Muscles of pectoral region

Serratus anterior

Movements of scapula:

Pectoralis major REF: Oncoplastic and Reconstructive Surgery for Breast Cancer: By A. Fitoussi, M. G. Berry, B. Couturaud, R. J. Salmon Page 45

“As the breast implant is mostly placed beneath the pectoralis major muscle, it is never dissected. A complete musculofascial pocket is created by lateral and inferolateral dissection of the pectoralis minor and serratus anterior. If indicated, mastectomy is performed with preservation of skin envelop, but nipple areola complex is included in the resection with fusiform incision that is more oblique inferiorly”

The four surgical approaches to emplacing a breast implant to the implant pocket are described in anatomical relation to the pectoralis major muscle.

1. Subglandular — the breast implant is emplaced to the retromammary space, between the breast tissue (the gland) and the pectoralis major muscle, which most approximates the plane of normal breast tissue, and affords the most aesthetic results. Yet, in women with thin pectoral soft-tissue, the subglandular position is likelier to show the ripples and wrinkles of the underlying implant. Moreover, the capsular contracture incidence rate is slightly greater with subglandular implantation.
2. Subfascial- the breast implant is emplaced beneath the fascia of the pectoralis major muscle; this is a variant of the subglandular position. The technical advantages of the subfascial implant-pocket technique are debated; proponent surgeons report that the layer of fascial tissue provides greater implant coverage and better sustains its position.
3. Subpectoral (dual plane) — the breast implant is emplaced beneath the pectoralis major muscle, after the surgeon releases the inferior muscular attachments, with or without partial dissection of the subglandular plane. Resultantly, the upper pole of the implant is partially beneath the pectoralis major muscle, while the lower pole of the implant is in the subglandular plane.
4. Submuscular — the breast implant is emplaced beneath the pectoralis major muscle, without releasing the inferior origin of the muscle proper. Total muscular coverage of the implant can be achieved by releasing the lateral muscles of the chest wall — either the serratus muscle or the pectoralis minor muscle, or both — and suturing it, or them, to the pectoralis major muscle. In breast reconstruction surgery, the submuscular implantation approach effects maximal coverage of the breast implants.

Serratus anterior [Ref: B.D.C. Anatomy 4/e vol. 1 p64]Repeat_.from Nov 08

The triangle of auscultation is a small triangular space on the back where the relatively thin musculature allows for respiratory sounds to be heard more clearly with a stethoscope.

It has the following boundaries:

• medially, by the Trapezius
• laterally by the scapula
• inferiorly by the Latissimus dorsi

The floor is formed by

–      7^th rib

–      6^th & 7^th intercostal spaces

–     Rhomboideus major

On the left side, the cardiac orifice of the stomach lies deep to the triangle, and in days before X-rays were discovered the sounds of swallowed liquids were auscultated over this triangle.

Pectoralis major and minor muscles are the most common congenitally absent muscles in humans.

Ref: Ultrasound of the Musculoskeletal System, 2007, Pages 51, 285; Principles of Neurology By Allan H. Ropper, Raymond Delacy Adams, Maurice Victor, Robert H. Brown, Page 1245; Clinical Pediatric Urology By A. Barry Belman, Lowell R. King, Stephen Alan Kramer, Page 947

This patient most likely sustained an injury to the long thoracic nerve (C5-C7), which innervates the serratus anterior muscle.

This muscle is located on the lateral portion of the thorax, attaching to the external surface of the lateral parts of the 1st – 8th ribs proximally and the anterior surface of the medial border of the scapula distally.

It is responsible for keeping the scapula applied to the thoracic wall, and protracts and rotates the scapula.

Other muscles and bones rely on the scapula to be “fixed”, as they use it as an anchor when producing movements of the humerus.

Injury to the long thoracic nerve, which lies on the medial wall of the axilla, can occur during weight lifting, thoracic or axillary surgery, or from a stab wound. The clinical features of a long thoracic nerve injury include a “winged” scapula (the protrusion of the scapula as the patient presses against a wall) and an inability to abduct the arm.

The deltoid and teres minor muscles are innervated by the axillary nerve (C5-C6), which winds around the humeral neck, and may be injured during the dislocation of the shoulder or a fracture to the neck of the humerus.

Injuries to this nerve present with weakness of shoulder abduction, and atrophy of the shoulder.

“Winging” of the scapula is not a prominent clinical feature of an axillary nerve injury.

The latissimus dorsi muscle is innervated by the thoracodorsal nerve (C6-C8), and is a large, fan-shaped muscle that extends, adducts, and medially rotates the humerus, and helps raise the body toward the arms during climbing and performing chin-ups.

Injury to the nerve that innervates this muscle can occur during surgical operations in the axilla, and makes the patient unable to perform a chin-up or go climbing.

