The Laminated Nature of the Pectoralis Major Muscle and the Redefinition of the Inframammary Fold

The breast is appreciated aesthetically and clinically for its shape, projection, and volume. Surgical techniques have evolved to manipulate the breast skin envelope, soft tissues, and chest wall anatomy, with and without prosthetic devices. The pectoralis major specifically is altered for pocket dissection and implant coverage. Both the aesthetic and reconstructive surgeons are aware of its relationship to the chest wall and the breast soft tissues. Both are able to achieve outstanding outcomes; however, the authors present an alternative appreciation of the pectoralis and its relationship to the breast.

Key points

  • The inframammary fold (IMF) is a critical landmark and aesthetic structure in breast surgery, yet it is poorly understood.

  • The skin envelope is considered a separate entity from the chest wall; however, its surgical manipulation is not independent of chest wall anatomy.

  • The pectoralis major muscle is a key structure in both cosmetic and reconstructive surgery, and its structure and performance are related to its inferior costal origins.

  • A better understanding of the relationship of the IMF, pectoralis, and chest wall anatomy can offer improved outcomes in breast surgery.

Introduction

The breast is appreciated aesthetically and clinically for its shape, projection, and volume. Multiple techniques have evolved over the years to modify, enhance, or recreate the breast mound. To this end surgical techniques have evolved to manipulate the breast skin envelope, soft tissues, and chest wall anatomy, with and without prosthetic devices. The pectoralis major specifically is altered for pocket dissection and implant coverage. Both the aesthetic and reconstructive surgeons are intimately aware of its relationship to the chest wall and the breast soft tissues. Both are able to achieve outstanding outcomes; however, the authors present an alternative appreciation of the pectoralis and its relationship to the breast. The authors liken the comparison to the tale retold by John Saxe of the 6 blind wise men and the elephant ( Fig. 1 ). Although Saxe claims the learned men were wrong, the authors propose to illustrate a broader perspective on the nature of the pectoralis.

Fig. 1
The blind men and the elephant. ( From Holton MA, Curry CM. Holton-Curry readers, volume 4. Chicago: Rand McNally & Company; 1914.)

The Blind Men and the Elephant, John Godfrey Saxe (1816–87)

It was six men of Indostan To learning much inclined, Who went to see the Elephant (Though all of them were blind), That each by observation Might satisfy his mind.

The First approached the Elephant, And happening to fall Against his broad and sturdy side, At once began to bawl: “God bless me! but the Elephant Is very like a WALL!”

The Second, feeling of the tusk, Cried, “Ho, what have we here, So very round and smooth and sharp? To me ’tis mighty clear This wonder of an Elephant Is very like a SPEAR!”

The Third approached the animal, And happening to take The squirming trunk within his hands, Thus boldly up and spake: “I see,” quoth he, “the Elephant Is very like a SNAKE!”

The Fourth reached out an eager hand, And felt about the knee “What most this wondrous beast is like Is mighty plain,” quoth he: “’Tis clear enough the Elephant Is very like a TREE!”

The Fifth, who chanced to touch the ear, Said: “E’en the blindest man Can tell what this resembles most; Deny the fact who can, This marvel of an Elephant Is very like a FAN!”

The Sixth no sooner had begun About the beast to grope, Than seizing on the swinging tail That fell within his scope, “I see,” quoth he, “the Elephant Is very like a ROPE!”

And so these men of Indostan Disputed loud and long, Each in his own opinion Exceeding stiff and strong, Though each was partly in the right, And all were in the wrong!

Introduction

The breast is appreciated aesthetically and clinically for its shape, projection, and volume. Multiple techniques have evolved over the years to modify, enhance, or recreate the breast mound. To this end surgical techniques have evolved to manipulate the breast skin envelope, soft tissues, and chest wall anatomy, with and without prosthetic devices. The pectoralis major specifically is altered for pocket dissection and implant coverage. Both the aesthetic and reconstructive surgeons are intimately aware of its relationship to the chest wall and the breast soft tissues. Both are able to achieve outstanding outcomes; however, the authors present an alternative appreciation of the pectoralis and its relationship to the breast. The authors liken the comparison to the tale retold by John Saxe of the 6 blind wise men and the elephant ( Fig. 1 ). Although Saxe claims the learned men were wrong, the authors propose to illustrate a broader perspective on the nature of the pectoralis.

Fig. 1
The blind men and the elephant. ( From Holton MA, Curry CM. Holton-Curry readers, volume 4. Chicago: Rand McNally & Company; 1914.)

The Blind Men and the Elephant, John Godfrey Saxe (1816–87)

It was six men of Indostan To learning much inclined, Who went to see the Elephant (Though all of them were blind), That each by observation Might satisfy his mind.

