| First metacarpal bone | |
|---|---|
 First metacarpal of the left hand (shown in red). Palmar view. | |
 The first metacarpal (Left) | |
| Details | |
| Identifiers | |
| Latin | os metacarpale I |
| FMA | 23899 |
| Anatomical terms of bone | |
The first metacarpal bone or the metacarpal bone of the thumb is the first bone proximal to the thumb. It is connected to the trapezium of the carpus at the first carpometacarpal joint and to the proximal thumb phalanx at the first metacarpophalangeal joint.
The first metacarpal bone is short and thick with a shaft thicker and broader than those of the other metacarpal bones. Its narrow shaft connects its widened base and rounded head; the former consisting of a thick cortical bone surrounding the open medullary canal; the latter two consisting of cancellous bone surrounded by a thin cortical shell. [1]
The head is less rounded and less spherical than those of the other metacarpals, making it better suited for a hinge-like articulation.
The distal articular surface is quadrilateral, wide, and flat; thicker and broader transversely and extends much further palmarly than dorsally. On the palmar aspect of the articular surface there is a pair of eminences or tubercles which articulate with the radial and ulnar sesamoid bones of the thumb metacarpophalangeal joint; the lateral eminence is larger than the medial.
The body or shaft is thick and broad — averaging 6 to 11 millimetres (0.24 to 0.43 in). On its dorsal side, the shaft is flat and wide, while the anteroposterior side is less pronounced; usually resulting in an oval-triangular cross-section.
The dorsal surface of the shaft is weakly convex longitudinally, while its palmar, radial, and ulnar surfaces tend to be concave. The palmar and medial surface exhibits a blunt ridge which separates a larger lateral part – the insertion of the opponens pollicis muscle – and a smaller medial part – the origin of the lateral head of the first dorsal interosseous muscle.
The base is significantly different from the bases of the other metacarpals. It is trumpet-shaped and ends in a saddle-shaped articular surface matching that of the trapezial articular surface. The configuration of the thumb carpometacarpal joint plays an important role in the mechanism of opposition. The articular surface is delimited by a thick, crest-like ridge extending around its circumference.
On the palmar and lateral side of the base is the insertion of the tendon of the abductor pollicis longus muscle, usually featuring a small tubercle. The origin of the first dorsal interosseous muscle is on the ulnar aspect of the base, and can sometimes extend onto the shaft. In contrast to the other metacarpals, the first metacarpal has no articular facets on the sides of its base (for intermetacarpal articulations) because it articulates exclusively with the trapezium.
The metacarpal bone of the thumb has two centres of ossification: a primary centre in the shaft and a secondary centre in the base. This contrasts to the other four metacarpal bones where the secondary centre is found in the head. The ossification process begins in the shaft during the ninth week of prenatal life, and in the base during the second year of life in girls and the third year in boys. [5] When the both sexes were considered together, the ossification of base of first metacarpal was seen to start between 13 and 41 months.[ citation needed ]
These centres unite before fifteenth year in girls and seventeenth year in boys. [5]
The thumb has several associated accessory bones. When present, these bones are usually found near the base and trapezium and are the products of an additional centre of ossification, usually of the trapezium, that failed to fuse with the associated bone. Named accessory bones include:
Fractures to metacarpal bones account for 30-40% of all hand fractures, of which 25% occur in the first metacarpal (second to fractures to the fifth metacarpal bone). 80% of fractures to the first metacarpal occur at its base. [6]
Common fractures to the thumb metacarpal include Bennett's fracture and Rolando's fracture
The carpal bones are the eight small bones that make up the wrist that connects the hand to the forearm. The term "carpus" is derived from the Latin carpus and the Greek καρπός (karpós), meaning "wrist". In human anatomy, the main role of the wrist is to facilitate effective positioning of the hand and powerful use of the extensors and flexors of the forearm, and the mobility of individual carpal bones increase the freedom of movements at the wrist.
The median nerve is a nerve in humans and other animals in the upper limb. It is one of the five main nerves originating from the brachial plexus.
In human anatomy, the wrist is variously defined as (1) the carpus or carpal bones, the complex of eight bones forming the proximal skeletal segment of the hand; (2) the wrist joint or radiocarpal joint, the joint between the radius and the carpus and; (3) the anatomical region surrounding the carpus including the distal parts of the bones of the forearm and the proximal parts of the metacarpus or five metacarpal bones and the series of joints between these bones, thus referred to as wrist joints. This region also includes the carpal tunnel, the anatomical snuff box, bracelet lines, the flexor retinaculum, and the extensor retinaculum.