The patient’s clinical findings in this case are inconsistent with an injury to the thoracodorsal nerve.

The pectoralis major muscle, which is innervated by the medial and lateral pectoral nerves, is involved in the adduction and medial rotation of the arm.

Injury to the nerves that innervate this muscle does not typically result in any disability, however the anterior axillary fold is absent on the affected side.

Boundaries of lower triangular space of arm are: medially it is bounded by long head of triceps, laterally by medial border of humerus and superiorly by teres major. Radial nerve and profunda brachii vessels are the contents of the lower triangular space.

Pectoralis minor crosses in front of axillary artery and divides it into three parts. The anterior relation of each part are; First part lies behing the pectoralis major muscle, second part lies behind the pectoralis minor and major muscle and third part lies behind pectoralis major.

The cords of brachial plexus are named according to their relation with the second part of  axillary artery, lateral cord runs lateral to the axillary artery, as well the medial and posterior cord lies medially and posterior to the axillary artery. Thus the muscle anteriorly to second part is pectoralis minor and major.

• Teres major and teres minor muscles and the long head of the triceps brachii muscle.
• Its contents is Circumflex scapular artery.

• Superior thoracic artery

• Thoracoacromial artery
• Lateral thoracic artery

• Subscapular artery
• Anterior humeral circumflex artery
• Posterior humeral circumflex artery

Serratus Anterior, innervated by the long thoracic nerve, draws the scapula forward. If it is denervated, there is no muscle to oppose the motion of the trapezius which is elevating and retracting the scapula. The medial border of the scapula falls away from the posterior chest wall and begins to look like an angel’s wing. This is termed a “winged scapula.” A winged scapula commonly occurs after an injury to the long thoracic nerve, which runs on the superficial surface of serratus anterior and is particularly vulnerable to trauma. The long thoracic nerve contains contributions from C5, 6, and 7, so remember the saying “C5, 6, and 7 keep the wings from heaven.”

The triangle of auscultation is a small triangular space on the back where the relatively thin musculature allows for respiratory sounds to be heard more clearly with a stethoscope. It has the following boundaries:

• Medial wall is formed by lateral border of trapezius
• Lateral wall is formed by medial border of scapula
• Inferiorly by the upper border of latissimus dorsi
• Floor is formed by: 7th rib, 6th and 7th intercostal spaces, rhomboids major

Blood supply of pectoralis major:

• Pectoralis major derives it blood supply mainly from pectoral branch of the thoracoacromial artery.
• Other arteries supplying the muscle are: First perforating branch of the internal thoracic artery (Internal mammary artery) and intercostal artery.

Serratus anterior protracts the scapula, it acts as a main muscle in reaching and pushing movements. It also helps in raising the arm fully. The muscular digitations of serratus anterior can be seen and felt when the outstretched hand pushes against resistance. In case of paralysis, the lower angle of the scapula stands out prominently, there is projection of scapula also termed as winging of scapula.

Must know:

Seratus anterior is innervated by the long thoracic nerve also known as nerve of bell.

Good to know:

Dropped shoulder occurs as a result of paralysis of the trapezius muscle. With paralysis of the trapezius muscle a drop shoulder with rotation of the angle of the scapula towards the midline and restricted abduction of the arm is caused. Trapezius is supplied by accessory nerve.

Long thoracic nerve (C5–C7). Branches off the C5–C7 roots, descends posteriorly to the roots of the plexus and the axillary artery and along the lateral surface of the serratus anterior muscle, with the lateral thoracic artery, while supplying the muscle. 

Of the muscles listed, pectoralis minor is the only one which is attached to the coracoid process. The deltoid originates from the clavicle, acromion and scapular spine and inserts on the deltoid process of the humerus. Pectoralis major originates from the clavicle, sternum, and ribs and inserts on the crest of the greater tubercle of the humerus. Serratus anterior originates on the ribs and inserts on the medial border of the costal surface of the scapula. So, none of these other muscles would be detached by a fracture of the coracoid process. 

A i.e. Pectoral branches of thoracoacromial artery; B i.e. Intercotal artery; C i.e. Lateral thoracic artery

• Pectoralis major muscle is supplied by one dominant vascular pedicle from pectoral branch of thoraco-acromial artery, supplied by several smaller secondary segmental vessels from deltoid & clavicular branches of thoracoacromial artery, and perforating branches of, intercostal, internal thoracic/internal mammary, superior thoracic and lateral thoracic arteries.
• Intercostal arteries supply blood to intercostal muscle, pectoral muscles, breast, skin, (by both anterior & posterior intercostal, arteries); spinalis, longissimus thoracic, iliocostalis, medial aspects of latissimus dorsi & trapezius (by dorsal branch of posterior intercostal artery) and serratus anterior (by muscular branch of posterior intercostal artery).

