Equine Lameness:an introduction to investigating lameness

What is lameness?

An abnormality of gait that is caused by pain and / or restriction of movement.

The most common causes of lameness

The basic processes that cause disease can be remembered by using the acronym DAMNIT:

D: degenerative, developmental
A: allergic, autoimmune
M: metabolic, mechanical
N: neoplastic (tumors), nutritional
I: infectious, inflammatory, immune-mediated, ischemic (low blood flow), iatrogenic (man-made), idiopathic (unknown)
T: traumatic, toxic

Most causes of lameness fall into the following categories:

• Degenerative e.g. degenerative joint disease (DJD, or osteoarthritis)
• developmental e.g. osteochondrosis (OCD), physitis (epiphysitis)
• metabolic e.g. laminitis (founder), exertional rhabdomyolysis (tying up)
• mechanical i.e. overload of a structure - either sudden, massive overload or repeated, marginal overload (wear & tear)
• infectious e.g. foot abscess, infected wound, cellulitis, joint infection
• inflammatory - most of the specific causes of lameness have an inflammatory component
• traumatic i.e. injury (external trauma)

Identifying the location of the problem

Which leg?

Observation is the key to identifying which is the lame leg:

• Abnormal stance-e.g. pointing the toe, resting one leg more than another, dropped fetlock
• Abnormal movement-head nod (forelimb lameness), hip hike (hindlimb lameness)
• Reduced arc of foot flight-often seen as stiffness or reluctance to flex the limb normally
• Shortened stride length-shortened 'swing' phase of the stride
• Abnormal foot placement-e.g. landing toe-first to spare the heel

Evaluate the horse's gait:

• on a level, even surface
• at the walk and the trot
• in a straight line and in a circle (led, lunged, or in a round pen)
  - make sure the horse is on a loose lead or lunge line
  - watch the horse in both directions on the circle
• from the side, in front, and the rear
• on different surfaces (e.g. hard and soft)

Bear in mind that there may be a problem in more than one leg.

Investigating the cause: Basic Skills

Locating the specific area involved requires two basic tools: your eyes and your hands.

The three skills required are Observation, Palpation, and Manipulation.

Observation:

• look for symmetry between left and right legs, and between the inside and outside of a normally symmetrical structure
• when asymmetry is found, is it caused by enlargement (e.g. swelling) or reduction in tissue mass?

Palpation:

• feel for heat, swelling, pain, and changes in tone or texture of a tissue
• characterize any swellings as hard, firm, soft, fluid-filled

Manipulation:

• move the structure or tissue through its normal range of motion
• check for pain, altered range of motion (increase or decrease), and crepitus (a grating, grinding, or crackling sensation)

Use these identifiers to identify the five basic signs of inflammation:

• Pain
• Heat
• Swelling
• Redness
• Loss of function

Investigating specific areas

Tailor your investigation to the structure you are evaluating:

The Foot - the most common site of lameness.

• Observation - symmetry of the hoof wall; integrity of the hoof wall (cracks, bulges, etc.) and sole (defects, foreign objects, etc.); discharge, discoloration, or odor; shoe and nails
• Palpation - coronary band (pain, swellings, depressions); heel bulbs; sole (thumb pressure); digital pulses (at fetlock or pastern)
• Manipulation - move the heels independently; tap the hoof wall; use hoof testers (if you have them)

Joints

• Observation - swelling, position (angulation)
• Palpation - nature of the swelling, heat, pain
• Manipulation - flex (bend) and extend (straighten) the joint, checking for pain and altered range of motion

Bones

• Observation - swelling
• Palpation - nature of the swelling, heat, pain
• Manipulation - pain, instability, crepitus

Tendons and Ligaments

• Observation - swelling
• Palpation - swelling (subtle swelling may not be obvious to the eye), location of the swelling (within or around the structure?), heat, pain, change in tension and texture - if possible, also palpate the sites where the structure attaches to bone
• Manipulation - pain, instability of the associated joint

Muscles

• Observation - swellings or atrophy (loss of muscle mass)
• Palpation - pain, change in tone and texture, crepitus, heat or coolness
• Manipulation - pain, reduced range of motion in the associated joint(s)

Neck and Back

The neck and back consist of a complex series of bones, joints, tendons, ligaments, and muscles:

• Observation - symmetry, posture, contour
• Palpation - nature of any swellings, pain, change in muscle tone and texture
• Manipulation - pain, reluctance to flex or extend, reduced range of motion

Other possible sources of lameness

Also consider these other possible sources of lameness:

• the skin
• the nervous system (brain, spinal cord, nerves)
• the tack (especially the saddle)
• the rider (bridle lameness or rein lameness)

Interpreting your findings

1. The pain response must be repeatable to be valid.
   - when you return to the suspect area you should get the same (or greater) response to palpation or manipulation each time
   - the pain response may be subtle (e.g. tensing up, turning the head to look at you, moving away from your hand), but if it is repeatable, it is probably significant
2. Assuming the opposite leg is normal, use it for comparison if unsure that your findings are significant.
3. Most lameness problems involve a structure in or below the knee or hock.
4. A specific diagnosis often is not possible without veterinary examination and diagnostic imaging

Veterinary Examination

Veterinary Surgeons use the following procedures to evaluate lameness and determine the cause:

• physical examination (observation, palpation, manipulation)
• gait evaluation
• joint flexion tests
• diagnostic anesthesia
  - regional nerve blocks and joint blocks
• diagnostic imaging
  - the method chosen depends on the veterinarian's suspicions
  - radiography (x-rays) - bones and joints
  - ultrasonography - soft-tissue problems, such as tendon and ligament injuries, and joint surfaces
  - thermography - body surface temperature imaging, looking for areas of inflammation (increased temp.) or reduced blood flow (decreased temp.)
  - nuclear scintigraphy (bone scan) - soft-tissue phase for soft-tissue inflammation; bone phase for bone or joint problems
  - computerized tomography (CT) - any tissue, but mostly used for bone problems
  - magnetic resonance imaging (MRI) - mostly soft tissues and joint surfaces
• therapeutic trial - presumptive diagnosis based on response to treatment

Dr. Christine King © 2001 BVSc, MACVSc, MVetClinStud

Thanks to Equine Health Science for sharing this article