A flexion test is when a part of the horse’s body is held in a flexed position for a period of time, then the horse immediately jogged/trotted off in hand to see if the test causes any obvious discomfort or worsening of lameness. With a positive test, the first few steps when the horse jogs off will show an obvious lameness including things like short striding and head bobs. If a hind leg, the horse may ”hop” when jogged off.
When doing a flexion test, it’s important to pay attention to what you’re doing or you may stress other areas, too, which will confuse your results. To start, make sure the horse is standing square before you begin, facing in the direction you want him to jog off.
Ask your handler to keep the horse as motionless as possible during the test, and to be ready to jog off at a trot as soon as you release the leg. You’ll probably have to cluck, clap or tap the horse to get him to move off quickly. If the horse walks instead of trotting, repeat the test. Conversely, some horses will high tail it away from you quickly when the leg is released, also making it difficult to see if there was any effect. Again, if this happens repeat the test.
When holding the leg in flexion, do not crank down on the joint. Flex it as far as it will go then use just enough pressure as needed to keep it there. Excessive pressure alone can cause pain.
The ability to flex just the right joint takes attention to anatomy and care not to flex more than one joint at a time.
Here’s how to do it:
Fetlocks: Pick up the leg and support it by the cannon bone, letting it ”dangle” close to the ground, with the knee or hock not lifted up higher than the opposite leg so that there is minimal flexion of the joints above the fetlock. Grasp the hoof at the toe and pull the hoof back toward the fetlock. Continue gently moving it back until you reach the point where it won’t move any further. Hold in position there for 30 seconds then jog off.
Knee: Suspend the lower leg by the middle of the cannon bone, with the fetlock hanging free. Keep the knee at the same height as the opposite leg, i.e., do not lift up on the leg. With one hand on the upper leg/forearm (to keep the leg from elevating) and one cupping the front of the cannon bone, fold the lower leg up toward the forearm as far as it will go. Hold in position for 30 to 60 seconds then release.
Hocks/Stifles: Because of the construction of the ligaments and muscles in the hind leg, it is impossible to flex the hock without also flexing the stifle. For this reason, hock flexion tests are also automatically stifle flexion tests. As with knee flexion tests, every effort should be made not to elevate the hock any higher than the hock on the opposite side. If you do, pelvic, back and sacroiliac areas may also be stressed. This flexion test also inevitably puts some degree of pressure over the hip joint and the trochanteric bursa area. With one hand resting gently on the back of the leg above the hock, use the other hand to cup the back of the cannon bone and fold the lower leg up toward the gaskin. Hold the hock in flexion for 60 seconds then jog the horse off promptly.
Higher joints: Problems of the shoulder, elbow, hip, pelvis and sarcoiliac joint are more difficult to diagnose by tests that manipulate joint position. There are several reasons for this. One is that pain in these regions is often accompanied by significant muscle spasm, which may actually be relieved temporarily by gentle traction on these areas. Another is that manipulating the position of these joints inevitably involves stress on one or more joints below and/or above them.
Feet and pasterns: Fetlock flexion tests also put stretch/strain along the front (anterior) surface of the lower joints, so conditions such as ringbone could potentially be aggravated For suspected pain originating from the hind-foot area (navicular bone, navicular bursa, deep digital flexor tendon, impar ligament), stand the horse on a block of wood so that the toe is supported but the back of the foot is not, and drops down toward the ground. Jog off after 60 seconds. This is actually a stretch and pressure test, rather than a flexion test. Stretch is put on the deep digital flexor tendon and impar ligament (holds the navicular bone to the coffin bone), and compresses the navicular bursa and the navicular bone.
Pros and Cons. Older horses and horses with chronic problems may jog off lame after flexion tests even if the area doesn’t bother them under normal conditions. Excessive force during flexion tests can also produce pain, as can holding the flexion for too long.
Flexion tests of the hind leg above the fetlock are of limited value because of the difficulty in flexing joints individually. Hind-leg lameness also often involves more than one site at the same time, e.g. hock pain and hip pain.
Bottom Line. Flexion tests require practice. They can pinpoint a joint, but not the problem.