1. Nine patients with radiological evidence of narrowing of the lumbar spinal canal, proved at operation, are reviewed.

2. They presented with either a claudicant or a sciatic clinical picture.

3. A classification into primary or secondary spinal stenosis is described. The primary type may be due to a reduction in either the sagittal, coronal or both diameters of the spinal canal.

4. Secondary narrowing of the canal may be superimposed upon a primary anatomical abnormality or may cause narrowing in a previously normal canal.

5. The symptoms are thought to be caused by a further reduction in the size of an already narrow canal, producing traction on the nerve tissue, which is then unable to move freely.

Surgical decision-making in lumbar spinal stenosis involves assessment of clinical parameters and the severity of the radiological stenosis. We suspected that surgeons based surgical decisions more on dural sac cross-sectional area (DSCA) than on the morphology of the dural sac. We carried out a survey among members of three European spine societies. The axial T2-weighted MR images from ten patients with varying degrees of DSCA and morphological grades according to the recently described morphological classification of lumbar spinal stenosis, with DSCA values disclosed in half the assessed images, were used for evaluation. We provided a clinical scenario to accompany the images, which were shown to 142 responding physicians, mainly orthopaedic surgeons but also some neurosurgeons and others directly involved in treating patients with spinal disorders. As the primary outcome we used the number of respondents who would proceed to surgery for a given DSCA or morphological grade. Substantial agreement among the respondents was observed, with severe or extreme stenosis as defined by the morphological grade leading to surgery. This decision was not dependent on the number of years in practice, medical density or specialty. Disclosing the DSCA did not alter operative decision-making. In all, 40 respondents (29%) had prior knowledge of the morphological grading system, but their responses showed no difference from those who had not. This study suggests that the participants were less influenced by DSCA than by the morphological appearance of the dural sac.

Classifying lumbar spinal stenosis according to morphology rather than surface measurements appears to be consistent with current clinical practice.