Lameness (equine)

Lameness is an abnormal gait or stance of an animal that is the result of dysfunction of the locomotor system. In the horse, it is most commonly caused by pain, but can be due to neurologic or mechanical dysfunction. Lameness is a common veterinary problem in racehorses, sport horses, and pleasure horses. It is one of the most costly health problems for the equine industry, both monetarily for the cost of diagnosis and treatment, and for the cost of time off resulting in loss-of-use.

Lameness is most commonly caused by pain, but may also be the result of neuromuscular disease or mechanical restriction. Lameness itself is a clinical sign, and not a diagnosis.

Pain is the most common cause of lameness in the horse. It is usually the result of trauma or orthopedic disease, but other causes such as metabolic dysfunction, circulatory disease, and infection can also cause pain and subsequent lameness.

Orthopedic causes of lameness are very common and may be the result of damage to the hoof, bone, joints, or soft tissue. Horses are predisposed to orthopedic lameness by conformational flaws, poor hoof balance, working on poor footing, repetitive movements, poor conditioning for a given activity, and competing at a very high athletic level.

Metabolic causes of lameness include hyperkalemic periodic paralysis (HYPP) and polysaccharide storage myopathy, which directly affect muscular function.

Circulatory causes of lameness occur when blood flow to an area is compromised. This may be due to abnormal blood clotting, as in the case of aortic-iliac thrombosis, or decreased blood flow (ischemia) to an area, such as is sometimes seen in laminitis.

Infectious causes of lameness are the result of inflammation and damage to tissue. These include problems such as cellulitis, hoof abscesses, and septic arthritis.

Mechanical lameness is caused by a physical abnormality, such as scar tissue, that prevents normal motion of a limb. Mechanical lameness does not cause pain. Classic examples of mechanical lameness include upward fixation of the patella and fibrotic myopathy, but any type of adhesion (often secondary to scarring during healing post-injury) or fibrosis can cause mechanical lameness.

Neurologic lameness may be the result of infection, trauma, toxicities, or congenital disease. Neurological evaluation of a lame horse may be warranted if the cause of the lameness is not obvious. Signs more commonly associated with a neurologic cause include unilateral muscle atrophy, paresis, paralysis, or dysmetria. Neurologic causes of lameness include:

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