Shoulder and Arm

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Chapter 2

Shoulder and Arm

Stephen Thompson, Luke Choi, Stephen Brockmeier, Mark D. Miller

Regional Anatomy and Surgical Intervals

Regional Anatomy

Osteology

Scapula (Fig. 2-1)

A broad flat bone that serves as an attachment for 17 muscles and 4 ligaments

The glenoid is typically retroverted 1.2 degrees with a normal range between 2 degrees of anteversion and 9 degrees of retroversion; glenohumeral osteoarthritis typically results in increased glenoid retroversion

The scapular spine is the superior aspect of the scapula

The coracoid is the anterior projection that serves as the origin for several muscles and ligaments

The acromion protects the superior aspect of the glenohumeral joint and is the origin of many of the deltoid and trapezius muscles; it articulates with the clavicle

FIGURE 2-1 The scapula. Note the acromion, coracoid, spine, and supraspinatus fossa.

Clavicle (Fig. 2-2)

An S-shaped, rounded bone that serves as a fulcrum for lateral movement of the arm

The first bone in the body to ossify and the last to fuse

FIGURE 2-2 The clavicle. Note its curved “S” shape.

Humerus (Fig. 2-3)

The largest diaphyseal bone in the upper extremity

The hemispherical head is retroverted approximately 30 degrees

The anatomic neck is directly below the head

The surgical neck is approximately 2 cm distal to the anatomic neck

The greater tuberosity is the attachment for the supraspinatus, infraspinatus, and teres minor

The lesser tuberosity is the attachment for the subscapularis

FIGURE 2-3 The humerus. Note the tuberosities and head.

Arthrology

Glenohumeral Joint (Fig. 2-4)

FIGURE 2-4 The glenohumeral joint. Note the long head of the biceps, the glenohumeral ligaments, and the labrum.

Acromioclavicular (AC) Joint (Fig. 2-5)

A plane/diarthrodial (gliding) joint that stabilizes the clavicle to the acromion

• Resists anteroposterior translation

• Coracoclavicular ligaments (trapezoid and conoid)

• Resist superior translation

FIGURE 2-5 The acromioclavicular joint. Note the coracoclavicular ligaments (conoid and trapezoid) and the joint capsule.

Sternoclavicular Joint

A plane (gliding) joint that stabilizes the clavicle to the sternum

• Sternoclavicular ligaments

• Costoclavicular ligament

Scapulothoracic Joint

Located at ribs 2-7, the scapulothoracic joint allows coupled motion with glenohumeral abduction in a 2 : 1 ratio

Muscles

Shoulder Muscle Groups (Fig. 2-6 and Table 2-1)

Connect the upper limb to the axial skeleton

• Trapezius, latissimus, rhomboid major and minor, and levator scapulae

Connect the upper limb to the thoracic wall

• Pectoralis major and minor, subclavius, and serratus anterior

Act on the glenohumeral joint

• Deltoid, teres major and minor, supraspinatus, infraspinatus, and subscapularis

FIGURE 2-6 The muscles of the shoulder and arm.

Table 2-1

Muscles of the Shoulder

MUSCLE	ORIGIN	INSERTION	ACTION	INNERVATION
Trapezius	Spinous process C7-T12	Clavicle, scapula (acromion, spinous process)	Rotate scapula	Cranial nerve XI
Lateral dorsi	Spinous process T6-S5, ilium	Humerus (ITG)	Extend, adduct, IR humerus	Thoracodorsal
Rhomboideus major	Spinous process T2-T5	Scapula (medial border)	Adduct scapula	Dorsal scapular
Rhomboideus minor	Spinous process C7-T1	Scapula (medial spine)	Adduct scapula	Dorsal scapular
Levator scapulae	Transverse process C1-C4	Scapula (superior medial)	Elevate, rotate scapula	C3, C4
Pectoralis major	Sternum, ribs, clavicle	Humerus (lateral ITG)	Adduct, IR arm	Mid and lower PN
Pectoralis minor	Ribs 3-5	Scapula (coracoid)	Protract scapula	MPN
Subclavius	Rib 1	Inferior clavicle	Depress clavicle	Upper trunk
Serratus anterior	Ribs 1-9	Scapula (ventral medial)	Prevent winging	Long thoracic
Deltoid	Lateral clavicle, scapula	Humerus (deltoid tuberosity)	Abduct arm (2)	Axillary
Teres major	Inferior scapula	Humerus (medial ITG)	Adduct, IR, extend	Lower subscapular
Subscapularis	Ventral scapula	Humerus (lesser tuberosity)	IR arm, anterior stability	Upper and lower subscapular
Supraspinatus	Superior scapula	Humerus (GT)	Abduct (1), ER arm stability	Suprascapular
Infraspinatus	Dorsal scapula	Humerus (GT)	Stability, ER arm	Suprascapular
Teres minor	Scapula (dorsolateral)	Humerus (GT)	Stability, ER arm	Axillary

ER, External rotation; GT, greater tuberosity; IR, internal rotation; ITG, intertubercular groove; MPN, medial pectoral nerve; PN, pectoral nerve.

