Artikel
Effects of selective Nerve Transfers on the Mammalian Motor Unit
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Veröffentlicht: | 28. September 2015 |
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Gliederung
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Introduction: Selective nerve transfers (SNTs) have been used extensively for the past decade to treat slow nerve regeneration, neuroma pain and improve prosthetic control. SNTs change the motor unit extensively by connecting motor neurons to new functional targets. Good outcomes have been reported but little is known of the structural and functional effects. This experimental study investigates the effects of SNTs using a high capacity donor nerve on the different motor unit levels.
Methods: In Sprague Dawley rats the ulnar nerve (UN) was selectively transferred to the long head of the biceps after neurotomy of the biceps motor branch. After 3, 6 or 12 weeks (each N=15), muscle force, weight and motor unit number estimation (MUNE) were analyzed and both biceps processed for muscle fiber typing. Motor neurons were labeled with Fluoro-Ruby in additional animals with or without SNT (N=17).
Results: All SNTs were functional and no dropouts occurred. Muscle force, muscle weight and MUNE increased progressively from 3 to 6 to 12 weeks. At 12 weeks muscle force was 88%, muscle weight 97,5% and MUNE 116,8%, all compared to contralateral control. Retrograde labeling showed 172,3% motor neurons compared to control (p= 0.006; t test). 18,75% of the UN’s motor neurons innervated the muscle after 12 week. Muscle fiber populations changed entirely, showing fiber type numbers prevalent in muscles innervated by the ulnar nerve.
Conclusion: This study shows the course of reinnervation and good functional outcome after a SNT using a high capacity donor nerve. The different motor unit composition led to impressive changes on all levels, most interestingly to functional and structural hyperinnervation of the muscle by the ulnar nerve. These analyses give cellular insights on the good clinical regeneration of SNTs and possible improvements for future applications.