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Evaluating the equine athlete for lameness and poor performance (Proceedings)
Every equine sport or disciple has its own set of common disorders, so a basic knowledge of the sport and training techniques is very useful in both finding the problem and communicating with the people involved.
Lameness problems and decreased performance are common in the equine athlete, and comprises a large part of performance horse veterinary medicine. Every equine sport or disciple has its own set of common disorders, so a basic knowledge of the sport and training techniques is very useful in both finding the problem and communicating with the people involved. However, the basic skills and knowledge necessary is the same for all equine disciplines.
Examining lame horses requires time and dedication. It is important to remember that not all lameness or performance evaluations can be completed in one day. Additionally, a trained staff and adequate facilities are essential. Ideally, areas where horses can be evaluated on hard and soft surfaces should be available, as well as an area where a horse can be examined under saddle.
The basic lameness exam begins with a thorough history of the presenting problem. The essential information that I like to obtain prior to looking at the horse includes the primary complaint of the owner or trainer, duration of the problem, prior treatment and any response to treatment, and expectations for the horse including future show schedule. It is important to remember that many times the presenting complaint may be simply a decrease in performance rather than a specific lameness issue. I rely a lot on what the trainer is seeing and feeling in the saddle. Often times a decrease in performance can be related to a lameness, however soreness in an area not bad enough to cause an obvious lameness can be highly significant in reducing the quality of performance of the horse. Other potential problems not related to lameness that are commonly seen in athletic horses are equine protozoal myelitis, gastric ulceration, and dental disease.
Whatever pattern of examination you choose should be based on individual preference, but I believe that a systematic approach should be taken to evaluate the entire animal. Once you are comfortable with your system, it can be used for every horse that you evaluate. This is a good way to pick up any subtle abnormalities that can help streamline your examination. This basic lameness or performance evaluation also serves as the basis for my pre-purchase examination.
Once I have obtained a history on the nature of the problem, I like to evaluate the horse in motion. A lot can be ascertained simply by watching the horse unload off of the trailer. Any obvious asymmetry in musculature or abnormal swellings can be seen. Many horses with bilateral rear limb soreness may have a hard time backing off of a step up trailer, and can even fall or go down while backing. As my unloading area is on gravel, I can observe how the horse behaves while walking. Horses that are sore in the feet may show an obvious lameness while walking or turning on the gravel.
After the horse is unloaded, I will observe the horse at a walk in-hand on the hard surface (asphalt). Once the horse is accustomed to the handler and surroundings I systematically evaluate the horse walking and jogging in both directions of the circle. It is important to have a handler that you work with every day and a set routine to the sequence of the evaluation. I always begin with the horse in a left circle and then proceed to the right. A lot can be ascertained during this initial examination even prior to laying your hands on the horse. While examining the horse on the circle, both the front and hind end can be evaluated at the same time. Occasionally I may examine the horse in a straight line, however the front and rear limbs can only be evaluated independently in this manner. If the lameness is very subtle or if the horse is not amenable to jogging in hand, I may observe the horse on a lunge line. Many horses in my practice are never taught to lunge, so this may be difficult and can carry some liability if the horse injures itself. If the problem is not clear during these manipulations, I may watch the horse move in a sand arena in hand or under saddle. Many very subtle problems are made much more apparent when the horse is worked under saddle by an experienced rider. For some horses with decreased performance, it may be necessary to watch the horse performing their discipline to ascertain if there is a problem
Often times young horses my be too ÒfreshÓ to examine initially, particularly if they have had any time off. In this situation I prefer to administer 0.3-0.5 cc of acepromazine IV and wait 5 minutes. This small amount of tranquilizer makes these horse much more manageable without masking lameness because the drug has no analgesic properties. In fact, horses with subtle lameness issues are more likely to demonstrate the problem after mild tranquilization.During the initial examination, I first try to determine if the horse is sound or lame. If a lameness is present I will determine if it is one or multiple legs, determine which direction of the circle or surface that the lameness is worse, and grade the lameness based on the AAEP grading scale (see below). Also, any obvious conformational defects that might predispose to certain problems can be seen. Once this information is obtained, I will then thoroughly palpate the horse and begin the flexion tests. Once again a set routine is important. If the lameness is on the front limb, I begin by palpating and flexing the left forelimb, followed by the right forelimb. If the lameness is on the hind end, I begin by palpating and flexing the left hind limb followed by the right hind limb. It is also important to apply hoof testers to all four feet, and to thoroughly palpate the neck, back, and pelvic musculature. A tremendous amount of information can be obtained by digital palpation of the limbs and back, paying particular attention to the tendons, ligaments, joints, and muscle groups. Once again a set routine that is followed on all horses will help determine what is normal and what is not. Also, if there is any question regarding the significance of sensitivity to palpation, the contralateral limb can be used for comparison. However, keep in mind than many problems are bilateral, so the animal may be sore to palpation of both limbs.
