A comparative study of proximal hindlimb flexion in horses: 5 versus 60 seconds

The flexion test is routinely used in lameness and prepurchase examinations. There is no accepted standard for duration of flexion or evidence that interpretation of results would differ with different durations of flexion.

There will be no difference in interpretation of proximal hindlimb flexion for 5 or 60 s.

Video recordings of lameness examinations of 34 client-owned horses were performed that included: baseline lameness, proximal hindlimb flexion for 60 s, and flexion of the same limb for 5 s. Videos were edited to blind reviewers to the hypothesis being tested. The baseline lameness video from each horse was paired with each flexion to make 2 pairs of videos for each case. Twenty video pairs were repeated to assess intraobserver repeatability. Fifteen experienced equine clinicians were asked to review the baseline lameness video followed by the flexion test and grade the response to flexion as either positive or negative. Potential associations between the duration of flexion and the likelihood of a positive flexion test were evaluated using generalised linear mixed models. A kappa value was calculated to assess the degree of intraobserver agreement on the repeated videos. Significance level was set at P<0.05.

Proximal hindlimb flexion of 60 s was more likely to be called positive than flexion of 5 s (P<0.0001), with the likelihood of the same interpretation 74% of the time. The first flexion performed was more likely to be called positive than subsequent flexions (P = 0.029). Intra-assessor agreement averaged 75% with κ= 0.49.

Proximal hindlimb flexion of a limb for 5 s does not yield the same result as flexing a limb for 60 s.

Shorter durations of flexion may be useful for clinicians that have good agreement with flexions of 5 and 60 s.