There are 3 groups of bones in the hand:
- The 8 carpal bones are the bones of the wrist.
- The 5 metacarpals (I to V) are the bones of the metacarpus.
- The phalanges are the bones of the digits -The thumb has only 2 and The remaining digits have 3.
The large bony framework of the palm is formed by the carpal bones and metacarpals of the fingers - index, middle, ring, and little fingers (metacarpals II to V) that tends to work as a unit. On the other hand, the metacarpal of the thumb independently functions and enables the flexibility at the carpometacarpal joint in order to have an opposite supply from the thumb to the fingers.
The carpus (G. Corpus = wrist) is composed of 8 carpal bones, that are arranged in 2 rows: proximal and distal. Every row contains 4 bones. The proximal row of carpal bones is composed of the following bones from lateral to medial side:
The distal row of carpal bones is composed of the following bones from lateral to medial side:
Mnemonic: She Looks Too Pretty. Try To Catch Her.
Identification of Individual Carpal Bones
The individual carpal bones can be recognized by taking a look at their shape and few other features.
Identification of the carpal bones.
The carpal bones are cartilaginous at birth. Every carpal bone ossifies by 1 center and all these hearts seem after beginning. The centers seem as follows:
Scaphoid fracture: Fracture of scaphoid is the most frequent fracture of carpus and normally happens because of fall on the outstretched hand. Fracture happens at the narrow waist of the scaphoid. Medically it presents as tenderness in the anatomical box. Blood vessels largely goes into the scaphoid via its both ends. But in 10-15% cases, all the blood vessels providing proximal section goes into it via its distal post. In this state when waistline of scaphoid is fractured, the proximal section is deprived of blood supply and may go through avascular necrosis.
The metacarpus is composed of 5 metacarpal bones. They're conventionally numbered 1 to 5 from lateral (radial) to medial (ulnar) side.
Every metacarpal is a small long bone and is composed of 3 parts: (a) head, (b) shaft, and (c) base.
The head is at distal end and rounded.
The shaft goes between head and base. It's concave on palmar aspect and on sides. The dorsal surface of shaft presents a triangular area in its distal part.
The base is proximal end and enlarged.
Peculiarities Of First Metacarpal
- The first metacarpal is the shortest and stoutest bone.
- It's rotated medially via 90° so that its dorsal surface faces laterally.
- Its base possesses concavo-convex (saddle-shaped) articular surface for articulation with trapezium.
- The head is not as convex and wider than other metacarpals.
- The sesamoid bones glide on radial and ulnar corners of head and creates impressions of gliding.
- Its base dose not joint with any other metacarpal.
- It's epiphysis at its proximal end contrary to other metacarpals, which have epiphysis at their distal end.
Every metacarpal ossifies by 2 centers: 1 primary center for the shaft and the 1 secondary center for the head. The period of appearance of centers and their fusion is provided in the box below:
- Bennet's fracture: It's an oblique fracture of the base of 1st metacarpal. It's intra-articular and could be related to subluxation or dislocation of metacarpal.
- Boxer's fracture: It's fracture of neck of metacarpal, and most generally includes neck of 5th metacarpal.
There are 14 phalanges in every hand: 2 in thumb and 3 in every finger.
Parts And Features
Every phalanx is a short long bone and has 3 parts: (a) base (proximal end), (b) head (distal end), and (c) shaft (going between the 2 ends).
- The bases of proximal phalanges have concave oval facet for articulation with the heads of metacarpals.
- The bases of middle and distal phalanges possess pulley shaped articular surfaces.
- The shaft tapers in the direction of the head.
- The dorsal surface is convex from side to side.
- The palmar surface is flat from side to side but gradually concave in the long axis.
- The heads of proximal and middle phalanges are pulley shaped.
- The heads of distal phalanges is non-articular and has rough horseshoe-shaped tuberosity.
Every phalanx ossifies by the 2 centers: 1 primary center for the shaft and 1 secondary center for the base. Their time of appearance is as follows:
- For proximal phalanx: 10th week of IUL.
- For middle phalanx: 12th week of IUL.
- For distal phalanx: 8th week of IUL.
Look: 2 years. Fusion: 16 years.
An undisplaced fracture of phalanx can be treated satisfactorily by strapping the fractured finger with the neighboring finger. The sesamoid bones in region of hand are found on the following sites:
- Sesamoid bone in the tendon of flexor carpi ulnaris (pisiform).
- Two sesamoid bones on the palmar surface of the head of first metacarpal.
- Sesamoid bone in the capsule of interphalangeal (IP) joint of thumb (in 75% cases).
- Sesamoid bone on the ulnar side of capsule of MCP joint of little finger (in 75% cases).
The sesamoid bones related to head of the first metacarpal bones are generally noticed in X-ray of hand.