AAEP Lameness Grading Scale:
Grade 1: Lameness is difficult to observe and not consistently apparent regardless of circumstances (such as weight carrying, circling, inclines, hard surfaces)
Grade 2: Lameness is difficult to observe at a walk or trotting a straight line but is consistently apparent under certain circumstances (such as weight carrying, circling, inclines, hard surfaces)
Grade 3: Lameness is consistently observable at a trot under all circumstances
Grade 4: Lameness is obvious with marked nodding, hitching, or shortened stride
Grade 5: Lameness is characterized by minimal weight bearing in motion or at rest and the inability to move
Routine flexion tests for the front legs include distal limb and carpal flexions. Upper limb flexion may be performed in special cases, but are not performed during routine evaluations. Routine flexion tests for the rear limbs include the distal limb, hock, and upper limb (ÒstifleÓ flexion. My handler is trained to time each of my flexions so that a more objective evaluation can be made. All distal limb flexions are performed for 30 seconds. Carpal, hock, and upper rear limb flexions are performed for 60 seconds. I pay particular attention to any resistance by the horse during the flexion test, as well as the gait following the flexion. I prefer to characterize my flexion tests as negative, positive, or strong positive. A negative flexion test means that there was no resistance during flexion and no alteration in gait following flexion. A positive flexion test means that there may be some resistance during the test, and/or a mild to moderate alteration in gait following flexion. A strong positive test means that there was obvious resistance during the test, and a marked alteration of gat following. Horses with strong positive flexion tests may need to be walked for a duration of time prior to completing the evaluation. The leg is generally flexed in the direction of the circle that the lameness is more apparent. Each flexion should be performed with the same amount of tension, again so a more objective assessment can be made. When I observe horses working under saddle, I will often times perform my flexion tests with the rider on the horse. Experience riders can often feel a difference in gait post-flexion, even when one is not obvious by simple observation.
In many horses that are examined for a particular problem, an additional problem is detected. Often times the secondary lameness can be due to compensation from the primarily lame limb. Multiple limb lameness is frequent in the equine athlete so an emphasis should be placed on the whole animal and the ÒcompensatoryÓ lameness should not be ignored.
Once I have established that there is indeed a lameness issue, I make it my mission to find a diagnosis as accurately as I can. Often times owners and trainers do not care about the diagnosis, they just want to know what to do to fix the problem. I strongly feel that the most appropriate treatment plan and prognosis can only come from an accurate diagnosis, which also maximizes the success of treatment.
An accurate diagnosis can only come through a series of diagnostic tests. Diagnostic anesthesia is still the method of choice for localizing the source of pain in the limb. I employ diagnostic anesthesia in almost every lameness case, with the exceptions being animals with an obvious problem (swollen/painful tendon) or those in which I suspect a fracture. In these cases imaging modalities are used prior to performing diagnostic anesthesia.
The method of blocking is dependent on each individual problem. The most typical method of starting at the foot and working proximal in the limb is the most effective method utilized. I prefer to start using perineural nerve blocks. These are easier and safer to use than intra-articular blocks in the standing, unsedated horse. If there is obvious joint effusion and there is a high suspicion that the lameness is coming from that joint, I may first perform an intra-articular block. With perineural nerve blocks, you must start distally and work proximally, as all sites distal to the site of anesthesia will be desensitized. When performing intra-articular anesthesia, you can jump around as the site of desensitization is localized to that joint. Additionally, in certain anatomic areas (particularly the stifle joint and proximal suspensory on the hind limb), I will examine those areas with ultrasonography prior to blocking. This is because the diagnostic capability of ultrasound is markedly decreased following blocking, as acoustic shadows from gas artifact and excessive fluid is often seen. Also, a standard surgical scrub should be performed prior to any intra-articular diagnostic anesthesia, just as one would do prior to any joint injections. In cases where there are multiple limbs involved, you should begin by blocking the lamest of the legs. It is also important to remember that there can be multiple issues within the same leg. Proper blocking requires both proper technique followed by a sufficient amount of time to allow the block to work. A big mistake is to evaluate a horse too quickly after a block, decide that there is no improvement, and then block higher. For most perineural nerve blocks in the distal limb, I give the horse a minimum of 7 minutes before I proceed with evaluation. The nerve blocks of the distal limb can be checked via skin desensitization, or desensitization of a previously sore area to palpation or hoof testers. For nerve blocks higher in the limb (suspensory), I prefer to wait a minimum of 10 minutes prior to the evaluation. For most joint blocks, I will first look at the horse 10 minutes following the block. If there has been some improvement in the gait, I will sequentially re-evaluate at 10 minute intervals.
