The
distal radioulnar joint (DRUJ) is a
pivot joint located between the
distal ends of the
radius and
ulna, which make up the
forearm. Formed by the
head of the ulna (the bony knob on the back of the wrist) and the
ulnar notch of the radius, the DRUJ is separated from the radiocarpal (wrist) joint by an
articular disk lying between the radius and the
styloid process of the ulna. The
capsule of the joint is lax and extends from the
inferior sacciform recess to the ulnar shaft. The DRUJ works with the
proximal radioulnar joint (at the elbow) for
pronation and
supination. The radiocarpal (wrist) joint is an
ellipsoid joint formed by the radius and the
articular disc proximally and the proximal row of carpal bones distally. The carpal bones on the ulnar side only make intermittent contact with the proximal side — the triquetrum only makes contact during ulnar abduction. The capsule, lax and un-branched, is thin on the dorsal side and can contain synovial folds. The capsule is continuous with the midcarpal joint and strengthened by numerous
ligaments, including the
palmar and
dorsal radiocarpal ligaments, and the
ulnar and
radial collateral ligaments. The parts forming the radiocarpal joint are the lower end of the
radius and under surface of the
articular disk above; and the
scaphoid,
lunate, and
triquetral bones below. The articular surface of the radius and the undersurface of the
articular disk form together with a transversely elliptical concave surface, the receiving cavity. The superior articular surfaces of the scaphoid, lunate, and triquetrum form a smooth convex surface, the
condyle, which is received into the concavity.
Carpal bones of the
hand: •
Proximal: A=
Scaphoid, B=
Lunate, C=
Triquetrum, D=
Pisiform •
Distal: E=
Trapezium, F=
Trapezoid, G=
Capitate, H=
Hamate In the hand proper a total of 13 bones form part of the wrist: eight
carpal bones—
scaphoid,
lunate,
triquetral,
pisiform,
trapezium,
trapezoid,
capitate, and
hamate— and five
metacarpal bones—the
first,
second,
third,
fourth, and
fifth metacarpal bones. The
midcarpal joint is the S-shaped joint space separating the proximal and distal rows of carpal bones. The
intercarpal joints, between the bones of each row, are strengthened by the
radiate carpal and
pisohamate ligaments and the
palmar,
interosseous, and
dorsal intercarpal ligaments. Some degree of mobility is possible between the bones of the proximal row while the bones of the distal row are connected to each other and to the metacarpal bones —at the
carpometacarpal joints— by strong ligaments —the
pisometacarpal and
palmar and
dorsal carpometacarpal ligament— that makes a functional entity of these bones. Additionally, the joints between the bases of the metacarpal bones —the
intermetacarpal articulations— are strengthened by
dorsal,
interosseous, and
palmar intermetacarpal ligaments.
Articulations The radiocarpal, intercarpal, midcarpal, carpometacarpal, and intermetacarpal joints often intercommunicate through a common synovial cavity.
Articular surfaces It has two articular surfaces named, proximal and distal articular surfaces respectively. The proximal articular surface is made up of the lower end of the radius and a triangular articular disc of the inferior radio-ulnar joint. On the other hand, the distal articular surface is made up of proximal surfaces of the scaphoid, triquetral and lunate bones. == Function ==