Flaps: Muscle and Musculocutaneous

Anatomy and Physiology

Muscle and myocutaneous flaps get organized according to the pattern of vascular supply. Mathes and Nahai developed a classification system recognizing five basic patterns of muscle circulation.[5] In type I muscles, such as tensor fascia lata, there is a single dominant vascular pedicle. Type II muscles, like the gracilis, have a dominant pedicle and minor/segmental pedicles. Type III muscles, for example, rectus abdominis and gluteus maximus, have two dominant pedicles, only one of which is necessary to supply the muscle. Type IV muscles, sartorius or tibialis anterior, have a segmental blood supply with no dominant pedicle. Finally, type V muscles, like pectoralis major or latissimus dorsi muscle, have a dominant pedicle and secondary segmental pedicles; in contrast to type II muscles, type V muscles can be supplied by secondary pedicles if the dominant pedicle gets sacrificed. Muscle flaps can be used locally, remaining attached to their blood supply in a pedicled fashion, or used for a distant reconstruction as a free tissue transfer, requiring microvascular anastomosis. Myocutaneous flaps are compound flaps with a solitary vascular supply incorporating skin, subcutaneous tissue, fascia, and the underlying muscle. Unlike conjoint or chimeric flaps, where each component of the flap has a distinct perforator originating from a source vessel, myocutaneous flaps are dissected en bloc so that all muscle perforators to the overlying soft tissue are preserved, thus facilitating more straightforward dissections.

While muscle flaps can fill dead space and serve as a vascularized graft surface, a well-executed myocutaneous flap can bring bulk to a recipient site and obviate the need for a skin graft. When planning myocutaneous flaps, a fundamental knowledge of the vascular territories of each source artery, or angiosome, allows for the proper design of the skin island.[6] Drs. Taylor and Palmer first described the angiosome concept in their paper, "The vascular territories (angiosomes) of the body: experimental study and clinical applications," in 1987.[6] Numerous other papers describe the vascular patterns for specific muscles and flaps. Hartrampf described a common vascular territory when he wrote regarding zones of the vascular supply of the TRAM (transverse rectus abdominis myocutaneous) flap for breast reconstruction.[7]

Once a pedicled or free-tissue transfer is performed, the newly transferred flap begins to incorporate into the surrounding tissue. Assuming a well-vascularized wound bed, vascular ingrowth is seen by four to five days though sufficient vascular ingrowth to supply a flap independent of its blood supply requires weeks.

Indications

Muscles and myocutaneous flaps are useful for various acquired oncologic or traumatic defects throughout the body. Myocutaneous flaps have historically been the choice in head and neck, pressure sore, perineal, extremity, and breast reconstructions.  Wounds that are high risk for infection and have large dead space are ideal for muscle flaps. When considering donor flaps, one must determine the size and tissue components necessary for reconstruction, the resultant function and morbidity of the donor site, and the eventual function and aesthetic outcome of the recipient site. While facial reanimation may require free tissue transfer with thin, pliable, and innervated muscle such as the gracilis, pressure sores require bulky myocutaneous flaps that can tolerate pressure better than a muscle flap with a skin graft. For extremity reconstruction, weight-bearing surfaces benefit from a myocutaneous flap, as repeated pressure on a skin grafted site can result in some breakdown.

Contraindications

While there are few absolute contraindications to muscle or myocutaneous flaps, relative contraindications to include personal or family history of thrombotic or bleeding events, prior radiation to donor areas, history of surgeries potentially compromising the vascular supply of the proposed muscle, and when the sacrifice of the donor muscle would lead to unacceptable disability. For example, when considering either pedicled or free latissimus dorsi flaps, a history of axillary dissection or radiation may have compromised the thoracodorsal vessels, and a different flap may be a consideration. Similarly, in patients who have undergone abdominal surgery through subcostal incisions or had a prior sacrifice of their internal mammary vessels for coronary surgery, pedicled rectus-muscle-based flaps may not have an intact blood supply.  In these instances, different options merit consideration. Tobacco use has been implicated in delayed wound healing and is a relative contraindication to flap surgery.[8] Relative contraindications also include utilizing a donor muscle that would irreparably compromise or destabilize joint function. Of note, hemodynamic instability requiring vasopressor support represents a contraindication to free tissue transfer.

