A longitudinal rat forelimb model for assessing in vivo neuromuscular function following extremity reperfusion injury

Rhabdomyolysis following revascularization of the ischemic upper extremity can lead to life- & limb-threatening sequelae. In the context of replantations and vascularized composite allografting, a reconstructive procedure usually reserved for upper limb amputees, prolonged tissue ischemia is detrimental to extremity functional recovery. Currently, validated survival small animal models of extremity reperfusion injury that permit longitudinal assessment of limb function are lacking. To date, studies that evaluated reperfusion injury-induced neuromuscular impairment rely on terminal ex vivo procedures and do not provide clinically translatable measurements. Furthermore, it is unclear if upper extremity musculature exhibits a different ischemic threshold compared to the lower limb given the relatively rare incidence of upper limb ischemia. Here, we present a reliable rat model of extremity post-reperfusion syndrome (PRS) that comprehensively recapitulates the biochemical hallmarks of rhabdomyolysis secondary to upper extremity reperfusion injury and allows for monitoring in vivo upper limb function using clinically relevant electrodiagnostic and kinematic metrics. In addition to inducing severe metabolic derangements, our forelimb PRS provided insights on gross motor and electrophysiological alterations upper-extremity reperfusion injury. We identify gait coordination parameters such as stride frequency and forelimb-hindlimb coordination index and electrophysiological metrics including compound muscle action potential amplitude as objective, non-invasive outcome measures for limb function assessment in small animal models of extremity PRS. This comprehensive, validated functional model can serve as an invaluable tool to evaluate therapeutics or preconditioning regimens to attenuate PRS and mitigate resulting neuromuscular dysfunction.