Intra-articular synovial folds of thoracolumbar junction zygapophyseal joints.

Transverse histological sections from T10-11, T11-12, T12-L1, and L1-2 zygapophyseal joints were examined in 32 post-mortem spines, using light microscopy, to record the presence of intra-articular synovial fold inclusions. In addition, three mid-joint sections from each joint were photographed using 35 mm colour film. From these slides, linear dimensions of the extent of intra-articular synovial fold projection between the zygapophyseal joints were measured using computer-aided planimetry. Small, fibrous folds were commonly found at the joint margins extending from the ligamentum flavum and the fibrous joint capsule. Larger, fibro-adipose synovial folds, projecting between the articular surfaces, were also noted, particularly at T12-L1 and L1-2.