Equipment

Microsurgical instrument sets and either loupe magnification or an operating microscope are necessary for muscle or myocutaneous free flap surgery. Additional pharmacologic agents such as lidocaine or papaverine should be available to address vasospasm. In cases where microvascular anastomoses are the plan (whether free tissue transfer or supercharging pedicled flaps), heparinized saline and IV thrombolytics should be available. Hand-held doppler units should be utilized in the operating room. When available, various tissue monitoring devices or implantable doppler devices may be helpful in the perioperative period.  Local or pedicled muscle flaps do not require any specialized equipment beyond a typical plastic surgery set.

Personnel

In general, flap surgery requires an operative team comfortable with microsurgical skills, especially when planning free muscle or myocutaneous flaps. High-volume flap centers with experienced operating room personnel may minimize issues in the perioperative period. Also, anesthesia providers should be comfortable with several facets of flap surgery, including the need for prolonged paralysis, heparin infusions, and maintaining normotension without vasopressors. In the perioperative period, nurses and support staff are essential to perform frequent flap checks and monitor for vital sign abnormalities.

Preparation

As with any surgery, preparation begins with a thorough history and physical and focuses specifically on planned flaps, the proposed donor muscle or myocutaneous flap, and recipient site concerns. Computed tomography with angiography, while not required, may be prudent when the status of key vascular pedicles or recipient vessels remains unclear. A hematologist should evaluate patients with any history of coagulation problems and, if necessary, started on anticoagulation for the perioperative period. Contaminated wounds should be washed out and debrided multiple times when possible to decrease the bacterial burden before flap coverage. Also, given the prolonged surgical and recovery times and the high metabolic demands of muscle and myocutaneous flaps, nutrition should be optimized when possible. Nursing and support staff comfortable with flap patients require confirmation before starting flap surgery. When myocutaneous flaps are the choice for pressure sore coverage, a thorough assessment by therapy services, offloading mattresses, and wheelchair pressure mapping with appropriate offloading leads to a more successful reconstruction.

Technique or Treatment

A thorough description of the harvest and transfer of various muscle and myocutaneous flaps is beyond the scope of this section. However, for each area of the body and the necessary components for reconstruction, knowledge of local muscle and myocutaneous options and possible free tissue transfer options will guide appropriate flap selection.

If planning a free-tissue transfer, then step one involves identifying adequate recipient vessels to power the muscle or myocutaneous flap. Then, flap dissection commences.

For muscle flaps, an incision is marked out, allowing for the most significant access to the muscle body and associated vascular pedicle and deepened to the muscle body with or without the overlying fascia. Unnecessary perforators are clipped or cauterized, and muscle gets delaminated from the surrounding soft-tissue envelope. For pedicled flaps, the muscle is skeletonized to ensure a tension-free arc of rotation or turnover, and Doppler signals can be checked to confirm pedicle patency. The pedicle may not have to be visualized to allow for safe transfer. For free muscle transfer, the vascular pedicle is isolated and clipped, and microvascular anastomosis is performed expeditiously to reduce ischemic damage to the muscle. The muscle is inset, and donor site hemostasis is achieved before closure. Drains and quilting sutures to help limit seromas are prudent maneuvers after removal of bulky muscles that may lead to large seroma cavities, most notoriously latissimus dorsi donor sites.

For myocutaneous flaps, the desired skin island is marked out, and the incision can be extended to facilitate flap dissection. Designing a skin island within the known flap angiosomes will minimize ischemia of the portions of the flap furthest from the vascular pedicle. Great care is necessary to avoid undermining the skin island as damage to muscular or fascial perforators will lead to skin necrosis. Otherwise, once at the muscle layer, dissection proceeds as described previously for muscle flaps. While primary closure of the donor site minimizes morbidity, adjacent tissue transfer or skin grafting of the donor site may be necessary if utilizing a sizeable myocutaneous flap.

