Positive flexion tests

Flexion test

A flexion test involves compression of joints and soft tissues through forced bending of the limbs.

Flexion tests of both the fore- and hindlimbs are common diagnostic tools, particularly used for the purposes of pre-purchase examination. Many of us have heard the words ‘failed flexion test’ or ‘positive flexion test’ when looking into buying or selling a horse, but what do these terms really mean? What is the significance of these results and how seriously should we be taking them?

What is a flexion test?

Simply put, a flexion test involves various joints and soft tissue structures of the lower limbs of the horse being stretched and/or compressed for a brief period of time by forcibly bending the limb. After the test the horse is immediately trotted off and observed for any signs of lameness.

Flexion tests are not unlike what you may experience if someone asked you to crouch for a minute or so and then run off immediately. You would usually be able to run off with no problem, but sometimes you may experience some soreness or pain or stiffness in a joint or tissue when you first try to run; you might even limp slightly, at least for the first few steps. If you had a known injury, for example a knee problem, you would do very badly on a flexion test. Therefore, as in humans, an abnormal response to a flexion test could be highlighting a serious problem (like a knee injury), but could also occur even in a normal limb either because the test was performed differently or overzealously, or simply because the horse was stiff or hadn’t warmed up properly.

What can a flexion test do?

Flexion tests are screening tests. They aim to identify any lameness that is not necessarily visible in the usual gaits. Flexion tests can therefore screen for subclinical problems that are not necessarily an issue currently, but may become an issue at some later stage in the horse’s life.

Flexion tests can therefore identify which limb or limbs have issues. The tests cannot specifically locate the issue, but they can reveal the need for further investigations of the limbs and joints. Nerve blocks, ultrasounds and x-rays are all worth considering after a positive flexion test.

What can a flexion test not do?

Flexion tests

The horse is immediately trotted off after the flexion and observed for signs of lameness.

A flexion test cannot tell you that there is definitely a problem in the limbs of the horse. Some horses will have negative flexion tests one day, and positive tests the next, simply because of stiffness or some other benign complaint.

Furthermore, there is little standardisation in how the tests are actually performed. Veterinarians disagree on the time required (from 5 to 180 seconds) and also the degree of force used. A flexion test performed for a short time and with little force may not elicit any change in gait, but that same limb flexed for longer with more significant force could leave that same horse limping. With so much variety in how the test is conducted, it is worthwhile watching the test to see the response for yourself.

Flexion tests can also not isolate and does not only affect one joint or tissue at a time. A flexion test not only places strain on numerous joints but it also stresses the joint capsule and associated ligaments and tendons. It also places stress on cartilage and bone which would elicit pain due to arthritic changes in the joint. It is therefore impossible for a flexion test to provide the location or cause of the lameness. It can just suggest that there is a problem in that limb.

The full article appears in the April issue of HQ (121) > Shop now