The importance of evaluating horses with performance problems both in hand, on the lunge and ridden, preferably by their normal rider, has been stressed by equine orthopaedic specialist Sue Dyson.
Dyson, who is head of clinical orthopaedics within the Centre for Equine Studies at Britain’s Animal Health Trust, says a significant number of pain-related gait abnormalities in horses are evident only when the horse is ridden, and are not apparent when the horse is hand-walked or lunged.
“Even when these horses are ridden, the lameness may not be overt,” Dyson writes in the latest issue of Equine Disease Quarterly.
“While there have been many recent technical advancements in the objective assessment of gait, these are generally of limited value for detection of bilaterally symmetrical alterations in gait that result in reduced performance such as generalized stiffness, lack of willingness to work, alteration in quality of movements such as lack of hindlimb engagement and impulsion, and alteration in the rider’s feel of the contact via the reins and bit to the horse’s mouth,” she says.
Dyson says a rider often assumes that these problems are attributable to thoracolumbar region pain, because the problems are only manifest when the horse is ridden.
“When observed on the lunge, such horses may lean into the circle — often more on one rein than the other — and show exaggerated contractions of the epaxial [back] muscles.
“However, studies have shown that experimentally induced forelimb or hindlimb lameness may reduce range of motion of the thoracolumbosacral vertebral column.”
X-rays may reveal impinging spinous processes, and this finding often results in a wrong conclusion implicating thoracolumbar pain as the primary problem.
“We have demonstrated that by using diagnostic analgesia to abolish overt or subclinical lameness, the rider often appreciates an increased range of motion of the horse’s back.”
To investigate these clinical observations, Dyson and her colleagues have studied normal horses subjectively free from lameness in hand, after a flexion test, on the lunge on both soft and firm surfaces and when ridden.
The researchers objectively measured body lean on the lunge and range of movement of the thoracolumbar region using inertial measurement units placed on the thoracolumbar and pelvic regions.
“These studies established normal ranges of motion for the thoracolumbosacral spine and demonstrated that sound horses have a small degree of bilaterally symmetrical body lean on the lunge.
“We also measured body lean on the lunge in lame horses and demonstrated that there is frequently asymmetry between left and right reins, with greater lean compared with normal on at least one rein.
“Substantial improvement in lameness by performing diagnostic analgesia resulted in reduced body lean on both reins and reestablishment of symmetry between left and right reins. Likewise, when lameness was improved by diagnostic analgesia, range of motion of the thoracolumbosacral regions increased, especially in the caudal thoracic and lumbar regions.”
Dyson says the study team observed that the tendency of a saddle to slip persistently to one side is most frequently associated with hindlimb lameness. “Abolition of lameness by diagnostic analgesia results in resolution of the saddle slip.”
The saddle most commonly slips to the side of the lame or more lame hindlimb, but less frequently slips toward the less lame limb.
“Presumably saddle slip is induced by altered range of motion of the thoracolumbosacral region, which may vary among horses. Saddle slip may actually be an indicator of the likely presence of hindlimb lameness.”
She continues: “Overt lameness may not be apparent when a horse is trotting, but musculoskeletal pain may be manifest at a canter by the horse’s tendency to become disunited or repeatedly change leading limbs behind or in front, crookedness, loss of a normal three time rhythm, placing the hindlimbs either abnormally close together spatially and temporally, or placing the limbs remarkably far apart.”
These observations, she says, may be apparent either on the lunge or when the horse is ridden.
“Abolition of baseline lameness seen in hand may paradoxically make the canter appear worse if sacroiliac pain is contributing to pain and poor performance.
“These observations highlight the importance of evaluating horses with performance problems both in hand, on the lunge and ridden, preferably by the normal rider.
“Horses should be assessed in walk, trot, and canter, bearing in mind that while one aspect of the gait may improve with diagnostic analgesia, another may deteriorate. Horses should also be assessed performing the movements which they find most difficult, because in some horses this may be the only condition when the problem is manifest.”
Equine musculoskeletal expert James MacLeod, in a commentary in the same issue, says everyone agrees that lameness is a major problem in the horse world.
MacLeod, who is with the University of Kentucky’s Gluck Equine Research Center, says musculoskeletal injuries are common and potentially very serious.
“Substantial progress has been made over the last several decades in areas of both lameness diagnosis and treatment. Importantly, the future holds as much promise as ever. Science and technology are continuing to drive advances in clinical disciplines.”
Cell biology, he says, is a good example. “It is now possible to broadly compare gene expression between individual tissues and cell types.
“Data-driven scientific approaches are discovering a large number of genes that nobody realized were important. The results are providing new insights into cellular identity, normal function, and disease mechanisms in areas that have direct relevance to lameness.”
New understanding about individual cell types enables diagnostic and therapeutic strategies to be refined, he says. “Going forward, veterinarians will increasingly have access to molecular biomarker panels to help refine their list of differential diagnoses, to select optimal therapies, and for patient monitoring.
“We already hear about these approaches with cancer patients, and the same concepts are applicable for bone, cartilage, tendon, ligament, and muscle tissues.
“The clinical goals include improved sensitivity in monitoring health as well as early identification of disease problems and how the patient is responding to treatment.
“On a therapeutic level, cell-based approaches are generating high levels of interest and for good reasons. The term ‘stem cells’ is mentioned frequently. Cells can be used therapeutically to deliver beneficial equine-specific growth and differentiation factors to an area of injury, to modulate the patient’s immune system in helpful ways, and in some cases to directly generate a repair tissue.
“There is much to learn and quite a bit of misinformation being disseminated, but cell-based therapies do indeed hold a lot of promise.
MacLeod stresses the need for ongoing research to tackle equine lameness challenges. “Objective scientific research and the resulting new knowledge are absolutely key, and need to be a top priority.”
Gluck Equine Disease Quarterly is funded by underwriters at Lloyd’s, London.