Bones of the Upper Limb

Part 2 · The upper limb

Clavicle to phalanges, the nerves at risk along the humerus, and the palpable landmarks

The design brief

The upper limb was freed from weight bearing. Everything about its skeleton follows from that.

• Its attachment to the axial skeleton is a single small synovial joint — the sternoclavicular — with everything else suspended by muscle. This buys enormous mobility at the cost of stability.
• Its bones are lighter and less robust than their lower-limb counterparts, and its sockets are shallow.
• Its distal segment is optimised not for propulsion but for manipulation: 27 bones in each hand, a saddle joint at the thumb, and a nervous system representation out of all proportion to its mass.

The price of that design is written across the trauma list: the clavicle is the most commonly fractured bone in childhood, the shoulder is the most commonly dislocated major joint, and the distal radius is the most commonly fractured bone in adults.

Learning outcomes

• Name the bones of the pectoral girdle and free upper limb and describe their principal features.
• Describe the clavicle’s unique developmental and structural features and explain its fracture pattern.
• Describe the scapula’s landmarks and their functional significance.
• Describe the humerus in full and state precisely which nerve is at risk at each level.
• Describe the radius and ulna, the interosseous membrane, and the mechanism of load transfer.
• Name and describe the carpal bones in both rows and the ossification sequence.
• Explain the common fracture patterns and eponymous injuries of the upper limb and their functional consequences.
• Palpate and name at least ten bony landmarks and state the clinical use of each.
• Interpret carpal alignment and the standard radiographic lines and angles.

The bones, in outline

Figure 1 · Bones of the upper limb

The girdle articulates with the axial skeleton at one point only — the sternoclavicular joint. The scapula has no bony articulation with the thorax; it is held by muscle in the functional scapulothoracic articulation.

The clavicle

An S-shaped strut, subcutaneous throughout its length, convex forwards medially and concave forwards laterally.

Unique features — four of them, each examinable

• The first bone to begin ossifying (week 5–6 of fetal life) and among the last to complete it (the medial epiphysis fuses at 22–25 years, making it a forensic age marker).
• The only long bone to ossify predominantly in membrane — with secondary endochondral growth plates at both ends.
• It has no medullary cavity in the usual sense.
• It is the only bony strut connecting the upper limb to the trunk.

Functions

• Acts as a strut, holding the scapula and hence the limb laterally away from the thorax, permitting free swing. Congenital absence (cleidocranial dysostosis) allows the shoulders to be approximated across the front of the chest.
• Transmits force from the limb to the axial skeleton.
• Protects the underlying neurovascular bundle — brachial plexus and subclavian vessels — as they pass between clavicle and first rib.
• Provides muscle attachment and, through its axial rotation at the sternoclavicular joint, contributes to full arm elevation.

Attachments (worth learning as a map)

Fracture

The commonest fracture of childhood and among the commonest overall. Around 80% occur at the junction of the middle and lateral thirds — the weakest point, where the two curvatures meet, the cross-section changes from prismatic to flattened, and no muscle or ligament attaches.

The classic deformity: the medial fragment is pulled up by sternocleidomastoid, and the lateral fragment is pulled down and medially by the weight of the limb and by pectoralis major.

Complications to know: neurovascular injury (subclavian vessels, brachial plexus — uncommon but serious), pneumothorax, malunion with cosmetic deformity, non-union (more common in the middle third with displacement), and medial physeal injury mistaken for sternoclavicular dislocation in adolescents — a posterior displacement here can compress the trachea, oesophagus or great vessels and is an emergency.

The scapula

A flat triangular bone lying on the posterolateral thorax over ribs 2 to 7, held entirely by muscle.

Borders, angles and surfaces

Processes

Scapular position and dyskinesis. Normal resting position:

• internally rotated ~30–45° from the coronal plane (the scapular plane), anteriorly tilted ~10–15°, upwardly rotated ~5–10°. Deviations from this are visible as dyskinesis
• the vertebral border and inferior angle prominence identify the pattern. Winging: medial border prominence = serratus anterior (long thoracic nerve, C5–7)
• lateral/superior displacement with a drooping shoulder = trapezius (spinal accessory nerve, CN XI)

The humerus

Figure 2 · Nerves at risk along the humerus

The longest bone of the upper limb, and the single most important bone for a physiotherapist to know in nerve terms — four different nerves are injured at four different levels.

Proximal end

Shaft

Distal end

The four nerves at four levels — the highest-yield table in this chapter

Learn this as a sequence down the bone; it converts a fracture level into a neurological prediction, and it is asked in every clinical examination.

Ossification

The humerus has one primary centre (shaft, week 8) and up to eight secondary centres. The proximal humeral epiphyses (head at ~1 year, greater tubercle ~3 years, lesser tubercle ~5 years) fuse to each other and then to the shaft at ~18–20 years — the last epiphysis of the upper limb to fuse, and the growing end, hence the proximal humerus is the growing end and the nutrient artery is directed away from it, distally. Distal centres appear in the sequence C-R-I-T-O-E: Capitellum (1 yr), Radial head (3), Internal (medial) epicondyle (5), Trochlea (7), Olecranon (9), External (lateral) epicondyle (11) — a sequence used to interpret paediatric elbow radiographs and detect a displaced medial epicondyle.

The radius and ulna

Radius — the lateral bone

Ulna — the medial bone

The interosseous membrane and load transfer

The membrane’s fibres run obliquely, downwards and medially from radius to ulna. This orientation means the membrane is taut when force is transmitted from hand to radius, transferring load medially to the ulna and hence to the humerus.

The functional distribution: approximately 80% of axial load crosses the wrist through the radius and only 20% through the ulnar side (TFCC), but by the elbow the distribution has shifted to about 60% through the radiocapitellar joint — the interosseous membrane having transferred the difference.

