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The Dorsal Interossei Manus muscles are members of the Central Compartment Group of intrinsic muscles of the hand, composed of the:
- Adductor pollicis
- Lumbricals manus
- Palmar interossei
- Dorsal interossei manus
There are four Dorsal Interossei Manus muscles, named #1, #2, #3, and #4 from radial/lateral (thumb side) to ulnar/medial (little finger side).
- The dorsal interossei manus attach from the metacarpals to the proximal phalanges of fingers #2, #3, and #4 on the side of the phalanx that is away from the “middle-finger side.”
- Dorsal interosseus manus #1 attaches onto figure #2 (index finger).
- Dorsal interosseus manus #2 attaches onto figure #3 (middle finger).
- Dorsal interosseus manus #3 also attaches onto figure #3 (middle finger).
- Dorsal interosseus manus #4 attaches onto figure #4 (ring finger).
- The dorsal interossei manus also attach distally into the dorsal digital expansion.
- Abducts fingers #2, and #4 at the metacarpophalangeal joints.
- Radially abducts finger #3 at the metacarpophalangeal joint.
- Ulnarly abducts finger #3 at the metacarpophalangeal joint.
- Flexes fingers #2, #3, #4 at the metacarpophalangeal joints.
- Extends fingers #2, #3, #4 at the proximal and distal interphalangeal joints.
- Because the dorsal interossei manus attach onto their respective fingers on the side that is away from the “middle-finger side,” they bring those fingers away from the reference line for abduction/adduction of the fingers, which is an imaginary line through the middle of the middle finger when the middle finger is in anatomic position; this is defined as abduction (or radial abduction or ulnar abduction).
- There is a mnemonic for remembering the abductors/adductors of the fingers: DAB PAD – Dorsals ABduct Palmars ADduct.