The Effect of the Rider
The majority of domesticated horses are required to carry the weight of a rider on their backs, although this weight is distributed by the muscles of the back, it will still have a direct impact on the skeleton. The shape of the equine back is determined by the thoracic and lumbar vertebrae, the thoracic vertebrae attach to the ribs and have prominent dorsal spinal processes which extend upwards from the vertebral body and create attachment points for the muscles that support the forelimbs, head and neck. The first seven thoracic vertebrae are hidden behind the large scapula (shoulder blade) and create the shape of the withers, the dorsal spinous processes become shorter to the base of the wither at approximately the 10th thoracic vertebrae and then level out to form the flatter shape of the back above the rib cage. Where the rib cage ends the lumbar vertebrae begin, lumbar vertebrae have long transverse processes extending from each side, these provide attachment for the broad back muscles that support the hind quarters.
Between each vertebrae there are intervertebral joints that allow movement to occur though the spine, this movement is limited and controlled by the ligaments and muscles of the back. When weight is applied to the horse’s back the intervertebral joints extend, this has the effect of bringing the dorsal spinous processes closer together and has been speculated as a factor in the development of kissing spines (a condition where the spinal processes touch resulting in pain and thickening of the processes). Ridden horses have also been found to show increased lateral stiffness through the thoracic spine, while increasing the weight of a rider has been shown to influence the stride patterns in horses. With a horse ultimately changing it's natural gait patterns to compensate for the weight of a rider it is easy to see how over time injuries and break down may occur. Despite the skeleton being designed for concussive absorption, small amounts of strain are likely to occur at the joints and soft tissue, over time this can result in arthritic changes, muscular pain and compensatory movement. Correct training programs are essential to ensure the skeleton has time to adjust to the demands put upon it and reduce the risk of injury long term.
The majority of domesticated horses are required to carry the weight of a rider on their backs, although this weight is distributed by the muscles of the back it will still have a direct impact on the skeleton.
36 December 2013, Issue 3 www.everythinghorseuk.co.uk www.everythinghorseuk.co.uk December 2013, Issue 3 37