Ischemia-Reperfusion Injury in a Composite Tissue Microsurgical Model

The authors present a novel microsurgical model to investigate ischemia-reperfusion (I/R) injury in composite tissue (muscle/skin) using a musculocutaneous flap. I/R was induced in a rodent biceps femoris musculocutaneous flap through collateral ligation and arteriovenous clamping. The authors hypothesized that I/R flaps would show greater tissue damage compared with sham.

Male rats were randomized into I/R ( n = 10) and sham ( n = 9) groups. The I/R group underwent flap elevation, collateral ligation, 3 hours of arteriovenous clamping, followed by reperfusion. The sham group had flap elevation only. Perfusion was monitored using laser-speckle imaging, and flap discoloration was assessed with blinded skin ischemia necrosis scores. Serum and the composite tissue (skin/muscle) were analyzed for injury on postoperative days (PODs) 1 or 3.

Clamping reduced perfusion ( P = 0.00), whereas unclamping increased perfusion ( P <0.00). Over time, flaps exposed to I/R were more ischemic (estimate, 0.39; P = 0.02). At POD1, the injury group had higher serum creatine kinase ( P = 0.04) and potassium ( P = 0.00) than the sham group. The injury group had more muscle apoptosis (34.7% versus 5.2%; P = 0.03), myonecrosis (30.3% versus 14.1%; P = 0.04), and inflammation (13.7% versus 4.9%; P = 0.02) than the sham group; myonecrosis and inflammation persisted into POD3. Skin apoptosis and inflammation were similar.

This model reliably reproduces I/R injury with a 3-hour ischemic period followed by early reperfusion. Animals subjected to the authors' technique showed greater tissue damage than the sham group, with muscle being more vulnerable than skin. Serum showed peak muscle injury at 24 hours, and histologic analysis showed myonecrosis and inflammation through 72 hours. This suggests that less than 24 hours' reperfusion (eg, critical window) may serve as the optimal time for possible intervention.

I/R injury is a complex phenomenon affecting vascular composite tissues. The mitochondrial superoxide dismutase may be more specific for I/R injury. There may be a critical window within which to mitigate injury (<24 hours after reperfusion). The authors' model helps investigate muscle/skin I/R injury.