|
The Lameness Examination: Overview |  |
| A systematic investigation of a lame horse is time consuming. The examination also benefits from standardized facilities such as a level, firm running-up track and ideally both a firm, nonslippery surface and a softer area for lunging or riding the lame horse. |
| The examination begins with a comprehensive medical history; type, age, and training regimen may give important clues to the lameness as will the time since onset of lameness and interim management. The interval since the last shoeing should be noted, as well as any suggestions that the lameness may improve with either rest or exercise. Response to anti-inflammatory or analgesic medications may provide useful information. Results of hematologic and biochemical analyses may shed
light on other problems that influence overall performance. Anemia may be associated with muscle fatigue, while enzymes such as AST and CK in combination are reasonably muscle-tissue specific; they rise as the result of severe muscle cell damage and may not be elevated in cases of moderate sprain of a single muscle, in particular if the pathology affects the connective tissues of the musculo-tendinous junction rather than the muscle fiber itself. |
| In cases of chronically elevated muscle-related enzymes suggestive of equine rhabdomyolysis, a muscle biopsy may be useful to check for subgroups such as polysaccharide storage myopathies (). |
| Although valuable, modern diagnostic imaging techniques are no substitute for detailed visual inspection and thorough manual palpation of the limbs in weightbearing and nonweightbearing positions. The high degree of variation between horses should be remembered, and comparision with the contralateral limb should always take place, although the latter may not necessarily be a useful control. Any heat, joint distention, or abnormal tissue tension should be noted, as well as the
reaction of the horse and range of flexion and extension of all joints. Specific areas of muscle wastage may also provide useful information. The feet should be thoroughly examined, including compression of the walls and sole with hoof testers. Wear patterns of shoes and feet should be noted. A number of abnormalities such as broken toe/pastern axis; mismatched hoof angles; under-run, contracted, and sheared heels, and disproportionate hoof size are seen more frequently in lame than
in sound horses. Shoes should be left on, as removing them at this stage might make the horse footsore and thereby preclude further examination. However, occasionally it may prove useful to remove the front shoes to demonstrate that the shoeing was the cause of the lameness. |
| The back and neck should be thoroughly examined with the horse restrained and standing square on a level surface. The neck should be assessed for range of movement in all planes and for evidence of muscle asymmetry and pain. The dorsal midline of the back should be straight, and equal tone should be present in the paravertebral musculature on either side of the midline. The same should be true of the gluteal musculature and the hamstrings. The definitive diagnosis of a strained or
torn muscle can be extremely difficult, especially in more chronic cases. Spatial alignment of the tubera coxae and sacrale should also be observed. Flexibility and extensibility of the back can be checked by alternately pinching the midline in the midthoracic and sacrococcygeal regions, while lateral flexion can be checked by turning the horse short around its own axis. |
| Examination during exercise becomes an option only if the degree of lameness is minor and chronic. If lameness is major and acute (eg, suspected fracture), additional exercise could result in a catastrophic breakdown with dire consequences for the horse. It is important to check whether the horse may have been given analgesic medication prior to the lameness examination. |
| A firm, nonslippery surface (eg, hardcore fine gravel) is ideal for trotting on a straight line and for lunging on a firm surface. It also provides an opportunity to listen to the footfall and consider this information along with the visual appraisal. However, feet of different shapes make slightly different impact sounds, which may be confusing. Although a horse may be regular in its stride, it may have a slightly weaker limb, particularly if recovering from a previous problem.
Lunging on tarmac (asphalt) or concrete increases the risk of the horse slipping. It also generally alters the gait so much that it has little value in lameness examination. Leading the horse on a circle at a trot also tends to alter the horse’s stride too much; the horse cannot move its neck and instead “sets” its head on the leader’s hand. Assessing the horse at a canter, which requires a softer surface, is always important. A surprising number of horses with lower back pain may
appear normal at a trot but are unable to maintain a normal 3-beat canter rhythm or may canter disunited. |
| Flexion tests are useful diagnostic tools. The range of movement and response to passive flexion, along with any suggestion of increased lameness or onset of lameness following flexion, should be observed. The distal phalanges in both forelimbs and hindlimbs should be flexed independently of carpus and hock to obtain maximal information. However, results of recent studies have suggested that “false-positive” results may be seen if excessive forces are applied. Consistency should
always be applied, and individual experience used. A single positive flexion test without associated lameness may not be of significance and in some horses has proved to be a lifelong observation. |
| To establish consistency, the entire examination should involve the same handler, the same bitting, and the same surfaces under foot. The horse should be controlled so that it is trotting at a useful, repeatable pace to evaluate the lameness (eg, trotting in a straight line with the horse straight through its neck and trunk). This “correct” pace varies between horses. Correct bitting, eg, using a Chifney bit, is important but can be confusing due to an altered posture when lunging
and should be avoided if possible. Very slight sedation (eg, 0.3 mL romifidine [10 mg/kg]) may also result in a horse with a more relaxed outline and allow a better assessment without seemingly influencing the degree of lameness. Slowing down the pace at the trot often illustrates a subtle lameness better because the horse loses its momentum and struggles with suspension in the affected limb(s). |
| A ridden assessment of the horse is often necessary, particularly with a subtle lameness or a horse that is unwilling to perform certain movements (eg, a dressage horse). A multilimb lameness without an obvious single-limb lameness may also be involved. The clinical signs may be minor (eg, signs of aversion as opposed to lameness). Subtle signs include an unwillingness to take a strong contact with the rider’s hand, a slight heat tilt, and tail swishing. Seeing the horse and rider
at work is necessary to look for subtle lamenesses. However, a good rider can, often inadvertently, hide a problem by his or her inherent expertise and ability to “correct” difficulties. Similarly, a bad rider can make a sound horse look lame (‘‘bridle lame’’). Deliberately riding on the wrong diagonal frequently helps illustrate a problem, especially those involving the back. A change of rider may occasionally be required to highlight a particular problem. Occasionally a horse
appears to be sound when lunged and ridden, but the rider feels that the performance is impaired. In such cases it may be worth working the horse on concomitant analgesic or anti-inflammatory medication at therapeutic levels for an adequate period (eg, phenylbutazone 2-3 g/day, PO for 7-14 days) to assess whether improvement occurs. If so, medication should be withdrawn and diagnostic anesthesia used beginning in an arbitrary limb, most often a forelimb. In this way, multiple limb
lamenesses (as many as 4), often mimicking the clinical picture associated with back pain, can be evaluated and treated. Some veterinarians choose to ride the horse as part of the lameness examination; however, in most cases time spent on the ground observing the horse on different surfaces and in different training situations is time better spent. |
| Because lameness may indicate a peripheral nerve dysfunction, a neurologic examination should always be part of the lameness examination and might include observing the horse execute “complicated” movements such as turning short, backing, “hopping” on one forelimb (with the other forelimb held up), and negotiating a curb. These tests help determine whether reduced proprioception, weakness, or spasticity are present or suggest abnormalities in the motor function of the major muscle
groups that flex and extend the limbs. In acute traumatic injuries of the nerves to the limbs, the presence of these gait deficits relative to the major muscle groups provide the key to diagnosis. Longstanding peripheral neuropathies also give rise to denervation atrophy of the innervated muscles as seen in suprascapular nerve trauma (“sweeney”), in which atrophy of both the infraspinatus and supraspinatus muscle develops. |
