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Interossei
- First dorsal interossei has two muscle bellies:
- Ulnar belly flexes, abducts, and pronates the index MCP joint
- Radial muscle belly helps to radially adduct the thumb MCP joint
- Together muscle bellies help extend the index PIPJ and DIPJ
- Primary MCP joint flexor
- The palmar and dorsal interossei insert into the extensor mechanism
- All interossei are innervated by the ulnar nerve
- All dorsal interossei have two muscle bellies. They insert into bone (proximal phalanx) and soft tissue (extensor mechanism).
- The first dorsal interossei is a little different from the other three because the insertion is mostly bone for both bellies
- In about 3% of cases the first dorsal interosseous is innervated by the median nerve
Thenar Muscles
A good way to remember the thenar muscles is that they spell OAF
O=Opponens pollicis
A=Abductor pollicis brevis
F=Flexor pollicis brevis
