Upper Limb – Shoulder and Arm Anatomy

Upper-Limb Overview

• 4 segments: Shoulder, Arm, Forearm, Hand

• Regions for study: Shoulder-Arm, Elbow-Forearm, Wrist-Hand

• Key functional features: high mobility, grasp, strike, fine motor

Shoulder Complex – Bones & Landmarks

• Clavicle: only bony link to trunk; S-shape; medial 2/3 convex, lateral 1/3 concave; key sites—conoid tubercle, trapezoid line, subclavian groove

• Scapula: spans ribs 2-7; fossae—supraspinous, infraspinous, subscapular; spine → acromion; coracoid process; glenoid fossa with supra/infra-glenoid tubercles

• Humerus (proximal): head 135^{\circ} inclination, retroverted; anatomic vs surgical neck; greater & lesser tubercles, intertubercular groove, deltoid tuberosity, radial groove

Shoulder Complex – Joints & Movements

• 4 articulations: Glenohumeral (GHJ), Sternoclavicular (SCJ), Acromioclavicular (ACJ), Scapulothoracic (ST)

• Scapulohumeral rhythm: 120^{\circ} GHJ + 60^{\circ} ST = 180^{\circ} elevation (ratio 2:1)

SCJ

• Synovial saddle; intra-articular disc; ligs—ant/post SC, interclavicular, costoclavicular

• Clinical: posterior dislocation threatens mediastinal structures

ACJ

• Synovial; fibrocartilaginous disc; capsular ligs + coracoclavicular lig (conoid, trapezoid) provide stability

• Common injury: "shoulder separation"

GHJ

• Large humeral head vs small glenoid → mobility > stability

• Static stabilizers: labrum, capsule, GH ligs (sup, mid, inf-ant/post bands + axillary pouch), coracohumeral lig, coracoacromial "roof"

• Dynamic stabilizers: rotator cuff & scapular muscles

• Dislocation patterns: anterior (Hill-Sachs, Bankart), posterior (reverse Hill-Sachs), inferior; axillary nerve at risk

Bursae

• Subacromial & subscapular bursae reduce friction; implicated in impingement pain

Muscle Groups (Key O, I, A, N, Blood)

Pectoral Region

• Pectoralis major (clavicular: lat pectoral n C5-7; sternocostal: med pectoral n C8-T1) – add, IR, flex/extend

• Pectoralis minor (med pectoral n C8-T1) – scapular protraction/depression

• Serratus anterior (long thoracic n C5-7) – protracts & upwardly rotates scapula; "winging" if paralysed

Superficial Posterior (Extrinsic)

• Trapezius (CN XI, C3-4) – upper elevate/upward rotate, middle retract, lower depress/upward rotate; blood: transverse cervical a

• Latissimus dorsi (thoracodorsal n C6-8) – add, ext, IR; blood: thoracodorsal a

Deep Posterior (Extrinsic)

• Levator scapulae & Rhomboids (dorsal scapular n C5) – elevate/ retract / downward rotate scapula

Scapulohumeral (Intrinsic)

• Deltoid (axillary n C5-6) – ant flex/IR, middle abd, post ext/ER

• Teres major (lower subscapular n C5-6) – add, ext, IR

• Rotator cuff:
  • Supraspinatus (suprascapular n C5-6) – initiates abd 0-15^{\circ}
  • Infraspinatus (suprascapular n) – ER
  • Teres minor (axillary n) – ER
  • Subscapularis (upper/lower subscapular n) – IR

Posterior Arm

• Triceps brachii (radial n C5-T1): long (infraglenoid tubercle), lateral, medial heads; elbow ext, long head shoulder ext

• Anconeus (radial n) assists extension, stabilises elbow

Anterior Arm

• Biceps brachii, Coracobrachialis, Brachialis – all musculocutaneous n (C5-7); functions: elbow flex/supination, shoulder flex/add

Neurovascular Structures

Arteries

• Subclavian → Axillary (after 1st rib) → Brachial (after teres major) → Radial & Ulnar (cubital fossa)

• Axillary parts: 1-sup thoracic; 2-thoracoacromial & lateral thoracic; 3-subscapular (→ thoracodorsal, circumflex scapular), ant & post circumflex humeral

• Scapular anastomosis: suprascapular + circumflex scapular + dorsal scapular

• Elbow anastomosis: radial/middle/sup & inf ulnar collaterals with recurrent branches

Brachial Plexus (C5-T1)

• Roots → Trunks (Sup, Mid, Inf) → Divisions (ant/post) → Cords (Lat, Med, Post) → Branches

• Terminal nerves: Musculocutaneous, Median, Ulnar, Radial, Axillary

• Key cord branches: lat/med pectoral; upper/lower subscapular; thoracodorsal; medial brachial & antebrachial cutaneous

• Anatomical spaces: Quadrangular (axillary n, post circumflex humeral a), Triangular (circumflex scapular a), Triangular interval (radial n, profunda brachii a)

Cutaneous Innervation vs Dermatomes

• Dermatomes: C5 (lat arm), C6 (lat forearm/thumb), C7 (digits 2-3), C8 (digits 4-5/med forearm), T1 (med arm)

