Sidewinder gait, a distressing condition with a grim prognosis, can have neurologic or musculoskeletal causes in horses, researchers report.
Researchers with the University of California, Davis, and the Animal Health Trust in England set out to learn more about the condition.
Horses that suffer from the syndrome are sometimes referred to as side walkers or crab walkers. The unusual gait characterized by a disjointed movement in which the trunk, pelvis, and pelvic limbs drift to one side while the thoracic limbs are usually normal.
In severe cases, horses spin or circle in one place, with their pelvic limbs moving in one direction while the thoracic limbs move in a compensatory manner.
“The complexity of this gait and apparent difficulty of affected horses to stand in one place, or to stand symmetrically loading the pelvic limbs, makes its investigation a diagnostic challenge,” Monica Aleman and her colleagues wrote in the Journal of Veterinary Internal Medicine.
“This syndrome is poorly understood and scarcely reported in the literature.”
The retrospective case study centered on horses seen at the William R. Pritchard Veterinary Medical Teaching Hospital at the University of California, Davis, and the Centre for Equine Studies at the Animal Health Trust in Newmarket, England. It also included input from equine private practices from 2000 to 2019.
Anecdotally, this gait has been presumed to have a sudden onset in older horses, usually with a poor prognosis that often results in euthanasia. Anecdotal reports also suggest some horses with more insidious onset problems have historically been awkward about picking up their feet for farrier work.
The authors hypothesized that sidewinder gait has various causes, including musculoskeletal, neurologic, or a combination of conditions resulting in this complex gait.
Twenty‐four horses of various breeds, with an average age of 18.9, were included.
The study team reported that onset was acute in 10 of the cases, sub-acute in six, and insidious in eight.
Sixteen of the cases were identified as having neurologic causes. They comprised five cases involving dynamic thoracolumbar spinal cord compression, two confirmed and two presumed cases of equine protozoal myeloencephalitis, four cases of thoracic myelopathy of unknown cause, two of gliosis, and one involving thrombosis of thoracic spinal cord segments.
Non‐neurologic causes were identified in eight cases. They comprised four cases of osteoarthritis of the coxofemoral joint, two multiple displaced pelvic fractures, a bilateral rupture of the ligamentum capitis ossis femoris in one case, and severe myonecrosis of multiple pelvic limb muscles in another.
The case fatality rate was 79% (19 of the 24 were euthanized). Resuming previous physical activity was not achieved in the surviving horses.
The authors concluded that sidewinder gait is usually observed in older horses and can have neurologic or musculoskeletal causes.
“Electromyography can be used as a diagnostic aid to determine neurologic versus non‐neurologic disease and further localize those of neurologic origin.”
The condition often has a poor prognosis, they said.
Discussing their findings, the researchers said the horses with neurologic disease tended to walk drifting and leaning toward the most affected side with the contralateral limb abducted.
Horses with musculoskeletal disease walked drifting and leaning contralateral to the most affected side likely due to pain, mechanical inability to support the limb, or both.
Evaluation and identification of the cause was often a diagnostic challenge because of the constant leaning and spinning to one side in some horses. “Sedation that might be needed to perform certain procedures can exacerbate leaning to the point of collapse, making further examination challenging or not possible.”
The study team comprised Aleman, Emily Berryhill, Kevin Woolard, Charlotte A. Easton‐Jones, Tania Kozikowski‐Nicholas, and Isabelle Kilcoyne, all with the University of California, Davis; and Sue Dyson, who was then with the Animal Health Trust.
Sidewinder gait in horses
Monica Aleman, Emily Berryhill, Kevin Woolard, Charlotte A. Easton‐Jones, Tania Kozikowski‐Nicholas, Sue Dyson and Isabelle Kilcoyne
Journal of Veterinary Internal Medicine, 1 August 2020 https://doi.org/10.1111/jvim.15870