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.
Metacarpophalangeal joints
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.
Interphalangeal joints
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.
