End-to-side nerve repair - A study in the forelimb of the rat

Abstract: Nerve injuries have a profound impact on individuals, suffering for the patients and induce cost for society. When dealing with severe nerve injuries that create a gap between nerve segments or when the injury is at the brachial plexus level, the clinical alternatives are limited. The brachial plexus model and its branches in the forelimb was evaluated as an experimental model for studies of nerve regeneration, particularly end-to-side nerve repair. Different types of nerve injuries and repair were induced to the forelimb of the rat, with specific focus on end-to-side nerve repair, i.e. when a distal end of an injured nerve is attached end-to-side to an intact nerve trunk. The radial or both median/ulnar nerves were subjected to a crush injury, a transection and conventional end-to-end nerve repair, a nerve graft procedure or a transection and end-to-side nerve repair. In the latter experiments, the distal nerve segment was attached end-to-side to the intact musculocutaneous nerve. Pawprints and tetanic muscle force were used for evaluation of functional outcome up to eight months after repair. Immunocytochemistry of the C-terminal flanking peptide of NPY (CPON), activating transcription factor 3 (ATF3; marker for cellular activation) and neurofilaments were used to investigate cell body activation and axonal outgrowth. Retrograde labeling detected the source of regenerated nerve fibres. Morphometry analysed the quality of the regenerating axons. Axonal outgrowth was related to the severity of the injury and repair method. A conditioning lesion shortened the time for functional recovery. In end-to-side nerve repair both sensory and motor neurons send axons to the recipient nerve. Retrograde labeling showed few doubled labelled cells indicating that collateral sprouting was only one mechanism by which regeneration occurred. Two recipient nerves could be supported from a single donor nerve. There was no advantage of attachment of also a proximal nerve stump as an extra source of axon to the same donor as an attempt to improve the regenerating capacity. The expression of CPON was dependent on the level of the nerve lesion, i.e. a more profound effect after a proximal injury. Application of an epineural window and/or sutures with or without end-to-side attachment of a nerve segment to a potential donor nerve was needed for ATF3 activation, while application of a piece of muscle or nerve alongside a donor nerve had no such effect. An injury to the donor nerve is a prerequisite for activation of neurons and non-neuronal cells leading to sprouting of axons. End-to-side nerve repair is an alternative method to reconstruct severe nerve injuries when a proximal nerve segment is not available.