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Short-term Electrophysiological Changes In Muscle After Injury by Tenotomy and Partial Sectioning: A Pilot Study
Shoshana L. Woo, MD, Melanie G. Urbanchek, PhD, Paul S. Cederna, MD, Nicholas B. Langhals, PhD.
University of Michigan, Ann Arbor, MI, USA.
Purpose: In amputation victims, partial muscle grafts will be required to create stable bio-artificial interfaces that can connect severed nerves to the electronics of a neuroprosthetic device. The purpose of this study was to examine the structural and electrophysiological changes in muscles three weeks following tenotomy and partial sectioning in the in vivo rat model.
Methods: In twelve F344 adult male rats, the extensor digitorum longus (EDL) muscle was isolated, and the proximal and distal EDL tendons were transected. Three experimental groups were defined by “muscle cut”: (1) whole EDL (“Whole”); (2) EDL divided in half longitudinally (“Half-Longitudinal”); and (3) EDL divided in half transversely (“Half-Transverse”). The neurovascular pedicle to each muscle was left intact. All muscles were then wrapped in small intestinal submucosa (SIS) and either left “free-floating” (no tendon anchoring) or anchored at the proximal and distal tendons to the underlying fascia at resting length. At three weeks, all EDL constructs were isolated. Electrophysiological tests were performed on six muscle constructs using a stimulating hook electrode on the common peroneal nerve and a recording needle electrode in the EDL. To minimize signal interference, the lateral compartment musculature was denervated, and the remaining muscles of the anterior compartment were excised. The remaining six muscle constructs were sent for histological examination.
Results: Muscle construct mass ranged from 69.6 to 211.4 mg (SD 49.0; n=12). Stimulation of the common peroneal nerve produced visible contractions and detectable compound muscle action potentials (CMAPs) in all tested muscle constructs (100%; n=6)[Figure 1]. Peak-to-peak amplitudes ranged from 6.8 to 20.7 mV (SD 5.7), with latencies ranging from 2.91 to 4.36 msec (SD 0.59) and threshold stimulation currents from 110 to 450 μA (SD 114). Whole muscle and non-anchored constructs displayed higher peak-to-peak amplitudes compared to their half-sized and anchored counterparts, respectively [Figure 2]. Histological examination demonstrated intact healthy muscle fibers in all muscle constructs regardless of muscle cut or anchoring status [Figure 3].
Conclusions: Partial muscles, or muscles injured by both tenotomy and partial excision, demonstrated electrophysiological and contractile function in the short-term in vivo rat model. Tendon fixation, or anchoring, was not required. These findings support the novel use of partial muscles in the construction of bio-artificial interfaces necessary for the surgical integration of robotic devices with the residual limbs of amputees. As this was a short-term pilot study, longer-term studies with larger sample sizes are warranted to determine how the effects of muscle cut and anchoring can be used for signal optimization in prosthetic control.
Acknowledgements: This work was supported by DARPA (N66001-11-C-4190) and the Plastic Surgery Foundation.
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