Understanding Lameness: A Summary of a Lecture for Horse Owners
By Doug Thal, DVM
This article is a summary of a lecture that I gave to horse owners in Santa Fe last year.
I have always felt it important to make horse owners more aware of lameness and its diagnosis. Lameness accounts for the greatest losses for the equine industry - hundreds of millions of dollars annually. Lameness affects individual horses of all kinds and at all levels, from subtle reduced performance to complete loss of use or euthanasia. Sadly, many horses are asked to perform when they are in pain because of rider failure to recognize lameness.
Understanding lameness basics (and working with an equine veterinarian with experience in lameness) helps a horse person to:
· Purchase horses (using a veterinary pre-purchase exam) who do not have current lameness and are of a conformation less likely to become lame.
· Recognize conformational predispositions in their horses and manage for treatment and prevention of lameness.
· Recognize or at least suspect when lameness is the root cause of your horse’s poor performance (versus training issues), and get the lameness problems diagnosed and treated.
· Breed better horses. Understanding lameness and basic form and function allows breeders to breed horses that are of superior conformation and thus less likely to become lame.
Some important points about lameness that every horse owner should know:
· Lameness can result from pain coming from any component of the limb which contains nerve endings. This means that skin wounds, connective tissue bruising, muscle pain, arthritis (joint inflammation), tendon sheath and bursal inflammation, tendon and ligament injury, and injuries to bone all can cause lameness. The important point here is that what is causing the pain cannot necessarily be distinguished based on the appearance of the lameness.
· Horses of certain types and uses have specific lameness problems more frequently. An example is arthritis in the knee (carpus) in race horses or hock arthritis in cutting horses.
· Forelimb lameness is easier for most people to recognize than hind limb lameness. The mechanics of the forelimb means that lameness is more consistent in appearance and more obvious to the untrained eye. Hind limb lameness is generally more difficult to visualize and diagnose (this is especially true of subtle upper limb problems). The massive musculature of the upper hind limb makes it much more difficult to see and feel deeper structures in this region and very difficult to image these structures using x-ray and ultrasound.
· A high percentage of lameness is below the level of the fetlock and frequently in the foot. Upper limb forelimb lameness is not common in adult horses. Upper limb lameness is more common in younger horses because developmental orthopedic disease (osteochondrosis, epiphysitis) is relatively common in these sites in young horses.
· Conformation correlates directly with function of the limb and is closely related to the development of lameness. Horses with poor conformation are more likely to experience problems with joints, tendons and ligaments than are horses of “normal” conformation. An example is angular limb like “pigeon toe”(toe-in at or below the fetlock level), for example, which cause a horse to paddle when it moves and sets it up for uneven mechanical forces in the limb which over time can lead to damage of joints and arthritis.
The lameness exam
The lameness exam is a detailed and methodical veterinary exam which allows the localization of lameness. As a horse owner it is important to understand the importance of this exam, and to understand the basis for it. The exam consists of a careful history, a standing exam, an exam in movement, flexion and hoof tester exams, diagnostic anesthesia (nerve blocks) and imaging (examples are x-ray, ultrasound, MRI). The lameness exam is as much an art as it is a science. The diagnosis comes out of a synthesis of findings from all of the above parts of the lameness exam. The exam is based on an understanding of anatomy, and requires experience and a methodical approach to perform well.
The first part of a thorough lameness evaluation is a thorough history of both the horse and the injury. Examples of information gathered about the horse are breed, age, and prior use. The history of the injury would include the date that lameness was first noticed, how severe the lameness has been, and how the injury occurred if this is known. All of these are important questions which veterinarians ask and horse owners should be try to provide accurate answers to.
Examination is done first at a distance to evaluate conformation and general appearance. More careful examination and palpation of specific structures for swelling, heat, pain, follows.
The next part of the exam is to see the horse in movement. Lameness is mostly evaluated at the trot. Most thorough lameness exams are performed on firm to hard, even footing. Examination often includes circles to both directions and may include inclines or specific patterns. For the diagnosis of some types of lameness problems, having a rider up can be advantageous.
