Bones of the Upper Limb
The upper limb contains all the bones from the shoulder girdle down to the fingertips. These bones work together to give you an enormous range of motion, from powerful overhead throws to the fine motor control needed to write or thread a needle. Understanding each bone's landmarks and how they articulate with neighboring bones is the foundation for learning muscles, joints, and clinical conditions later on.
Bones of the Upper Limb (Appendicular Skeleton)
Clavicle
The clavicle is an S-shaped bone that acts as a strut, holding the upper limb away from the trunk. It articulates medially with the manubrium of the sternum and laterally with the acromion of the scapula. Because of its exposed position, the clavicle is one of the most commonly fractured bones in the body.
Scapula
The scapula is a triangular, flat bone on the posterior thorax. Key landmarks to know:
- Spine: a prominent posterior ridge you can palpate through the skin
- Acromion: the lateral extension of the spine that articulates with the clavicle
- Glenoid cavity: a shallow socket that articulates with the head of the humerus (its shallowness allows great mobility but sacrifices stability)
- Coracoid process: an anterior, hook-like projection serving as an attachment point for muscles and ligaments
Humerus
The humerus is the single long bone of the arm (not the forearm). Important features:
- Head: rounded proximal end that articulates with the glenoid cavity of the scapula
- Greater and lesser tubercles: attachment points for rotator cuff muscles; separated by the intertubercular (bicipital) groove
- Deltoid tuberosity: a roughened area on the lateral shaft where the deltoid muscle attaches
- Medial and lateral epicondyles: bony projections at the distal end serving as attachment points for forearm muscles
- Trochlea: medial, spool-shaped surface that articulates with the ulna
- Capitulum: lateral, rounded surface that articulates with the head of the radius
Radius
The radius is the lateral bone of the forearm (on the thumb side in anatomical position).
- Head: proximal disc-shaped end that articulates with the capitulum of the humerus and the radial notch of the ulna
- Radial tuberosity: a roughened area just distal to the neck where the biceps brachii tendon inserts
- Styloid process: a distal projection on the lateral side; serves as an attachment point for the brachioradialis muscle and ligaments
The radius crosses over the ulna during pronation, which is why you can rotate your forearm.
Ulna
The ulna is the medial bone of the forearm (on the pinky side in anatomical position).
- Olecranon: the proximal projection that forms the point of your elbow; the triceps brachii attaches here
- Trochlear notch: the large C-shaped notch that wraps around the trochlea of the humerus
- Coronoid process: an anterior projection that helps stabilize the humeroulnar joint
- Styloid process: a small distal projection; serves as an attachment point for the ulnar collateral ligament of the wrist
Carpals
Eight small bones arranged in two rows form the wrist:
- Proximal row (lateral to medial): scaphoid, lunate, triquetrum, pisiform
- Distal row (lateral to medial): trapezium, trapezoid, capitate, hamate
A common mnemonic: So Long To Pinky, Here Comes The Thumb (proximal row lateral to medial, then distal row medial to lateral). The scaphoid is the most commonly fractured carpal bone because it spans both rows and bears significant force during a fall on an outstretched hand.
Metacarpals
Five bones form the palm of the hand, numbered I–V from lateral (thumb side) to medial (pinky side). Each has a base (proximal), shaft, and head (distal). The heads of the metacarpals form your knuckles.
Phalanges
These are the finger bones. Each finger has three phalanges (proximal, middle, distal), except the thumb (pollex), which has only two (proximal and distal). That gives you 14 phalanges per hand.
Articulations of the Upper Limb
Each joint type determines what movements are possible at that location. Knowing the joint classification helps you predict the range of motion.
- Sternoclavicular joint: sternal end of clavicle with the manubrium. This is a saddle-type synovial joint that permits limited multi-planar movement. It's the only bony attachment of the upper limb to the axial skeleton.
- Acromioclavicular (AC) joint: acromion of the scapula with the acromial end of the clavicle. A plane-type synovial joint allowing limited gliding.
- Glenohumeral (shoulder) joint: glenoid cavity of the scapula with the head of the humerus. A ball-and-socket synovial joint providing the greatest range of motion of any joint in the body, but also the most commonly dislocated.
