The four extensor digitorum tendons pass through the fourth extensor compartment at the wrist under the extensor retinaculum and fan out across the dorsal hand to the extensor expansions. Juncturae tendinum (tendinous connections between adjacent tendons at the level of the metacarpals) limit independent finger extension, particularly of the ring finger, and prevent complete extension tendon rupture from retracting proximally. The EDC tendons merge with the interosseous and lumbrical contributions at the extensor expansion.
| Muscle |
|
|---|---|
| Attachment | Extends through the fourth extensor compartment at the wrist to the extensor expansions of fingers 2 through 5 |
Finger MCP extension and assists in IP joint extension through the extensor expansion
Sagittal band rupture at the MCP joint, often from a direct blow such as punching (boxer's knuckle) or from rheumatoid attrition, allows the EDC tendon to sublux ulnarward off the metacarpal head during finger flexion, producing a painful snap and extension lag from the flexed position. Acute injuries are splinted with the MCP in extension for about 6 weeks, while chronic instability needs surgical repair or reconstruction. Dorsal wrist lacerations (zone 5, under or near the retinaculum) require repair of each divided slip, and the juncturae tendinum can preserve some extension after a single tendon laceration, masking the injury. Tenosynovitis of the EDC at the wrist under the extensor retinaculum produces dorsal wrist pain and crepitus.
EDC tendon subluxation from the metacarpal head producing snapping and MCP extension lag managed with extension splinting acutely and surgical repair for chronic instability.
Laceration of EDC tendons at the dorsal wrist producing finger extension lag, repaired by suturing each tendon with early controlled mobilisation.
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