Finger Bones (Hand)
Phalanges Manus
location_on Fingers of the hand, distal to the metacarpals
The 14 phalanges of each hand form the bony framework of the fingers. The thumb has two phalanges (proximal and distal), while each of the other four fingers has three (proximal, middle, and distal). Each phalanx has a base, shaft, and head. The interphalangeal joints are true hinge joints allowing only flexion and extension. Phalangeal fractures are the most common fractures of the upper limb.
Key Anatomical Features
- 14 per hand: 2 for the thumb, 3 each for the index through little fingers
- Proximal phalanges are the longest, middle are intermediate, distal are the shortest
- Distal phalanges have ungual tuberosities that support the fingernails
- Flexor digitorum superficialis inserts on the middle phalanx sides
- Flexor digitorum profundus inserts on the palmar base of the distal phalanx
- Extensor expansion covers the dorsal surface and receives lumbrical and interosseous insertions
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Flexor digitorum superficialis | Lateral ridges of middle phalanx (splits to allow profundus through) | Flexes the proximal interphalangeal joint |
| Flexor digitorum profundus | Palmar base of distal phalanx | Flexes the distal interphalangeal joint |
| Extensor digitorum | Dorsal base of middle and distal phalanges via extensor expansion | Extends the metacarpophalangeal and interphalangeal joints |
| Lumbricals | Lateral bands of extensor expansion | Flex MCP joints and extend IP joints simultaneously |
| Interossei | Extensor expansion lateral bands | Flex MCP joints and extend IP joints, abduct/adduct fingers |
| Flexor pollicis longus | Palmar base of thumb distal phalanx | Flexes the thumb interphalangeal joint |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Proximal interphalangeal (PIP) joints | Synovial hinge | Proximal to middle phalanx |
| Distal interphalangeal (DIP) joints | Synovial hinge | Middle to distal phalanx |
| Metacarpophalangeal (MCP) joints | Synovial condyloid | Metacarpal head to proximal phalanx base |
Common Pathologies
Mallet finger
Disruption of the terminal extensor tendon at its insertion on the distal phalanx, causing a drooping fingertip that cannot actively extend at the DIP joint. May involve a bony avulsion fragment.
Jersey finger
Avulsion of the flexor digitorum profundus tendon from the distal phalanx, causing inability to flex the DIP joint. Most common in the ring finger.
Boutonniere deformity
Disruption of the central slip of the extensor expansion over the PIP joint, causing PIP flexion and DIP hyperextension from lateral band volar migration.
Phalangeal fracture
The most common fracture of the upper extremity. Rotational malunion is the key complication. Distal phalanx tuft fractures from crush injuries are the most frequent type.
Clinical Relevance
Finger fractures require careful assessment of rotational alignment: when the fingers are flexed, all should point to the scaphoid. Even 5 degrees of malrotation causes visible overlapping. PIP joint injuries are notoriously problematic because of the complex interaction of flexor tendons, extensor apparatus, collateral ligaments, and volar plate in a very small space. Early motion is essential to prevent stiffness after finger injuries.
Development and Ossification
Each phalanx ossifies from two centers: a primary center for the shaft (8th-12th fetal week) and a secondary center at the base (ages 1-3). The epiphysis fuses between ages 14 and 18. The distal phalanx of the thumb is the first phalanx to ossify.
Did You Know?
- Phalanx comes from the Greek for a line of soldiers, as the finger bones line up in rows
- Phalangeal fractures are the most common fractures of the entire upper extremity
- The thumb lacks a middle phalanx; anatomists debate whether it lost one during evolution or never had one
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