Upper limb

Extensor expansion of the hand (Extensor hood, lateral bands, intertendinous connections)

Apparatus extensorius digitorum manus (Extensor hoods, Lateral bands, Connexus intertendinei)

Origin

Dorsal aspect of MCP joints of digits II–V, receiving extensor digitorum tendons

Insertion

Central slip inserts onto base of middle phalanx; lateral bands (joined by lumbricals/interossei) fuse into terminal tendon on distal phalanx base; interconnected by juncturae tendinum

Function

Complex biomechanical apparatus coordinating MCP extension with PIP and DIP extension; balances intrinsic and extrinsic hand forces

Innervation

Radial nerve (PIN), median nerve (lumbricals 1–2), and ulnar nerve (interossei, lumbricals 3–4)

Movement & chain

Coordinated digital extension and delicate finger posturing

Palpation

Palpable along dorsal aspect of proximal and middle phalanges

Clinical

Mallet finger (terminal extensor tendon avulsion at DIP joint base causing extensor lag); Boutonnière deformity (central slip rupture with volar subluxation of lateral bands); Swan-neck deformity.

Segmental innervation

C6–T1

In clinical practice

Continuous DIP extension splinting (Stack splint) for 6–8 weeks for Mallet finger, and specialized hand therapy

Region in the model

Upper limb