1 Introduction to lumbar stenosis classifications

Lumbar spinal stenosis is the narrowing of any part of the lumbar spinal canal. Although alluded to as early as the beginning of the 19th century, Verbiest described and popularized the idea of acquired lumbar stenosis in the mid to late 20th century. There have been numerous descriptions of the anatomical relationship of traversing and exiting nerve roots to a stenosed lumbar spine [1, 2]. The most common cause of lumbar stenosis is degenerative spondylosis and subsequent facet hypertrophy and other degenerative changes. Lumbar stenosis can also present as a congenital condition, or be a manifestation of other conditions, notably achondroplasia.

2 Current classification systems for lumbar stenosis

Similar to cervical stenosis, the severity of lumbar stenosis has not been measured by eponymous classifications, but rather by radiographic and anatomic measurements. In 1977, Verbiest described lumbar stenosis based on sagittal canal diameter as seen on a lateral x-ray [3]. A canal diameter of less than 10 mm was deemed as “absolute” stenosis, 10mm to 12 mm as “relative” stenosis, and greater than 13 mm was considered normal. Unlike the cervical spine, the midsagittal canal diameter is not the ideal measurement tool of lumbar stenosis. The decrease in cross-sectional canal area is primarily a function of facet hypertrophy. Facet hypertrophy converts the morphology of the lumbar canal from a normal round or ovoid appearance to a stenotic trefoil appearance as seen on cross sectional cuts. Thus, lumbar stenosis can exist in the setting of a normal midsagittal canal diameter.

With advanced imaging, cross-sectional areas can be assessed, allowing for a more accurate measure of stenosis. In 1985, Bolender et al suggested that a dural cross-sectional area of less than 100 mm2 correlated with central stenosis [4]. A canal diameter of 100 mm2 to 130 mm2 was defined as “early stenosis”.

Central cross-sectional area, while improving the assessment of central stenosis, does not specifically address lateral recess or foraminal stenosis. Hasegawa et al reported that a foraminal height of less than 15 mm, or a posterior disc height of less than 4 mm suggested foraminal stenosis [5]. Sagittal lateral recess measurements of 3 mm or less were considered to be suggestive of lateral recess stenosis; however, this criterion has been met with significant interobserver reliability.

3 Summary

The presentation of symptomatic lumbar stenosis may include numbness, paresthesias, weakness, decreased walking and standing tolerance, and bowel or bladder changes. While lumbar canal measurements have been well described, there is no classification system to assess clinical severity of resultant neurogenic claudication.

Typically, treatment is done in a systematic fashion and may include Williams flexion exercises, NSAIDs, epidural steroid injections, or surgery. The decision for treatment is based on clinical presentation, radiographic presentation, and previous treatments. A comprehensive classification system should include clinical and radiographic criteria when assessing severity of disease. The construction of such a classification would be challenged by variability of clinical presentation, radiographic correlation, and presence of comorbidities. In addition, objective outcomes measures may be difficult to assess and quantify. Although the construction of such a classification system may be slightly useful correlating outcomes to preoperative severity, it is unlikely to alter treatment decision-making and ultimately may be a very long run for a short slide.