Variations in zygapophyseal joint orientation and level of transition at the thoracolumbar junction. Preliminary survey using computed tomography.

Variation in zygapophyseal joint orientation at the thoracolumbar transitional junction was investigated using computed tomography (CT). The study population (N = 214) comprised 176 cases of abdominal scans, 9 thoracolumbar junction referrals and 29 cadaveric vertebral columns. Scans through the superior endplates of T11, T12, L1 and L2 were selected and joint angles calculated using a computer aided digitiser. Analysis revealed 29% of cases presented coronally oriented superior and sagittally orientated inferior joint processes at T12. This pattern occurred in 16% of cases at T11 and 0.5% at L1. A gradual transition occurred in 54% of cases and involved the adjacent inter-segmental joints of T11 and T12. Articular tropism (greater than 20 degrees) was most frequent at T11-12 (21%), followed by T12-L1 (9%).