A human-scale porcine fasciocutaneous and muscle flap model for the evaluation of ortho-plastic reconstructions of lower-limb defects

<b>Introduction</b>: Fasciocutaneous and muscle flaps are used for the reconstruction of lower-limb composite bone and soft-tissue defects. Flap-mediated contributions to the healing microenvironment are less described. We present a comparative porcine model with a standardized bone and soft-tissue defect reconstructed by fasciocutaneous or muscle flaps and characterize the early tissue response following flap transfer. <b>Methods</b>: Using both hindlimbs of 10 female pigs, symmetrical tibial bone and soft-tissue defects were created and reconstructed with fasciocutaneous flaps ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo></mml:mrow> </mml:math> 8) or muscle flaps ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo></mml:mrow> </mml:math> 8) or were closed primarily ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>n</mml:mi> <mml:mo>=</mml:mo></mml:mrow> </mml:math> 4, controls). Interstitial metabolites (glucose, lactate, and pyruvate) were sampled by microdialysis from flap and control tissue for 11 h before, during, and after 60 min of global flap ischemia (simulating free flap transfer). Flap histopathology was graded for the acute inflammatory response. <b>Results</b>: All pigs and flaps completed the study. Both flaps exhibited ischemia-reperfusion-induced metabolic alterations relative to the control tissue. The lactate-to-pyruvate ratio increased 3-fold in muscle flaps during ischemia, while fasciocutaneous flaps showed lactate and a lactate-to-pyruvate ratio that were 1.5-fold higher during reperfusion. Histopathology demonstrated early cellular activity at the bone lesion-flap interface in both flap types, with greater oedema and hyperaemia in fasciocutaneous flaps. <b>Conclusion</b>: We established a reproducible comparative large-animal model integrating interstitial metabolite and histopathological analyses to describe early flap-mediated tissue responses. Early flap-specific differences in metabolic and structural patterns may influence flap function and the healing microenvironment. The model provides a basis for evaluating clinically relevant ortho-plastic outcomes.