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. Pain is the most common cause of lameness in horses. 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 an abnormality in normal anatomy (such as a kneecap that is stuck in an abnormal position). Disorders caused by nerve dysfunction (neuromuscular disorders) can also cause lameness. For example, horses with stringhalt display overly flexed limbs when walking that is characteristic of the syndrome. It is important that a veterinarian properly distinguish the cause of lameness in order to treat the condition properly.
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. Developmental orthopedic disease (such as limb deformities); poor conformation (such as pigeon toes or bowleggedness); improper hoof balance or shoeing; failure to adequately condition performance horses; improper footing (hard, slippery, or rocky surfaces); hard exercise; and repetitive stresses on bones, tendons, ligaments, and joints in performance horses can also cause lameness. 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, including the use of hoof testers to look for sore spots in the sole. 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 often necessary to identify which limb or site is affected. However, it 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. Your veterinarian will walk and jog the horse to observe its gait. Usually, the lameness is more pronounced when the horse is lunged in a circle. Your veterinarian may also flex the limb joints individually to localize the affected site. 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).
The most consistent sign of lameness in one forelimb is the head nod. The head and neck of the horse rise when the lame forelimb strikes the ground, and they fall when the sound limb strikes the ground. The pelvic rise is the most consistent and easily observed sign of hindlimb lameness. The entire pelvis rises when the lame limb strikes the ground and falls when the sound limb strikes the ground. These posture changes help to reduce that amount of pressure and weight that has to be held by the lame limb.
Because lameness may indicate a nerve dysfunction, a neurologic examination is often performed as part of the lameness examination. This might include tight circles, backing, walking downhill and navigating over curbs or ground poles.
Imaging techniques provide important information necessary to diagnose and treat specific conditions ( see Imaging Techniques for Evaluation of Lameness 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, ultrasonography, computed tomography (CT scan), and magnetic resonance imaging (MRI). Physiologic imaging methods, including scintigraphy and thermography, evaluate metabolism or circulation of the entire horse, 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.
The use of regional, or local, nerve blocks (local anesthetics or analgesics) to help diagnose lameness is an important part of the examination. In addition to diagnosing lameness, nerve blocks can allow some surgical procedures to be performed without the need for general anesthesia. They can also be used to temporarily relieve pain. 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.