Superior preservation of capillaries, myofibrils and mitochondria after long-term extracorporeal perfusion of free muscle flaps – A descriptive electron microscopy study

BACKGROUND: Extracorporeal perfusion (ECP) is a promising technique for prolonged tissue preservation, but might have side effects. For instance, increased radical oxygen species or capillary endothelial damage. OBJECTIVE: To assess ultra-morphological muscle damage during 36-hour ECP of porcine musculocutaneous flaps, hypothesizing that it would delay the onset of damage compared to static cold storage (SCS). METHODS: Bilateral flaps were retrieved from three Dutch Landrace pigs. Three flaps were preserved for 36 hours by hypothermic storage 4-6°C (control group) and three flaps by ECP with cooled University of Wisconsin solution. Muscle biopsies were taken at 0 h, 12 h and 36 h and assessed with transmission electron microscopy. RESULTS: Muscle architecture was best preserved by ECP, with a delayed onset and decreased severity of muscle damage. After 36 hours, damage was two-fold lower in ECP-flaps compared to SCS-flaps. Myofibril architecture was best preserved. Mitochondria were greatly preserved with swelling being the most prominent feature. Capillaries were moderately but differently damaged during ECP, with focal endothelial thinning as opposed to luminal obstruction in SCS-preserved flaps. CONCLUSIONS: This experiment described favourable cellular preservation of skeletal muscle flaps during ECP compared to SCS. Results showed less severe ultra-morphological damage and a later onset of damage.