Once I have established that the nerve block is successful (the intended area is desensitized), I will repeat the lameness exam in the same pattern that I originally started. In horses that have subtle gait abnormalities, it is important to repeat the flexion tests in addition to watching the horse in motion. Additionally, if the problem was most apparent while the horse was working under saddle, I will re-evaluate under saddle post blocking. A successful nerve block is one in which a significant improvement in gait is seen. Complete analgesia is a goal when performing diagnostic anesthesia, but in many horses this level of pain relief is never achieved. Improvement in degree of lameness greater that 70-80% after most perineural or intra-articular techniques should be considered a positive response in most horses. Once this degree of improvement is obtained, you can move on to additional diagnostics or continue nerve blocks on the leg with the secondary lameness (sometimes a secondary lameness only becomes obvious once the primary lame leg is blocked out).
In certain situations, either the results of the nerve blocks are inconclusive, or the diagnostics fail to find an obvious abnormality. If this occurs, I prefer to start from scratch on a separate day. If perineural blocks were previously performed, I will then alternatively perform intra-articular anesthesia. If the results are still inconclusive, I will move on to advance diagnostics such as nuclear scintigraphy.
If the problem can be localized via diagnostic anesthesia, additional diagnostics including radiography and ultrasonography are utilized. Most of the time, these two imaging modalities are both used, as the more information you can obtain regarding the etiology of the problem, the more successful you can be in treatment. I also employ fluoroscopy in my practice, particularly to evaluate the entire periphery of joint surfaces, as the angle of the fluoroscope beam can be fine tuned to give you 360 degree coverage of the joint. If a lesion is visualized with the fluoroscope at a special angle or part of the joint that can be missed with the conventional radiographic views, I will then radiograph the area mimicking the angle that was used with the fluoroscope.
For cases where the diagnosis is not clear, several different options are available. One option is to treat the most likely problem that exists based on the localization of the lameness, discipline of the horse, and your experience. Treating problems in this manner is actually just another diagnostic technique. If the horse fails to respond in the anticipated fashion or in an appropriate time frame, either additional treatment methods may be tried, but I prefer to perform additional diagnostics. For some horses that are not on a strict show or training schedule, an appropriate period of rest may be given. Depending on the individual case and severity, I usually start with 30 days of rest.
For horses where the lameness can be localized, but conventional diagnostics fail to identify an obvious problem, I prefer to perform additional advanced imaging techniques, such as magnetic resonance imaging (MRI). In my experience, when a lameness can be definitively localized via diagnostic anesthesia but conventional diagnostics are inconclusive, an MRI will very likely delineate the problem. I will also use MRI in cases that have failed to respond to treatment in a predictable manor. In these cases, MRI will almost always find a secondary problem that was not evident on conventional radiographs, or will find that the lesion is more severe than originally anticipated. As I have stated earlier in this paper, an accurate diagnosis is absolutely essential in treating any case of lameness or decreased performance. MRI has revolutionized our ability to diagnose and treat equine sports injuries.
For some cases, an obvious problem can not be found in the physical and lameness exam. This is particularly true in cases of poor performance. It is important to remember that not all sources of lameness can be isolated via diagnostic anesthesia. This is especially true as you move up the limb (both fore and hind). In addition to problems in the limbs, subtle spinal problems can also be responsible for decreased performance. In cases such as these, nuclear scintigraphy (bone scan) is often utilized. Scintigraphy is very sensitive at detecting abnormal bone turnover or non-adaptive bone remodeling. Sites of particular interest in horses with poor performance are the neck and back areas. Nuclear scintigraphy in my opinion is the most sensitive detector of problems in these areas. It is also common to find multiple sites of abnormal bone turnover in these complicated lameness cases.
Everything that the horse owner or trainer is concerned with, particularly treatment and prognosis, stems from an accurate diagnosis. A thorough physical and lameness exam is an extremely important part of pointing you in the right direction. When every animal is examined in the same fashion, subtle abnormalities are more easily detected. Remember, time and patience are key ingredients in working up the horse for poor performance.