Introduction of lameness

Introduction of lameness in animals include definition of lameness, grading of lameness, classification and some basic points of diagnosis.

Definition of Lameness

Lameness is defined as an abnormal gait in which the horse does not travel in a sound and regular manner. Lameness can be the result of a conformational defect, overexertion, neurological disorder, injury, or a disease process affecting the muscle, tendon, and/or bone. Horses are very athletic animals and pain will alter their normal gait. As a result, horses are often presented for lameness evaluation because a decrease in performance has been noted, not necessarily because the horse has an obvious limp.

For as long as the horse has been domesticated, the topic of lameness and soundness has been of great importance. Early in the relationship between man and horse, the usefulness of any horse was measured by its soundness and ability to remain so. Over time, man has relied less and less on the horse as a beast of burden. As a result, contemporary discussions about lameness revolve around the athletic horse and its use in competition. Not to be overlooked are those horses used for pleasure riding, as their usefulness can also be limited by lameness.

Grading of lameness

Grade 0	No lameness under any circumstances
Grade 1	Lameness is difficult to observe and is not consistently apparent
Grade 2	Lameness is difficult to observe when trotting in a straight line but is consistently apparent under certain circumstances
Grade 3	Lameness is observable at the trot in a straight line
Grade 4	Lameness is obvious at the walk
Grade 6	Lameness produces minimal weight-bearing or an inability to move

Lameness is unlike other conditions that affect the horse. With most ailments, the horse is either sick or healthy. With lameness, there are many different degrees of unsoundness. These range from barely perceivable alterations in movement all the way to severe lameness which is impossible to overlook. As one might expect, this range of lameness produces a range of complaints, everything from loss of form over a jump or during a specific movement, to increased time for a speed event, to intermittent lameness while working in hand or under saddle, to obvious lameness of one or more limbs. To complicate matters further, subtle loss of performance may not be a lameness issue. Many factors such as training, nutrition, shoeing, and dentistry all can contribute to a loss of performance. Conditioning is also an important consideration.

HOW IS LAMENESS DIAGNOSED?

The traditional lameness evaluation is conducted in a systematic 5 step approach-

1. History and Complete Physical Exam.
2. Palpation of the neck, back and hip muscles, tendons; signs of joint effusion; digital pulses, and hoof tester application.
3. Body conformational assessment.
4. Brief Neurologic Exam to rule out the presence of a neurological condition as a cause of lameness.
5. Gait Analysis: Examination of the horse at a walk, trot and/ or canter, both in a straight line and circling on a lunge line, ideally over hard and soft surfaces. Sometimes this evaluation is conducted while the horse is being ridden. Flexion tests are used to temporarily exacerbate an obscure condition. After completion of these steps the use of nerve or joint blocks will likely be necessary to localize the source of pain. Once this has been identified other diagnostics such as radiographs, ultrasound, MRI or CT may be warranted to determine the definitive cause of the lameness.

WHAT TO WATCH DURING THE GAIT ANALYSIS?

Commonly, lame horses are evaluated in hand, at the trot and in a straight line. If the horse is going away from us we look at the rear end and when the horses is trotting towards us we focus our attention on the front end.

During the gait analysis the veterinarian looks for changes in the normal gait, for example: decreased length of stride or excessive dropping of the fetlocks. In the sound horse, at the walk, the hind feet should land at or in front of the forelimb footprint, and while moving in a tight circle, should be fluid without abnormal postures like “picking up” the head while being turned (a sign of pain in the fore limbs).

Down on Sound

If an animal is LAME IN THE FRONT, the head will go down when the sound limb comes in contact with the ground. If the animal is LAME BEHIND, the head will go down when the lame limb contacts the ground.

Hip Hike

When a horse is lame, the pelvis will not rise as high when pushing off of the lame limb, or fall as far landing on the lame limb. “Hip hike” is determine by the total vertical displacement of the tuber coxae (in os coxae bone) during trotting. The side which shows the greatest displacement (hip hike) is the lame limb. “Lunging”

When horses are lunging, their torso is tilted toward the center of the circle. This creates a potential natural asymmetry in both vertical head and vertical pelvic movement. This asymmetry can be quite dramatic in some horses, even when lameness is not present. Lunging typically exacerbates forelimb lameness and masks hind limb lameness.