Shoulder and Arm

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

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

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

Glenohumeral Joint ( Fig. 2-4 )

• This spheroidal (ball and socket) joint is designed for motion over stability

• Static restraints

  • Articular congruity

  • Labrum—deepens the socket by 50% and provides a barrier against excessive translation

  • Negative intraarticular pressure

  • Capsule

  • Ligaments

    • Glenohumeral ligaments (superior, middle, and inferior)

      • Resist anterior translation

      • The anterior band of the inferior glenohumeral ligament is the most important

    • Coracohumeral ligament

      • Resists inferior translation

    • Coracoclavicular ligament

      • Resists superior translation

• Dynamic restraints

  • Rotator cuff muscles

  • Biceps tendon

  • Coupled scapulothoracic motion

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

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

• Ligaments

  • Capsule

    • Resists anteroposterior translation

  • Coracoclavicular ligaments (trapezoid and conoid)

    • Resist superior translation

Sternoclavicular Joint

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

• Ligaments

  • Capsule

  • 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

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

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

• Three anterior muscles—coracobrachialis, biceps, and brachialis

• One posterior muscle—triceps

Brachial Plexus ( Fig. 2-7 )

• From the ventral rami of C5-T1

• Organized into five components

  • Roots

  • Trunks

  • Divisions

  • Cords

  • Branches

• Preclavicular branches

  • Dorsal scapular nerve

  • Long thoracic nerve

  • Suprascapular nerve

  • Nerve to the subclavius

Major Arm Branches ( Fig. 2-8 )

• Musculocutaneous nerve (lateral cord)

  • Runs from medial to central anteriorly

  • Supplies the biceps (short head), coracobrachialis, and part of the brachialis

• Radial nerve (posterior cord)

  • Spirals behind the humerus from medial to lateral

  • Supplies the triceps (all three heads) in the arm

• Median nerve (medial and lateral cords)

  • Runs just medial to the brachial artery in the medial arm

  • No major branches in the arm

• Ulnar nerve (medial cord)

  • Runs just lateral to the brachial artery in the medial arm

  • No major branches in the arm

Subclavian Artery

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

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

Brachial Artery

• Named at the lower border of the teres major

• Lies medial in the arm and crosses centrally at the elbow

• Major branches

  • Anterior humeral circumflex

  • Posterior humeral circumflex

  • Profunda brachii (deep brachial)

Shoulder ( Fig. 2-14 )

Nerves

Axillary Nerve

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

• At risk

  • 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

Arm