【Objective】
Ischemic myopathy is a devastating situation that can lead to permanent loss of muscle function, and subsequent limb contracture due to fibrotic changes. Literature has shown that muscle functional outcomes worsened with prolonged ischemia. Similar phenomenon can also be seen with free muscle transfers that shows little recovery after prolonged arterial ischemia. As such, the first aim of the study is to investigate the degree of NMJ morphological changes and resulting function after various time points of ischemia in target muscle. The second aim of this study is to investigate whether prolonged ischemia have an effect on re-innervating muscle after nerve cut-and-repair. The third aim is to investigate if supercharge end to side (SETS) from an adjacent donor nerve can salvage the loss of function in re-innervating muscles undergoing simultaneous ischemia.
【Materials and Methods】
In the first aim, a mice forelimb ischemia model was used by temporarily clamping the brachial artery for a set time and permanently ablating collateral vessels. In the second aim, we conflated the experimental design with median nerve cut and repair and permanently cutting the ulnar nerve. For the third aim, SETS was performed by transferring the proximal ulnar nerve stump into the distal median nerve. Functional recovery was measured by grip test and electrophysiological study. The forelimb flexor muscles were harvested for immunofluorescent staining and histologic evaluation. Functional recovery was measured by grip test and electrophysiological study. The forelimb flexor muscles were stained with ß-III Tubulin and 𝛼-bungarotoxin for innervation pattern and NMJ morphology. The percentage of NMJs with tSC processes was evaluated after staining with S100.
【Results】
With increasing ischemic time, there is decrease in CMAP and grip strength. NMJ re-innervation was significantly worst at 12 and 24 hours with only 39% and 27% fully innervated NMJ (p<0.05), while at 4 and 8 hours it was 72% and 67% (not significantly worse than control at 81%). The addition of SETS provided significant increase in CMAP and grip strength for all groups, especially in the 12 and 24 hours ischemia group. SETS did not increase the percentage of full innervation, but increased the percentage of “partially” innervated NMJ significantly. (p<0.05)
【Conclusions】
Muscles under ischemia do present with comparable worsening damage to the NMJ and progressively worsening functional outcomes. SETS to the innervating nerve of an ischemic muscle provides potential therapeutic benefits to target muscle characterized by the increase in the percentage of partially innervated motor end plates.

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