A flexion test is a preliminary veterinary procedure performed on a horse, generally during a prepurchase or a lameness exam. The purpose is to accentuate any pain that may be associated with a joint or soft-tissue structure, allowing the practitioner to localize a lameness to a specific area, or to alert a practitioner to the presence of sub-clinical disease that may be present during a pre-purchase exam.
Performing a flexion test
The animal's leg is held in a flexed position for 30 seconds to up to 3 minutes (although most veterinarians do not go longer than a minute), and then the horse is immediately trotted off and its gait is analyzed for abnormalities and unevenness. Flexions stretch the joint capsule, increase intra-articular and subchondral bone pressure, and compress surrounding soft tissue structures, which accentuates any pain associated with these structures.
An increase in lameness following a flexion test suggests that those joints or surrounding soft tissue structures may be a source of pain for the horse. The horse may take a few uneven steps, or may be lame for several minutes following the procedure. Flexion tests are considered positive if lameness is increased, although usually lameness is forgiven for the first few steps following flexion. The horse's response should be graded with each flexion and recorded. This allows comparison in lameness when rechecking after treatment has been implemented.
In addition to watching for lameness in the flexed limb, the examiner also looks for lameness in the standing, contralateral (opposite) limb. An increase in lameness associated with the contralateral limb can suggest certain causes pain, such as bilateral hock or carpal disease.
Distal limb flexion
The distal (lower) limb flexion applies the most pressure to the fetlock, pastern, and coffin joints. This flexion is usually performed by pulling the toe of the hoof backward towards the cannon bone, and holding sustained pressure on the joints. The fetlock and phalanges may be somewhat isolated by changing technique, but these joints are never completely isolated from the others, especially in the hind limbs. False positive results from this flexion are especially common in the front fetlock joints.
Carpal flexion
The carpal (knee) flexion test is performed by pulling the cannon bone up towards the radius. In a normal horse, the heels of the foot should contact the animal's elbow. Positive results are usually strongly supportive of carpal disease, but negative results do not rule it out.
Elbow flexion
Elbow flexion is usually only performed when joint abnormality is found during physical examination. Flexion may be performed by lifting the forelimb (antebrachium) so that it is parallel to the ground, while allowing the knee and distal limb to hang free to help prevent pressure on these joints. Unfortunately, elbow flexion often produces some flexion in the shoulder, and these joints are difficult to localize.
Upper forelimb flexion
There are two main methods of upper forelimb flexion. The first method involves pulling the limb forward, so that the elbow flexes and the shoulder extends. This method tends to place more strain on the structures of the caudal elbow and cranial shoulder, and is best at localizing lameness to the bicipital bursa or the supraglenoid tubercle of the scapula, but also places strain on the biceps and triceps muscles and tendons, and the olecranon. The alternative method involves pulling the limb caudally, which flexes the shoulder and extends the elbow.
Hock flexion
Hock flexion is almost always accompanied by flexion of the fetlock, stifle, and hip joints, so a positive flexion does not clearly indicate hock pain. A very marked response is actually more common with stifle pain, rather than hock pain. The flexion is performed by pulling the cannon bone upward so that the upper joints of the leg flex, while avoiding flexion of the fetlock joint or significant pressure on the flexor tendons.
A flexion test that produces lameness on the contralateral, standing limb usually occurs with sacroiliac disease.