The First approached the Elephant, And happening to fall Against his broad and sturdy side, At once began to bawl: “God bless me! but the Elephant Is very like a WALL!”

The Second, feeling of the tusk, Cried, “Ho, what have we here, So very round and smooth and sharp? To me ’tis mighty clear This wonder of an Elephant Is very like a SPEAR!”

The Third approached the animal, And happening to take The squirming trunk within his hands, Thus boldly up and spake: “I see,” quoth he, “the Elephant Is very like a SNAKE!”

The Fourth reached out an eager hand, And felt about the knee “What most this wondrous beast is like Is mighty plain,” quoth he: “’Tis clear enough the Elephant Is very like a TREE!”

The Fifth, who chanced to touch the ear, Said: “E’en the blindest man Can tell what this resembles most; Deny the fact who can, This marvel of an Elephant Is very like a FAN!”

The Sixth no sooner had begun About the beast to grope, Than seizing on the swinging tail That fell within his scope, “I see,” quoth he, “the Elephant Is very like a ROPE!”

And so these men of Indostan Disputed loud and long, Each in his own opinion Exceeding stiff and strong, Though each was partly in the right, And all were in the wrong!

Review of the literature

The IMF is a critical visual marker for the breast, and its importance in both aesthetic and breast reconstruction surgery is the foundation of achieving acceptable results as emphasized by Carlson, the first of the wise men describing the IMF as an aesthetic structure. Yet its structure and definition have been difficult to understand. To compound this, the relationship of the IMF with chest wall anatomy is only casually understood. A broader appreciation of the IMF as it relates to the skin, muscle, and chest wall aids in obtaining improved outcomes. Observations from clinical and cadaveric dissection are described to broaden this appreciation.

In a cadaveric study by Maillard and Garey, the IMF was approached from a subglandular approach with the breast soft tissues bluntly dissected off the chest wall until resistance was encountered. A crescent-shaped ligamentous band was identified stretching between the superficial surface of the pectoralis major muscle and the overlying skin. Bayati and Seckel later identified the IMF as a ligamentous structure arising from the periosteum of the fifth rib medially and extending to the interspace between the fifth and sixth ribs laterally. The ligament inserts onto the deep dermis in the region of the inframammary skin fold. In this study, the IMF was approached from a subpectoral approach with the pectoralis bluntly dissected off the chest wall. After avulsion of the insertions of the pectoralis muscle off the fifth rib, the ligament they identified at the inframammary crease resisted further blunt dissection inferiorly. From this resistance the IMF serves a suspensory role. Further dissection beyond this area of resistance risks loss of support structure for an implant and with future bottoming out and double-bubble phenomenon. The second of the wise men describing the IMF as a physical support structure for the implant.

Whether the IMF exists as a ligamentous structure or a dense collagen network, the IMF functions as a zone of adherence between the dermis and the underlying pectoralis fascia. How this zone exists is poorly understood. In a study of 20 fresh cadavers, Matousek and Corlett identified a network of fascial condensations around the breast ( Fig. 2 ). This fascial ring around the breast provides fixation between the deep muscle fascia and the anterior breast capsule. Inferiorly from the level of the fifth rib and inserting on the inferior pole of the breast they have named the triangular fascial condensation ( Fig. 3 ). Furthermore, they identified short horizontal ligaments arising from the deep fascia of the rectus abdominis to Scarpa fascia and inserting into the inferior limit of the fold. Thus, the third wise man appreciating the IMF as part of the fascial framework of the breast.

Fig. 2
The surface anatomic landmarks created by the ring of fascial attachments of the breast.

Fig. 3
Diagram of a sagittal section through the nipple, demonstrating the anterior and posterior breast capsule, ligaments, and triangular fascial condensation.

The pectoralis and the IMF are considered separate structures that are related only by proximity. As mentioned previously, the relationship with the pectoralis muscle is only vaguely understood. A study by Nanigian and Wong examined the IMF as it relates to the inferior origin of the pectoralis major muscle. In a study of 20 female cadavers and 10 patients with planned mastectomy, the inframammary crease was marked transcutaneously with methylene blue and then approached internally along the superficial surface of the pectoralis muscle. The inferior origin of the pectoralis was identified visually, and the distance to the blue markings was measured. The average distance of the IMF below the visually identified inferior pectoralis origin was approximately 2 cm in both groups. The rib origin of the pectoralis was not identified, and the pectoralis muscle was not dissected from its inferior origin in this study. Madsen and Chim later evaluated the anatomic variance of the pectoralis muscle in the context of breast reconstruction. Fifty patients who underwent mastectomy were evaluated preoperatively and intraoperatively, and the relationship of the pectoralis origin with the IMF was assessed. The lowest inferior origin of the pectoralis was found at the fifth rib in 12%, sixth rib in 68%, and seventh rib in 20%. The IMF was noted to rest 1 rib level below the pectoralis in 36% of patients and at the same level in 61%. The implications for the anatomic location of the IMF to the pectoralis origin are of particular relevance for breast reconstructive surgery. Here, the fourth wise man who believes the 2 structures have no relationship other than proximity. The structures are considered to exist independently, yet with both breast augmentation and reconstruction the 2 structures have an intimate relationship.