A i.e. Laterally rotates the scapula B i.e. It is attached to the medial side of scapula C i.e. protects scapula

Serratus anterior helps in vertical overhead abductionQ (assisted by trapezius), forward punchQ (assisted by pectoralis minor) & forced inspirationQ; it’s paralysis leads to winging of scapulaQ

B. i.e. Pectoralis major

Ans. is ‘b’ i.e. Pectoralis major 

The chest wall includes ribs, intercostal muscles and serratus anterior muscle, but not the pectoral muscles.

Ans. is ‘c’ i.e. (Pectoralis major removed) 

Lets see the nomenclature of various surgeries on breast

• Simple or Total mastectomy

– it removes all breast tissue, the nipple-areola complex, and skin.

• Extended simple mastectomy

– Simple mastectomy + removal of level I axillary lymph nodes.

• Modified radical mastectomy

it removes all breast tissue, the nipple-areola complex, skin and the level I and level II axillary lymph nodes.

• Halstead’s Radical mastectomy

removes all breast tissue and skin, the nipple areola complex, the pectoralis major and minor muscles and the level I, II and III axillary lymph nodes.

• Modified Radical Mastectomy
• Two forms of modified radical mastectomy are in use
• Auchincloss (pronounced as ‘aushincloss’) procedure

– Here both the pectoralis major and minor muscles are preserved with removal of level I and II axillary lymph nodes

Patey’s Procedure

here the pectoralis minor muscle is removed to allow complete dissection of level III axillary lymph nodes

• Scanlon’s modification of Patey’s procedure

– here the pectoralis minor muscle is divided instead of removing. Division of pectoralis minor muscle allows complete removal of level III lymph nodes

• Halstead Radical Mastectomy
• In this operation following structures are removed.

i)         the whole breast

ii)       the portion of skin overlying the tumor, which includes the nipple-areola complex.

iii)    the subcutaneous fat and the deep fascia vertically from the lower border of the clavicle upto the upper quarter of the sheath of the rectus abdominis and horizontally from the strenum to the anterior border of lattissimus dorsi

iv)     pectoralis major muscle

v)       pectoralis minor muscle and clavipectoral fascia

vi)     upper part of the aponeurosis of the external oblique and anterior parts of a few digitations of the serratus anterior muscle

vii)    all fatty and loose areolar tissue along with level I, II & III axillary lymph nodes

• Structures saved are :

i)         the axillary vein and the cephalic vein

ii)       the long thoracic nerve of Bell (Nerve to serratus anterior). The nerve to latissimus dorsi may be sacrified if required.

• Also know
• Extended Radical Mastectomy – Radical mastectomy + removal of internal mammary lymph nodes

Super Radical Mastectomy – Radical mastectomy + removal of internal mammary, mediastinal and supraclavicular lymph nodes.

Ans. is ‘c’ Pectoralis major myocutaneous flap 

Subclavius forms the anterior wall of axilla

Pectoralis major arises from the anterior surface of the sternal half of the clavicle; from breadth of the half of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib; from the cartilages of all the true ribs, with the exception, frequently, of the first or seventh and from the aponeurosis of the abdominal external oblique muscle. From this extensive origin the fibers converge in a flat tendon, about 5 cm in breadth, which is inserted into the lateral lip of the bicipital groove of the humerus.

Ans. D: All of the above

Anterior axillary fold is rounded in shaped and is formed by pectoralis major (lower border). Posterior axillary fold is formed by teres major and latisimus dorsi.

Serratus anterior causes protraction of scapula.

• It is supplied by long thoracic nerve (Nerve of Bell).
• It forms medial boundary of axilla.

Serratus anterior

• Origin : Outer surface of upper 8 ribs by 8 digitations (multipennate muscles).
• Insertion : Medial border of scapula and inferior angle.
• Nerve supply : Long thoracic nerve (nerve of bell).
• Actions : Action of serratus anterior are –
• Rotates the scapula so that glenoid cavity is raised upward & forward – Helps in Vertical over head abduction (in this action assisted by trapezius).
• Draws the scapula forward around the throcic wall so paralysis leads to winging of scapula.°
• Also used when arm is pushed forward in horizontal position as in forward punch (helped by Pectoralis minor in this action)e.
• Steadies the scapula during weight carrying.
• Helps in forced inspiration.2 (Accessory muscle of inspiration).
• Because of greater pull exerted on the inferior angle, inferior angle passes laterally and forward and the glenoid cavity is raised upward & forward; in this action the muscle is assisted by trapezius.

• Superior thoracic artery

• Thoracoacromial artery
• Lateral thoracic artery

• Subscapular artery
• Anterior humeral circumflex artery
• Posterior humeral circumflex artery