Influence of zygapophyseal joint orientation on hyaline cartilage at the thoracolumbar junction.

Hyaline articular cartilage from 102 thoracolumbar junction zygapophyseal joints was examined using light microscopy. One section from the upper, middle and lower third of each joint at the T10-11, T11-12, T12-L1 and L1-2 spinal levels was photographed using 35 mm color film. Hyaline articular cartilage cross-sectional area of the superior and inferior articular processes of each joint pair, at each level, was digitized using computer-aided planimetry. Differences in area were compared with joint orientation (symmetry or tropism) and geometry of each joint pair at each spinal level. Variation in hyaline cartilage cross-sectional area between joint pairs could be attributed to: a) geometric differences, b) the presence of a mortice joint, or c) osteoarthritic changes, with or without tropism. These findings were most frequently demonstrated at the transitional levels of T11-12 and T12-L1.