OBJECTIVETo investigate the histologic effect of botulinum toxin type A (Botox A) injection on myocutaneous flap expansion in minipigs model.

METHODSSeven minipigs were included in this study. Two symmetric tattoo area, 10 cm x 6 cm in size, were selected on the bilateral flank of the pigs. The Botox A was injected into one tattoo area randomly, 4 U every point, 2 cm apart, with a total dose of 96 U. The same dose of sterile normal saline (0.9%) was injected in the same fashion on the opposite side as control. 3 days after injection , two 200 ml expanders were inserted beneath the cutaneous muscle at the tattoo area. After complete expansion of 200 ml, the specimens were drawn from both groups symmetrically and were stained by means of HE and Masson. The histologic changes of myocutaneous flap were compared. Thickness of each layer in myocutaneous flap was measured in histological section.

RESULTSThe thickness of cutaneous muscle, capsule, dermis were (275.74 +/- 28.93) microm, (468.03 +/- 34.28) microm, (1990.79 +/- 102.10) microm in Botox group, and (409.13 +/- 44.63) microm, (626.55 +/- 44.05) microm, (2508.44 +/- 70.71) microm in saline group, respectively, show a significant difference between the two groups (P < 0.01). The Masson stained slice showed that collagen average gray of capsule in Botox group was 185.38 +/- 9.56, which was significantly higher than that in the saline group (120.77 +/- 10.31, P < 0.01). Light microscope (HE stained sections ) showed that muscle in Botox group was significantly atrophy and cross-section of muscle fiber decreased. The muscle fiber in saline group was generally normal. It was observed through transmission electron microscope that the light and dark band of muscle cell became fuzzy and the Z line bending in Botox group. The light and dark band in saline group arranged neatly, the Z line was clear.

CONCLUSIONSApplication of Botox A in myocutaneous flap expansion can make the muscle atrophy and reduce the content of collagen in capsule layer, making the myocutaneous flap thinner which is suitable for reconstruction in face and neck.