What your veterinarian does in a systematic lameness examination and whyAs horses move, there is a tremendous concussive force exerted upon their feet, limbs, joints, muscles, and tendons.
Concussion to the feet, limbs, and soft tissue occurs as the feet hit the ground and the limbs bear weight. There are additional concussive forces when the limbs propel the horse's body forward. Several factors that work together may cause any one or a combination of these structures to become sore or injured. As a result of an injury or soreness, a horse's willingness to work, go to the paddock, load in the gate, race, and its way of going may be adversely affected.
The factors that may affect a horse's physical soundness include: the horse's age, conformation, shoeing, conditioning, gait, speed, stride length, appropriate tack and its fit, handling, footing, and the actions of the people on and around it. Any one or a combination of these factors may cause a horse to become mildly sore or injured. Horses respond to this musculoskeletal soreness and injury much the same way people do. Because of varying personalities and pain thresholds, a particular problem may cause one horse to back off work and come up lame, while another horse with the same problem may barely be adversely affected at all.
Furthermore, a primary problem in one joint or leg may result in a secondary injury or soreness in the same or another limb. This secondary problem occurs as a horse attempts to ease its pain and discomfort from the initial injury by compensating and altering its way of going. Often the compensatory secondary soreness that develops is more of a problem for the horse and trainer than the initial injury or soreness. Specific injuries and soreness can alter a horse's gait in characteristic ways. However, the slow development of a primary problem or the occurrence of one or more secondary injuries may obscure the early recognition and subsequent treatment of the initial injury.
Recognition and identification of musculoskeletal problem areas of a horse may be done by a variety of examination methods and techniques. In some instances, a description of a horse's way of going is all that is needed to localize the affected joint, bone, or soft tissue. The other extreme that may be required to definitively identify the affected area or areas is an in-depth, time-consuming lameness exam with auxiliary tests and diagnostic equipment.

The exam
The following procedures may or may not be performed during a particular lameness examination, depending upon the situation. The end result of any type of lameness exam, however, is the same: the identification of injured or significant sore areas. Once an area is localized, steps are taken to determine the extent and severity of the injury so a prognosis can be made and appropriate treatment started.
A good history is important. Some injuries are associated with age, way of going, and track conditions. Historically, horses that are lame or sore may not want to change leads, may get out, may wash out, may not want to extend, and may not trot in hand when brought out of their stalls. The history may also provide clues to the duration, change, or addition of a problem.
Following the history, examination of a horse for lameness begins with careful observation of the horse at rest. Visual examination of the feet, limbs, head, neck, and body may indicate a suspect area. A horse's body stance and limb placement may reveal all the legs are rested equally or only an affected foreleg or handle is continuously rested. A horse may stand "pointing," with an affected forelimb held in front of the other. One or more legs may be abnormally far underneath, in front of, or behind the body. If the horse takes a step or turns, an involved limb may have a short stride or slower return to weight bearing. Fillings involving joints, abnormal or asymmetrical swellings, abrasions or scars, and asymmetrical vein distention in one limb versus the other are also noted.
Evaluation of conformation may provide clues to suspect areas that would not be able to withstand the repetitive concussive forces that are encountered on a daily basis. A horse's head and neck weigh approximately one-fifth of the horse's total body weight and act as a balancing beam. Thus, because of their conformation and forward center of gravity, about two-thirds of a horse's weight is distributed over their front legs. If a horse's conformation is adequate to good, and care of the feet is adequate or better, the stress and concussive forces associated with training and racing are more equally distributed throughout the support structures of the front legs, hind legs, and body. These are the horses that generally withstand training and racing stresses most successfully.
After visual examination of a horse at rest, hands-on palpation is the next step in the evaluation of a horse's soundness. While a horse's leg is weight-bearing, and again when the leg is flexed and non-weight-bearing, one feels for any abnormal heat, swellings, pulses, asymmetries, or the response and extent of pain to palpation. The palpation examination includes all of the joints, limbs including feet, body, and neck. In addition, some veterinarians will palpate points (i.e., acupressure, Gochenouer, etc.) that elicit a response from a horse when associated joint or soft tissue structures are adversely involved. Hoof testers are applied to each foot and the size, shape, balance, and conformation of each foot is evaluated at that time.

Horse in motion
The next examination level involves the horse in motion. With the horse walking in a straight line, circle, or figure eight, it is observed from the side, front, and back. Many features of the gait are evaluated. These include: the length, symmetry, and arc of the stride; placement and flight path of the feet; carriage of the head, neck, and hips; and symmetry and flight paths of the front and rear legs. Besides watching a horse go, valuable clues to subtle changes may also be gained from careful listening to differences in sounds as the horse's feet hit the ground.
Examination of the moving horse at the trot often provides the most useful information. The trot is a diagonally symmetrical gait that places more stress on involved limbs. In order to minimize discomfort, a horse will attempt to shift weight off of a sore limb. Head "bobbing" and hip "hiking" are often the result of this attempt to take weight off of the affected limb when it bears weight and hits the ground. Consequently, the head comes down when the sound or more sound front leg bears weight. While the horse is trotting in a straight line, circle, or figure eight, observation is made from the front, side, and back. Once again, careful listening may also provide valuable clues.
The next level in the localization of a lameness involves manipulative and flexion tests. By using a series of these tests, the pain in an involved leg may be temporarily increased. The lameness thereby becomes exaggerated and more noticeable. The use of hoof testers may again be used at this time to put pressure on a sore area of the hoof and to temporarily exaggerate a lameness.

Nerve and joint blocks
In cases where the preceding steps do not identify or localize a gait abnormality, specific nerve and joint blocks may be performed. These blocks are useful diagnostic tools because they desensitize specific areas and can alleviate pain. A soreness may be localized to a specific area if a horse's gait improves after a diagnostic nerve block. In cases of soreness or lameness of equal intensity in front or rear legs, a diagnostic block may result in the apparent worsening of the "unblocked" nondesensitized leg. This is due to the temporary removal of pain in the "blocked" sore leg, thus returning it to normal or nearly normal functioning. Consequently, the other leg appears worse.
There are other steps that may be involved in a lameness examination of a horse. These can include the evaluation of a horse at the canter and under saddle. Other diagnostic tools can include: radiographic series, ultrasonic series, contrast radiography, fluoroscopy, thermography, scintography (nuclear medicine), high speed cinematography and gait analysis, force plates, and arthroscopy.
Once an area is localized, further diagnostic tests such as radiography, fluoroscopy, or ultrasonography may be done to determine the extent of an injury and provide a realistic prognosis. Following the localization and identification of an injury, a plan is developed for the short-term management and long-term treatment of the injury-the goal being to return and maintain the horse at normal function.
An important key to successful lameness examinations is to appreciate the obvious and to recognize the obscure.