Upper Limb Bones

The bones of the upper limb form the skeletal framework of the arm, forearm, wrist, and hand. Their arrangement permits a remarkable range of movement, allowing the hand to be positioned in space for grasping, manipulation, communication, and precise motor activity.

The free upper limb contains the humerus in the arm, the radius and ulna in the forearm, and the carpal bones, metacarpals, and phalanges in the hand. These bones articulate through the shoulder, elbow, radioulnar, wrist, and numerous joints of the hand.

Unlike the lower limb, which is strongly specialized for weight bearing and stability, the upper limb skeleton emphasizes mobility. Its bones and joints permit extensive rotation and positioning while providing attachment sites for the muscles responsible for both powerful and highly refined movements.

Organization of the Upper Limb Skeleton

Region	Bones
Arm	Humerus
Forearm	Radius and ulna
Wrist	Eight carpal bones
Hand	Five metacarpals and fourteen phalanges

Number of Bones

Each free upper limb contains 30 bones: one humerus, one radius, one ulna, eight carpals, five metacarpals, and fourteen phalanges.

Humerus

The humerus is the long bone of the arm. Proximally it articulates with the glenoid cavity of the scapula at the glenohumeral joint. Distally it articulates with the radius and ulna at the elbow.

The humerus provides extensive attachment for muscles acting on the shoulder and elbow and is closely related to several major nerves and blood vessels.

Proximal Humerus

The proximal humerus includes the head, anatomical neck, surgical neck, greater tubercle, lesser tubercle, and intertubercular sulcus.

Head of the Humerus

The humeral head is a rounded articular surface directed mainly medially and somewhat superiorly and posteriorly. It articulates with the shallow glenoid cavity of the scapula.

Anatomical Neck

The anatomical neck is a slight constriction immediately adjacent to the articular surface of the humeral head. It marks the attachment region of much of the glenohumeral joint capsule.

Surgical Neck

The surgical neck lies distal to the tubercles and is a clinically important site of humeral fracture. The axillary nerve and posterior circumflex humeral vessels are closely related to this region.

Greater Tubercle

The greater tubercle is positioned laterally and provides attachment for supraspinatus, infraspinatus, and teres minor.

Lesser Tubercle

The lesser tubercle projects anteriorly and provides insertion for subscapularis.

Intertubercular Sulcus

The intertubercular sulcus, or bicipital groove, lies between the greater and lesser tubercles. The tendon of the long head of biceps brachii passes through this region.

Rotator Cuff Insertions on the Humerus

Muscle	Humeral Attachment
Supraspinatus	Superior facet of greater tubercle
Infraspinatus	Middle facet of greater tubercle
Teres minor	Inferior facet of greater tubercle
Subscapularis	Lesser tubercle

Shaft of the Humerus

The shaft extends between the expanded proximal and distal ends. Important features include the deltoid tuberosity and radial groove.

Deltoid Tuberosity

The deltoid tuberosity is a roughened prominence on the lateral shaft where the deltoid muscle inserts.

Radial Groove

The radial groove runs obliquely across the posterior humeral shaft. The radial nerve and profunda brachii vessels travel in close relationship to this groove.

Distal Humerus

The distal humerus widens to form the articular structures and epicondyles of the elbow.

Capitulum

The capitulum is the rounded lateral articular surface of the distal humerus. It articulates with the head of the radius.

Trochlea

The trochlea is the spool-shaped medial articular surface and articulates with the trochlear notch of the ulna.

Medial Epicondyle

The medial epicondyle is a prominent medial projection that provides attachment for the common flexor tendon. The ulnar nerve passes posterior to it.

Lateral Epicondyle

The lateral epicondyle provides attachment for the common extensor tendon and several structures associated with the lateral elbow.

Olecranon Fossa

The olecranon fossa is a deep depression on the posterior distal humerus that receives the olecranon of the ulna during elbow extension.

Coronoid and Radial Fossae

Anteriorly, the coronoid fossa accommodates the coronoid process of the ulna during flexion, while the radial fossa receives the margin of the radial head.

Major Humeral Landmarks

Landmark	Importance
Head	Articulates with glenoid cavity
Surgical neck	Common fracture site near axillary nerve
Greater tubercle	Rotator cuff attachment
Lesser tubercle	Subscapularis insertion
Deltoid tuberosity	Deltoid insertion
Radial groove	Related to radial nerve
Capitulum	Articulates with radius
Trochlea	Articulates with ulna

Ulna

The ulna is the medial bone of the forearm in anatomical position. It is large proximally, where it forms the principal hinge articulation with the humerus, and becomes relatively narrow distally.

Proximal Ulna

The proximal ulna contains the olecranon, coronoid process, trochlear notch, radial notch, and ulnar tuberosity.

