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LAMENESS IN HORSES
Introduction
Often, our relationship with the horse depends largely on its athletic ability. A lameness issue may result in varying periods of inactivity for the horse. Therefore, lameness constitutes a huge source of financial and athletic loss within the equine industry. All lame horses require a thorough diagnostic examination. In some cases, the examination may be simple; in others, an extensive investigation, including nerve blocks and diagnostic imaging, may be required.
Lameness is an abnormality of the horse's gait or stance. Lameness may be caused by pain, a mechanical problem, or a neurological condition. Most of the time, lameness results from pain in the musculoskeletal system (muscles, tendons, ligaments, bones, or joints) leading to abnormal movement at the walk, trot, or canter.
Lameness Examination
Diagnosing lameness is a lot like detective work. Since one cannot ask the horse where it hurts, your veterinarian must put the horse through a series of tests in order to determine the source of the lameness. Over time, a standard series of tests have been developed that helps the veterinarian determine the source of the lameness. Many of the tests are universal and therefore, veterinarians across the country can discuss the results of particular tests.
The evaluation process and comprehensive lameness examination requires patience by you and your veterinarian. Challenging lameness cases may take several days to investigate and are even more difficult to evaluate once the lameness becomes chronic. Horses, particularly those with chronic problems, may develop compensatory gait abnormalities to deal with the primary problem. This may complicate the lameness evaluation and possibly its treatment. Therefore, it is important to have a lameness evaluated as soon as it is recognized.
History: Typically, a thorough history will be collected at the beginning of the lameness examination. It is helpful to select a veterinarian with knowledge of your specific interest, whether this is dressage, jumping, barrel racing, trail riding, etc.
Physical examination: In addition to a detailed history, your veterinarian may perform a brief physical exam. Then, your veterinarian will take some time to evaluate your horse standing still. First, the horse may be viewed from a distance and then close-up. This part of the workup is called a "static" examination and involves a critical look at your horse's conformation and attitude. The veterinarian will examine your horse’s feet. Hoof testers (Figure 1) will be applied to the feet, and the limbs and back will be palpated (felt) for presence of heat (warmth), pain, and swelling. Assessing the back may be important because poor performance or obscure lameness may originate from or have an impact on the back (Figure 2).
Figure 1: Hoof testers are applied across the hoof wall and the bottom of the hoof to check for painful areas.
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Figure 2: Thorough palpation of the back is an important part of a lameness examination.
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A "dynamic" or “moving” examination is then performed to evaluate the horse's gait. If you would like to watch the procedure, you will need an assistant to handle your horse because your veterinarian may require your horse to be walked or trotted in hand, lunged, or ridden on soft and hard ground.
Flexion testing: Following the static and dynamic examinations, stress tests may be performed to help localize the site of lameness. Flexion tests are the most common type of stress test. Flexion tests may be helpful if the lameness is subtle or there are no obvious signs of a problem (Figure 3). Typically, flexion tests involve bending or "flexing" a joint for 30 seconds to two minutes. Then the horse is trotted for about 20-30 yards and evaluated for an increase in lameness. If a particular flexion test intensifies the lameness, your veterinarian may concentrate on that area of the body or that joint as the source of the lameness during the rest of the examination.
Figure 3: The horse's leg is held in a flexed position to stress the joint. The horse will be assessed at a trot to determine if this flexion test accentuates the lameness.
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Diagnostic local anesthesia (“nerve or joint blocks”): An accurate knowledge of anatomy is required to perform and interpret diagnostic "blocks" during a lameness examination. When performing diagnostic nerve blocks, local anesthetic is infused either around a nerve or injected into a joint or other synovial structure, eg, tendon sheath, bursa, etc. (Figure 4). If the lameness disappears or improves markedly following administration of anesthesia, your veterinarian will have localized the site of lameness.
Figure 4: Nerves to a portion of the foot are blocked with a local anesthetic to see if the lameness resolves.
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Intra-articular (joint) anesthesia requires sterile technique. Sterile technique will reduce the risk of introducing bacteria into the joint. Bacteria in the joint can cause septic or infectious arthritis. This is an infrequent, but serious potential side effect of joint (or synovial structure) injections. The advantages and risks associated with diagnostic anesthesia should be discussed with your veterinarian during the lameness examination.
After nerve blocks have localized an area causing the lameness, diagnostic imaging, eg, radiography, ultrasonography, etc, can be used to further understand the lameness condition. If the lameness cannot be localized by nerve blocks, other diagnostic imaging techniques can be employed (see below). Occasionally, the process of "blocking" will be by-passed and diagnostic imaging will be performed, particularly if the affected region is already identified.
Diagnostic Imaging
Radiographs (x-rays): Radiographs are often used to show changes in bone and joint surfaces (Figure 5). With many conditions, visible bone changes are not present early in the disease; therefore, radiographs may not help determine the cause of the lameness. Poor quality radiographs may not provide diagnostic information and will need to be retaken under better conditions. Recent advances in digital radiography, most notably portability and affordability, are allowing veterinarians to use this technique in equine lameness diagnosis. Digital radiography allows the veterinarian to enlarge problem areas and highlight them, making the images easier to read and interpret.
Figure 5: The technician holds an x-ray plate behind the horse's limb so that a radiograph can be taken. Some horses may need to be sedated so they stand quietly for the x-ray.
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Ultrasonography (“ultrasounds”): Ultrasonography is the most practical and accurate method for assessing tendons, ligaments, and other soft tissues.
Scintigraphy (“bone scans”): Bone scans are usually performed in horses when the lameness is very subtle, intermittent, or when a non-displaced fracture (small crack) is suspected. Bone scans should be performed prior to nerve or joint blocks in some cases. During scintigraphy, the horse is given an IV injection, which contains a small quantity of radioactive material. The radioactive material will become distributed throughout the horse’s body and can be detected using a gamma camera, which is coupled to a computer. The information gained can be used to determine sites of abnormality and thus, possible causes of lameness. Scintigraphy is safe for horses, but the horse must remain at a special quarantine facility for a short period following injection of the radioactive material, usually 24 hours.
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 6). MRI usually requires general anesthesia and a facility designed especially for horses (Figure 7), although standing MRI machines are available at the expense of image quality. Interpretation of MRI images requires advanced training and experience.
Figure 6: This is an MRI of a horse with bone inflammation in the front of the pastern (light grey region) that could not be detected on radiographs.
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Figure 7. Special facilities and advanced training are required to perform MRI's on horses and other animals.
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When To Seek Referral
In order to properly investigate the cause of lameness, your veterinarian must have a thorough knowledge of the mechanisms and anatomical structures behind a horse's movement. Board-certified ACVS Veterinary Surgeons in equine practice have received formal training in the diagnosis and treatment of lameness and orthopedic diseases in horses. Most ACVS Diplomates in equine practice work in referral hospitals where your horse can benefit from the most advanced and sophisticated diagnostic tools and treatment options.
—Antonio M. Cruz, DVM, MVM, MSc, DrMedVet
Diplomate ACVS
Posted 8/21/2006
Revised 8/20/2010 by Dr. Cruz
Reviewed 8/20/2010 by Drs. Schwartz, Kapatkin, and Bowman
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