The trapezoid bone is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row of carpal bones that give structure to the palm of the hand. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is homologous with the "second distal carpal" of reptiles and amphibians.
The trapezium bone is a carpal bone in the hand. It forms the radial border of the carpal tunnel.
In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones are analogous to the metatarsal bones in the foot.
The capitate bone is a bone in the human wrist found in the center of the carpal bone region, located at the distal end of the radius and ulna bones. It articulates with the third metacarpal bone and forms the third carpometacarpal joint. The capitate bone is the largest of the carpal bones in the human hand. It presents, above, a rounded portion or head, which is received into the concavity formed by the scaphoid and lunate bones; a constricted portion or neck; and below this, the body. The bone is also found in many other mammals, and is homologous with the "third distal carpal" of reptiles and amphibians.
The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is usually slightly longer than the radius, but the radius is thicker. Therefore the radius is considered to be the larger of the two. It is a long bone, prism-shaped and slightly curved longitudinally.
The upper limbs or upper extremities are the forelimbs of an upright-postured tetrapod vertebrate, extending from the scapulae and clavicles down to and including the digits, including all the musculatures and ligaments involved with the shoulder, elbow, wrist and knuckle joints. In humans, each upper limb is divided into the arm, forearm and hand, and is primarily used for climbing, lifting and manipulating objects.
The flexor pollicis brevis is a muscle in the hand that flexes the thumb. It is one of three thenar muscles. It has both a superficial part and a deep part.
In human anatomy, the adductor pollicis muscle is a muscle in the hand that functions to adduct the thumb. It has two heads: transverse and oblique.
In human anatomy, the extensor pollicis brevis is a skeletal muscle on the dorsal side of the forearm. It lies on the medial side of, and is closely connected with, the abductor pollicis longus. The extensor pollicis brevis (EPB) belongs to the deep group of the posterior fascial compartment of the forearm.[1] It is a part of the lateral border of the anatomical snuffbox.
In human anatomy, the palmar or volar interossei are three small, unipennate muscles in the hand that lie between the metacarpal bones and are attached to the index, ring, and little fingers. They are smaller than the dorsal interossei of the hand.
The opponens pollicis is a small, triangular muscle in the hand, which functions to oppose the thumb. It is one of the three thenar muscles. It lies deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis.
The carpometacarpal (CMC) joints are five joints in the wrist that articulate the distal row of carpal bones and the proximal bases of the five metacarpal bones.
In human anatomy, the dorsal interossei (DI) are four muscles in the back of the hand that act to abduct (spread) the index, middle, and ring fingers away from hand's midline and assist in flexion at the metacarpophalangeal joints and extension at the interphalangeal joints of the index, middle and ring fingers.
The second metacarpal bone is the longest, and its base the largest, of all the metacarpal bones.
In the human hand, palmar or volar plates are found in the metacarpophalangeal (MCP) and interphalangeal (IP) joints, where they reinforce the joint capsules, enhance joint stability, and limit hyperextension. The plates of the MCP and IP joints are structurally and functionally similar, except that in the MCP joints they are interconnected by a deep transverse ligament. In the MCP joints, they also indirectly provide stability to the longitudinal palmar arches of the hand. The volar plate of the thumb MCP joint has a transverse longitudinal rectangular shape, shorter than those in the fingers.
The extrinsic extensor muscles of the hand are located in the back of the forearm and have long tendons connecting them to bones in the hand, where they exert their action. Extrinsic denotes their location outside the hand. Extensor denotes their action which is to extend, or open flat, joints in the hand. They include the extensor carpi radialis longus (ECRL), extensor carpi radialis brevis (ECRB), extensor digitorum (ED), extensor digiti minimi (EDM), extensor carpi ulnaris (ECU), abductor pollicis longus (APL), extensor pollicis brevis (EPB), extensor pollicis longus (EPL), and extensor indicis (EI).
The muscles of the thumb are nine skeletal muscles located in the hand and forearm. The muscles allow for flexion, extension, adduction, abduction and opposition of the thumb. The muscles acting on the thumb can be divided into two groups: The extrinsic hand muscles, with their muscle bellies located in the forearm, and the intrinsic hand muscles, with their muscles bellies located in the hand proper.
