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 skills 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:
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
