Comparative Study of Proximal Hind Limb Flexion in Horses: Five Versus 60 Seconds

Proximal hind limb flexion of 60 seconds is more likely to be interpreted as positive than is 5-second flexion.

1. Introduction

Flexion tests are routinely used in lameness evaluations. There is no accepted standard for duration of flexion or evidence that interpretation would differ with different durations. We hypothesized that there would be no difference in interpretation of flexion for 5 or 60 seconds.

2. Materials and Methods

Video recordings of lameness examinations of 34 horses were performed, including baseline lameness and proximal hind limb flexion for 5 and 60 seconds of the same leg. Videos were edited to blind reviewers to the hypothesis. The baseline lameness video was paired with each flexion to make two pairs of videos. Twenty video pairs were repeated to assess intra-observer repeatability. Fifteen clinicians reviewed the videos and graded response to flexion as positive or negative. Potential associations between the duration and the likelihood of a positive interpretation were evaluated using generalized linear mixed models. A κ value was calculated to assess intra-observer agreement on the repeated videos. 

3. Results

Full hind limb flexion of 60 seconds was more likely to be called positive than was flexion of 5 seconds (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 were subsequent flexions (P = 0.029). Intra-assessor agreement averaged 75%, with κ = 0.49.

4. Discussion

Proximal hind limb flexion for 5 seconds did not yield the same result as 60 seconds; however, shorter duration may have utility for practitioners to abbreviate the examination.