A NEW ANIMAL MODEL FOR COMPARISON OF FASCIOCUTANEOUS AND MUSCLE FLAPS IN THE TREATMENT OF COMPLEX TISSUE DEFECTS AND OSTEOMYELITIS

Aim Treatment of bone infections includes debridement, specific antibiotic therapy, and effective wound coverage, often requiring flap surgery. The superiority of fasciocutaneous or muscle free flaps, remains unanswered. Hence these flaps are interchangeably applied to cover complex tissue defects and osteomyelitis. We aimed to establish a porcine flap model and evaluate its potential to assess the tissue-healing efficacy of fasciocutaneous and muscle flaps. Method Using both hindlegs of 10 pigs, symmetric tibial bone and soft tissue defects were created and covered with either fasciocutaneous flaps (n=8), muscle flaps (n=8), or primary wound closure (n=4) as controls. Ischaemic metabolites (glucose, lactate, and pyruvate) were sampled with microdialysis in the flaps and subcutaneous control tissue for 11h before, during, and after 60 min of global flap ischemia (simulating free flaps). Flap histopathology with grading of the acute inflammatory response was performed. Results All pigs and flaps completed the study. During ischemia, we found rapid decreases in glucose and glucose-lactate ratio levels and increases in lactate and lactate-pyruvate ratio levels in both flaps. This was followed by secondary reversed reperfusion changes, with the most labile kinetics in the muscle flaps during ischemia and in the fasciocutaneous flaps during late reperfusion. The histopathological mean inflammatory parameters were increased in the fasciocutaneous flaps compared to the muscle flaps. Conclusions We successfully established a robust and reproducible flap model for evaluating ortho-plastic reconstructions. Following 60 minutes of flap ischemia, then reperfusion, we demonstrated increased tissue structural changes with a slower metabolic rate and a possible shift towards an ischemic state in the fasciocutaneous flaps compared to muscle flaps. Flap-dependent differences in metabolic patterns and acute inflammatory responses may have important implications for the bone healing and anti-infective microenvironment underneath. Next, we will apply the model to assess fasciocutaneous versus muscle flaps in a long-term- and an osteomyelitis setup.