Laminated nature of pectoralis

Crescent-Shaped Origin of Muscle

The pectoralis muscle is a flat fan-shaped muscle on the anterior chest wall that acts to adduct and rotate the arm. The muscle has a crescentic origin from the medial half of the clavicle, the manubrium and body of the sternum, the costal cartilages of the second to sixth ribs, and the aponeurosis of the external oblique muscle ( Fig. 4 ). All fibers converge toward the axilla to merge and insert on the lip of the bicipital groove of the humerus. The medial and inferior origins have the most clinical significance to the breast surgeon.

Fig. 4
Bones of the anterior chest wall showing the origin and insertion of pectoralis major. ( From Moore KL, Agur AR, Dalley AF. Clinically oriented anatomy. Baltimore: Lippincott, Williams and Wilkins/Wolters Kluwer, 2013; with permission.)

The muscle is elevated and separated from the pectoralis minor for both augmentation and breast reconstruction to allow submuscular placement of the implant. With dual-plane augmentation and breast reconstruction the inferior origin of the pectoralis is divided. Much controversy exists regarding the extent and degree of inferior and medial division. Underdissection can result in undesirable shape and projection. Overdissection can result in symmastia, window shading, and implant malposition.

Dual Layer of Pectoralis

The inferior border of the pectoralis is released off the chest wall to initiate breast reconstruction and with dual-plane augmentation. However, it is in the reconstructive arena where one is able to visualize the transected end of the muscle. In both partial submuscular and acellular dermis-based reconstructions, the free end of the muscle is sutured. After several years of manipulation, it was finally appreciated that the free edge represented only a portion of the muscle. Through serendipitous observation, the retracted edge of the undersurface of the muscle was retrieved to reveal the smooth undersurface of the pectoralis ( Fig. 5 ). This observation spawned the hypothesis that the pectoralis muscle actually represents a laminated structure at the inferiormost level. When the inferior edge of the muscle is secured, one is traditionally only manipulating the superficial layer, while the deeper layer retracts superiorly. The significance of an incompletely controlled pectoralis muscle is addressed later.

Fig. 5
Intraoperative view of the cut surface of the inferior border of the pectoralis major. ( A ) Superficial layer, ( B ) superficial and deep layer, and ( C ) deep layer with smooth undersurface.

Careful review of the pectoralis anatomy reveals an inferior origin from the fifth and sixth ribs. Cadaveric dissection into the substance of the muscle identified a deep layer coming off the fifth rib and a superficial layer from the sixth. Blunt dissection easily separates the layers, with the deeper plane representing approximately 30% of the muscle volume ( Fig. 6 ). When the inferior border of the pectoralis is manipulated, only the superficial layer is being secured, unless the retracted deeper layer is deliberately retrieved and included with the superficial layer. The fifth wise man only appreciates the pectoralis major as a solid unit.

Fig. 6
Cadaver dissection of anterior chest wall. ( A ) Lateral approach to subpectoral space with origin from fourth, fifth, and sixth ribs, ( B ) separation of superficial and deep layers with rib origins marked, ( C ) deep layer bluntly separated and exposed, ( D ) deep layer retracted to reveal smooth undersurface of muscle.

Relationship to Inframammary Fold

Medial inflection point

The IMF is a critical landmark and essential feature of the aesthetically pleasing breast. The exact limit of the IMF varies with the size of the breast and the size of the patient. The medial IMF and the lateral IMF may not be easily identified. In larger patients, the medial extent can seem to connect with the opposite breast and laterally may appear to go into the back. Most experienced surgeons have learned that manipulation of the breast is helpful to identify the medial and lateral extents of the IMF. The authors propose the terms medial inflection point (MIP) and lateral inflection point (LIP), as they more accurately represent the distal ends of the IMF when the breast is folded in on itself ( Fig. 7 ). The MIP and LIP likely represent external manifestations of the medial and lateral triangular fascial condensation (see Fig. 2 ). The MIP-LIP plane represents the base diameter of the breast footprint.

Nov 21, 2017 | Posted by in Dental Materials | Comments Off on The Laminated Nature of the Pectoralis Major Muscle and the Redefinition of the Inframammary Fold
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