problem. Currently there is no universally accepted quantitative approach to the radiological measurement of LSS. LSS can be described qualitatively with reference to facet and ligamentous hypertrophy, lack of perineural or intraforaminal fat, and reduced CSF around the cauda equina. Quantitative descriptions do exist e.g., lumbar canal antero-posterior diameter, but these are unidimensional and do not consider normal variation in anatomy. We propose a universal and individualised measurement system for the quantitative radiological assessment of lumbar spinal stenosis.

Methods: A retrospective case series of patients who had undergone surgery for symptomatic lumbar spinal stenosis over a 3 year period. Pre-operative lumbar spine MRI were analysed. Each patient had the degree of lumbar canal stenosis quantified using our novel approach.

Results: Our novel formula for the quantitative radiological assessment of lumbar spinal stenosis is two dimensional, repeatable and presented as a percentage, to correct for the individual patient. The surface area of the lumbar spinal canal at the level of stenosis is measured in mm2 plus the adjacent 2 levels which are then averaged. The calculation then becomes (A-S/A) x 100 = R, where S is the canal surface area at the stenosed level in mm2, A is the average canal surface area of the two levels adjacent to the level of interest and R is the relative degree of lumbar spinal canal stenosis expressed as a percentage. Measurements are calculated using axial T2 weighted images.

Conclusions: This novel quantitative measurement formula for the radiological assessment of lumbar canal spinal stenosis is quick and simple to calculate and most importantly adjusts for the individual patient's normal or degenerative anatomy. This new measurement tool will need validation against specific clinical and operative criteria in the future.