Joints of the Hand Anatomy
The carpometacarpal, metacarpophalangeal and interphalangeal joints are synovial and allow the hand to perform its various functions, including the intricate movements involved in gripping objects. The intrinsic muscles perform delicate movements of the fingers; power is provided by contraction of the muscles in the compartments of the forearm.
There are three separate carpometacarpal joints, one for the thumb and two for the fingers. The joint between the first metacarpal and trapezium (Fig. 3.100) possesses saddle-shaped articular surfaces and a lax capsule. This joint permits flexion and extension in a plane parallel to that of the palm, and adduction and abduction in a plane at right angles to that of the palm (and in the plane of the thumbnail). During opposition (the combined movements of medial rotation, adduction and flexion), the thumb rotates so that it may touch any of the fingers pulp-to-pulp. Median nerve injury results in significant disability because opposition is essential in everyday manipulative movements.
The remaining two carpometacarpal joints, those for the fingers, are plane joints and less mobile than the first. Laterally, a joint cavity lies between the second and third metacarpals and the trapezoid and capitate, while medially the fourth and fifth metacarpals articulate with the hamate (Fig. 3.97). These carpometacarpal joints communicate with the three plane (intermetacarpal) joints that lie between the bases of the medial four metacarpals.
These joints occur between the rounded heads of the metacarpals and concave bases of the proximal phalanges (Fig. 3.38). Each joint capsule is reinforced at the sides by collateral ligaments and is thickened anteriorly to form a fibrocartilaginous plate. The plates of the medial four digits are interconnected by the deep transverse metacarpal ligament. The joints permit flexion, extension, adduction and abduction. Because the collateral ligaments tighten during flexion, adduction and abduction are possible only in the extended position.
Each of these joints possesses a capsule reinforced by collateral ligaments (Fig. 3.101). However, posteriorly, the capsule is deficient and is replaced by the extensor expansion (Fig. 3.102). These are hinge joints that allow only flexion and extension.
The carpometacarpal, metacarpophalangeal and interphalangeal joints are supplied by branches of adjacent vessels and nerves traversing the palm and digits.