How to deal with equine lameness

A lame horse is defined as having either an abnormal gait or being incapable of a normal gait. The most common causes of lameness in horses include infection (e.g. foot abscess), traumatic injuries, conditions acquired before birth (e.g., contracted tendons) or after birth (e.g., osteochondritis dissecans). Factors unrelated to the musculoskeletal system such as metabolic, circulatory, and nervous system abnormalities (e.g., wobbler syndrome) can also cause a horse to become lame. Lameness resulting from musculoskeletal abnormalities is the leading cause of poor performance in athletic horses and thus the ability to diagnose and treat lameness is an important aspect in veterinary medicine. The ability to assess lameness requires a detailed knowledge of the horse’s anatomy, biomechanics, conformation, breed characteristics, an ability to assess a variety of different gaits – i.e. walk, trot, canter and will depend on the clinician's level of experience.

Many causes of lameness can be diagnosed with a thorough history, palpation of the limbs, observation of the horses gait and hoof tester examination. In some horses in addition to this local nerve blocks or joint blocks may be required. More lameness is seen in the forelimbs than the hindlimbs and almost 95% of forelimb lameness occur from the knee down. When the hind limb is involved, however, many more are seen in the upper part of the limb, especially in the hock or stifle. It can take careful examination, extensive diagnostics and more than one evaluation of a horse to diagnosed more complex lameness. 

It is always important to start a lameness examination with a complete history of the lameness, a general physical examination of the horse to rule out other, potentially more serious diseases, and a thorough conformation assessment. The horse’s gait or movement must then be evaluated initially while walking, but then trotting both in a straight line and in a circle. Usually this is done by a handler leading the horse but occasionally will be done under the saddle. A variety of surfaces may be used depending on the horse and the suspected lameness. Hard level surfaces are most often used to evaluate lameness, however, in some cases the use of a sand or grass surface may be warranted.

Through gait analysis, the veterinarian can then establish which limb or limbs are involved by observing the horse in motion. Many horses are lame in more than one leg at the time of examination. 

Once the limb (or limbs) involved in the lameness is identified, the veterinarian will palpate each lame limb to better determine which particular region is affected. Hoof testers are frequently used at this point to assess the presence of pain in the foot. The goal of this phase of the examination is to find evidence of heat, pain, and swelling to better pinpoint the exact cause of the lameness. 

Manipulating the joints by flexing and extending the limbs and assessing which joints or structures are painful, and/or if a decrease in the range of motion exists is an important part of localising the lameness. Flexion tests are often used to see if lameness increases afterwards which can help isolate the lameness to that area of the leg. Lameness in the horse is often quantified by veterinarians using a lameness grading system. This subjective grading system is based on a five-point scale ranging from 0 to 5. Using this standardized grading system allows consistent description of lamenesses and allows progressive tracking of a lameness in the same horse over time. 

The five grades are as follows:

• Grade 0 is defined as no detectable lameness under any circumstances.
• Grade 1 is defined as lameness that is difficult to observe and is inconsistently apparent regardless of the circumstances (e.g., in hand or under saddle, hard surface, incline, circling).
• Grade 2 lameness is difficult to detect at a walk or trot in a straight line, but is consistently apparent under particular circumstances (e.g., under saddle, hard surface, incline).
• Grade 3 lameness is consistently observed at a trot in all circumstances.
• Grade 4 lameness is obvious with a marked head nod, hip hike, and/or shortened stride.
• Grade 5 lameness is obvious with minimal weight bearing either during motion or at rest. The horse might be unable to move.

Please note some clinicians use a grading system of 10 stages.

Nerve and joint blocks are a valuable tool in lameness diagnosis and areas can be temporarily blocked from sensing pain with local anaesthetics such as mepivicaine and prilocaine and lignocaine. For example, blocking the palmar digital nerves that supply the foot can desensitise the heel and sole region to help diagnose pain in the back half of the hoof caused by conditions such as navicular disease. Once a nerve/ joint block has been performed, the horse is re-evaluated to determine if the lameness has lessened or diminished and, if so, to what extent. Performance horses are often lame in more than one limb, so blocking out one lameness can potentially reveal another. Alternatively, if no improvement in lameness grade is noted, then the source of pain likely resides in another anatomic location. Sequential blocks can then be performed until the source of the lameness is located. 

Once the source of the lameness is identified, radiographic assessment is often the next step towards finding a diagnosis. Ultrasonography is also often utilised especially where tendons and ligaments are thought to be involved or where there are no significant radiographic changes. 

In some cases, despite a thorough lameness examination the cause of lameness may be difficult to determine. For example the lameness may only be evident under certain conditions such as under saddle or the lameness comes and goes. In these cases advanced imaging techniques may be employed to determine the exact cause of lameness or to confirm the lameness diagnosis that the clinician suspects based on examination and diagnostics up to this point. Advanced imaging techniques available in Australia include nuclear scintigraphy (bone scan) a bone scan (nuclear scintigraphy), magnetic resonance imaging (MRI), and computed tomography (CT). 

The treatment and prognosis for any lameness will vary dramatically depending on the use of the horse and the exact nature of the lameness. Treatment plans may vary widely depending on these factors. Conservative therapies such as box rest, hand walking and paddock rest may suffice for minor lamenesses. Anti-inflammatories such as phenylbutazone, flunxine meglumine and meloxicam may be indicated. Medical treatments such as joint injection with cortisone (short acting or long acting) and hyaluronic acid, IRAP (interleukin-1 receptor antagonist protein), stem cell treatment, platelet-rich plasma (PRP), oral supplements or systemic injections of hyaluronic acid or pentosan are beneficial in different circumstances. Whenever medical treatments are administered to performance horses swab times must be adhered to for the different disciplines and the Australian rules of racing must be followed by the treating veterinarian. 

There are also a wide variety of surgical treatment options for select cases (e.g., chip fragment removal, arthroscopy, fracture repair).

This content was originally published by Equine Veterinarians Australia (EVA), a special interest group of The Australian Veterinary Association.