Arm Muscles (Fig. 2-6, D, and Table 2-2)

Three anterior muscles—coracobrachialis, biceps, and brachialis

One posterior muscle—triceps

Table 2-2

Muscles of the Arm

MUSCLE	ORIGIN	INSERTION	ACTION	INNERVATION
Coracobrachialis	Coracoid	Mid humerus medial	Flexion, adduction	Musculocutaneous
Biceps	Coracoid (SH)	Radial tuberosity	Supination, flexion	Musculocutaneous
	Supraglenoid (LH)
Brachialis	Anterior humerus	Ulnar tuberosity (anterior)	Flexes forearm	Musculocutaneous, radial
Triceps	Infraglenoid (LH)	Olecranon	Extends forearm	Radial
	Posterior humerus (LH)
	Posterior humerus (MH)

LH, Long head; MH, middle head; SH, short head.

Nerves

Brachial Plexus (Fig. 2-7)

From the ventral rami of C5-T1

Organized into five components

Preclavicular branches

• Dorsal scapular nerve

• Long thoracic nerve

• Suprascapular nerve

• Nerve to the subclavius

FIGURE 2-7 The brachial plexus. Note the arrangement of the roots, trunks, divisions, cords, and branches. n., Nerve.

Vascularity (Fig. 2-9)

Subclavian Artery

Becomes the axillary artery at the outer border of the first rib

FIGURE 2-9 The shoulder and arm arteries.

Axillary Artery (Table 2-3)

Three divisions based on the relationship to the pectoralis minor (1, proximal; 2, deep; 3, distal; Table 2-3)

(1) Proximal: supreme thoracic

(2) Deep: thoracoacromial and lateral thoracic (deltoid, acromial, pectoralis, and clavicular)

(3) Distal: subscapular, anterior, and posterior humeral circumflex

Table 2-3

Axillary Artery Branches

PART	BRANCH	COURSE
1	Supreme thoracic	Medial to the serratus anterior and pectorals
2	Thoracoacromial	Four branches (deltoid, acromial, pectoralis, and clavicular)
	Lateral thoracic	Descends to the serratus anterior
3	Subscapular	Two branches (thoracodorsal and circumflex scapular [triangular space])
	Anterior humeral circumflex	Blood supply to the humeral head–arcuate artery lateral to the bicipital groove
	Posterior humeral circumflex	Branch in the quadrangular space accompanying the axillary nerve

Brachial Artery

Named at the lower border of the teres major

Lies medial in the arm and crosses centrally at the elbow

• Anterior humeral circumflex

• Posterior humeral circumflex

• Profunda brachii (deep brachial)

Cross-Sectional Anatomy

FIGURE 2-10 Cross-sectional anatomy of the shoulder and arm. a., Artery; m., muscle; n., nerve; v., vein.

Surgical Intervals

FIGURE 2-11 Surgical intervals. Internervous planes for approaches to the shoulder and arm.

Landmarks (Fig. 2-12)

Coracoid process

Supraspinatus fossa

FIGURE 2-12 Landmarks. A, Anterior. B, Posterior. C, Superior.

Radiologic Landmarks (Fig. 2-13, A and B)

Hazards

Shoulder (Fig. 2-14)

Nerves

Axillary Nerve

A branch of the posterior cord that supplies the deltoid and teres minor muscles

• Inferiorly as it transverses just below the glenohumeral joint

• Adduct and externally rotate the arm and stay directly on the neck of the glenoid with dissection

• Avoid retractor placement below the subscapularis and capsule

• Palpate the nerve with blunt dissection and use electrocautery without muscle relaxation

• Laterally with any incision or dissection 5 cm or more distal to the lateral acromion

• Place a marking suture at that location, and do not dissect below it

• Posteriorly, in quadrangular space

• Do not dissect below the teres minor

FIGURE 2-13 Radiologic landmarks. A, The true anteroposterior (AP; Grashey) view of the shoulder. B, The AP (Zanca) view of the acromioclavicular joint.

FIGURE 2-14 Major hazards. Note the course of the axillary, musculocutaneous, and suprascapular nerves.

Musculocutaneous Nerve

A branch of the lateral cord that supplies the coracobrachialis, the short head of the biceps, and a portion of the brachialis and terminates as the lateral antebrachial cutaneous nerve

• Approximately 5 cm below the coracoid

• Be careful with medial retraction

• Externally rotate the arm to reduce risk

Suprascapular Nerve

A preclavicular branch of the upper trunk that supplies the supraspinatus and infraspinatus

• Excessive medial retraction or dissection or both can injure this nerve and affect one or both of the muscles it innervates

Vascularity

Subclavian Artery and Vein

Run inferior to the clavicle

• Dissect subperiosteally when exposing the undersurface of the clavicle

Acromial Branch of the Thoracoacromial Artery

Runs in the medial aspect of the coracoacromial ligament

• Coagulate or tie off this vessel with superior dissection

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