THE EFFECTS OF TISSUE EXPANSION ON THE HEMODYNAMIC AND SURVIVAL CHARACTERISTICS OF REVERSE-FLOW ISLAND FLAPS - AN EXPERIMENTAL-STUDY IN RABBITS

The effects of tissue expansion on the hemodynamic and survival charac teristics of reverse-flow island skin flaps were investigated in New Z ealand White rabbits. The animals were divided into 3 groups of 15: gr oup I (control) had no surgery prior to flap elevation, group II (none xpansion) had a noninflated expander, and group III (expansion) had an inflated expander of 80 ml. After 3 weeks of expansion, a reverse-flo w island flap based on the distal saphenous pedicle was elevated. A se ries of hemodynamic studies was performed to test reverse venous flow- in particular, valve competence. Besides observing the reverse flow un der an operating microscope, the changes in the intravenous pressure w ere measured at 0, 5, 15, 30, 60, and 120 minutes after flap elevation . Moreover, reverse-flow resistance (RFR) was measured in each group t o test the competence of venous valves. At each time interval, the val ues of intravenous pressure were significantly lower (p < 0.01) in gro up III than in the groups I and II. However there was no statistically significant difference between group I and group II. The RFR was meas ured as 126.7 +/- 33.52 mmHg in group I, 59.3 +/- 29.86 mmHg in group II (p < 0.01), and 25.1 +/- 7.68 mmHg in group III (p < 0.01). Ten day s after flap elevation the mean survival of group III (100%) was stati stically higher than that of group I (57.4 +/- 18.3%; p < 0.01) and gr oup II (81.6 +/- 12.8%; p < 0.05). These findings simply suggest that controlled tissue expansion improves retrograde venous drainage and in creases the survival of reverse-flow island flaps in rabbits. Abnormal dilatation of the venous tree and incompetence of the venous valves s eem to be the main factors in explaining the decrease in the values of RFR and intravenous pressure in the expanded flaps. The potential mec hanisms to explain the effects of tissue expansion, and the clinical i mplications are discussed.