LAMENESS IN THE HORSE: AN OWNER'S OVERVIEW
Adapted from the Online Horse Health Course (Available Summer 2010)
My Horse University
Horses are remarkably strong and adaptable creatures. The circumstances of domestication and use, coupled with the design of their own bodies, however, make them highly susceptible to lameness – the catch-all term for a host of injuries and ailments that impede a horse’s ability to move normally. Lameness can vary from mild to severe and from transient to permanent. Almost every horse will experience some kind of lameness during its lifetime.
To be able to identify and understand lameness in horses, you must know how to distinguish between normal and altered movement. It is helpful to have a working grasp of equine anatomy, conformation, and biomechanics. Anyone involved in the care and welfare of horses should also have some familiarity with the many types of lameness that can affect a horse in various parts of its body and feet, as well as what can be done to try to prevent lameness.
Though lameness is a term that covers a broad spectrum of ailments, it can be defined simply as an abnormality in a horse’s movement caused by pain or reduced range of motion. It is commonly used interchangeably with the term unsoundness since a “sound” horse is one that is not lame. Though often thought of as a problem of the feet or legs, lameness can involve virtually any part of the body and can originate in bone or soft tissue.
Veterinarians often use a grading scale to describe various degrees of lameness. Most use a scale from 0 to 5, with 0 being sound and 5 being non-weight bearing on a limb.
Additional terms used to categorize lameness are acute and chronic. Acute refers to lameness that came on recently and often suddenly while chronic refers to an ongoing lameness that the horse has had for a longer period of time. Both acute and chronic lameness can fall anywhere on the severity scale; but, in general, chronic lameness tends to be relatively mild.
Other important variables of lameness are whether it is persistent or intermittent, and progressive or static. Many people confuse the terms persistent with chronic, but the latter refers to the length of time of the problem while the former means that the lameness (which could be recent or not) has been consistently observable since its onset – not coming and going.
Figure 1. Lameness can involve any part of the body of a horse/ This veterinarian is checking a horse for back soreness. (Image right)
Causes of Lameness: 16 Disease Processes
Lameness has a dizzying array of causes, but they generally fall into one of sixteen disease processes. These are easier to remember if you use a memory aid popular with veterinary students, the acronym “DAMNIT”:
D: degenerative, developmental
A: allergic, autoimmune
M: metabolic, mechanical
N: neoplastic (tumors), nutritional
I: infectious, inflammatory, immune-mediated, ischemic (low blood flow), iatrogenic (man-made), idiopathic (unknown)
T: traumatic, toxic
Within each of these categories are multiple causes, and some causes, such as laminitis, may span several categories.
The incidences of lameness most commonly seen result from stone bruises, trauma, laminitis (founder), overload injuries, or arthritis.
Figure 2. A horse showing signs of lameness. source: Dr. Marteniuk (Image left)
Stone bruises: Stone bruises occur when the horse steps on something high enough and hard enough to cause damage to the sole of the foot. Some weeks after a stone bruise occurs, a pinkish discoloration may appear in the sole horn, though this is a grown-out remnant of the injury, not evidence of fresh bruising. In some cases, stone bruises can lead to the development of abscesses inside the hoof, which, while generally not serious, are extremely painful and can cause severe lameness until they resolve.
Trauma: External trauma such as lacerations, contusions, puncture wounds, and fractures in any part of a horse’s body can cause mild to severe lameness, depending on the extent of the injury. In some cases, the initial injury does not cause lameness; but if there is a break in the skin and the wound becomes infected, lameness may result.
Laminitis: Laminitis is an extremely painful and potentially devastating cause of lameness that is all too common in domestic equines. It happens when the laminae – the tubule-like tissue that connects the hoof capsule to the coffin bone – become inflamed resulting from dietary imbalance (for example, grain overload), metabolic disorder, excessive impact/loading (running on a hard surface), or a reaction to certain medications. This inflammation can damage the laminae so much that the hoof wall begins to separate from the bone and rotate downwards. Such rotation is termed chronic laminitis or founder, though many people mistakenly use the latter term to refer to any stage or degree of laminitis.
