Collateral Ligaments of the Metacarpophalangeal Joints, Anterior View

Description

Running distally from the metacarpal heads to the bases of the proximal phalanges, the proper collateral ligaments of the metacarpophalangeal (MCP) joints appear as paired, cord-like bands on the radial and ulnar aspects of each knuckle. From an anterior (palmar) perspective, these fibers sit deep to the flexor tendon pathways and blend with the joint capsule, while remaining clearly lateral to the sagittal plane of each digit. The metacarpals and proximal phalanges provide the bony landmarks for ligament origin and insertion, with the ligament footprints positioned slightly dorsal to the true midline of the metacarpal head and coursing obliquely to the proximal phalangeal base. Joint alignment is easy to read. Collateral ligament behavior across MCP flexion and extension is a frequent teaching point and a recurring source of clinical error: the proper collaterals tighten in flexion and slacken in extension, whereas the accessory collateral fibers (when shown) relate to the volar plate and influence stability near full extension. That distinction underpins the physical exam for ulnar collateral ligament injury of the thumb MCP (gamekeeper’s or skier’s thumb), where stress testing in flexion better isolates the proper collateral, and a displaced tear can become trapped superficial to the adductor aponeurosis (Stener lesion). The same anatomy guides reduction and splinting strategy after MCP dislocation, where the volar plate and collateral complex can block closed reduction. Hand anatomy and orthopedic modules use this view to teach MCP joint stability, varus and valgus stress testing positions, and the relationship between synovial articulation, capsule, and collateral fibers. It also suits operative and patient-education graphics for thumb UCL repair, MCP ligament reconstruction, and radiology captions correlating ligament injuries with avulsion fragments at the proximal phalanx base. Anatomical accuracy verified by SciePro's Medical Advisory Board.