In vivo analysis of the microcirculation of osteomyocutaneous flaps using fluorescence microscopy

Previous studies have indicated that freely transferred osteomyocutaneous n aps may fail despite anastomotic patency. While microvascular dysfunction i s thought to be one of the major causes for this type of flap failure, litt le is known of its underlying mechanisms, probably due to the lack of adequ ate experimental models allowing detailed intravital microcirculatory analy sis. Herein we report quantitative analysis of the microcirculation of peri osteum, muscle? subcutis and skin by intravital fluorescence microscopy usi ng an osteomyocutaneous free flap model in the hindlimb of rats. The microc irculation of the different tissues was studied after microanastomotic tran sfer (free flap), and was compared to that after solely elevating the tissu e, mimicking a pedicled osteomyocutaneous flap. Transferred flaps, which we re exposed to 1 h of ischaemia during the anastomotic procedure, showed a s light but significant decrease (P < 0.05) of functional capillary density i n muscle, subcutis and skin when compared with the microcirculation of pedi cled naps, while capillary diameters, red blood cell velocity and blood flo w of perfused capillaries remained almost unaffected. The decrease of funct ional capillary density was associated by a significant (P < 0.05) inflamma tory response, as indicated by the increased number of leukocytes adherent to the endothelial lining of postcapillary venules. While the functional ca pillary density of periosteum was not affected by the free transfer procedu re, the inflammatory response was found similar when compared with that obs erved in muscle and subcutis. Thus, our study indicates that even after a s hort l-h ischaemic time period, capillary perfusion failure and leukocyte-e ndothelial cell interaction are the main events, characterising microvascul ar dysfunction after free transfer of osteomyocutaneous flaps. Using the mo del described herein, intravital microscopic analysis of the microcirculati on proved an appropriate tool to study the individual microvascular respons e after free tissue transfer, and may thus be used to evaluate the effectiv eness of novel therapeutic regimens which aim at counteracting microcircula tory dysfunction in free osteomyocutaneous flaps. (C) 1999 The British Asso ciation of Plastic Surgeons.