Olecranon

The olecranon is the large proximal projection forming the palpable point of the elbow. It provides insertion for triceps brachii and enters the olecranon fossa during extension.

Coronoid Process

The coronoid process projects anteriorly below the olecranon and contributes to the lower boundary of the trochlear notch.

Trochlear Notch

The trochlear notch is the large C-shaped articular surface between the olecranon and coronoid process. It articulates with the trochlea of the humerus.

Radial Notch

The radial notch lies on the lateral aspect of the proximal ulna and articulates with the circumference of the radial head at the proximal radioulnar joint.

Ulnar Tuberosity

The ulnar tuberosity lies distal to the coronoid process and provides attachment for brachialis.

Shaft of the Ulna

The shaft of the ulna has several surfaces and borders. Its interosseous border provides attachment for the interosseous membrane connecting the radius and ulna.

Distal Ulna

The distal ulna terminates in a small rounded head and an ulnar styloid process.

Head of the Ulna

The head articulates laterally with the ulnar notch of the radius at the distal radioulnar joint.

Ulnar Styloid Process

The ulnar styloid process projects distally from the posteromedial aspect of the distal ulna and provides attachment for supporting structures of the wrist.

Radius

The radius is the lateral forearm bone in anatomical position. It is relatively small proximally and broad distally.

The radius plays a major role in wrist articulation and rotates around the ulna during pronation and supination.

Proximal Radius

The proximal radius consists of the head, neck, and radial tuberosity.

Head of the Radius

The radial head is disc-shaped. Its superior surface articulates with the capitulum, while its circumference articulates with the radial notch of the ulna within the annular ligament.

Neck of the Radius

The narrow neck lies immediately distal to the radial head.

Radial Tuberosity

The radial tuberosity lies on the proximal radius and provides insertion for biceps brachii.

Shaft of the Radius

The radial shaft broadens toward the wrist. Its medial interosseous border provides attachment for the interosseous membrane.

Distal Radius

The distal radius is broad and forms the major bony contribution of the forearm to the radiocarpal joint.

Radial Styloid Process

The radial styloid process projects distally from the lateral side and is readily palpable at the wrist.

Ulnar Notch

The ulnar notch lies medially and articulates with the head of the ulna at the distal radioulnar joint.

Dorsal Tubercle

The dorsal tubercle of the radius, also known as Lister's tubercle, is a posterior prominence that acts as a pulley for the tendon of extensor pollicis longus.

Radius and Ulna Comparison

Feature	Radius	Ulna
Position	Lateral, thumb side	Medial, little-finger side
Proximal size	Smaller	Larger
Distal size	Larger	Smaller
Major elbow articulation	Capitulum	Trochlea
Direct radiocarpal contribution	Major contribution	No direct articulation with carpal bones
Role in pronation and supination	Rotates around ulna	Acts as relatively stable axis

Interosseous Membrane of the Forearm

The radius and ulna are connected along much of their shafts by the interosseous membrane. This strong fibrous sheet stabilizes the bones, provides muscle attachment, and participates in transmission of forces through the forearm.

Pronation and Supination

The radius and ulna are arranged to permit rotation of the forearm. During supination, they are approximately parallel. During pronation, the radius crosses anteriorly over the ulna.

Movement occurs at both the proximal and distal radioulnar joints.

Bones of the Hand

Each hand contains 27 bones: eight carpals, five metacarpals, and fourteen phalanges.

The arrangement of these bones combines stability with extensive mobility, allowing both powerful grasping and fine precision movements.

Carpal Bones

The eight carpal bones form the wrist and are arranged in proximal and distal rows.

Proximal Row of Carpals

From lateral to medial in anatomical position, the proximal row consists of the scaphoid, lunate, triquetrum, and pisiform.

Distal Row of Carpals

From lateral to medial, the distal row consists of the trapezium, trapezoid, capitate, and hamate.

Eight Carpal Bones

Row	Bone	Notable Feature
Proximal	Scaphoid	Commonly fractured carpal
Proximal	Lunate	Central proximal carpal
Proximal	Triquetrum	Medial proximal carpal
Proximal	Pisiform	Sesamoid bone within flexor carpi ulnaris tendon
Distal	Trapezium	Articulates with first metacarpal
Distal	Trapezoid	Articulates principally with second metacarpal
Distal	Capitate	Largest carpal bone
Distal	Hamate	Has prominent hook

Scaphoid

The scaphoid lies on the lateral side of the proximal carpal row and articulates with the radius. It spans the proximal and distal carpal rows functionally and is important in wrist stability.

Its tubercle contributes to the lateral boundary of the carpal tunnel.

Lunate

The lunate lies between the scaphoid and triquetrum in the proximal row. It articulates proximally with the radius and participates centrally in wrist mechanics.

