Determination of the stiffness of the equine cervical spine

This aim of this study was to test the hypothesis that the stiffness of the equine cervical spine depends on the direction of force applied and on spinal position. Muscles and nuchal ligament were removed from the cervical spines of 17 horses that were without a history of cervical or neurological disease. The cervical spines were then flexed/extended dorsoventrally (with the spine straight and with the occiput rotated 30° against T1) and laterolaterally. Mean dorsoventral stiffness was 297 N/m (±135) in flexion, 1347 N/m (±2083) in extension, 421 N/m (±164) in lateral flexion, 279 N/m (±93) in rotated flexion, and 386 N/m (±191) in rotated extension. There was a positive correlation between the length of cervical spine and stiffness for dorsoventral flexion (r = 0.63; P < 0.01) and extension (r = 0.53; P < 0.05). The stiffness of the equine cervical spine depended on the direction of the loading and was 2–7 times less than thoracolumbar stiffness in horses.