This research proposal seeks to improve the current procedures to determinate the botulinum neurotoxin (BoNT) injection site. More precisely, we propose to complement the ultrasonography with an in vivo location of the IZ, using a non-invasive technique based on surface multielectrode electromyography grid, which is called high density-surface EMG (HD-EMG). According to our hypothesis, the use of HD-EMG shall allow an accurate localization of the IZs of the muscles, offering a better complement to the methodology applied so far to define the BoNT injection site. To achieve that goal, a randomized clinical trial comparing the effectiveness of two guiding methods to define the BoNT injection site in the gastrocnemius muscles (main ankle extensors or plantar flexors) will be conducted. One arm will be treated with the best available option, which includes ultrasonography + localized IZ using anatomical references. The second arm will be managed using ultrasonography + in vivo location of the IZ through. The last will be measured using HD-EMG by recording the motor unit action potentials along the muscle fibers. This technique can identify the location of the IZ by the change of phase of those potentials. The effectiveness will be evaluated by changes in biomechanical parameters of the gait, assessed using a three-dimensional motion analysis system. The outcomes will be biomechanical gait variables associated with the ankle joint (ankle joint moment, dorsiflexion range, among others) and functional tests (spasticity using Ashworth scale, 6-minute walk test and the Timed Up and Go Test). These outcomes will be evaluated at baseline (T0), at three (T3w) and six weeks (T6w), post BoNT injection. The differences between sessions will be evaluated as measurements of effectiveness (Delta1 = T3w-T0; Delta2 = T6w - T0). To compare the effectiveness between groups, these delta values will be compared using a student's t-test or a Mann-Whitney U test, as appropriate. Also, a Cohen's d will be calculated to determine the magnitude of these differences. In addition, the post-hoc power (1-β) will be measured. All statistical analyses will be performed in the STATA software (version 14.0 Stata-Corp LP, USA), considering a one tailed analysis, and a confidence level of 95%. Statistically significant differences will be considered those associated with a p-value lower than 0.05. We expect to find greater effectiveness in the group that receives the injection of BoNT, guided by the in vivo location of the IZ using HD-EMG.
