Preliminary data on the effect of osseous anatomy on ex vivo joint mobility in the equine thoracolumbar region

Summary Reasons for performing study The thoracolumbar region is clinically important in horses; however, the link between joint mobility and bony joint morphology has not been tested quantitatively. Objectives To establish which aspects of vertebral morphology correlate with ex vivo range of motion in the thoracolumbar region of Equus caballus, and demonstrate methodologies for linking vertebral form and function. Study design Morphometric study of osteological specimens. Methods A digital model was created of a disarticulated thoracolumbar region to examine bone‐to‐bone interactions during in silico bending. Linear measurements and geometric morphometric landmarks were taken from 6 vertebrae per specimen (specimens n = 5, vertebrae n = 30), and compared with experimental range of motion in dorsiflexion, ventroflexion, lateroflexion and axial rotation data using Spearman's rank correlation, to test a priori hypotheses regarding thoracolumbar functional anatomy. Results Decreased sagittal mobility correlates with a tall, heart‐shaped vertebral body, although bony interactions restrict dorsiflexion more than ventroflexion. Lateroflexion correlates with a narrow vertebral body, a short transverse process lever arm, and narrowly placed horizontally oriented zygapophyses. Lateral joints also restrict lateroflexion in the posterior lumbar region. Axial rotation is related to the shape of the zygapophyseal joint. Conclusions These preliminary data suggest that vertebral joint morphology does determine experimentally measured range of motion, but patterns depend upon the type of motion. These methods are useful for identifying functionally relevant morphological variation and suggest osteological features are important in determining motion.