Applied Upper Limb Anatomy

Most commonly fractured bone in the body; typical site is the junction of the middle and lateral thirds, the weakest point of the S-curve.

• Medial fragment displaced superiorly by sternocleidomastoid; lateral fragment drops from limb weight and is pulled medially by pectoralis major.
• Subclavian vessels and brachial plexus lie directly posteroinferior: rarely but seriously at risk in displaced fractures.

• Anterior dislocation accounts for the vast majority of cases, related to the shallow glenoid and relatively weak anteroinferior capsule; typically from forced abduction and lateral rotation.
• Risks the axillary nerve (winds around the surgical neck) and can produce a Bankart lesion (anteroinferior labral tear) or Hill-Sachs lesion (posterolateral humeral head impaction).
• Posterior dislocation is rare, classically associated with seizures or electric shock (forceful, unopposed internal rotator contraction).

• Occurs with anterior shoulder dislocation or surgical neck fractures, given its close relationship to both structures within the quadrangular space.
• Motor loss: deltoid and teres minor, weak abduction beyond the first 15°.
• Sensory loss: regimental badge area over the lower lateral deltoid.

• Supraspinatus is most commonly torn, related to its relatively poor vascularity near the insertion ("critical zone") and repetitive subacromial impingement.
• Produces a painful arc of abduction (roughly 60–120°) and weakness initiating/sustaining abduction.
• Chronic full-thickness tears allow superior migration of the humeral head against the acromion.

• Caused by long thoracic nerve injury (axillary surgery, mastectomy, penetrating or traction trauma), paralysing serratus anterior.
• Medial border and inferior angle of the scapula lift off the thoracic wall, most evident on pushing against resistance.
• Impairs full overhead arm elevation, since serratus anterior contributes to scapular rotation.

• Upper brachial plexus injury (C5–C6) from excessive increase in the neck-shoulder angle, birth trauma or a fall onto the shoulder.
• Affects axillary, suprascapular, musculocutaneous nerves, and nerve to subclavius.
• Produces the "waiter's tip" posture: adducted, medially rotated arm, extended elbow, pronated forearm, flexed wrist.

• Lower brachial plexus injury (C8–T1) from excessive upward traction on the arm, birth trauma (breech delivery) or a fall while grasping an overhead object.
• Affects the intrinsic hand muscles, producing a claw hand.
• May involve T1 sympathetic fibres, causing Horner syndrome (ptosis, miosis, anhidrosis) if the lesion is proximal enough.

• The radial nerve lies in direct contact with the posterior humeral shaft within the radial (spiral) groove.
• A mid-shaft fracture can injure the nerve here, causing wrist drop.
• Sensory loss may extend to the first dorsal web space, though variable given proximal sensory branches often arise before the groove.

• Common sites: axilla (crutch pressure), radial groove (mid-shaft fracture, "Saturday night palsy"), and the arcade of Frohse within supinator (posterior interosseous nerve entrapment).
• Proximal injury causes wrist drop (loss of wrist and finger extension); posterior interosseous nerve lesions spare wrist extension (via ECRL/brachioradialis) but cause finger drop.
• Sensory loss over the first dorsal web space (absent in isolated posterior interosseous nerve lesions, which are purely motor).

• Common in children, typically from a fall on an outstretched hand with the elbow hyperextended.
• Risks the brachial artery and median nerve, which lie directly anterior to the distal humerus.
• Vascular compromise can progress to Volkmann ischaemic contracture if unrecognised or inadequately treated.

• Elbow-level lesion: loss of pronation, weak wrist flexion, loss of FPL/lateral FDP function producing the pointing (benediction) sign on attempted fist making; thenar weakness.
• Wrist-level lesion: thenar wasting/weakness with sensory loss over the lateral 3½ digits; palm sensation spared if the lesion is confined within the carpal tunnel (palmar cutaneous branch arises proximally).
• Long-standing severe median and ulnar combined loss produces an "ape hand" deformity.

• Vulnerable posterior to the medial epicondyle (elbow) and within Guyon canal (wrist).
• Produces claw hand, more pronounced with a distal (wrist-level) lesion than a proximal (elbow-level) one, the ulnar paradox: because a proximal lesion also disables FDP's deforming pull.
• Froment sign: compensatory FPL (median-innervated) activation on key pinch testing, indicating weak adductor pollicis (ulnar-innervated).

• Usually posterior, from a fall on an outstretched hand with the elbow partially flexed.
• Disrupts the normal equilateral triangle relationship between the olecranon and the two epicondyles (preserved in supracondylar fractures, disrupted in true dislocation), a useful clinical/radiographic distinguishing feature.
• Risks the ulnar nerve and, less commonly, the brachial artery, given their close proximity to the joint.

