An Assessment Of Fatigue and Co-contraction following Nerve Transfer in Reinnervated Elbow Flexor Muscles
Matthew B Wilcox, BSc (Hons)1; Hazel Brown, Specialist Physiotherapist2; Kathryn Johnson, OT Lead3; Marco Sinisi, MD3; Tom J Quick, MBBS MA(Cantab) FRCS(Tr&Orth)2
1University College London, London, United Kingdom, 2Royal National Orthopaedic Hospital, London, United Kingdom, 3Royal National Orthopaedic Hospital, Stanmore, United Kingdom
Peripheral Nerve injury (PNI) is common following blunt or penetrating trauma. Despite the best efforts of the reconstructive nerve surgeon, muscle reinnervation is often incomplete. Studies have shown that peak volitional force (as assessed by MRC grading) is not predictive of the subjective patient experience of muscle reinnervation. Subsequent focus groups and qualitative studies of nerve injured patients have identified muscle fatigability as a central theme of muscle reinnervation. This study aimed to characterise fatigue in a standardised surgical model of muscle reinnervation.
This study recruited 12 patients who were at least 1 year post-Oberlin nerve transfer to reinnervate elbow flexors (biceps-brachialis). Fatigue was objectively assessed by repeated and sustained isometric contractions of the elbow flexor muscles using a Handheld Dynamometer. Co-contraction was concurrently assessed by surface EMG (sEMG) ratios of biceps to triceps. This protocol was executed in the nerve injured arm and the contralateral uninjured arm of participants.
1) Mean peak force of reinnervated elbow flexor muscles was 37% of the uninjured contralateral arm (7.7kg (SD 3.8) compared to 20.7kg (SD 6.8)).
2) Nerve injured arms demonstrated significantly earlier fatigability (p<0.01 paired t-test) in the sustained model of fatigue assessment.
3) Re-innervated elbow flexor muscles manifested a shift in sEMG frequency spectra to a range associated with Type 1 muscle fibres (20-125Hz).
3) Co-contraction ratios were higher in reinnervated muscles compared to uninjured muscle in repeatability and sustainability assessments of fatigue. Moreover, co-contraction increased with fatigue in reinnervated muscle.
This study presents clinically relevant characteristics of reinnervated muscle and has demonstrated how this differs from uninjured muscle. Adoption of these metrics into clinical practice and outcomes assessment will allow a more meaningful comparison to be made between differing treatment options and drive advancements in motor recovery therapy.
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