metacarpals

Metacarpals are the five long bones of the hand that lie between the wrist (carpal bones) and the fingers. They form the palm and are numbered I to V from the thumb side.

Anatomy and articulations: Each metacarpal has a proximal base, a slender shaft, and a distal head. The bases articulate with the distal row of carpal bones to form the carpometacarpal joints, with the first metacarpal uniquely forming a saddle joint with the trapezium to enable thumb opposition. The distal heads articulate with the proximal phalanges to form the metacarpophalangeal joints, which function as knuckles during finger flexion and extension.

Function and mechanics: The metacarpals provide the structural framework of the palm, transmit loads from the fingers to the forearm, and contribute to grip and dexterity. Their curvature and alignment help distribute forces during grasping and allow a range of hand movements, including precision and power grips.

Clinical relevance: Metacarpal fractures are common, typically resulting from direct blows, falls, or crush injuries. The fifth metacarpal is particularly susceptible to fractures (often called a boxer's fracture when involving the neck of the bone). Treatment depends on fracture location, displacement, and stability, ranging from immobilization to reduction or surgical fixation. Variations in size and shape exist among individuals, and certain injuries can affect hand function if not properly managed.

Summary: The five metacarpal bones connect the wrist to the fingers, provide palm stability, enable knuckle movements at the metacarpophalangeal joints, and play a central role in hand mechanics and grip.