The narrow lumbar canal. A clinical and radiological review.

The importance of the size and shape of the spinal canal in relation to the occurrence of symptoms of cord or root compression, especially when spondylotic changes supervene, has been recognised for some time. Most of the earlier work concerned the cervical region (Pallis, Jones and Spillane 1954), but in more recent years a similar condition has been fully recognised in the lumbar region also (Verbiest 1954 ; Epstein, Epstein and Lavine 1962 ; Teng and Papatheodorou 1963 ; Highman 1965). In the neck the antero-posterior measurement of the spinal canal is easily assessed on the lateral radiograph, and absolute values have been postulated for normal individuals (Wolf, Khilnani and Malis 1956; Payne and Spillane 1957; Burrows 1963), so that a small canal can readily be appreciated. In the lumbar region comparable antero-posterior measurements are not so widely used, partly at least because the posterior margin of the canal is more difficult to locate in the lateral radiograph. Verbiest (1954), in fact, stated that it was not possible to recognise the anomaly of a narrow lumbar canal on plain radiography and relied entirely on myelography. Huizinga, Heiden and Vinken (1952) made charts of the normal maximum and minimum antero-posterior measurements of the lumbar canal in human skeletons. Verbiest (1955) measured the diameter of the canal at operation in cases of developmental narrowness, and illustrated the instrument used. On the other hand, referring to the plain radiographs, Epstein and colleagues (1962) postulated that any antero-posterior diameter of less than 1 5 millimetres indicated narrowing of the canal. They also measured the interpedicular distance in the lumbar region by the method described by Elsberg and Dyke (1934) and found that the distance was at the lower limits of normal in a third of cases. In an attempt to recognise the presence of narrowing of the lumbar spinal canal on the plain radiographs we have for some years been relating the antero-posterior diameter of the canal and the interpedicular distance to the size of the adjacent vertebral body. Although we do not claim any detailed accuracy for the method, we have found it of some value in assessing the size of a lumbar spinal canal. We wish therefore to describe the method, and also to present an analysis of thirteen patients found to have a narrow lumbar canal with spondylosis: ten of these patients came to operation.