Flexion exams are an important part of lameness evaluation. Flexion exams involve putting specific joints or regions of the limb under stress for a specified time. The horse’s degree of lameness is assessed before and after flexion. The results (change of degree of lameness following flexion) give additional information regarding areas of pain. As with many parts of the exam, flexion tests must be interpreted in light of what is normal for that specific horse.
Hoof testing involves the use of a pincer-like tool to put pressure on specific regions of the foot in search of a pain response. As with flexion exams, the key to smart interpretation of hoof tester examination is knowledge of what constitutes a normal response. This can only be gained through a methodical approach and lots of experience with different types of horses.
At this point in the exam, we should know which limb is the lame one, and we may or may not have a hunch as to where in the limb the problem is. If the examiner is not certain of where the problem is, then nerve blocks are performed to try to isolate the area of lameness.
Nerve blocks are used to methodically numb portions of the limb. Also known as diagnostic anesthesia, “blocking” is injection of a local anesthetic agent around specific nerves or into specific joints or other structures. The horse is evaluated before the block, the area in question is numbed, and the horse is asked again to trot off. Either there is improvement in the lameness or not. If there is not, the process is continued on specific nerves progressing up the limb until the lameness is visibly lessened. Specific joints and tendon sheaths can be blocked for a more specific localization of lameness. Blocks into a joint or tendon sheath require surgical cleanliness to prevent infection of these structures.
Only once we have found the region from which the pain is coming from do we use diagnostic imaging to describe the structures in that area. This includes x-ray (radiology) to image bone, ultrasound to image soft tissues, and may include less familiar technologies like MRI, CAT Scan, and nuclear scintigraphy (bone scan).
· X-ray is the first line of imaging for bone. It is less useful for soft tissues. X-ray is often performed in the field with portable equipment. More difficult studies can often be performed better in a clinic setting. Digital x-ray is new technology which does not rely on film. It is quickly becoming the standard for equine x-ray.
· Ultrasound utilizes sound waves traveling through tissues to image those tissues. It is excellent for imaging soft tissues, but cannot penetrate healthy bone. It is used commonly to image tendons, ligaments, the surfaces of bone, and other soft tissues.
All of the above pieces, when they are performed properly, and assembled and interpreted correctly, provide an accurate diagnosis. Until we have an accurate diagnosis there is no way to know what the treatment and prognosis of the problem will be.
The future of the lameness exam is based on advances in imaging and more technologically advanced treatments, but the cornerstone is a knowledgeable veterinarian and a thorough exam.
· MRI is being used more commonly in equine lameness diagnosis and is changing our understanding of lameness of the lower limb. MRI allows both soft tissue and bone to be examined in great detail. In some cases, the detailed information coming from MRI can allow more targeted treatment and a better understanding of the prognosis for return to use.
· Other improvements in imaging include digital x-ray and ultrasound, nuclear scintigraphy (bone scan) and CT scan.
· Advanced treatment options are becoming more available and may provide better solutions for certain lameness problems. Examples of these newer treatments are shock wave and stem cell treatment.
Conclusion
· Horse owners should establish a relationship with their equine veterinarian and use him or her to help clarify lameness questions.
· An educated horse owner should understand basic equine anatomy and the basic concepts of the lameness exam.
· Always call sooner on a suspected lameness problem rather than waiting.
· Be careful of inaccurate lameness information on the internet. Use your equine vet to help screen this information for you.
· Be careful of the supplement game. There are hundreds of products out there that make a variety of claims for solving lameness problems. These products are expensive and in many cases have no proof of effectiveness. There is no regulation on these products and so it is up to the consumer to beware. In my opinion, money is generally better spent on a lameness exam and the search for a correct diagnosis.
· New technology like MRI will add knowledge to the field but is no substitute for a good exam. A thorough, methodical clinical exam will always be the cornerstone of lameness diagnosis. Be prepared to haul your horse to a clinic for the diagnosis of complex lameness problems. For many reasons, these exams are better performed in a clinic setting.