The MCP collateral ligaments have a cam-shaped metacarpal head origin that makes them taut in MCP flexion and lax in extension. This biomechanical property means MCP joints must be immobilised in flexion (70-90 degrees) to keep the collaterals at maximum length and prevent contracture — a principle fundamental to hand injury management. After injury or surgery, collateral ligament shortening in extension produces the intrinsic minus contracture.
| Origin | Metacarpal head lateral tubercles |
|---|---|
| Insertion | Lateral proximal phalanx base |
| Actions | Lateral MCP joint stability — taut in flexion (cam effect), lax in extension allowing abduction-adduction |
|---|
The intrinsic plus position (MCP flexion, IP extension) is the standard position for hand immobilisation after injury and surgery — it keeps MCP collaterals at full length and IP joint volar plates unfolded, preventing the most common post-traumatic contracture patterns. Any hand splint that immobilises MCPs in extension risks permanent MCP collateral shortening.
MCP collateral ligament shortening from immobilisation in extension producing fixed MCP extension contracture prevented by intrinsic-plus splinting.
