Quantitative Assessment of the Fifth Lumbar Spinal Canal by Computed Tomography in Symptomatic L4–L5 Disc Disease

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Abstract
Interpedicular distance, interfacet distance, midsagittal diameter and cross-sectional area at the upper aspect of the 5th lumbar spinal canal were measured from the computed tomographic (CT) scans of the spine performed in a period of 1 yr. The patients were divided into 4 groups. Group I (25 patients) was the normal control group. Group II comprised 29 symptomatic patients who were thought to have an L4-L5 herniated nucleus pulposus (HNP) by CT and did not undergo surgery. Group IIIA was made up of 24 patients who underwent an L4-L5 discectomy and had favorable results and group IIIB (3 patients) included those who failed to improve following surgery. The symptomatic patient with an L4-L5 HNP by CT who did not undergo operative treatment had a mean canal size as measured by midsagittal diameter and cross-sectional area that was smaller (P < 0.05) than in a normal control group. In the patients who required an L4-L5 discectomy, these same measurements were smaller (P < 0.001) when compared with the nonoperative group. In the 3 failure patients, all 4 measurements were significantly smaller than in patients in group IIIA with the interfacet distance and the cross-sectional area differences being the greatest (P < 0.001). The patients who are likely to undergo operative treatment have a midsagittal diameter that is < 1.6 cm and a cross-sectional area that is < 2.5 cm2. In the congenitally small canal the cross-sectional area more accurately reflects the degree of stenosis and a cross-sectional area that is < 2 standard deviations from the normal or < 2 cm2 is considered to represent congenital spinal canal stenosis.