Metacarpophalangeal

Metacarpophalangeal joints, commonly abbreviated MCP joints, are the joints between the heads of the metacarpal bones and the bases of the proximal phalanges in the hand. There are five MCP joints, one for each finger. Each joint features a convex metacarpal head articulating with a concave proximal phalanx base, and they are enclosed by a fibrous joint capsule.

The MCP joints are reinforced by ligaments and plates that provide stability. The radial and ulnar collateral ligaments resist sideways stress, while the palmar (volar) plates strengthen the front of the joint and limit hyperextension. Deep transverse metacarpal ligaments connect the heads of the metacarpals to help align the joints during grasp. The joints are synovial and receive blood supply from digital arteries, with sensory innervation provided by digital nerves.

Function and movement: MCP joints are ellipsoid (condylar) synovial joints that allow two degrees of freedom: flexion–extension and abduction–adduction. They also permit limited circumduction and rotation. In the fingers, flexion and extension are the primary motions, enabling gripping and releasing, while abduction and adduction adjust finger spacing relative to the hand’s midline. Range of motion varies by digit and individual, but flexion generally reaches substantial degrees and extension can approach neutral or slight hyperextension in some people.

Clinical significance: MCP joints are commonly involved in inflammatory arthropathies such as rheumatoid arthritis, where swelling can cause deformities including ulnar drift. Traumatic injuries include collateral ligament tears from lateral forces, and the thumb’s MCP joint can suffer ulnar collateral ligament injuries (often called skier’s or gamekeeper’s thumb). Osteoarthritis and other degenerative conditions may also affect MCP joints.