In a closer look at the standard forelimb flexion test, researchers from Ireland and the Netherlands found that any forelimb lameness detectable with this method generally shows up in the fetlock joint. They also found that the exam can render a false positive result in this joint (indicating that the horse is lame when in reality he is not), depending on how much force is used when conducting the exam.
During a flexion test, a veterinarian flexes a horse's legs one at a time, either stretching or compressing different areas of the legs. Once a leg has been flexed, the horse is trotted in a straight line and the veterinarian watches for signs of lameness. Flexion tests are most commonly used in prepurchase and lameness exams.
René van Weeren, DVM, PhD, Dipl. ECVS of Utrecht University and his colleagues indicated in their recent study that the fetlock joint is the most important area to examine for problems if a horse displays a positive result in a forelimb flexion test focused on the lower, or distal, aspect of the leg.
"The flexion test does not tell much about the hoof and its internal structures, or the pastern region," relayed van Weeren. "If the test is positive, the pain-causing factor will likely be in (or around) the fetlock."
He also noted that the fetlock joint and the area immediately around the joint contribute most to a false positive result in such a test.
During the study researchers used a force of 250 Newtons (54 lbs) to flex the horses' lower forelegs for 60 seconds. Each of the eight Dutch Warmbloods used in the study displayed a positive result after being flexed.
Most veterinarians use a force of approximately 150 Newtons (32 lbs) when performing a flexion test, but according to the researchers, "there are no unequivocal published guidelines on how the test should be performed, and little or no research into the mechanisms of action and the effect of the test on various anatomical structures is available."
For these reasons, van Weeren cautions veterinarians and owners not to put too much emphasis on flexion tests in a prepurchase exam: "Don't overvalue flexion tests. I'd rather buy a good-moving horse with a positive flexion test in one limb than a stiff-gaited animal that is negative on all four limbs."
Previous studies have indicated that the horse's age, workload, and gender also have an impact on the positive or negative results of a flexion test.
The study, "Which anatomical region determines a positive flexion test of the distal aspect of a forelimb in a nonlame horse?" was published in the September 2010 issue of the Equine Veterinary Journal. The abstract can be found at PubMed.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.