Lameness - Horse

Introduction

Lameness is an indication of a structural or functional disorder in one or more limbs or the back that is evident while the horse is standing or in movement.

Lameness can be caused by trauma, congenital or acquired abnormalities, infection, metabolic disturbances, circulatory and nervous disorders, or a combination of these.

Lameness results from painful and non-painful alterations in gait, called mechanical lameness or it may result from neurological dysfunction.

The diagnosis of lameness requires a detailed knowledge of anatomy, a thorough history and clinical examination and the use of further diagnostic tests.

The Lameness Examination

History

A comprehensive history including age, type and training regimen may give important clues as well as the time of onset of the lameness and the management up to now. Any farrier work should be noted and any periods when the lameness seems to worsen or improve.

Response to anti-inflammatory medication might also be useful information.

Haematology and biochemistry analyses might indicate problems that influence overall performance such as anaemia or raised AST and CK indicating rhabdomyolysis.

Clinical Examination and Palpation

Thorough palpation and manipulation of limbs in weightbearing and non-weightbearing positions should be undertaken. The contralateral limbs provides a useful comparison in most cases.

Any heat, joint distension, abnormal tissue tension and the reaction of the horse to joint flexion and extension should be noted.

Areas of muscle wastage might provide useful information.

The feet should be examined thoroughly and hoof testers should be applied to the hoof walls and soles. In general, shoes should be left on during a lameness examination as removing them might make the horse footsore.

The back and neck should be examined with the horse standing square. The neck should be assessed for range of movement and the musculature of the neck and back should be equal on either side.

Gait Evaluation

This is only an option if the lameness is minor and chronic. Horses with an acute and major lameness should undergo radiographs or ultrasonography as soon as possible.

The horse is trotted back and forth in a straight line and lunged on hard and soft surfaces. Visual appraisal of the lameness should be possible, and impact sounds and footfall should be listened for.

Flexion Tests

These are useful to assess the range of movement and response to passive flexion, along with any increase in lameness or onset of lameness following flexion. The distal leg should be flexed independently of the carpus and hock in the first instance, then a more proximal flexion test can be performed.

The test should be consistently applied using the same handler and surface.

Ridden Examination

This is often necessary in subtle lameness cases or multi-limb lamenesses. Minor signs might include aversion to certain movements, a slight head tilt, tail swishing. Different riders might have to be used due to different riding styles which might mask or accentuate a lameness.

Neurological Examination

Some lameness might be due to peripheral nerve dysfunction and a neurological examination should be performed during a lameness evaluation.

The horse can be asked to execute complicated movements such as turning in small circles, backing and hopping on one forelimb. This helps evaluate for reduced proprioception, weakness and spasticity.

Diagnostic Analgesia

This is an important component of the lameness examination if the site of pain is uncertain. It involves infiltration of an area with local anaesthetic and further evaluation of gait to see if an improvement in the lameness has occurred. It should not be used in cases of suspected fracture as the horse might bear more weight on the limb and exacerbate the condition.

Cases in which diagnostic analgesia is useful include: foot pain, navicular disease, joint disease and proximal suspensory desmitis.

Perineural Analgesia

This should start distally and work proximally until a response is seen.

Commonly performed blocks include: palmar/plantar digital nerve block, abaxial sesamoid nerve block, low 4-point/6-point nerve block, subcarpal/subtarsal nerve block and more proximal blocks.

Intrasynovial Analgesia

This may start proximally if indicated, as distal analgesia can still be performed if necessary.

Radiographic guidance is commonly used for introduction into the navicular bursa.

Joints blocked most commonly include: coffin, fetlock, carpal, tarsal and stifle joints.

Imaging Techniques

Many different techniques can be used to evaluate areas of interest.

Radiography

Multiple projections should be used to assess bony tissues and assess chronic changes.

Contrast radiography is also very useful in articular cartilage pathology and to assess the involvement of joints.

Ultrasonography

This can be used to assess any soft tissues. Lower wavelengths are used for deeper tissues.

It is most useful in evaluation tendons and ligaments but can also assess muscles and bone and cartilage surfaces for damage.

MRI

This is primarily used for the assessment of structures in the foot such as the Deep Digital Flexor Tendon, ligaments and navicular bone, due to equipment and size constraints.

CT

Use of CT is limited to the head, legs and cranial part of the neck due to the size of the gantry opening. A general anaesthetic is necessary.

It is useful for evaluating subchondral bone disease, osteoarthritis and complex bone fractures. It also allows bone density measurements to be made.

Scintigraphy

This is a physiologic imaging technique that assesses metabolism and circulation. Radioactive particles are administered intravenously and their distribution is evaluated by a gamma camera. They accumulate in areas of active bone remodelling and also in areas of soft tissue injury due to increased blood flow to the area.

Lameness - Horse Learning Resources
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References

Kahn, C. (2005) Merck Veterinary Manual Merck and co

Stashak, T. (2002) Adams' Lameness in Horses Wiley-Blackwell

Stashak, T. (1996) Practice guide to lameness in horses Wiley-Blackwell