Triquetrum

The triquetrum is positioned medially in the proximal row and articulates with the pisiform on its palmar surface.

Pisiform

The pisiform is a small sesamoid bone embedded within the tendon of flexor carpi ulnaris. It lies anterior to the triquetrum and is readily palpable.

Trapezium

The trapezium articulates with the first metacarpal at the carpometacarpal joint of the thumb. The geometry of this joint permits the extensive movements required for opposition.

Trapezoid

The trapezoid is a relatively small bone in the distal row, positioned between the trapezium and capitate and strongly associated with the base of the second metacarpal.

Capitate

The capitate is the largest carpal bone and occupies a central position in the wrist. Its rounded proximal head articulates with bones of the proximal carpal row.

Hamate

The hamate is located on the medial side of the distal carpal row. Its anterior projection, the hook of hamate, provides attachment for soft tissues and contributes to the medial boundary of the carpal tunnel.

Carpal Tunnel Boundaries

The carpal bones form a concave arch anteriorly. The flexor retinaculum spans this arch to form the carpal tunnel.

Bony Attachments of the Flexor Retinaculum

Side	Landmarks
Lateral	Tubercle of scaphoid and tubercle of trapezium
Medial	Pisiform and hook of hamate

Metacarpals

Five metacarpal bones form the skeleton of the palm. They are numbered I through V from the thumb side toward the little finger.

Each typical metacarpal has a proximal base, a shaft, and a distal head.

First Metacarpal

The first metacarpal is shorter and more mobile than the others. Its base articulates with the trapezium at a saddle-type carpometacarpal joint that is essential for thumb opposition.

Second and Third Metacarpals

The second and third metacarpals are relatively firmly attached to the distal carpal row and form a comparatively stable central axis of the hand.

Fourth and Fifth Metacarpals

The fourth and fifth carpometacarpal joints permit greater movement than the central metacarpals. This mobility allows the ulnar side of the hand to cup during grasping.

Heads of the Metacarpals

The metacarpal heads form the bony prominences commonly called the knuckles when the metacarpophalangeal joints are flexed.

Phalanges

The digits contain 14 phalanges. The thumb has two phalanges, while each of the other four digits has three.

Distribution of Phalanges

Digit	Phalanges
Thumb	Proximal and distal
Index finger	Proximal, middle, distal
Middle finger	Proximal, middle, distal
Ring finger	Proximal, middle, distal
Little finger	Proximal, middle, distal

Structure of the Phalanges

Each phalanx has a base, shaft, and head. Distal phalanges terminate in expanded distal tufts that support the soft tissues of the fingertips and nail beds.

Sesamoid Bones of the Hand

Small sesamoid bones may occur in tendons around the hand. A pair is commonly present on the palmar side of the first metacarpophalangeal joint of the thumb.

Shoulder Articulation

The head of the humerus articulates with the glenoid cavity of the scapula to form the glenohumeral joint. The large humeral head and shallow glenoid cavity favor mobility while requiring substantial soft tissue stabilization.

Elbow Articulations

The elbow region includes the humeroulnar and humeroradial articulations together with the proximal radioulnar joint.

The trochlea articulates with the ulna, while the capitulum articulates with the radial head.

Wrist Articulation

At the radiocarpal joint, the distal radius and articular disc articulate with the proximal carpal row, principally the scaphoid and lunate, with the triquetrum participating depending on wrist position.

The ulna does not directly articulate with the carpal bones.

Major Articulations of Upper Limb Bones

Bone	Major Articulations
Humerus	Scapula, radius, ulna
Radius	Humerus, ulna, proximal carpal row
Ulna	Humerus and radius
Carpals	Radius, adjacent carpals, metacarpals
Metacarpals	Carpals, adjacent metacarpals, proximal phalanges
Phalanges	Metacarpals and adjacent phalanges

Force Transmission Through the Upper Limb

Forces applied to the hand can travel proximally through the carpal bones and radius. The interosseous membrane helps redistribute forces between the radius and ulna, and loads then pass through the elbow and humerus toward the shoulder girdle.

Surface Anatomy

Many upper limb bones are readily palpable and provide important landmarks for physical examination, imaging, procedures, and orientation.

Important Palpable Landmarks

Landmark	Region
Greater tubercle of humerus	Proximal arm beneath deltoid
Medial epicondyle	Medial elbow
Lateral epicondyle	Lateral elbow
Olecranon	Posterior elbow
Head of radius	Lateral elbow
Ulnar styloid	Medial wrist
Radial styloid	Lateral wrist
Scaphoid	Anatomical snuffbox region
Pisiform	Palmar medial wrist
Metacarpal heads	Knuckles

Humeral Surgical Neck Fracture

Fractures through the surgical neck of the humerus can endanger the axillary nerve and posterior circumflex humeral vessels because of their close anatomical relationship.

