A New Principle in Roentgenography of the Lateral Lumbar Spine

Abstract

The x-ray examination of the lumbar spine has always been attended by considerable difficulty. Anatomically, the spine consists of twenty-four vertebral bodies separated by cartilaginous pads to permit flexibility. Roentgenographically, the demonstration of each vertebra and each intervertebral joint space is desired. This should be accomplished without distorting the shadow of the vertebral body over the joint space. As the patient lies on the side in position for a lateral roentgenogram, there is a curve in the spine due to the difference in width at the shoulder and hip areas, as compared to the waist. This is especially marked in women. There are two methods generally advocated for correction of the curve of the spine when the patient is positioned for a lateral roentgenogram of the lumbar spine. One calls for tilting the tube until the central beam of radiation is at right angles to the plane of the region involved. In the other the spine is bolstered at the waist to eliminate the curve. Compensation is thus made for the curvature, but one important factor is neglected. That factor is the nature of the beam of radiation. X-rays leave the anode of the tube in a divergent beam, only the central portion of which is perpendicular to the table top or the cassette. When the tube is tilted, as in the first method (Fig. 1), the central ray is directed through the level of the third lumbar vertebra. The intervertebral spaces in this region are demonstrated, but above this they are not well shown, being obscure in the upper lumbar and lower thoracic area. This is due to the upward curve of the spine in this region and the divergence of the x-ray beam. In the second method (Fig. 2) the spine is bolstered up to a more horizontal plane with non-opaque pads. This method completely disregards the divergent nature of the radiation. As a result, the intervertebral spaces at either end are obscured, only those in the central portion of the roentgenogram being properly demonstrated. Each method serves a purpose, but neither is satisfactory for the delineation of the entire lumbar spine on a single film. The procedure to be described will consistently give accurate results and will show more vertebral bodies and interspaces without distortion than either of the methods mentioned above. The divergent beam of radiation is utilized to definite advantage instead of being regarded as something to be avoided. The distance factor is variable, being based on the radius of the curve of the spine, instead of being fixed at some convenient level. The patient is placed in the usual position for lateral roentgenography of the lumbar spine. Because of its flexibility, and the fact that the shoulder and hip areas are wider than that of the waist, the spine lies in a long sweeping curve from the shoulders to the lumbosacral joint (Fig. 3). The tube is centered over the low point of this curve and directed perpendicularly to the table top.