Clinical consequences:

• Essex-Lopresti injury — radial head fracture with interosseous membrane rupture and distal radio-ulnar joint disruption. Excising the radial head then allows the radius to migrate proximally, producing chronic wrist pain and ulnar impaction. The lesson: never excise a radial head without checking the wrist
• Ulnar variance — the relative length of the ulna at the wrist. Positive variance (long ulna) predisposes to ulnar impaction syndrome and TFCC tears; negative variance is associated with Kienböck’s disease of the lunate. Distal radius fracture with radial shortening converts a neutral wrist into a positive-variance one, which is why radial length restoration matters
• Both-bone forearm fractures must be anatomically reduced: the forearm is functionally a joint, and malunion with loss of the radial bow costs rotation

Named forearm fracture patterns

Mnemonic for the two that are always confused: MUGR — Monteggia = Ulna fracture; Galeazzi = Radius fracture.

The carpus

Figure 3 · The eight carpal bones

Figure 4 · The carpal bones and the carpal tunnel

Eight bones in two rows of four, arranged as a transverse arch concave anteriorly, roofed by the flexor retinaculum to form the carpal tunnel.

Mnemonic: So Long To Pinky, Here Comes The Thumb (read proximal row lateral→medial, then distal row medial→lateral).

Individual bones — what actually matters

Flexor retinaculum attachments (all four are carpal tubercles): laterally the tubercle of the scaphoid and the tubercle of the trapezium; medially the pisiform and the hook of the hamate.

Ossification of the carpus

All carpal bones are cartilaginous at birth. They ossify in a broadly anticlockwise sequence starting with the capitate: capitate and hamate (~2–3 months), triquetrum (~2–3 years), lunate (~4), scaphoid, trapezium, trapezoid (~5–6), pisiform (~9–12, the last). A useful rule of thumb: the number of ossified carpal bones roughly equals the child’s age in years, up to about six. This is a standard skeletal-age assessment method (Greulich and Pyle).

Carpal alignment and radiographic reading

• On a lateral view, the radius, lunate, capitate and third metacarpal should be collinear.
• Scapholunate angle: normally 30–60°. Greater than 70° suggests dorsal intercalated segment instability (DISI), typically after scapholunate ligament rupture.
• Scapholunate gap > 3 mm on an AP view (“Terry Thomas sign”) indicates scapholunate dissociation.
• Gilula’s arcs — three smooth arcs traced along the proximal and distal borders of the proximal row and the proximal border of the distal row. Any step or break indicates carpal disruption.

Metacarpals and phalanges

Five metacarpals, each with a base (proximal), shaft and head (distal). The heads form the knuckles.

• The first metacarpal is shortest and stoutest, is rotated ~90° relative to the others (Chapter 6), and has its epiphysis at the base — whereas metacarpals 2–5 have theirs at the head. (In the phalanges, all epiphyses are at the base.)
• The second and third carpometacarpal joints are essentially immobile, forming the fixed central pillar of the hand; the fourth and fifth permit ~15–25° of flexion, allowing the ulnar side to cup around an object.
• Boxer’s fracture — fracture of the fifth metacarpal neck with volar angulation, from a punch. Up to 30–40° of angulation is tolerated here because of the mobile CMC joint; the equivalent angulation at the index metacarpal is not tolerated.
• Bennett’s fracture — intra-articular fracture-dislocation of the base of the first metacarpal; the small volar-ulnar fragment stays attached to the anterior oblique ligament while the shaft is pulled proximally and radially by abductor pollicis longus. Rolando’s fracture is its comminuted T- or Y-shaped equivalent.

Fourteen phalanges per hand: proximal, middle and distal for digits 2–5; proximal and distal only for the thumb. Distal phalanges bear a terminal tuft (ungual tuberosity) supporting the pulp and nail bed.

Sesamoids are constant at the first MCP joint (two, in the tendons of flexor pollicis brevis and adductor pollicis) and variable elsewhere.

Surface anatomy: the palpable landmarks

Learn these as a sequence you can perform on a patient, with the reason for each.

Two clinically important length measurements:

• True length: acromion (or the coracoid/anterior acromial angle) to the lateral epicondyle to the radial styloid
• Apparent length: xiphisternum or suprasternal notch to the radial styloid — apparent shortening without true shortening indicates a girdle or postural problem rather than bone loss

Where students consistently go wrong

• Forgetting the clavicle’s membranous ossification. It is the only long bone with this feature.
• Getting the tubercle facets wrong. Greater tubercle, top to bottom: supraspinatus, infraspinatus, teres minor. Lesser tubercle: subscapularis.
• Confusing anatomical and surgical neck. The surgical neck is the fracture site and the axillary nerve level.
• Misassigning the four nerve levels of the humerus. Learn the table in §9.5.
• Reversing Monteggia and Galeazzi. MUGR.
• Missing a scaphoid fracture because the radiograph is normal. Up to a quarter are.
• Excising a radial head without checking the wrist. Essex-Lopresti.
• Forgetting the elbow triangle relationship. It distinguishes dislocation from supracondylar fracture at the bedside.
• Splinting the hand flat. The safe position is MCPs at 70–90° flexion with IPs extended and thumb abducted.
• Calling coracoid tenderness a sign. It is tender in most normal people.

Check yourself

15 questions on this chapter. Tap one to see the answer and the reasoning.

Quick review

Further reading

Chapter 9 of 24 · Human Anatomy · Physiotherapist India Next: Chapter 10 — The Shoulder Region: four joints, the rotator cuff, and why stability here is muscular rather than bony.

Reviewed by the Physiotherapist India Team. · Human Anatomy contents