Radiologic Considerations in Preplacement Examinations of the Lumbar Spine

Abstract

In setting up a program for interpretation of the radiographs of the low back it was immediately realized that some specific rules would have to be established that would be uniform, easily adhered to, and adequately interpreted. One of the main conditions requiring this attention was spondylolisthesis. For this paper we will limit ourselves to the classification used in reporting this defect, its incidence, and that of isthmus defects, as noted in 4,000 consecutive pre-employment radiographic examinations of the low back. As Dr. Winston has explained (p. 664), the views obtained included anteroposterior, lateral, and right and left posterior obliques. The anteroposterior and lateral views were made on 14 × 17-inch films, with the latter view centered 11/2 inches below the crest of the ilium. The oblique views, on 10 × 12-inch films, were centered at the lumbosacral interspace. These radiographs were all interpreted twice, with a review of any in which there had been a difference of classification. It is essential that certain standards of reporting be established so that the report sent to the Medical Director be adequately understood. Realizing that occasionally we have foreshortened vertebral bodies, we decided to use the perpendicular line test which was originally described by Ullmann, but more recently by Garland. We refer to this, for the sake of adequate reporting, as the “Garland sign.” We well realize that with this criterion a few instances of spondylolisthesis may not be reported as such, but feel sure that all instances measuring up to this standard will be true spondylolisthesis. We have seen instances in which this entity has been reported on the original interpretation but did not fulfill the perpendicular line requirements. In our final report and classification such cases were classed as isthmus defects, without spondylolisthesis according to the Garland sign. Thus, the reader knows that the defects were present but that the vertebral body had not slipped far enough to touch the perpendicular line from the anterior superior tip of the vertebral body just below. Using this criterion, we found the incidence of spondylolisthesis in our series to vary from 2.7 to 5.3 per cent per thousand (Fig. 1). We regard this as a normal variation in groups of 1,000 relatively young men and believe that it certainly represents the percentage of true anterior slip according to the perpendicular line test. The incidence for the entire group is slightly below that found by Friedman, Fischer and Van Demark, Bailey, and others. The last lumbar vertebra was found to be by far the most frequently involved (Table I). As will be noted, we found no spondylolisthesis above the fourth lumbar vertebra, according to the perpendicular line test.