Video analysis of standing — an alternative footprint analysis to assess functional loss following injury to the rat sciatic nerve

The rat sciatic nerve is a well-established animal model for the study of recovery from peripheral nerve injuries. Footprint analysis is the most widely used non-invasive method of measuring functional recovery after injury in this model. We describe a new alternative video analysis of standing (or static footprint video analysis) to assess functional loss following injury to the rat sciatic nerve, during animal standing or periodic rest on a flat transparent surface. We found good correlation between video recording during standing and dynamic ink track footprint parameter measurements for both 1-5 and injured 2-4 toe spreads only. Reproducibility for these three parameters was also better using the video method. Uninjured 2-4 toe spread by video showed a poor correlation and similar reproducibility as compared with ink. However, both print length parameters measured by video had poorer correlation and greater variability, particularly the print length factor (PLF) was weakly correlated with that determined by ink. Contribution of the footprint factors on the estimated functional loss has also changed in conditions during standing. It was most prominent for the 1-5 toe spread factor (TSF), near marginal for the 2-4 or intermediary toe spread factor (ITF), and weak, statistically insignificant for the PLF. Thus, the introduction of a new functional loss index, or so-called static sciatic index (SSI), and its estimating formula was mandatory. Moreover, using a simple ratio of injured/uninjured 1-5 video toe spread as a substitute for the SSI, we could achieve considerable simplification of the method without any significant loss of accuracy. Our video analysis of standing is technically easier to perform than the corresponding footprint video analysis during walking, but still preserves all advantages of video versus conventional ink track method, i.e. there are few non-measurable footprints, better repeatability, high accuracy and more precise quantification of the degree of functional loss after sciatic nerve injury in the rat.