Ultrasound-Guided Multi-Branch Rectus Femoris Nerve Block for Spasticity Assessment.

Background: Stiff-knee gait commonly involves rectus femoris spasticity in patients with central nervous system lesions. Diagnostic nerve blocks aid in predicting treatment outcomes; however, current techniques may overlook multiple nerve branches that innervate the rectus femoris muscle, potentially resulting in an incomplete assessment of treatment outcomes. Methods: We present an ultrasound-guided approach that we currently use in our practice, using anatomical landmarks, including the femoral artery, the sartorius muscle, and the rectus femoris' characteristic "J-shaped" internal tendon. The technique employs an "elevator" scanning method to identify all motor nerve branches (typically 2-3) entering the proximal third of the rectus femoris muscle. Each branch is blocked using an in-plane needle approach with 1-2 mL of 2% lidocaine. Results: The technique enables the visualization of hyperechoic nerve branches entering the rectus femoris muscle from medial to lateral, sometimes accompanied by small vascular branches that are identifiable with a Doppler ultrasound. Optimal ultrasound settings include probes >8 MHz, appropriate focus positioning, and dynamic range < 60 dB. The multi-branch approach produces rapid-onset motor weakness (5-10 min). Conclusions: This comprehensive multi-branch rectus femoris nerve block technique may enhance diagnostic accuracy for spasticity assessment, potentially leading to more informed treatment selection for stiff-knee gait.