The hand consists of 27 bones: 14 phalangeal bones, 5 metacarpal bones, and 8 carpal bones arranged in five rays of metacarpals and phalanges having its base at the carpometacarpal (CMC) articulation (Figure 268-1).
A. Bones of the hand and wrist. B. Carpal tunnel.
The carpal bones are made up of two rows, each with four bones. The bones are concave volarly and are bridged by the flexor retinaculum. This forms the carpal tunnel through which the median nerve and the nine long flexor tendons of the fingers pass (flexor pollicis longus [FPL]; flexor digitorum profundus [FDP] from the index, middle, ring, and small fingers; and flexor digitorum superficialis [FDS] from the index, middle, ring and small fingers) (Figure 268-2).
Joints, ligaments, and tendons of the digits.
The index and middle finger CMC articulations have relatively little mobility, whereas the thumb, ring, and small finger CMC articulations have greater mobility at the CMC joint, which allows grasping and adaptive movements of the hand. More metacarpal deformity can be accepted in the great mobility CMC joints.
Multiple soft tissue structures support the bones and joints of the hand: capsules and ligaments provide stability, whereas muscles/tendons of the hand and forearm generate mobility (Figures 268-2, 268-3, and 268-4). The collateral ligaments of the metacarpophalangeal (MCP) joints are tightest in flexion in the index through small fingers (to allow stability in grasp), while the collateral ligaments of the MCP thumb are tight in flexion and extension (which also provide stability for the thumb in all positions) (Figure 268-3). The collateral ligaments of the interphalangeal (IP) joints are also tight throughout the entire range of motion.
The intrinsic muscles of the hand are those that have both their origins and insertions within the hand. They consist of the thenar and hypothenar muscles, the adductor pollicis, the interossei, and the lumbricals (Figures 268-3, 268-4, and 268-5).
A. Palmar (volar) view of the hand showing the relationship of the some of the intrisic muscles, and flexor tendons and sheaths. B. Cross-sectional view of digit at the middle phalanx. C. Lumbricals.
A. Dorsal view of the hand showing the extensor tendons and retinaculum, and intrinsic musculature. B. Cross-sectional view with the six extensor compartments.