Lameness is any abnormality in a horse's gait. It is an indication of a structural or functional disorder in one or more limbs of a horse that is apparent during motion or in the standing position. Another term for lameness is claudication.
What Causes Lameness?
Most often, lameness is due to muscle, joint or bone abnormalities. However, nervous system and, on rare occasions, circulatory system disorders, should be considered. In addition, lameness can be triggered by trauma, congenital or acquired abnormalities, infection, metabolic disturbances, circulatory and nervous disorders or a combination of these.
How to Diagnose Lameness
An important part of diagnosing and treating lameness is collecting a complete history of the horse. Veterinarians often have a good clue as to what lameness problems are likely to affect your horse by simply reviewing the animal's history. Here are some factors to consider in diagnosing lameness:
Age. Age can be a significant clue. Neonates can walk with angular limb deformities and joint infection (i.e., septic arthritis). Young horses can walk with signs of bone development disorders (e.g., osteochondritis dessicans). Older horses may walk with ringbone (i.e., phalangeal exostosis).
Sex. On some occasions, the sex of a horse may be useful in diagnosing lameness.
The breed and use of the horse. How horses are ridden or how they perform can predispose them to different types of injury to joints and muscle. For example, knee chips (i.e., carpal chip fractures) occur more commonly in racehorses, whereas hock disease occurs more often in Western and English performance horses.
Severity and duration. Severe lameness that develops very quickly (i.e., acute) is most often associated with foot abscess. However, severe muscle and tendon trauma, bone fracture, infection need to be considered. Mild lameness that slowly progresses is more commonly associated with chronic arthritic changes.
Location. In general, the vast majority of lameness in horses occurs secondary to joint pain from the fetlocks (equivalent to the knuckle in people) in the front limbs distally (downward), and the hock (equivalent to the ankle in people) distally in the rear limbs.
How a lame horse is examined depends largely on the type of lameness. Some lameness cases are easily diagnosed by history, presentation and a quick physical examination. However, other lameness disorders (often mild lameness), may require a lot of observation, joint flexion, palpation local anesthesia (i.e., nerve blocks), and in some cases radiography, ultrasonography, nuclear scintigraphy and other diagnostic modalities to diagnose.
In general, the lameness examination starts with a good look at the horse's posture and motion. After that, the sequence of events depends on the specific problem and the veterinarian's experience. The following sequence will vary from case to case.
Hoof testers. Pressure is applied by hoof testers (plier-like tools) to test for hoof pain.
Palpation. Next, the veterinarian may feel the anatomy of the limbs, looking for swelling, pain and heat.
Flexion of the joints. This is equivalent to a person with some knee arthritis getting into a catcher's position for a minute or two and then getting up and trying to walk.
Diagnostic nerve blocks. Horses can't tell us where it hurts. Often diagnostic nerve blocks are performed to identify whether or not pain is relieved. The nerve blocks often begin low on the limb and move upward. Lidocaine or carbocaine are injected in the area of the nerve and then anything this nerve senses will be nearly pain free. If the area of pain is within the area of pain block (analgesia), then the animal will be relatively sound for a short period. If the horse is not improved, then the next block is performed up the limb. This continues until pain is relieved. This allows the veterinarian to localize the pain and focus the next level of diagnostic techniques on those areas.
Radiography. Radiography is a method to evaluate bone and soft tissue. The radiograph machine generates X-rays that pass through the part of the body in question. Denser areas (e.g., bone) block more of the X-rays than less dense areas (e.g., muscle). The leftover X-rays hit the X-ray plate. The plate then reacts to the X-rays by emitting small amounts of light. The light then exposes a piece of photographic film, producing a radiogram (i.e., X-ray, radiograph). This helps identify bone and soft-tissue changes that may not be evident on physical examination and more clearly defines the abnormalities that are present.
Ultrasonography. Ultrasonography is an imaging method in which high frequency ultrasound is emitted into a tissue, and then the sound that is deflected back to the probe is recorded. Different densities of tissue deflect different amounts of sound back to the probe. Sound is not deflected in water and completely deflected by bone.
Nuclear scintigraphy. Nuclear scintigraphy is a means of identifying active bone (often an abnormality in adult horses) and other tissues. Radioactive materials are injected into the horse and the radioactive uptake of a tissue can be identified using a gamma camera. The gamma camera counts the number of radioactive particles in an area.
Other techniques. Magnetic Resonance Imaging (MRI) and CT scanners can be used to evaluate extreme detail in horse's limb anatomy. However, at this time their use is limited and anesthesia is required to complete the procedures.