Lateral Pectoral Osteomusculocutaneous Flap

J. W. LITTLE III

J. R. LYONS

An obvious further extension of the pectoralis musculocutaneous flap is the inclusion of skeletal tissue deep to the muscle as a composite flap to allow one-stage immediate reconstruction of the mandible (1).

Others have included rib (2, 3, 4, 5, 6), but because the costal origins of the pectoralis major muscle arise only from the cartilaginous portions of the second through sixth ribs (7), we contend that these flaps represent essentially chondromusculocutaneous flaps with bony rib extensions. Certainly, exclusion or resection of the cartilage component would render the bony parts little more than free grafts. While cartilaginous rib serves, perhaps, as an effective mandibular spacer, it surely cannot allow the solid
reconstruction through bony interposition and union that is preferred in mandibular repair.

A component of the pectoral muscle system does have its origin from the true bony rib cage: the pectoralis minor muscle arising from the third through fifth bony ribs lateral to the costochondral junction. We recommend, therefore, a composite system that incorporates a key portion of this muscle in a lateral pectoral flap—formally, a pectoralis major-pectoralis minor osteomusculocutaneous flap.

INDICATIONS

Such a composite transfer is indicated whenever mandibulectomy is performed, whether or not accompanied by neck dissection. Although conventional secondary bone grafting remains a satisfactory alternative for mandibular restoration in the nonirradiated patient without undue scarring, we consider vascularized bony transfer mandatory in unfavorable situations.

Osteomusculocutaneous flaps based on the sternocleidomastoid system are negated by surgical and radiation therapy to the neck (8). Sternal transfer on the pectoralis system is useful (9), but we prefer our bony component and donor site. Although dissection of the lateral pectoral composite flap is demanding and practiced elevation requires 2 hours, it offers obvious advantages compared with free bony transfer by microvascular techniques.

ANATOMY

The blood supply of the pectoral muscles by way of the thoracoacromial artery is well described (10, 11, 12, 13, 14). The pectoral branch sends a significant vessel to the pectoralis minor muscle before continuing on the deep surface of the pectoralis major as its dominant vascular supply. The descending portion of the vessel, while closely applied to the undersurface of the pectoralis major muscle, remains free from the muscle in a distinct fibroareolar layer that is further protected on its deep surface by a significant fascial sheet.

A secondary supply to the pectoralis comes by way of the lateral thoracic artery. After a highly variable origin from the second part of the axillary artery, the subscapular trunk, or the thoracoacromial artery, the vessel follows the lateral border of the pectoralis minor, supplying this muscle and the serratus anterior before reaching the undersurface of the pectoralis major. It anastomoses freely with the pectoral branch of the thoracoacromial artery, the thoracodorsal artery of the subscapular trunk, and the intercostal arteries of the lateral thoracic wall.

It is the arborized bed of the lateral thoracic artery that we consider the collateral bridge between the thoracoacromial supply of the pectoralis major free border and, through pectoralis minor and serratus anterior attachments, the lateral bony fifth rib. It is perhaps surprising that the lower half of the pectoralis minor muscle alone can serve this function without the need to include the entire unit with its proximal blood supply, but such has consistently been the case.

The lateral pectoral osteomusculocutaneous flap includes a lateral segment of vascularized fifth rib that is carried within a soft-tissue bloc that contains the entire musculature of the chest wall from the superior border of the fourth rib to the inferior border of the sixth between the costochondral and anterior axillary lines. This muscle bloc includes a segment of free-border pectoralis major, the lower half of pectoralis minor, and portions of serratus anterior, external oblique, and external and internal intercostal muscles.

FLAP DESIGN AND DIMENSIONS

The major part of the pectoralis major muscle can be spared, minimizing both functional and aesthetic deformities to the chest wall. The resulting narrow, flat pedicle is far more appropriate for passage through most necks. If muscle bulk is truly required throughout the neck, we suggest including the entire pectoralis minor muscle with its proximal blood supply, detaching the muscle from the coracoid while continuing to preserve the pectoralis major span intact. Incidentally, we have found the thin pedicle as effective as the bulky muscular one in protecting an irradiated carotid where overlying neck flaps have failed.

The pectoralis major-pectoralis minor osteomusculocutaneous flap differs from previous flaps in three respects: (a) the attached rib is lateral and therefore bony, (b) the accompanying skin paddle is lateral and therefore hairless even in relatively hirsute patients, and (c) the pedicle is muscle free and therefore thin.

We prefer a lateral inframammary location for the skin island, even in cases not involving rib transfer. Not only is the subcutaneous tissue of this region frequently scant, but so also is the hair production. Although others advocating fascial-cutaneous extensions beyond the muscle have selected more medial sites for their paddles, recent in vivo injection studies suggest that a lateral distribution of the thoracoacromial axis may predominate, at least under the influence of competing hemodynamic territories.

Inframammary skin islands have measured up to 12 × 12 cm. The pivot point of this island flap occurs immediately below the midclavicle. The arc of rotation allows the skin island to reach the posterior pharynx and the rib to reach the contralateral mandibular angle.

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