Overloading: Overloading injuries occur when a horse’s limbs and/or feet experience greater force than they can safely accommodate, resulting in strains, sprains, or fractures. Performance horses are most vulnerable to overload injuries, especially those involved in sports that demand tremendous speed, rapid changes of direction, or jumping. Any horse, however, can incur an overload injury by moving or twisting suddenly, even when not carrying a rider. Overgrown or imbalanced hooves can also contribute to overload injuries.
Arthritis: Arthritis is an inflammatory condition affecting the joints causing varying degrees of pain, stiffness, and lameness. It can be the result of trauma (sudden or from repetitive stress), infection, or an autoimmune disorder. While arthritis is most often seen in older horses, it can affect horses of virtually any age. Horses that are started and trained extensively at a young age have been known to develop arthritis by the time they are 3 years old.
Signs of Lameness
Moderate to severe lameness is usually easy to recognize since a horse will often display a marked abnormality in its gait, a distinctly odd stance, or an inability to bear weight on the affected limb. In extreme cases, the animal may be recumbent and unable to stand at all. When lameness is more subtle, however, it can be difficult to spot. A horse with a subtle lameness may demonstrate any number of behaviors that are easy to misconstrue as a training problem or some other kind of problem. In order to avoid pushing a horse that may have a legitimate physical problem, it is necessary to recognize not only the obvious signs of lameness but also the more subtle ones.
Front end pain: Unilateral front end lameness is generally easy to spot since it usually involves some degree of “head-bobbing” or nodding. Other symptoms include toe pointing: the horse stands with the sore forelimb in front of the normal placement with the heel lifted partially or totally off the ground. Bilateral front end lameness may cause symptoms such as short, choppy strides, frequent weight shifting when standing, or a “sawhorse stance,” in which the front legs are “camped” or stretched forward. The hind legs are also more forward than usual as the horse tries to take more of its weight on its hind end.
Figure 3. This horse is favoring its front leg.
Hind end pain: A horse with lameness in the hind end will often take distinctly shorter steps with one hind leg (most easily observed from the side), and will frequently drop one hip much lower than the other (easiest to see from behind the horse as it is moving away). Depending on where the problem is, the horse may show secondary symptoms such as poor hind limb propulsion, back pain, difficulty picking up a lead or making transitions, bucking, cantering disunited (cross-cantering), resistance to a bend or turn, or uncharacteristic misbehavior when being tacked up.
Foot pain: The most common symptoms of foot pain include toe pointing, the “sawhorse stance,” frequent shifting of weight when standing, reluctance to turn tightly, and toe-first landing during movement.
Multiple sites: Whether the signs are distinct or subtle, pain can commonly occur in more than one location, often affecting two or more limbs. This can be a result of a systemic problem (such as laminitis) or a result of the body attempting to compensate for the initial lameness, thus putting strain on other parts of the body. Localization and identification of the cause of lameness in such cases can be particularly tricky.
Diagnosing lameness in a horse has been called both an art and a science. The science involves objective observation, often coupled with a variety of tests that can be as simple as applying hoof testers or as high-tech as magnetic resonance imaging (MRI). The art comes in when the practitioner has to assess balance and symmetry, subtleties of movement, and other symptoms that can be fleeting or open to interpretation.
Because it can be difficult to pinpoint the location and determine the cause of lameness, diagnosing it can be a lengthy and expensive process. Horse owners often find this frustrating, especially if they don’t understand what the veterinarian is doing, or why it is necessary to go through all the various procedures. Understanding the reasons for and aspects of a lameness examination will not only help you make sense of what your vet is doing but will also allow you to give your vet more precise information about your horse’s condition that may help make a diagnosis.
Almost every horse will experience some kind of lameness during its lifetime. The severity of the lameness and prognosis for recovery varies according to each particular situation. Knowledge of lameness and the problems that arise from it can help owners or handlers in the general care of their horses. Understanding the fundamentals of lameness can also be very useful when talking with veterinarians about specific lameness concerns.