Posterior element variation at the thoracolumbar transition: a morphometric study using computed tomography

Variation in posterior element orientation at the thoracolumbar junction was investigated using computed tomography. The study population (n = 630) aged from 10 to 93 years, comprised 551 abdominal scans, 26 thoracolumbar junction scans and 53 cadaveric spines. Scans of T10-11, T11-12, T12-L1 and L1-2 zygapophyseal joints were selected, with joint orientation calculated using a computer-aided digitizer. In 59·6% of cases the change from coronal to sagittal joint orientation was achieved gradually over three levels between T10-11 to T12-L1. This progressive transitional pattern was identified between T9-10 to T11-12 in 0·5% and between T11-12 to L1-2 in 11·4%. An abrupt transition between T11-12 T12-L1 occurred in 18·1% of cases, with 10·2% at T10-11-T11-12 and 0·2% at T12-L1 to L1-2. Zygapophyseal joint asymmetry (>10°) was most frequent at T11-12 (40·8%), followed by T12-L1 17·7%). Ossification anomalies of the L1 transverse processes were demonstrated in 2·06% of cases.