Flexion tests: What do they mean?

This is a picture of Simon, a horse I used to own. Doesn't he look gorgeous here? He had a great temperament, very quiet -- his idea of a spook was to prick both ears forward. He didn't like dressage, though. He liked to jump. I posted this photo to Equine.com and sold him in ten days. The first would-be buyer backed out because the prepurchase exam showed problems with his flexion test and radiographs. The second buyer was informed about the vet exam, but she pooh-poohed the results. She bought him in 2003, and this 17.3 Danish cross is jumping and competing in the 3' division. Makes ya wonder about pre-purchase exams in general, and flexions in particular.

What's a flexion test?
Flexion tests have been around awhile. The flexion test was first described in 1923 in the Swedish veterinary literature. In this test, the vet manually flexes, or articulates, each leg individually. The leg is held in a position with all joint angles closed for a period of time, usually about a minute, then the vet releases the leg. The horse is immediately asked to trot away, and the first few strides are closely evaluated. Unevenness in the gait post flexion is thought to be a sign of an underlying physical problem.

My .02, standard disclaimers apply
Time out here. The human equivalent of a flexion test would be forcing someone to crouch for a few minutes then making them jump up and bound off. I'm 46, and fairly fit. Ask me to crouch and jump, the main question is will I land on my knees, butt, or face. Frankly I'm indignant on behalf of horses everywhere. Dude, ever heard of warming up? This is why I think flexions are a kind of lame (so sorry). There are some researchers who would agree.

Lack of standards
Researcher David Ramey finds numerous problems with flexion tests. He notes that there are no standards a) for the optimum force to use and b) for the duration of the flexion test. A Belgium study puts the recommended force at 10kg, or 22 lbs (another study suggested 14kg or 31 lbs!). The Belgium study showed that 10kg for 60 seconds was the maximum force at which sound horses did not react to a flexion test. While usually flexions are held for about a minute, practicing vets flex for anywhere from 30 seconds to 3 minutes. Ouch.

Can flexions predict future soundness?
There is a decent amount of research literature on the value of flexion test. This literature suggests the flexion test itself does not reliably predict a horse's future soundness. Why is everyone doing them then? I guess old traditions die hard. Below I've summarized findings from a few of the larger studies out there.

The Ramey Study
David Ramey did one a comprehensive studies of flexion tests. He examined 50 horses, or 100 front legs. All horses were judged to be clinically sound on hard ground prior to the test. Both front legs of each horse were flexed twice; once with normal pressure, and once with "extra firmness." The horses were also x-rayed for abnormality in the joints. Findings are below:

• Of 50 horses, 20 of them, or 40%, showed some positive response (positive=lameness) to the regular flexion.
• Forty-nine of the 50 horses showed a degree of lameness in response to a "firm" flexion. Thirty-nine of the firmly flexed horses were lame on a scale of 4 out of 5 or greater.
  
• Flexion results were compared with each horse's x-rays. Abnormal x-rays didn't correlate with a finding of lameness on flexion. Twenty-four of the 50 horses had radiographic abnormalities, but only eight of these showed any lameness on flexion.
  
• Working and older horses were more likely to show a degree of lameness on flexion. (reprisal: Hey dude, ever hear of warming up?)

Busschers and van Hoogmoed Studies
A study by Busschers of 100 horses sound showed similar findings to Ramey. Their study included both front and hind legs of horses actively working/competing...

• Like Ramey, they found that the amount of pressure applied and the length of the flexion affected the outcome of the test.
  
• Sound horses tended to be slightly positive (showing lameness) in the hind limb.
  
• Mares were more likely to show a degree of lameness on flexion than geldings.
  
• Repeating a flexion in 10 minute or 30 minute intervals increased the likelihood of a horse showing some lameness on flexion.
  
• Repeating a flexion 48 hours later did not increase the likelihood of a positive flexion (flexion showing lameness).
  
• The horses were retested in 6-months. On the retest, the number flexions showing a degree of lameness decreased significantly and the horse's range of motion increased significantly.
  
• Sixty percent of 100 sound riding horses in this study showed some degree of lameness on flexion.
  

The researcher van Hoogmoed did a retrospective study of prepurchase exams for 500 horses, including x-rays and flexions of both hind and forelegs. He compared radiographs for each horse to their flexion test results. He found:

• Warmbloods tend to have more extensive changes in the navicular bone and coffin joint relative to Thoroughbreds, but they were not as lame.
• Higher grade ( more abnormal) x-rays of the coffin and navicular bone tend to correlate/occur with lameness in the flexion results.
• For the hock, higher grade (more abnormal) x-rays do not necessarily occur with flexions showing lameness. Horses with "bad" hock x-rays often flexed sound.

What does this all mean? The bottom line is be careful about interpreting flexion tests. Most vets are far less concerned about "problem" flexions or x-rays on a horse that is older, in work, and has a performance record. For younger horses, a positive flexion or suspect radiographs may justify a more guarded prognosis. Investing money in an animal is a risk, and we use the tools that are available to us. And as we always do with horses, we cross our fingers...

REFERENCES

Busschers E. Use of the flexion test of the distal forelimb in the sound horse: repeatability and effect of age, gender, weight, height and fetlock joint range of motion. J Vet Med A Physiol Pathol Clin Med. 2001 Sep;48(7):413-27.

Ramey, David. Prospective evaluation of forelimb flexion tests in
practice: Clinical response, radiographiac correlations, and predictive
value for future lamenesss. AAEP Proceedings 1997, v. 43, p. 116.

van Hoogmoed LM, Retrospective evaluation of equine prepurchase examinations performed 1991-2000. Equine Vet J. 2003 Jun;35(4):341-2.