- Elbow joint: actually a compound joint with two articulations:
- Humeroulnar joint (hinge-type): trochlea of humerus with trochlear notch of ulna, allowing flexion and extension
- Humeroradial joint (hinge-type): capitulum of humerus with head of radius, also contributing to flexion and extension
- Proximal radioulnar joint: head of the radius with the radial notch of the ulna. A pivot-type synovial joint allowing the radius to rotate during pronation and supination.
- Distal radioulnar joint: head of the ulna with the ulnar notch of the radius. Also a pivot-type joint working with the proximal radioulnar joint for pronation and supination.
- Radiocarpal (wrist) joint: distal end of the radius with the proximal carpal row (mainly scaphoid and lunate). A condyloid-type synovial joint allowing flexion, extension, abduction (radial deviation), and adduction (ulnar deviation).
- Intercarpal joints: between adjacent carpal bones. Plane-type synovial joints with limited gliding that collectively contribute to wrist flexibility.
- Carpometacarpal (CMC) joints: distal carpal row with metacarpal bases. Most are plane-type, but the CMC joint of the thumb (trapezium with metacarpal I) is a saddle-type joint. This saddle configuration is what gives the thumb its opposition, a movement critical for gripping.
- Metacarpophalangeal (MCP) joints: metacarpal heads with proximal phalanx bases. Condyloid-type synovial joints allowing flexion, extension, abduction, and adduction.
- Interphalangeal (IP) joints: between adjacent phalanges. Hinge-type synovial joints allowing only flexion and extension.
Carpal Tunnel Anatomy and Significance
Structure
The carpal tunnel is a narrow passageway on the palmar side of the wrist. Its floor and walls are formed by the concave arch of the carpal bones, and its roof is the flexor retinaculum (transverse carpal ligament). Passing through this tunnel are:
- The median nerve
- The tendons of the flexor digitorum superficialis, flexor digitorum profundus, and flexor pollicis longus
Functional Significance
The tunnel channels these structures from the forearm into the hand while protecting them during wrist movements. Because the tunnel is rigid (bone on three sides, ligament on top), there's very little room for swelling.
Clinical Relevance: Carpal Tunnel Syndrome
Carpal tunnel syndrome occurs when the median nerve is compressed within the tunnel. Common causes include:
- Inflammation of the flexor tendons from repetitive strain
- Conditions that reduce tunnel size: wrist fractures, arthritis, fluid retention during pregnancy
Symptoms follow the median nerve distribution:
- Pain, numbness, and tingling in the thumb, index finger, middle finger, and the lateral half of the ring finger
- In severe cases, weakness and atrophy of the thenar muscles (the fleshy mound at the base of the thumb)
Diagnosis involves clinical tests (Tinel's sign, Phalen's test) and nerve conduction studies. Treatment ranges from conservative approaches (wrist splinting, NSAIDs, corticosteroid injections) to surgical carpal tunnel release, where the transverse carpal ligament is divided to decompress the nerve.
Bone Landmarks and Structural Features
The long bones of the upper limb (humerus, radius, ulna) share a common structural plan:
- Diaphysis: the shaft of the bone
- Epiphyses: the proximal and distal ends, typically covered in articular cartilage where they form joints
- Metaphyses: the transitional regions between the diaphysis and each epiphysis; in growing bone, this is where the epiphyseal (growth) plate is located
Types of bone landmarks you'll encounter repeatedly:
- Processes: bony projections (e.g., coracoid process of the scapula)
- Tuberosities: large, roughened areas for muscle attachment (e.g., radial tuberosity)
- Tubercles: smaller, rounded projections (e.g., greater and lesser tubercles of the humerus)
- Epicondyles: projections above a condyle (e.g., medial and lateral epicondyles of the humerus)
- Fossae: shallow depressions (e.g., olecranon fossa on the posterior distal humerus)
All the synovial joints in the upper limb share certain features: they're lined with a synovial membrane that produces synovial fluid for lubrication, and they're enclosed by a joint capsule that provides stability. The specific type of synovial joint (hinge, pivot, ball-and-socket, etc.) determines which movements are permitted.