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 characteristics of reverse-flow island skin flaps were investigated in New Zealand White rabbits. The animals were divided into 3 groups of 15: group I (control) had no surgery prior to flap elevation, group II (nonexpansion) had a noninflated expander, and group III (expansion) had an inflated expander of 80 ml. After 3 weeks of expansion, a reverse-flow island flap based on the distal saphenous pedicle was elevated. A series of hemodynamic studies was performed to test reverse venous flow--in particular, valve competence. Besides observing the reverse flow under an operating microscope, the changes in the intravenous pressure were measured at 0, 5, 15, 30, 60, and 120 minutes after flap elevation. Moreover, reverse-flow resistance (RFR) was measured in each group to test the competence of venous valves. At each time interval, the values of intravenous pressure were significantly lower (p < 0.01) in group III than in the groups I and II. However there was no statistically significant difference between group I and group II. The RFR was measured 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 days after flap elevation the mean survival of group III (100%) was statistically higher than that of group I (57.4 +/- 18.3%; p < 0.01) and group II (81.6 +/- 12.8%; p < 0.05). These findings simply suggest that controlled tissue expansion improves retrograde venous drainage and increases the survival of reverse-flow island flaps in rabbits. Abnormal dilatation of the venous tree and incompetence of the venous valves seem to be the main factors in explaining the decrease in the values of RFR and intravenous pressure in the expanded flaps. The potential mechanisms to explain the effects of tissue expansion, and the clinical implications are discussed.