Experimental investigation of expanded myocutaneous flaps in rabbits

Expansion of the musculocutaneouscutaneous latissimus dorsi (LTD) flap offers the opportunity to pre-elevate a thin and enlarged muscle flap and still have primary closure of the donor site. Our aim was to examine in an experimental model the viability, the area of expansion, the contractility and histomorphometry of the muscle as a microsurgical unit. In eight rabbits, one LTD muscle was slowly expanded using a 30 cc tissue expander which was overexpanded to a volume of 35 cc. The contralateral LTD muscle served as a control. The area of expansion was measured radiologically by means of metallic muscle markers implanted on the muscle fascia. The in vitro muscle contraction, muscle fibre composition and fibre area were determined. The results indicated: 1) the expanded LTD muscle remained richly supplied by its neurovascular pedicle and the transfer as a free flap should be considered. 2) the muscle markers were unstable and thus planimetrical measurements based on the radiographs were invalid. 3) the contractile properties of the expanded muscle were preserved. 4) histomorphometrical analysis of the cross-sections of the expanded LTD muscles displayed no significant reduction in mean muscle fibre area compared to control fibres. But a significant increase in fast fatigue resistant fibres and connective tissue was found. Conclusion: Expanded muscles may be used as a microvascular unit for dynamic reconstruction. Measurement of the area of expansion by means of muscle markers placed in the muscle fascia is invalid.