• Peripheral cutaneous: axillary – sup lat arm; musculocutaneous – lat forearm; radial – post/lat arm & hand dorsum; median – palmar lat 3.5 digits + dorsal tips; ulnar – medial 1.5 digits palmar/dorsal

Myotome Testing (with reflex)

• C5: deltoid abd, biceps flex; biceps reflex

• C6: wrist ext, biceps; brachioradialis reflex

• C7: triceps, wrist flex, finger ext; triceps reflex

• C8: finger flexors; no reflex

• T1: interossei; no reflex

High-Yield Clinical Notes

• Clavicle fracture common (fall); risk to subclavian vessels & brachial plexus

• SCJ posterior dislocation → airway/vascular compromise

• ACJ separation (sports fall)

• Shoulder impingement: subacromial space narrowing (rotator cuff/bursa)

• Rotator cuff tears: supraspinatus most frequent

• Axillary nerve injury: ant-inf GH dislocation, humeral neck fracture; sensory loss over deltoid

• Radial nerve palsy: mid-shaft humeral fracture; wrist drop

• Long thoracic nerve injury: serratus paralysis → scapular winging

• Thoracodorsal nerve injury: weak shoulder add/ext

• Brachial plexus variations & entrapments (thoracic outlet, Struthers lig, Arcade of Frohse, cubital & carpal tunnels)

Objectives

• Identify bones, joints, ligaments, muscles, nerves, vessels of upper limb

• Differentiate dermatomes vs peripheral cutaneous innervation; define myotomes

• Apply clinical anatomy to common pathologies

Upper-Limb Overview

• 4 segments: Shoulder, Arm, Forearm, Hand

• Regions for study: Shoulder-Arm, Elbow-Forearm, Wrist-Hand

• Key functional features: high mobility, grasp, strike, fine motor manipulation, and weight-bearing capabilities.

Shoulder Complex – Bones & Landmarks

• Clavicle: only bony link to trunk; S-shape due to two primary curves; medial 2/3 convex anteriorly, lateral 1/3 concave anteriorly; key sites include the conoid tubercle and trapezoid line on the inferior surface (attachment for coracoclavicular ligament), and the subclavian groove (for subclavian artery and nerve to subclavius).

• Scapula: a flat triangular bone spanning ribs 2-7, articulating with the humerus and clavicle; fossae—supraspinous (origin of supraspinatus), infraspinous (origin of infraspinatus), subscapular (origin of subscapularis); spine projects posteriorly, ending laterally as the acromion; coracoid process (beak-like projection, provides attachment for muscles like pectoralis minor, coracobrachialis, short head of biceps brachii, and ligaments like coracoacromial, coracohumeral, coracoclavicular); glenoid fossa (a shallow articular depression that articulates with the humeral head) with supra and infra-glenoid tubercles (origins for long head of biceps and triceps).

• Humerus (proximal): head is medial, directed superiorly and posteriorly, with a 135^{\circ} inclination angle and retroverted relative to the elbow joint; anatomic neck (site of epiphyseal plate in youth, distal to head); surgical neck (narrower region inferior to tubercles, common fracture site due to close relation with axillary nerve and posterior circumflex humeral artery); greater & lesser tubercles (prominent sites for rotator cuff muscle insertions), intertubercular groove (between tubercles, transmits long head of biceps tendon and ascending branch of anterior circumflex humeral artery); deltoid tuberosity (rough V-shaped area for deltoid insertion); radial groove (spiral groove on posterior shaft, lodges radial nerve and profunda brachii artery).

Shoulder Complex – Joints & Movements

• 4 articulations involving the shoulder girdle: Glenohumeral (GHJ), Sternoclavicular (SCJ), Acromioclavicular (ACJ), Scapulothoracic (ST – a physiological joint, not true synovial articulation).

• Scapulohumeral rhythm: Coordinated movement of the scapula and humerus during arm elevation, where 120^{\circ} of glenohumeral joint motion combines with 60^{\circ} of scapulothoracic motion to achieve 180^{\circ} of full arm elevation (a ratio of 2:1 GHJ:ST motion after the initial 30^{\circ} of GHJ abduction). This rhythm optimizes the length-tension relationship of the deltoid and maintains the glenoid fossa in an optimal position for the humeral head.

SCJ

• Synovial saddle joint; strong capsule with an intra-articular disc that divides the joint into two synovial cavities, increasing congruity and acting as a shock absorber; ligaments include ant/post sternoclavicular ligaments (reinforcing capsule), interclavicular ligament (connects clavicles across sternal notch), and costoclavicular ligament (strongest, anchoring clavicle to 1st rib, limiting superior displacement).

• Clinical: posterior dislocation is rare but often life-threatening as it threatens mediastinal structures (trachea, esophagus, great vessels).

ACJ

• Synovial plane joint; often contains a fibrocartilaginous disc; protected by a fibrous capsule and reinforced by capsular ligaments (superior and inferior acromioclavicular ligaments) plus the strong coracoclavicular ligament (composed of two parts: conoid and trapezoid ligaments) which provides vertical stability to the ACJ.

• Common injury: