Anatomy and functional significance of the long extensors to the fingers and thumb.

Intrinsic and extrinsic hand muscles power finger extension. These two muscle groups have different anatomy that allows complimentary function at the interphalangeal joints and opposing function at the metacarpophalangeal joints. Independent extension of each finger is not possible because of anatomic constraints including the juncturae tendinum and intertendinous fascia between the extrinsic extensor tendons on the dorsum of the hand. Anatomic variations of the extrinsic extensor tendons are frequent and knowledge is important when assessing the traumatized or diseased hand.