History: Typically a thorough history will be collected at the beginning of your visit to a referral facility. Knowledge of the sport you are engaged in is most helpful when doing a lameness exam, so it is important to select a veterinarian with knowledge of your specific interest, whether this is dressage, jumping, or barrel racing, or trail riding.
Physical Examination: After taking a detailed history, your specialist will take some time to evaluate your horse standing, first from a distance and then close-by. This is called a "static" examination and involves a critical look at your horse's conformation and attitude. The veterinarian will exam your horses feet, including use of hoof testers (Figure 1), and will palpate (feel) the legs for joint swelling, lumps, bumps, and warm or tender areas.
Figure 1: Hoof testers are applied across the hoof wall and the bottom of the hoof to check for painful areas.
A "dynamic" investigation is then performed to evaluate the horse's gait. Usually this is done under several conditions, depending on your horse's suspected problems. Your specialist may require your horse to be lunged, trotted, hand walked, or ridden on soft and hard ground.
Flexion Test: Following static and dynamic exams, stress tests are often performed to increase the severity of the lameness. The most common stress test is a flexion test, which is very helpful when the lameness is subtle or when no external signs of a problem can be detected (Figure 2). Typically, flexion tests involve stressing a joint (by bending or "flexing" it) for 30 seconds to two minutes. The horse is then trotted for a distance of about 40-50 yards to see if the lameness is more severe. At the end of the stress test, your specialist may have detected which area of the horse's body is the source of the problem and will concentrate on it during the rest of the exam.
Figure 2: The horse's leg is held in a bent position to stress the joint. The horse is then examined at a trot to see if it is more lame.
Nerve or Joint Blocks: To determine the specific location of the lameness, nerve or joint blocks with local anesthetic may be performed (Figure 3). Anesthetic blocks reduce or eliminate the lameness by anesthetizing a joint or a small region of your horse's leg. An accurate knowledge of anatomy is required to interpret these diagnostic "blocks". Once the lameness disappears, your veterinarian will then have narrowed the problem so that other imaging tests such as radiographs or ultrasound can be used. While "blocking" a nerve subcutaneously has hardly any side effects, joint blocks must be performed under sterile conditions because of the risk of introducing bacteria into the joint. This complication, known as septic or infectious arthritis, is an unusual but serious potential side-effect of intra-articular injections.
Occasionally, the process of "blocking" will be by-passed and imaging diagnostics will be performed, particularly if the affected region is already identified.
Figure 3: Nerves to a portion of the foot are blocked with a local anesthetic to see if the lameness resolves.
Radiographs (x-rays): Radiographs are often used to show changes in bone and joint surfaces (Figure 4). With many conditions, such as arthritis, visible bone changes are not present early in the disease and therefore radiographs may not help determine the cause of the lameness. Radiographs that are of poor quality may often be non-diagnostic and will need to be retaken under better conditions.
Many ACVS Veterinary Surgeons have digital radiography- computerized x-rays- that allow the specialist to enlarge problem areas and highlight them, making them easier to read.
Figure 4: The technician holds an x-ray plate behind the horse's leg so that a radiograph can be taken. Horses may need to be sedated so they stand quietly for the x-ray.
Ultrasonography: Ultrasound- the use of sound waves to evaluate the thickness and character of tissues- is often helpful for looking at tendons and other soft tissues.
Scintigraphy: Bone scan or scintigraphy is a test that uses radioactive material to identify the general region of the body causing the lameness. Bone scans are usually performed before nerve or joint blocks and in horses where the lameness may be very subtle or intermittent or when a non-displaced fracture (for instance, a small crack) is suspected. Once the abnormal region is identified, the area is usually imaged with other methods (i.e. radiographs) to determine the specific problem. Scintigraphy is safe for horses but requires special facilities to protect the people that are administering the test or caring for the animal.
Magnetic resonance imaging (MRI): Magnetic resonance imaging is revolutionizing the field of equine diagnostic imaging and orthopedics. MRI scans use magnetic fields to create images of the tissues inside the body (Figure 5). Image quality is related to the strength of the machine, which is measure in a unit called a "Tesla". The traditional MRI has a strength of 1 to 1.5 Tesla and therefore produces high-quality images. However, because of its tube shape, it requires general anesthesia and a facility designed especially for horses (Figure 6). "Open" magnets are "U-shaped, allowing the horse to stand inside of the ring. This type of MRI machine typically has less than half strength of the traditional machine (usually < 0.5 Tesla) and therefore produces lower-quality images. Interpretation of MRI images requires advanced training and experience.
Figure 5: MRI of a horse's foot. This horse had boney reaction and tendon inflammation along the back of the foot that was not visible on regular x-rays.
Figure 6. Special facilities and advanced training are required to perform MRI's on horses and other animals.
