The extensor digitorum communis is the primary finger extensor, running through the fourth extensor compartment to the extensor expansions of all four fingers. Juncturae tendinum connect adjacent tendons on the dorsal hand, limiting independent extension (particularly of the ring finger). The EDC can only effectively extend the IP joints when the lumbricals and interossei assist through the extensor expansion; without intrinsic muscle function the EDC produces MCP hyperextension rather than IP extension (the intrinsic minus hand).
| Origin | Lateral epicondyle via the common extensor origin |
|---|---|
| Insertion | Extensor expansions of fingers 2 through 5 (via the sagittal bands at the MCP and the lateral bands to the PIP and DIP joints) |
| Nerve Supply | Posterior interosseous nerve (C7, C8) |
| Blood Supply | Posterior interosseous artery |
| Actions | Extension of fingers 2 through 5 at the MCP joint; Assists in wrist extension when the fingers are not extended; Assists in IP joint extension through the extensor expansion |
|---|
The central slip of the extensor expansion at the PIP joint is the specific part of the EDC expansion that extends the PIP joint; its disruption produces the Boutonnière deformity where PIP flexion and DIP hyperextension develop as the lateral bands migrate volar to the PIP joint axis.
Central slip disruption from forced PIP joint flexion produces the Boutonnière deformity — PIP flexion and DIP hyperextension. Acute central slip injuries are managed with PIP extension splinting for 6 weeks without DIP immobilisation to allow the oblique retinacular ligament to rebalance. The elson test (resisted PIP extension with the finger over a table edge) diagnoses central slip disruption by showing paradoxical DIP rigidity.
The EDC tendons are visible and palpable on the dorsal hand as the four cords running to each finger, becoming prominent during finger extension and visible as separate cords in thin-handed individuals.
EDC central slip avulsion producing Boutonnière deformity managed with PIP extension splinting for 6 weeks.
