Synovial folds in equine articular process joints

Cervical synovial folds have been suggested as a potential cause of neck pain in humans. Little is known about the extent and characteristics of cervical synovial folds in horses.

The objective of this explorative study was to determine the frequency of synovial folds in equine cervical articular process joints and to provide a characterisation of the size and morphology of the synovial folds.

Equine cervical articular process joints from 6 horses were included in the study, ranging from cervical vertebra 2 (C2) to cervical vertebra 7 (C7) bilaterally. The articular process joints were dissected, and the cranial and caudal synovial folds of each joint were measured and embedded in paraffin. Synovial folds were analysed histologically and classified according to type, as adipose, fibrous and mixed type. Factors potentially influencing fold size were investigated, including joint number (from C2/C3 to C6/C7), fold type, position of fold within the joint (cranial or caudal) and side of neck (right or left).

Synovial folds were identified in 98% of cervical articular process joints examined. The width of the synovial folds varied from 4 to 41 mm, and the height from 1 to 17.8 mm. Thirty-eight per cent of the synovial folds were of adipose type, 41% of fibrous type and 21% of mixed type. Synovial fold size was significantly influenced by the side of the neck and fold type.

This study provides a characterisation of the frequency, size and morphology of equine cervical synovial folds in 6 horses. Synovial folds were present in 98% of the cervical articular process joints examined, and the size of the synovial folds indicates that they could be damaged by acute injury or chronic disease in the cervical articular process joints.