Sagittal Diameter of the Lumbar Spinal Canal in Children and Adults

Abstract

The significance of spinal canal size as determined by radiographic measurements was first appreciated in 1934 when Elsberg and Dyke published normal standards for maximum adult interpediculate distances and demonstrated their application in the diagnosis of intraspinal tumor (3). Boijsen later showed that, in the cervical region, sagittal diameters were more sensitive than interpediculate distances for tumor detection and published maximum normal adult values for these measurements (1). These early works concerning the large spinal canal stimulated interest in the small canal. With respect to the cervical spine, it is now known that growth of posterior spondylotic osteophytes causes stenosis of the spinal canal which, if severe enough, results in spinal cord compression (10). Generally, with greater initial size of the canal, there is more space around the spinal cord and more encroachment can be tolerated without cord compression (7). Accordingly, the individual with developmental stenosis of the spinal canal is more susceptible to cord damage from spondylosis than the one with a canal of more generous proportions. We have published normal maximum and minimum values for the sagittal measurements of the cervical spinal canal in subjects from three to eighteen years of age, the latter being thought equivalent to “adult” norms (6). With these standards, in numerous adults developmental stenosis of the cervical spinal canal has been detected; some cases have been symptomatic because of complicating spondylosis, vertebral subluxation, or hyperextension injury. Children have also been observed occasionally with this anomaly but, to date, none have been symptomatic. Stenosis is not found exclusively in cervical vertebrae. It may involve the greater part of the vertebral column, as in some achondroplastic dwarfs, or it may concern only the lumbar vertebrae (a review of the literature would seem to indicate that stenosis at thoracic levels must be rare). The sagittal diameter of the lumbar spinal canal is generally larger than that of the cervical. The cauda equina occupies proportionately less space in the canal than does the cervical enlargement. Accordingly, given a comparable degree of stenosis, it seems unlikely that the cauda equina will be compressed as frequently as the cervical enlargement. Nevertheless, the greater the stenosis, the less the amount of encroachment that can be tolerated without risking compression. Purpose of Investigation The purpose of this study was to establish the range of normal values of the lumbar spinal canal midsagittal diameter in children and adults in the interest of facilitating clinical investigation of lumbar canal stenosis. Children were included because a previous publication indicated that even in early years lumbar canal stenosis may be clinically significant (8).