A horse is said to be lame when its normal stance or gait is changed by a problem in one or more of the limbs, the neck, the trunk, or the quarters. Lameness is not a specific disease but may indicate a disorder in the musculoskeletal system. When unaccompanied by pain, the lameness may be mechanical. A horse with mechanical lameness may develop an abnormal gait as a result of scarred and thickened connective tissues or of an abnormality of movement produced by a syndrome such as stringhalt. It is important that a veterinarian properly distinguish the cause of mechanical lameness.
Physically immature horses that are subjected to repetitive stress on bones are prone to lameness. Immature bones may be anatomically normal but weak due to the age of the horse. Such bone weakness may also be caused by developmental orthopedic disease. An example of repetitive stress on bones is the continuous training of racehorses around left-handed bends. This can produce shin soreness, stress fractures, or imbalances of the feet that abnormally distribute body weight among the limbs. Other factors that cause lameness include direct or indirect trauma to a limb, fatigue in racehorses racing over long distances, or inflammation—more often than not without infection—of joints, tendons, and ligaments.
Lameness in one part of a limb will often produce soreness in another area of the limb as well. It can also lead to a secondary lameness in the fore- or hindlimb on the opposite side of the body.
The Lameness Examination
A thorough investigation of a lame horse is necessary in order to ensure a correct diagnosis and appropriate treatment. The examination begins with a full medical history. The horse's type, age, and training regimen may give important clues to the lameness. Your veterinarian will ask how much time has passed since the onset of lameness and how it has been managed. The length of time since the last shoeing will be noted, as well as any indication that the lameness improves with either rest or exercise. The horse's response to anti-inflammatory or pain-relieving medications may provide useful information. Results of laboratory tests may reveal other problems that influence overall performance.
A detailed visual inspection is followed by a hands-on examination of the limbs in weight-bearing and non-weight-bearing positions to identify any heat, pain, swelling of joints, or abnormal tissue tension. Your veterinarian will also study your horse's reactions, look for any muscle loss, and measure the range of movement in the joints. Your veterinarian will observe whether lameness seems to increase or decrease after flexing or extending the joint.
The feet are thoroughly examined, inspecting any compression of the walls or soles with hoof testers. Wear patterns of shoes and feet are noted. In addition to the legs and feet, the back and neck should be thoroughly examined with the horse restrained and standing on a level surface.
Examination during exercise is done only if the degree of lameness is minor and longterm. If lameness is major and severe (for example, a suspected fracture), additional exercise could catastrophically injure the horse. It is important to tell your veterinarian if your horse was given pain-relieving medication before a lameness examination. In some cases, a ridden assessment of the horse may be necessary, particularly with a subtle lameness or a horse that is unwilling to perform certain movements (for example, a dressage horse).
Because lameness may indicate a nerve dysfunction, a neurologic examination should always be part of the lameness examination. This might include observing the horse execute “complicated” movements such as turning short, backing, “hopping” on one forelimb (with the other forelimb held up), and negotiating a small step. These tests help identify reduced response to stimuli, weakness, or spasms, as well as abnormalities in the motor function of the major muscle groups that flex and extend the limbs.
Imaging techniques provide important information necessary to diagnose and treat specific conditions (see Bone, Joint, and Muscle Disorders in Horses: Imaging Techniques for Evaluation of Lameness). Imaging can be divided into anatomic and physiologic methods. Anatomic methods are used to view physical structures, and physiologic methods assess how the anatomy functions. Anatomic imaging methods include x-rays and ultrasonography. Physiologic imaging methods, including scintigraphy and thermography, evaluate metabolism or circulation, completing the picture of the disorder. Imaging techniques may help narrow the problem to a specific region when other diagnostic methods fail. Imaging may also be necessary if the lameness is very subtle, or if the horse resists handling or an injection. Imaging may also help prevent injury by allowing early detection of the physiologic changes associated with injuries.
Arthroscopy can be used to both evaluate and treat musculoskeletal disorders, particularly those involving the soft tissues of the joint. It is a minor surgical technique in which an endoscope (a long, flexible tube with a tiny camera in the tip) is inserted through a small surgical incision. Most arthroscopies take place with the horse under general anesthesia. Because it is a minimally invasive surgery, arthroscopy allows for rapid healing of soft tissues.
With diagnostic arthroscopies, an attached camera transmits images to a monitor allowing the veterinarian to see inside the joint. Corrective surgeries (such as removal of bone fragments or cartilage, or repair of fractures) can often be performed at the same time. Arthroscopy also enables biopsies within the joint.
Endoscopes may also be used to explore and correct problems involving the tendons or bursae, particularly in cases of infection. For a number of disorders, these techniques have revolutionized treatment and dramatically improved recovery rates.
The use of regional, or local, painkillers (analgesics) to help diagnose lameness is an important part of the examination. This procedure is done before x-rays are taken. It is used when physical examination fails to identify the affected area (for example, in cases such as superficial foot pain, inflammation of the navicular bone and forefoot of the horse, traumatic joint disease, or inflammation of a ligament). A horse given diagnostic analgesia should be lame enough that any improvement can be detected. In conditions of severe lameness, the analgesia should be used with great care. Suddenly removing the protective effect of pain can cause a horse to further damage an injured area.
In most cases, interpreting the results of diagnostic analgesia is fairly straightforward. Pain reduction lessens the lameness, helping your veterinarian isolate the location of the injury. But various factors may complicate the procedure. Severe pain can be difficult to block fully. Also, mechanical and neurologic lameness, which are not necessarily painful to the horse, may be undetectable with analgesia. Sometimes a local anesthetic diffuses more widely than planned, reducing diagnostic accuracy. The arrangement of nerves in a given area may vary from horse to horse, and visible lameness may lessen as a horse “warms up.” Overall, however, regional analgesia remains very useful for diagnosing lameness.
Last full review/revision July 2011 by Russell R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Andrew P. Bathe, MA, VetMB, DACVS, DEO, MRCVS; Leo B. Jeffcott, MA, BVM, PhD, FRCVS, DVSc, VD; Svend E. Kold, DMV, MRCVS, RCVS Specialist in Equine Surgery (Orthopedics); C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS; Tracy A. Turner, DVM, MS, DACVS, DABT; Stephanie J. Valberg, DVM, PhD, DACVIM; John F. Van Vleet, DVM, PhD