Fig. 2

Conversion of velocity- and weight-dependent gait parameters into velocity- and weight-independent residuals. Stride length, step width, percentage stance time, and the single-limb support phase are known to strongly correlate with an animal’s walking velocity and size. Failure to account for the effects of velocity and weight in the analysis of a rodent’s gait will reduce the sensitivity of subsequent statistical analyses owing to an increase in unexplained variance (or mean squared error) [11]. To account for the effects of animal size and walking velocity, stride length, step width, percentage stance time, and the single-limb support phase were normalized to the predicted gait profile of velocity- and weight-matched naïve Lewis rats. This normalization process is shown for single-limb percentage stance time at 1 week and 6 weeks postsurgery. The control line is based upon historical data for the gait characteristics of naïve Lewis rats (solid line with 99 % confidence bands). This database is available for download at bme.ufl.edu/labs/allen and represents 280 gait trials collected in 28 different naïve Lewis rats at 49 different weights over a period of 8 years. The control line is used to predict the stride length, step width, percentage stance time, and the single-limb support phase for a size- and velocity-matched Lewis rat. With this prediction, velocity- and weight-independent residuals of stride length, step width, percentage stance time, and the single-limb support phase can be calculated by subtracting the predicted value for a velocity- and weight-matched Lewis rat. Once data are transformed into velocity- and weight-independent residuals, multiple trials of a rat are averaged such that the average gait profile for an animal directly corresponds to single histological profile in the correlation analyses. These eight values for each group time point were used to construct the data presented in Figs. 3 and 5. MCLT medial collateral ligament transection, MMT medial meniscus transection