OBJECTIVE: To determine the proximity of neural structures to the boundaries of the interpedicular zone of the intervertebral canal in cadaveric adult human spines at the L4-5 and L5-S1 spinal levels.

DESIGN: Nine randomly chosen blocks of human lumbosacral spinal tissues were processed for histological examination and mensuration of their left and right L4-5 and L5-S1 interpedicular zones of the intervertebral canals (foramina). Measurements of the important interpedicular zone were made using a computerized morphometry system to determine (i) the ratio between the cross-sectional area of the interpedicular zone canal and its large neural structure(s), (ii) the proximity of these neural structures to the boundary of the interpedicular zone, and (iii) the horizontal length of the interpedicular zone of the intervertebral canal.

RESULTS: The mean cross-sectional area ratio of the interpedicular zone of the intervertebral canal to large neural structure(s) is 22.9 (SD 6.7)-30.8 (SD 4.4)% at the L4-5 level and 24.9 (SD 5.3)-31.1 (SD 5.3)% at L5-S1. The cross-sectional area of the interpedicular zone is 3.3 (SD 0.5)-4.8 (SD 1.7) times (X) larger than that of the large neural structures at the L4-5 level, and 3.3 (SD 0.6)-4.2 (SD 0.8) at the L5-S1 level. The mean minimum distance between the large neural structure(s) and the boundary of the interpedicular zone ranges from 0.4 (SD 0.4)-0.8 (SD 0.9) mm at the L4-5 level and from 0.4 (SD 0.4)-0.6 (SD 0.3) mm at the L5-S1 level. The horizontal length of the interpedicular zone of the intervertebral canal ranges from 8.2-12.2 mm.

CONCLUSION: Within the interpedicular zone of the intervertebral canal, the minimum distance between neural structures and the boundary can be as little as 0.4 (SD 0.4) mm. The possible ramifications of this finding are discussed with regard to a previous gross anatomical study performed by Crelin (1973) that emphasized the anatomically and clinically less relevant lateral border of the intervertebral canal.

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