Extensor expansion of hand

The extensor expansion of hand (a.k.a. the dorsal digital expansion) is a complex triangular aponeurotic structure through which the extensor tendon inserts onto the phalanges. This broader term encompasses the entire dorsal fibrous arrangement, extending from the metacarpophalangeal (MCP) joint proximally and spreading distally over the proximal and middle phalanges.

Key components of this complex include:

• The extensor hood proximally, which helps to hold the extensor tendons in place over the MCP joint.

• The central slip, which inserts into the base of the middle phalanx.

• The lateral bands, which diverge and insert into the base of the distal phalanx.

• Some anatomical descriptions also include the retinacular ligaments as part of the extensor expansion of hand.

This intricate architecture of the extensor expansion of hand serves two primary functions:

• It effectively holds the long extensor tendons in their correct position on the dorsum of the digits, preventing bowstringing during movement.

• Crucially, it provides insertion points for the intrinsic hand muscles, specifically the lumbricals and interossei (palmar and dorsal).

This unique anatomical arrangement allows for a highly coordinated and precise control of finger movements:

• The extensor digitorum, lumbricals, and interossei collectively work to produce extension at the proximal and distal interphalangeal joints, while simultaneously permitting flexion at the metacarpophalangeal joints.