MS techniques applied to superiorly based TRAM flaps are controversial. In superiorly based flaps, the medial, lateral, or both portions of muscle may be preserved if they are not involved with the vascular pedicle or significant perforators. Proponents of muscle sparing in superiorly based flaps suggest that decreased muscle bulk where the rectus abdominis muscle turns at the costal margin may reduce the tendency for venous congestion in the flap (5). Shestak (3) recommended using a handheld high-frequency (20-mHz) Doppler to identify the intramuscular pathways for the medial and lateral rows of perforators. The medial 60% of the muscle width may be harvested with the flap, preserving the lateral border of the muscle. Despite these clinical reports, the practice of splitting the muscle in superiorly based flaps is not recommended by many. There are no reports directly comparing the incidence of vascular complications in muscle-sparing and non–muscle-sparing superiorly based TRAM flaps. Thus, it is unclear under what circumstances it is safe.

The routine practice of muscle sparing in pedicled TRAM flaps is contrary to what is known about the vascular anatomy of the rectus abdominis muscle. Studies of the TRAM flap blood supply confirm that the superior epigastric artery is not the primary blood supply to the lower abdominal skin and subcutaneous tissue (6,7). The principal perforators to the flap are terminal branches of the inferior epigastric system. Superiorly based flaps derive a blood supply through multiple narrow “choke” vessels that link the superior and deep inferior epigastric systems within the rectus abdominis muscle and above the level of the umbilicus. Significant axial arteries are present in perhaps 35% of cases (8). The pattern of venous drainage is similar to that of the arteries, but the veins lie more superficial in the muscle. They are vulnerable to injury, especially with dissection of the muscle near the transverse inscriptions (9). For this reason, to ensure maximum reliable blood supply, it has been recommended to actually harvest a portion of anterior rectus fascia, not dissecting it from the muscle, at each tendinous inscription in superiorly based TRAM flaps.

The significance of blood vessel anatomy in the rectus muscle was shown by intraoperative studies of superiorly based TRAM flaps by Harris et al. (10). They demonstrated that a functional watershed exists between the inferior and superior epigastric arteries in the rectus abdominis muscle just above the level of the umbilicus. Blood pressure directly measured in the stump of the inferior epigastric artery in a flap perfused only from the superior system averages 19% of mean arterial pressure in most patients. Survival of all skin and subcutaneous tissue below the level of the umbilicus requires reversal in the normal direction of arterial and venous flow in the rectus abdominis muscle. This documented net perfusion is consistent with anatomic studies. Moon and Taylor identified three patterns of blood supply to the rectus abdominis muscle (7). They labeled these as type I, II, or III, based on whether there were one, two, or three major vessels supplying the inferior portion of the muscle, respectively. A type I (i.e., single-vessel) pattern was present in approximately one third of the cases, with fewer anastomoses with the superior system compared with type II or III. It is therefore hazardous to routinely split the muscle in a superiorly based flap because this anatomy may not be visualized with routine flap elevation. For these reasons, routine application of MS techniques is not advisable for TRAM flaps based on the superior epigastric vessels. I do not perform conventional pedicled TRAM flaps using MS techniques.

The inferior epigastric system is the primary blood supply to the lower abdominal skin and subcutaneous tissue used in the
TRAM flap. This permits greater flexibility in flap design, permitting safe musculofascial preservation in selected inferiorly based flaps without compromise of outcomes in breast appearance (11). A variety of methods have been described, but because the purpose of these methods is to improve function, it is sensible to attempt to preserve the lateral portion of muscle with intact innervation. The rectus abdominis muscle has a segmental motor supply that enters via the intercostal neurovascular bundles at intervals along the lateral aspect. The anatomy of the neurovascular bundles relative to the inferior epigastric artery pedicle is variable (12). If it is possible to dissect between these nerves without damaging the flap pedicle in the muscle, then muscle sparing can be performed. A vascular pattern in which the deep inferior epigastric vessels divide into two major intramuscular vessels is well suited to this type of muscle-sparing harvest. This is a type II pattern according to the nomenclature proposed by Moon and Taylor, and it is found in the majority of cases (57%) (7).

Despite the intuitive appeal that MS results in decreased abdominal wall morbidity following TRAM flap harvest, a review of the literature leads to mixed conclusions. Some studies suggest that reduced harvest will lower both short-term (4) and long-term (13) impairment of abdominal wall strength and exercise ability. Other studies do not detect a significant difference (14,15,16,17,18). Noninvasive imaging after surgery demonstrates atrophic changes along the entire remaining length of rectus abdominis muscle after TRAM flap harvest, regardless of how much is taken with the flap (19). Studies that directly compare free TRAM without musculofascial preservation to DIEP flap (i.e., TRAM flap with complete musculofascial preservation) harvest appear to document decreased postoperative pain, abdominal wall complications, and long-term functional disability with the DIEP flap based on objective measures (e.g., dynamometry) (20,21,22). Nevertheless, patient self-assessment in these same studies does not show a significant difference in donor-site strength, pain, aesthetics, or ability to perform daily life activities. Nahabedian et al. found that functional ability was related to patient body weight and age, not to preservation of muscle or intercostal nerves (23). Counterintuitive results regarding the relationship between abdominal wall function and rectus abdominis muscle disruption may be related to muscle denervation where the muscle is split (24), as well as to elimination of fascia plication and tightening when closing the donor site with DIEP flaps. Despite conflicting evidence, the body of data available seems to suggest that MS with TRAM flap harvest may confer some benefit.

The decision to perform MS-TRAM must be contingent on the anticipated affect on blood supply. The possibility of compromised flap perfusion using MS techniques is illustrated in a personal series of cases published by Kroll (4) of 310 breast reconstructions that showed a 37.5% incidence of partial flap loss and a 62.5% incidence of fat necrosis when DIEP flaps were routinely performed for all patients. Partial flap loss and fat necrosis were reduced to 8.7% and 17.4%, respectively, when the patients were selected for DIEP flap based on the characteristics of the perforating artery and vein, and limiting the amount of tissue used in the flap. Free TRAM flaps in this series showed the lowest rates of partial flap loss and fat necrosis at 2.2% and 12.9%, respectively. More recently, Lindsey reported improved rates of flap survival and extremely low rates of fat necrosis by selectively performing either DIEP or MS-TRAM following an algorithm based on the diameter of the perforators identified during surgery (25). Along with variability of arterial supply, there appears to be greater potential for venous insufficiency compared with the free TRAM flap. The veins accompanying arterial perforators are thin walled and of small caliber. They are prone to compression when surrounding tissues are dissected away, especially where they enter the deep surface of the flap that rests against the chest wall. Because of the possible reduction in flap blood supply that can result, these techniques should be used with caution in patients who have conditions such as obesity or a history of tobacco smoking that are associated with wound-healing complications related to blood supply (26,27). In these circumstances, the flap must be designed to maximize the blood supply. It is possible to augment the blood supply by harvesting two pedicles and revascularizing each side of the flap either to a separate recipient vessel or to the pedicle selected for revascularizing the entire system. Various combinations have been described, including DIEP/MS-TRAM (28) and SIEA/MS-TRAM (29).