The decision to re-innervate muscle for free-tissue transfer depends on the reconstructive goal. Often pedicled muscle or myocutaneous flaps, the sacrifice of the nerve may prevent unwanted animation and lead to long-term atrophy allowing for better contour. In instances where just a portion of the muscle is needed to fashion a flap, e.g., a vertical rectus abdominis myocutaneous flap or partial superior latissimus muscle, care is undertaken to preserve the remaining muscle blood supply to minimize donor site morbidity.

Complications

Complications of muscle and myocutaneous flaps include infection, partial or total flap loss, seroma or hematoma of donor and recipient sites, fat necrosis, and wound dehiscence. Specific flaps such as the TRAM flap may lead to hernia or significant abdominal laxity, while latissimus dorsi donor sites are notorious for seroma formation if not adequately drained.[9][10] Even moderately sized hematomas in a confined space can compress the vascular pedicle and lead to total flap failure.Post-operatively, flap patients require monitoring for signs of flap compromise. Muscle flaps that begin to appear gray or bleed poorly with pinprick are ischemic and should go to the operating room immediately for exploration. Myocutaneous flaps have an added benefit of a skin paddle that serves as a monitor for overall flap status. Venous congestion of the skin paddle may appear as a blue hue indicative of venous congestion or thrombosis. Unlike fasciocutaneous flaps, muscle and myocutaneous flaps tolerate ischemia poorly, and any concern for flap ischemia necessitates an expeditious return to the operating room for flap exploration. Depending on the location of muscle or myocutaneous flaps, appropriate positioning measures should be undertaken to ensure vascular pedicles do not become compressed. Extremity flap patients should adhere to a dangle protocol to avoid the devastating effects of venous congestion.

Clinical Significance

Muscle and myocutaneous flaps, utilized in pedicled or free tissue transfer, are work-horse flaps with numerous advantages in oncologic and traumatic reconstruction.

Enhancing Healthcare Team Outcomes

The optimal care for muscle and myocutaneous flap patients involves an experienced microsurgeon, anesthesia, and operating room staff familiar with complexities of flap surgery, nurses attentive to flap monitoring, and a facility with appropriate instrumentation and support. Preoperatively, access to CT angiogram allows for confirmation of recipient vessels and evaluation of proposed flap vascular anatomy in cases of prior surgery. Intraoperatively, communication between the anesthesia and surgical team is vital to minimize hemodynamic fluctuations and maintain paralysis. Surgical-specialty nursing can be of great benefit during the procedure, especially if they have training or experience in flap procedures.

Postoperatively, wound-management specialty-trained nurses familiar with managing flap patients are instrumental in quickly identifying flap issues that may require reintervention. With their additional training, they can be more aware of situations that may require intervention and notify the surgeon or managing physician promptly. Likewise, updating other providers, pharmacists, and therapy teams will ensure that appropriate medication and therapy restrictions are in place during the perioperative period. If physical therapy is needed, the PT should keep the entire team abreast of progress and coordinate with the nurse or physician on continued care leading to release from active care.

The use of muscular and musculocutaneous flaps in surgical interventions requires the coordination and communication of the entire interprofessional healthcare team so that the patient receives the best possible care leading to optimal results. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

Routine post-surgical care is required; this will often include flap checks, wound care, pain management, and dangle protocols, depending on the type of reconstruction performed. Specifics are beyond the scope of this activity.

Nursing, Allied Health, and Interprofessional Team Monitoring

If the patient had a free tissue transfer, a free flap monitoring protocol is required to increase the chances of salvage if a complication were to occur.  Free flap protocols vary by attending surgeon preference and type of reconstruction performed. Specifics are also beyond the scope of this activity.