Hind-limb lameness sparks uneven movement in the area of the horse’s back underneath and behind the saddle, researchers report.
The asymmetry identified in the back was dependent on the hind-limb lameness, they found.
When nerve blocks were used to improve hind-limb movement, the asymmetry reduced in the thoracolumbosacral region – that’s broadly the area where the saddle is placed – and the range of back motion improved.
Researchers Line Greve, Sue Dyson and Thilo Pfau set out in their study to investigate changes in thoracolumbosacral movement when pain-causing lameness was improved by local analgesia using nerve blocks.
The trio, writing in The Veterinary Journal, noted that lameness, thoracolumbosacral pain and a reduced range of motion often coexisted.
A better understanding of their relationship was needed, they said, given that previous research had highlighted challenges in establishing whether changes in thoracolumbar movement were caused by primary back pain or were secondary to lameness.
Thirteen horses with different types of hind-limb lameness were enlisted for the study.
The animals were trotted in straight lines and lunged on a 10-metre diameter circle on left and right reins both before and after their lameness was substantially improved by the use of nerve blocks to deal with the discomfort.
Inertial sensors were used to collect data from the withers and along the back.
The back asymmetry and reduced range of motion associated with lameness were both altered immediately when the lameness was improved by analgesia.
The trio had thought this would be the case, especially given that previous research in 2013 and 2014 by Dyson and Greve had shown that saddles slipped consistently to one side in around half of horses with hind-limb lameness, indicating that it may alter thoracolumbar movement in ridden horses.
Another study by the pair suggested that lameness resulted in a reduced ability in horses to use the thoracolumbar epaxial muscles correctly.
The findings of the latest research provided a starting point for learning more about the basic mechanisms by which lameness may lead to altered back functionality, they said.
“Whether different changes in thoracolumbosacral movement are seen in horses with primary thoracolumbosacral pain and no associated lameness remains to be determined.”
The vertebral column may be critical in providing an efficient transfer of force between the hind limbs and forelimbs, they said, and it was possible that the reduced range of motion of the vertebral column observed in the current study was related to the compensatory mechanism of force distribution.
Their findings supported the clinical observation that reduced thoracolumbar range of motion may point to primary hind limb lameness or sacroiliac joint region pain.
“No conclusions about specific types of lameness can be drawn because of the small number of horses,” they said. “However, common patterns were identified.”
The findings also support clinical observations that a rider may feel back stiffness in a horse with a restricted hind-limb gait. The top line muscles, especially behind the saddle, may be sore. This does not necessarily mean that the horse has a primary back problem causing the limited hind-limb impulsion and engagement. It is equally if not more likely that the back stiffness and soreness is secondary to primary hind-limb lameness.
Greve is affiliated with the Centre for Equine Studies at the Animal Health Trust and the Royal Veterinary College in London. Dyson is with the Centre for Equine Studies and Pfau is with the Royal Veterinary College.
L.Greve, S.Dyson, T.Pfau, Alterations in thoracolumbosacral
movement when pain causing lameness has been improved by diagnostic analgesia
The abstract can be read here.