title: Remodeling of motor units after nerve regeneration studied by quantitative electromyography.
abstract: OBJECTIVE
  Peripheral nerve has the capacity to regenerate after nerve lesions; during reinnervation of muscle motor units are gradually reestablished. The aim of this study was to follow the time course of reestablishing and remodeling of motor units in relation to recovery of force after different types of nerve repair.
  
  
  METHODS
  Reinnervation of muscle was compared clinically and electrophysiologically in complete median or ulnar nerve lesions with short gap lengths in the distal forearm repaired with a collagen nerve conduit (11 nerves) or nerve suture (10 nerves). Reestablishment of motor units was studied by quantitative EMG and recording of evoked compound muscle action potential (CMAP) during a 24-month observation period after nerve repair.
  
  
  RESULTS
  Force recovered partially to about 80% of normal. Denervation activity gradually decreased during reinnervation though it was still increased at 24 months. Nascent motor unit potentials (MUPs) at early reinnervation were prolonged and polyphasic. During longitudinal studies, MUPs remained prolonged and their amplitudes gradually increased markedly. Firing of MUPs was unstable throughout the study. CMAPs gradually increased and the number of motor units recovered to approximately 20% of normal. There was weak evidence of CMAP amplitude recovery after suture ahead of conduit repair but without treatment related differences at 2 years.
  
  
  CONCLUSIONS
  Surgical repair of nerve lesions with a nerve conduit or suture supported recovery of force and of motor unit reinnervation to the same extent. Changes occurred at a higher rate during early regeneration and slower after 12 months but should be followed for at least 2 years to assess outcome. EMG changes reflected extensive remodeling of motor units from early nascent units to a mature state with greatly enlarged units due to axonal regeneration and collateral sprouting and maturation of regenerated nerve and reinnervated muscle fibers after both types of repair.
  
  
  CONCLUSIONS
  Remodeling of motor units after peripheral nerve lesions provides the basis for better recovery of force than the number of motor axons and units. There were no differences after repair with a collagen nerve conduit and nerve suture at short nerve gap lengths. The reduced number of motor units indicates that further improvement of repair procedures and nerve environment is needed.
authors.affiliation: Department of Clinical Neurophysiology, Rigshospitalet, Copenhagen, Denmark; Department of Neuroscience and Pharmacology, University of Copenhagen, Denmark. Electronic address: christian.krarup@regionh.dk.
authors.forename: Christian
authors.initials: C
authors.lastname: Krarup
authors.affiliation: Department of Orthopedic Surgery, Gentofte Hospital, Hellerup, Denmark.
authors.forename: Michel
authors.initials: M
authors.lastname: Boeckstyns
authors.affiliation: Department of Orthopedic Surgery, Rigshospitalet, Copenhagen, Denmark.
authors.forename: Allan
authors.initials: A
authors.lastname: Ibsen
authors.affiliation: Department of Clinical Neurophysiology, Rigshospitalet, Copenhagen, Denmark; Department of Neuroscience and Pharmacology, University of Copenhagen, Denmark.
authors.forename: Mihai
authors.initials: M
authors.lastname: Moldovan
authors.affiliation: Integra LifeSciences Corp, Plainsboro, NJ, USA.
authors.forename: Simon
authors.initials: S
authors.lastname: Archibald
mesh_terms: D000328:Adult; D004576:Electromyography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008475:Median Nerve / Q000293:injuries / Q000502:physiology*; D008875:Middle Aged; D009416:Nerve Regeneration / Q000502:physiology*; D011999:Recruitment, Neurophysiological / Q000502:physiology*; D014459:Ulnar Nerve / Q000293:injuries / Q000502:physiology*; D055815:Young Adult
keywords: EMG; Motor unit potential; Muscle reinnervation; Nerve conduit; Nerve lesion; Nerve repair; Nerve suture; Regeneration