Humeral Shaft Fracture

A fracture of the humeral shaft can injure the radial nerve, particularly where it travels along the posterior shaft in the radial groove.

Medial Epicondyle and Ulnar Nerve

The ulnar nerve passes posterior to the medial epicondyle. Its superficial location here explains the characteristic sensation produced when this region is struck.

Supracondylar Fracture

Supracondylar fractures occur in the distal humerus, particularly in children. Because important neurovascular structures pass through the anterior elbow region, displacement can threaten the brachial artery and nearby nerves.

Olecranon Fracture

The superficial olecranon can be fractured by direct trauma or forceful contraction of triceps brachii. Displacement may disrupt the extensor mechanism of the elbow.

Radial Head Fracture

Radial head fractures commonly follow a fall onto an outstretched hand. Because the radial head participates in both elbow articulation and forearm rotation, injury can impair flexion, extension, pronation, and supination.

Colles Fracture

A Colles fracture is a fracture of the distal radius classically associated with dorsal displacement or angulation of the distal fragment. It often results from a fall onto an extended hand.

Scaphoid Fracture

The scaphoid is the most commonly fractured carpal bone. Injury often follows a fall onto an outstretched hand and may produce tenderness in the anatomical snuffbox.

The pattern of blood supply to the scaphoid is clinically important because some fractures can compromise perfusion of the proximal fragment and increase the risk of osteonecrosis.

Lunate Dislocation

The lunate can become dislocated during significant wrist trauma. Because of its close relationship to the carpal tunnel, displacement may compress the median nerve.

Hook of Hamate Fracture

The hook of hamate can fracture following direct trauma or repetitive forces transmitted through objects held in the hand. Nearby ulnar neurovascular structures can be affected.

Metacarpal Fractures

Metacarpal fractures vary according to location and mechanism. Fracture of the neck of the fifth metacarpal is a common injury associated with direct axial loading through a clenched fist.

Phalangeal Fractures

The phalanges are vulnerable to direct trauma, crushing injuries, twisting, and sports-related mechanisms. Alignment is important because malrotation can significantly interfere with normal finger function.

Development and Ossification

Most bones of the upper limb develop predominantly through endochondral ossification. Primary ossification centers form within the shafts of long bones, while secondary centers develop in epiphyses and selected processes.

Growth plates permit longitudinal growth until skeletal maturity.

Functional Specialization of the Hand

The hand skeleton is particularly specialized for grasping and manipulation. Mobility at the thumb carpometacarpal joint permits opposition, while the relatively stable second and third metacarpals provide a firm central framework.

Greater mobility on the ulnar side allows the palm to cup around objects.

Thumb Opposition

Opposition brings the thumb pad toward the pads of the other digits. The saddle-shaped articulation between the trapezium and first metacarpal is a major skeletal basis for this movement.

Functions of Upper Limb Bones

Function	Role
Positioning	Allows the hand to be placed throughout a large spatial range
Movement	Provides levers for upper limb muscles
Grasping	Supports power and precision grips
Manipulation	Permits refined movements of hand and digits
Force transmission	Transfers loads between hand, forearm, arm, and shoulder girdle
Muscle attachment	Provides numerous origins and insertions
Joint formation	Forms shoulder, elbow, wrist, and hand articulations

Key Features of Upper Limb Bones

Feature	Key Point
Arm bone	Humerus
Lateral forearm bone	Radius
Medial forearm bone	Ulna
Number of carpals	8
Number of metacarpals	5
Number of phalanges	14
Largest carpal	Capitate
Commonly fractured carpal	Scaphoid
Thumb carpometacarpal bone	Trapezium
Total bones in each free upper limb	30

Anatomical and Functional Importance

The upper limb skeleton is organized to maximize mobility while maintaining sufficient stability for controlled movement. The humerus provides a long lever between the highly mobile shoulder and the elbow, while the radius and ulna permit both hinge-like elbow movement and rotation of the forearm.

At the wrist, the eight carpal bones create a compact but mobile transition between the forearm and hand. Distally, the metacarpals and phalanges provide the skeletal basis for grasping, opposition, precision handling, and fine motor activity.

Important bony landmarks also have close relationships with nerves and vessels. The axillary nerve is related to the surgical neck of the humerus, the radial nerve to the humeral shaft, and the ulnar nerve to the medial epicondyle. These relationships explain characteristic neurological injuries associated with particular fractures.

The bones of the upper limb therefore integrate shoulder mobility, elbow stability, forearm rotation, wrist movement, thumb opposition, grasping, precision manipulation, muscle leverage, and transmission of forces between the hand and shoulder girdle.