Vascularized Muscle Flaps
Vascularized free muscle flaps are indicated for complex reconstruction of:
- Defects requiring filling of dead space
- Coverage of exposed vital structures
- Treatment of osteomyelitis
- Functional reconstruction of muscle loss or absence in congenital conditions
- Coverage of exposed orthopedic hardware
The indications are numerous and varied, but most common for reconstruction of complex defects with exposed vital structures such as bone, tendon, nerve, vein graft or other major vessels. Often, muscle flaps are used for defects where skin grafting or local flaps would not adequately address the defect, or where skin grafting or local flaps have previously failed.
Selection of Muscle over Other Types of Flaps
Muscle flaps are often the first and best choice. However, muscle flap selection after failure of treatment with other modalities necessitates diagnosis of the etiology of previous failure. The issues that would negatively impact free flap success should be assessed. For instance, if a previous lower extremity gastrocnemius flap failed to adequately treat a complex open tibial wound, the surgeon should ascertain if poor vascular inflow to the leg compromised muscle perfusion. Similarly, if inadequate debridement and control of the bed promoted infection and wound recurrence, the bed should be adequately debrided or controlled before a free flap is performed. Other factors that may have led to local flap or conservative treatment failure include inadequate immobilization in the postoperative period, or overly aggressive dangling/dependency. Both can lead to wound dehiscence and or vascular compromise and pedicle thrombosis. Of course, multiple other contributors to failure of treatment such as poorly controlled diabetes, active smoking, immunosuppression, etc. need be considered.
When underlying treatable conditions that promote failure are corrected or addressed, the choice of muscle flap over other free flaps depends on surgeon preference and comfort, pedicle needs, wound dimensions, donor site morbidity, defect location and the need for future surgical treatment.
Advantages of Muscle Flaps
Muscle flaps have significant advantages over skin and/or fasciocutaneous flaps. They have many features that make them well suited to reconstruction of complex wounds. Muscles are indicated to:
- Obliterate dead space
- Increase perfusion and resistance to infection
- Provide functional innervated coverage
- Cover exposed vital structures
Complex three dimensional wounds can be filled and obliterated with muscle to reduce the potential of fluid collection/and or dead space that can be susceptible to infection or bursa formation. Mathes and Chang demonstrated elegantly that muscle has tremendous infection fighting ability, perhaps because it has increased vascular perfusion in comparison to fasciocutaneous or skin flaps. This quality makes muscle a good choice for complex wounds, especially wounds that have been contaminated by long term dressing changes and or subatmospheric pressure dressings.
Selection of a muscle flap is not a substitute for adequate debridement and control of underlying infection or contamination. Infection or colonization should be controlled before flap coverage of any kind by appropriate wound management, antibiotic coverage and treatment of comorbidities if possilbe.
Skin grafting of muscle can be a potential advantage of these flaps, but it can also be a disadvantage depending on circumstances. A skin paddle may alleviate the need for grafting if it is harvested with the flap. But it may not be appropriate in some cases. Skin grafts heal more slowly in the initial post-operative period than skin flaps and this should be considered. The decreased durability of a skin graft over muscle relative to a skin flap in the first few weeks after surgery can be a drawback. There are times when a slow healing or a failed skin graft can interfere with recovery by impeding mobilization and therapy, and delay secondary surgery such as bone grafting. A slow healing skin graft with eschar or open areas might delay radiation or chemotherapy.
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