Faranak Rostamjoud, Friðrika Björk Þorkelsdóttir and Kristín Briem
Introduction: This study aimed to improve EMG electrode placement on residual limbs of transtibial amputees (TTAs) using ultrasound imaging to locate residual lower leg muscle bellies and quantify their thickness in a relaxed vs. contracted state. Additionally, compare discrepancies in ultrasound- and palpation-identified spots, as well as the quality of EMG signals.
Methods: Ten TTAs attended two sessions. In session 1, Tibialis Anterior (TA), Peroneus Longus (PL), Gastrocnemius Lateral/Medial (GL/GM) were examined via ultrasound. The thickness during relaxed and contracted state were recorded (three trials) and the thickest part was marked for electrode placement. During session 2, a Certified Prosthetist Orthotist identified electrode placement via palpation. The distance between palpation- and ultrasound-identified spots was documented. EMG data was collected from both locations during contraction.
Results: Across all muscles, thickness significantly increased from relaxed to contracted state (p<0.001). Muscle had a major effect (p<0.001), with GM having the highest mean thickness and PL the lowest. Muscles and state had no interaction (p=0.8013). All muscles had intraclass correlation coefficients above 0.89, indicating excellent measurement correlation. The average (SD) distance between two identified spots was: TA (11.4mm ±10.9), PL (25.5mm ±22.5), GL (25.7mm ±15.7), and GM (14.5mm ±12.3). Ultrasound-identified spots showed higher signal amplitudes (3.6e-05mv vs. 2.9e-05mv, p<0.05) and signal-to-noise ratios (26.4 ±9.9 vs. 24.4 ±9.4, p=0.35).
Discussion: The changes in muscle thickness during contraction aligned with previous studies on a healthy population1-3. In conclusion, ultrasound imaging can improve electrode placement, quality of EMG signal acquisition for TTAs and potentially enhance prosthetic control.
