The flexor pollicis brevis is one of the intrinsic muscles of the hand within the thenar group.
The intrinsic muscles of the hand are involved with precision movements and consist of the following muscles:
- Thenar muscles: flexor pollicis brevis, abductor pollics brevis, opponens pollicis
- Hypothenar muscles: abductor digiti minimi, flexor digiti minimi brevis, opponens digiti minimi
- Interosseus muscles
- Other: palmaris brevis, adductor pollicis
The intrinsic muscles of the hand are innervated by the deep branch of the ulnar nerve, except the tehnar muscles and the lateral two lumbricals. A mnemonic for remembering this is Meat LOAF, Meat = Median nerve innervates the Lateral lumbricals, Opponens pollicis, Abductor pollicis brevis and Flexor pollicis brevis
- Superficial head: distal border of the flexor retinaculum, tubercule of trapezium
- Deep head: trapezoid and capitate bones, palmar ligaments of the distal carpal bones
- Radial aspect of the base of the proximal phalanx of the thumb
- Flexion at the metacarpohalangeal joint of the thumb
- Deep head: Deep branch of ulnar nerve
- Superficial head: median nerve
At the wrist, the ulnar nerve divides into superficial and deep terminal branches.
Proximal to the wrist, the ulnar nerve gives off a dorsal branch, which itself divides into 2-3 dorsal digital nerves suppling the little finger and medial side of the ring finger.
Superficial terminal branch
- Supplies palmaris brevis and the medial palmar skin
- Divides into 2 palmar digital nerves
Deep terminal branch
- Passes laterally across the hand, accompanies the deep branch of the ulnar artery
- Passes between abductor digiti minimi and flexor digiti minimi, perforates opponens digiti minimi
- Innervates hypothenar muscles at its origin, and as it passes laterally supplies the interossei, 3rd and 4th lumbricals and ends by supplying adductor pollicis and the deep part of flexor pollicis brevis
- Superficial palmar arch of the radial artery
- Branches from princeps pollicis and radialis indicis