The Experimental Study On Survival Mechanism And Microcirculation Pattern Of Scar Flap

Objective:Patients with extensive burn injury are in short of normal skin,thus,usually have no chance to undergo flap surgery for postburn reconstruction.Scar tissue might be used as potential source of flap for those patients.However,the survival mechanism and microcirculation patterns of the scar flap remain unknown.The aims of this study are to investigate the survival mechanism of the scar flap in a burn-injury perforator flap in the rat model and to explore the microcirculation patterns of the scar flap by simulation of scar flap harvest using fresh human resected scar tissue.Methods:① Sprague Dawley rats were randomly divided into 3 groups.The dorsal three-perforasome perforator flap of rats in different groups was contacted with 100℃water for 10,15 and 20 seconds,respectively.② The effect of burn injury on the microcirculation,microvascular density and diameter in the choke zone,and the postburn remodeling of microcirculation were investigated by using laser speckle perfusion imaging technology,gelatin lead oxide angiography,histological analysis,and Western blotting in a scalded three-perforasome flap model.③The effect of the burn injury on the survival of the scar flap was evaluated by raising a scalded threeperforasome scar flap based on the deep circumflex iliac artery and calculating the survival rate of the scar flap at 7 days postoperatively.Indocyanine green angiography and gelatin lead oxide angiography were used to observe the flap perfusion and function of the choke vessels.④ The scar flap harvest was simulated using fresh human resected scar tissue.Indocyanine green angiography was used to evaluate the flap perfusion and survival rate of the simulated scar flap was calculated.Results:①10,15,20-second scald resulted in a superficial second degree burns,a deep second degree burns,and deep third degree burns,respectively.② Burn injury with different severity all caused harm to the function of the skin microcirculation.Following superficial and deep second-degree burns,skin perfusion restored to the preburn level,but there was no trace of recovery in blood perfusion within 7 days following deep third degree burns.The density of the blood vessels in the entire three-perforasome area recovered to the pre-burn level within 14 days following superficial second-degree burns,slightly increased following deep second-degree burns,and obviously decreased following deep third-degree burns.The microvascular density and diameter in the choke zone after the superficial second-degree burns were similar to those in the normal skin at the postburn 7 day;the microvascular density increased significantly(P=0.027)after deep second-degree burns and the microvascular diameter dramatically reduced(P=0.001)after deep third-degree burns.The expressions of VEGF and VEGFR-2 in the choke zone remained unchanged within 28 days after superficial second-degree burns;the expressions of VEGF and VEGFR-2 increased after deep second-degree burns;VEGFR-2 expression remained unchanged and VEGF expression increased occasionally at some point after deep third-degree burns.③ The survival rate of scar flaps after superficial second-degree burns was comparable to that of normal skin flaps;the survival rate of scar flaps after deep second-degree burns was higher than the normal skin flaps(P=0.003)and scar flaps after superficial second-degree burns(P=0.003).After superficial and deep second-degree burns,the blood flow velocity in the entire flap and choke zone was greater than the normal flap.④ Clinical simulation of scar flap harvest was performed in four patients.Three scar flaps,which included single perforator,presented with survival rates of 40.84%,81.25%,and 78.23%,respectively;One scar flap contained three perforasomes,in which the perfusion reached the third perforasome,and the simulated scar flap survived at a rate of 72.67%.Conclusions:The superficial second-degree burns had no influence on the microvascular growth and dilation in the choke zone;The blood perfusion restored to the pre-burn level following superficial second-degree burns;The survival rate of the scar flap following superficial second-degree burns was equivalent to that of the normal perforator flap.The deep second-degree burns led to increased microvascular density and dilation of the vessels in the choke zone.The blood perfusion of the skin restored to the normal level after deep second-degree burns.Because deep second-degree burns had a delay effect on the flap,the survival rate of the scar flap was higher than the skin flap.The deep third-degree burns resulted in severe damage to the vessels in the choke zone,and the perfusion was unable to restore within 7 days after scalding.The skin with deep third-degree burns was unsuitable for scar flap harvest.Indocyanine green angiography could be used to assess blood perfusion of the scar flap and guide flap harvest.