Digits of hand

There are five digits of hand, which include the thumb and index, middle, ring, and little fingers.

Bony structure:

• The digits contain phalanges (bones). Each digit has three phalanges (proximal, middle, and distal), except for the thumb, which has two (proximal and distal).

• The proximal phalanges connect with the distal heads of metacarpals to form metacarpophalangeal joints. The 1st metacarpal connects with the thumb, while the 2nd to 5th metacarpals connect with the index, middle, ring, and little fingers. Note that the 1st metacarpal forms a saddle joint with the trapezium, enabling a wider range of thumb movements compared to limited gliding movements allowed by the carpometacarpal joints in other digits.

• Flexion and extension are possible through proximal and distal interphalangeal joints between the phalanges.

Ligaments:

• The fibrous capsule of each metacarpophalangeal joint and proximal and distal interphalangeal joint is reinforced by respective palmar ligaments and medial and lateral collateral ligaments.

• Deep transverse metacarpal ligaments provide stability to the metacarpus skeletal framework by connecting the digits of hand (excluding the thumb). They attach to the palmar ligaments and the extensor hoods at the metacarpophalangeal joints.

• Extensor hood, or triangular dorsal digital expansions, are formed by the fan-shaped tendons of extensor digitorum and extensor pollicis. The apices of extensor hoods connect to the distal phalanges, the central regions connect to the middle phalanges, and the bases wrap around the metacarpophalangeal joints. They serve as insertion points for deep transverse metacarpal ligaments, as well as various intrinsic and extrinsic hand muscles, enabling intricate movements of the digits.

• Fibrous digital sheath surround the digits and hold the tendons of flexor digitorum superficialis and profundus close to the phalanges.

Muscles, tendons, innervation, and vasculature:

• For information on the muscles, neurovasculature of the digits of hand, please refer to the description of the hand.