Midpedicular distance: an alternative pedicular distance measurement

1. To introduce the measurement of midpedicular distance (MPD). 2. To study the correlation of the MPD measured on AP plain film and CT scan film and compared with the correlation of the interpedicular distance (IPD) measurement.

The MPD, the distance between intersection point of midvertical and midhorizontal lines drawn on the two pedicles of the same vertebra, was measured on lumbar spine (L1, L2) AP plain film. The IPD, the distance between the inner cortical shadow of the pedicles, was also measured on the same film. The measurements of MPD and IPD were then carried out on the same individual's CT scan film (which had an imprint scale). The study was performed on 35 subjects (20 males, 15 females) with an average age of 48.2 years (range 19-81 years). The correlation of the value measured on plain film and CT scan film was studied using Pearson's correlation test.

The MPD measurement on plain film had higher correlation with MPD measurement on CT scan film (L1 level: r = 0.778, L2 level: r = 0.732, p<0.001) compared with the IPD measurement (L1 level: r = 0.672, L2 level: r = 0.604, p<0.001).

The midpedicular distance measurement on lumbar spine AP plain film can better be used to reflect the pedicular distance than the interpedicular distance.