Upper limb

Capsules, collateral ligaments, and palmar plates of digits (MCP, PIP, DIP)

Capsulae, ligamenta collateralia et palmaria digitorum manus (MCP, PIP, DIP)

Origin

Heads of metacarpals and phalanges of digits I–V

Insertion

Bases of adjacent phalanges and dense fibrocartilaginous palmar (volar) plates

Function

Cam-effect of MCP collaterals (loose in extension for spread, taut in 90° flexion for grip); volar plates prevent PIP/DIP hyperextension; thumb UCL stabilizes key pinch

Innervation

Median and ulnar digital nerves (C7–T1)

Movement & chain

Flexion, extension; MCP abduction/adduction in extension

Palpation

Readily palpable along medial/lateral joint lines and palmar creases of fingers

Clinical

Skier's thumb / Gamekeeper's thumb (thumb MCP ulnar collateral ligament tear with potential Stener lesion); PIP volar plate avulsion fracture; Swan-neck and Boutonnière deformities.

Segmental innervation

C7–T1

In clinical practice

Thumb UCL stress testing, buddy taping, and immobilization in 'intrinsic-plus' position

Region in the model

Upper limb