This weekend I’ll be working at the All Breed Open Horse Show, where amateur equestrians can compete in a variety of events, including Showmanship, Trail, Western Riding, and Hunter Under Saddle. Most of these competitions are enjoyable and safe for both horse and rider; however, high level events, such as Show Jumping and Cross-Country, can induce strain injuries in elite equine athletes. In a 1999 review, Gillis reported on injuries to ligaments associated with the vertebral column, particularly those incurred by horses in Show Jumping, where extreme flexion of the spinal column is common.
Because injury to the supraspinous ligament (SSL) may be associated with back pain in horses, Henson and colleagues (2007) used ultrasonography to examine this connective tissue structure in unridden and ridden horses, and in horses with clinical back pain. Their hypothesis was that unridden horses (n=13) should have fewer ultrasonographic changes, indicative of desmopathy (inflammation of or damage to the supraspinous ligament), than do ridden horses (n=13) and horses with clinical back pain (n=13). The diagram below illustrates the ligaments of the human vertebral column, but these structures are very similar in all mammals. The bodies of individual vertebrae are anterior in the bipedal human (ventral in quadrupeds), and the spinous processes are posterior (dorsal in quadrupeds). In horses, the SSL runs along the dorsal tips of the spinous processes, from the base of the skull to about the level of the fifth lumbar vertebra; as in humans, the equine SSL is expanded in the cervical region to form the ligamentum nuchae. The SSL receives multiple tendon insertions from the longissimus dorsi, an intrinsic back muscle.
Sagittal view of the human vertebral column and associated ligaments
Three categories of abnormal SSL appearance were considered in the analyses of the ultrasonographic images: 1) hypoechoic images (acute desmopathy), 2) hyperechoic images (chronic desmopathy), 3) loss or disruption of the parallel fiber pattern. In the 39 horses examined, 163 abnormal findings were identified, with an average of 2.08 per horse. Although the imaging area for the SSL extended from thoracic vertebra 6 (T6) to T18, no lesions were found between T6 and T10 (withers region, where the SSL is wider), and 68% of the lesions were found between T14 and T17. Most importantly, there was no significant difference in the number of SSL lesions identified, for the three groups of horses: ridden, unridden, and those with clinical back pain. The authors recommend that a variety of approaches should be used to evaluate equine back pain, including ultrasound, clinical history, local anesthesia techniques, and physical examination. Because of the similarities in vertebral ligament structure in all mammals, these findings may have relevance to whiplash injuries and chronic lower back pain in humans.
“Special Horse Show Edition” of Weekend Animal Disease Models posts
Gillis, C. (1999). Spinal ligament pathology. Vet. Clin. North Am. Equine Pract. 15, 97-101.
Henson, F.M., Lamas, L., Knezevic, S., Jeffcott, L.B. (2007). Ultrasonographic evaluation of the supraspinous ligament in a series of ridden and unridden horses and horses with unrelated back pathology. BMC Veterinary Research, 3(1), 3. DOI: 10.1186/1746-6148-3-3