Synonyms
Wrist, scaphoid bone, scaphoid bone, navicular bone, lunate bone, lunate bone, triangular bone, triangular bone, large polygonal bone, trapezium bone, small polygonal bone, tapezoid bone, capitate bone, capitatum bone, hooked leg, hamate bone, pea bone, pisiform bone
- Ulna (ulna)
- Spoke (radius)
- Wrist
- Stylus process (Processus styloideus ulnae)
- Moon leg (Os lunatum)
- Scaphoid (Os naviculare)
The so-called carpal is located between the end of the radius and the metacapical bone (Os metacapalia) and is formed by the individual carpal bones. The carpal bones lie in two rows. The first carpal row forms the wrist with the end of the radius.
In the first carpal row (directly at the wrist), the scaphoid bone (Os scaphoideum, formerly Os naviculare) is located starting at the thumb side, next to it the moon bone (Os lunatum), next to it the triangular bone (Os triquetum). The so-called pea bone is located most on the small finger side and is not a “real” carpal bone. The second carpal row (closer to the fingertips) starts on the thumb side with the large polygonal bone (Os trapezium), next to it the small polygonal bone (Os trapezoidum), next to it the head bone (Os capitatum) and on the little finger side the hooked leg (Os hamatum).
All carpal bones are tightly connected by fixed ligaments. The mobility of the individual bones against each other is limited. Since the carpal bones are convex when viewed from the side, a longitudinal groove forms on the palm side, which forms the carpal tunnel.
The scaphoid bone (Os scaphoideum) is the second largest bone of the carpal and lies on the thumb side, in the row of bones close to the body. It is convex curved and has six sides. Via these sides it is connected to the adjacent carpal bones and the radius of the forearm.
Because of these many connections, the majority of the scaphoid is covered with cartilage, which makes up the joint surfaces. The hump (Tuberculum ossis scaphoidei) of the scaphoid bone serves as the muscular origin and can be felt well on the palm of the hand. The lunate bone (Os lunatum) is located in the middle of the rear row of bones of the carpus and, as the name suggests, resembles a half moon.
In the direction of the thumb it borders on the scaphoid and on the other side on the triangular bone. Like the scaphoid, it is also in articulated connection with the radius of the forearm, as well as with the head bone and the hook bone of the bone row far from the body. A fall on the hand can lead to the so-called “perilunary dislocation”, whereby the connections to the other carpal bones are broken off.
This is however rather rare. The triangular bone (Os triquetrum) is an approximately pyramid-shaped bone of the carpal bone row close to the body. With its base it borders laterally on the moon bone, with which, together with the scaphoid bone, it makes the joint connection to the spoke of the forearm.
To the front it borders on the hooked leg and has a small joint surface at its tip towards the palm of the hand. The pea bone is supported on this joint surface. The pea bone (Os pisiforme) is the smallest bone of the carpus.
It is attached to the triangular bone and is located at the end of the ball of the little finger close to the body, where it can also be felt through the skin. Since it is embedded in the tendon of the ulnar flexor of the hand (M. flexor carpi ulnaris), it is one of the so-called sesamoid bones. These serve as spacers between the surrounding bones and the tendon and act as a kind of pulley, increasing the strength of the muscle.
The large polygonal bone is located on the thumb side in the row of carpal bones far from the body. With the first metacarpal bone, it forms the thumb saddle joint. Its other joints are connected to the small polygon bone and the scaphoid bone, and via a small joint surface to the metacarpal bone of the index finger.
The large polygonal bone is palpable when the back of the hand is pulled up (dorsal extension) by a small bump on its upper side. The small polygonal bone (Os trapezoideum) is located in the bone row far from the body between the large polygonal bone and the capitate bone, with which it is in articulated connection. Furthermore, it borders on the metacarpal bone of the index finger and thus forms part of the carpal-metacarpal joint.
The head bone (Os capitatum) is the largest of the eight carpal bones and is located in the row of bones farthest from the body. On its sides it borders on the small polygonal bone and the hooked leg. The lunar and scaphoid bones connect it to the row of bones close to the carpal bone.Its share of the carpal-middle hand joint is mainly formed by its connection to the metacarpal bone of the middle finger and smaller joint surfaces to the second and fourth metacarpal bones.
The hooked leg (Os hamatum) owes its name to a hook-shaped bony projection which, starting from it, protrudes towards the palm of the hand. Together with the pea bone, this forms the Eminentia carpi ulnaris, which serves as the starting point for a tight fibrous ligament (retinaculum flexorum) of the wrist. The hooked leg is connected to the capitate bone as well as the triangular and lunar bones via joint surfaces.
Like the other bones in the distal row of the carpal bone, it forms part of the carpal-metacarpal joint. This is represented by its joint connections to the metacarpal bones of the ring finger and the little finger. The spoke (radius) forms the wrist with the first carpal row.
The wrist is a so-called ellipsoid joint (egg joint with two skin axes, similar to a ball joint). The wrist can be extended by approx. 90° (back of the hand = extension) and bent by approx.
70° (flexion). On the small finger side, the wrist can be extended by approx. 40° (ulnar abduction) and approx.
20° on the thumb side (radial abduction). Due to the taut ligament connection within the individual carpal bones, there is only limited mobility between the first and second row of wrists (metacarpal joint). The second carpal row forms with the metacarpal bone of the hand the carpal-metacarpal joint (Carpometacarpal joint), which also has only a small range of motion.
