The metacarpals are long bones located in the hand, forming the middle section between the wrist and the fingers. They serve as a bridge, connecting the bones of the wrist, known as carpals, to the bones of the fingers, called phalanges.
Understanding Their Place in the Hand
The metacarpals are precisely positioned to form the main structure of the palm. There are five metacarpal bones in each hand, with each one corresponding to a specific finger, including the thumb. These bones are numbered from one to five, starting with the thumb (Metacarpal I) and moving towards the little finger (Metacarpal V).
These five bones are arranged in a way that creates the arch of the palm, providing the hand with its shape and flexibility. You can easily feel these bones on the back of your own hand, extending from just below your wrist to the base of your knuckles. The heads of the metacarpals are particularly noticeable when you make a fist, as they form the prominent knuckles.
Anatomy and Role
Each metacarpal is classified as a long bone and consists of three main parts: a base, a shaft, and a head. The base is the proximal end, meaning it is closer to the wrist, and it articulates with the carpal bones. Specifically, the first metacarpal (thumb) articulates with the trapezium, while the second connects with the trapezium, trapezoid, and capitate. The third metacarpal articulates with the capitate, and the fourth and fifth metacarpals connect with the hamate bone.
The shaft, or body, is the long, central portion of the metacarpal bone. It is curved, being convex on the back of the hand and concave on the palm side. The head is the rounded, distal end of the metacarpal, located closer to the fingers. These heads articulate with the proximal phalanges, forming the metacarpophalangeal (MCP) joints, commonly known as the knuckles.
The metacarpals collectively provide the hand’s structural framework, enabling a wide range of movements such as flexion, extension, abduction, and adduction. They offer a stable base for finger movement, which is essential for activities like gripping, pinching, and other fine motor skills.
Common Conditions Affecting Metacarpals
Metacarpal bones are susceptible to various injuries and conditions. Fractures are among the most common issues affecting these bones. A frequent example is a “Boxer’s fracture,” which typically involves a break in the neck of the fifth metacarpal, the bone leading to the little finger. This type of fracture often results from hitting an object with a clenched fist.
Other types of metacarpal fractures can occur in the base or shaft of the bone due to direct impact, crushing injuries, or falls. Symptoms of a metacarpal fracture generally include pain, swelling, tenderness, and sometimes a noticeable deformity or bruising. Stress fractures of the metacarpals can develop from repetitive strain, particularly in athletes involved in sports like tennis. Arthritis can also affect the joints involving metacarpals, especially at the base of the thumb, where the first metacarpal meets the trapezium.