Motor Unit Characteristics after Targeted Muscle Reinnervation

Area of Science:

• Biomedical Engineering
• Neuroscience
• Rehabilitation Medicine

Background:

• Targeted muscle reinnervation (TMR) is a surgical procedure to restore prosthetic function and alleviate phantom limb pain.
• Knowledge regarding the characteristics of reinnervated motor units post-TMR is limited.

Purpose of the Study:

• To compare motor unit action potential (MUAP) characteristics in TMR patients versus able-bodied controls.
• To investigate the implications of these characteristics for prosthetic control.

Main Methods:

• High-density surface electromyography (EMG) signals were recorded from the pectoralis muscles of five TMR patients and nine controls.
• EMG signals were decomposed to analyze individual motor unit action potential (MUAP) features, including surface area, duration, and amplitude.

Main Results:

• TMR patients exhibited significantly smaller normalized MUAP surface areas and shorter MUAP durations compared to controls.
• No significant difference in mean MUAP amplitude was found between the groups.
• MUAP surface representations in TMR patients frequently overlapped, with single motor task representations occupying less than 12% of the electrode surface.

Conclusions:

• Smaller MUAP surface areas in TMR patients may not inherently improve prosthetic control due to significant overlap.
• Neural information-based control strategies could enhance prosthetic performance in TMR patients.
• The size of reinnervated motor units appears to be influenced by the size of the innervating motor neuron.