• Typically from a fall on an outstretched hand with the forearm pronated, transmitting force through the radius to the elbow.
• May limit pronation/supination due to mechanical block or pain within the joint.
• Associated with Monteggia fracture-dislocation (proximal ulna fracture with radial head dislocation) when combined with ulnar shaft injury.

• Most common carpal fracture, typically from a fall on an outstretched hand; classic site is the waist of the scaphoid.
• Blood supply is retrograde from the radial artery, entering distally, waist fractures risk avascular necrosis of the proximal pole.
• Clinical sign: tenderness in the floor of the anatomical snuffbox; initial X-rays can be normal, so clinical suspicion warrants immobilisation and repeat imaging.

• Distal radius fracture with dorsal displacement and angulation, classically from a fall on an outstretched, dorsiflexed hand.
• Produces the classic "dinner fork" deformity on lateral inspection of the wrist.
• May be associated with an avulsion of the ulnar styloid process.

• Compression of the median nerve within the rigid, non-expansile carpal tunnel, from any process increasing tunnel content volume or reducing capacity (tenosynovitis, oedema, pregnancy, fracture malunion, repetitive strain).
• Sensory symptoms in the lateral 3½ digits, sparing the palm (palmar cutaneous branch exits proximal to the tunnel); thenar weakness/wasting in advanced cases.
• Positive Tinel (tapping) and Phalen (sustained flexion) signs reproduce symptoms.

• Compression of the ulnar nerve and artery within Guyon canal, causes include ganglion cysts, hook of hamate fractures, and repetitive pressure ("cyclist's palsy").
• Motor and/or sensory ulnar deficits that spare the dorsum of the hand, since the dorsal cutaneous branch arises proximal to the canal, distinguishes it from a more proximal (elbow-level) ulnar lesion.
• Can selectively affect only the motor (deep) or sensory (superficial) branch depending on the precise site of compression within the canal.

• Entrapment classically occurs at the arcade of Frohse, the fibrous proximal edge of supinator; also from radial head fractures/dislocations or elbow surgery.
• Wrist extension is preserved (ECRL and brachioradialis are supplied by the radial trunk proximal to this point), but finger extension at the MCP joints and radial deviation on extension (from ECU loss) are affected.
• Purely motor deficit: no cutaneous sensory loss, since the nerve's sensory contribution ends before this point.

• Results from radial nerve injury proximal to the branches supplying the wrist extensors, typically mid-shaft humeral fracture or radial groove compression.
• Loss of wrist and finger extension leaves the wrist in a flexed position at rest.
• Grip strength is also functionally reduced, since finger flexors are mechanically disadvantaged without wrist extensor stabilisation.

• Results from ulnar nerve injury (more pronounced with distal/wrist-level lesions, the ulnar paradox) or combined median-ulnar injury (severe, affecting all digits).
• Loss of lumbrical function removes MCP flexion/IP extension coordination, producing MCP hyperextension with IP flexion, typically most visible in the ring and little fingers (ulnar-only lesions) or all fingers (combined lesions).
• Long-standing cases show hollowing of the interosseous spaces (guttering) from intrinsic muscle wasting.

• Results from a severe or long-standing median nerve lesion (typically proximal), causing wasting and weakness of the thenar muscles.
• The thumb loses opposition and abduction, falling into the plane of the other fingers (adducted, extended position), losing the normal "thumbs-out" contour of the thenar eminence.
• Functionally devastating for precision grip and opposition-dependent tasks.

• Progressive fibrotic thickening and contracture of the palmar aponeurosis and its digital extensions.
• Most commonly affects the ring and little finger rays, producing flexion contracture at the MCP and PIP joints.
• Anatomically distinct from a neurological cause: it is a primary connective tissue/fascial process, not a nerve palsy.

• Raised pressure within a closed fascial compartment (arm, forearm, or hand) exceeds capillary perfusion pressure, compromising tissue perfusion.
• Forearm compartments are particularly vulnerable given their tight fascial boundaries and the interosseous membrane, especially after fractures, crush injury, or reperfusion following vascular repair.
• Classic features include pain out of proportion to injury and pain on passive stretch of the affected muscles, a surgical emergency requiring fasciotomy before irreversible muscle/nerve ischaemia occurs.

• End-stage sequela of untreated forearm compartment syndrome, classically following a supracondylar humeral fracture with brachial artery compromise.
• Ischaemic necrosis and subsequent fibrosis of the deep flexor compartment (particularly flexor digitorum profundus and flexor pollicis longus) produces a fixed flexion contracture of the wrist and fingers.
• Associated with variable degrees of median (and sometimes ulnar) nerve damage from the same ischaemic insult, compounding the functional deficit.