Thenar and Adductor Hand Muscles

Bones

Radius
Ulna
Hand

Key Points:

• The muscles of the thenar and adductor compartments of the hand act on digit 1, the thumb.
• Adduction of the digits moves them towards the midline (digit 3).
• Abduction of the digits moves them away from it.

Thenar Compartment

• Each thenar muscle originates on the flexor retinaculum and trapezium.

Opponens pollicis

• Inserts on the lateral side of the first metacarpal
• Provides thumb opposition.

Flexor pollicis brevis

• Inserts on base of proximal phalanx of the thumb
• Flexes the thumb.

Abductor pollicis brevis

• In addition to arising from the flexor retinaculum and trapezium, also originates on the scaphoid.
• Inserts on the lateral side of the base of the proximal phalanx,
• Abducts the thumb away from the plane of the palm.
• Abductor pollicis brevis also assists opponens pollicis in the early stages of opposition.

Adductor compartment

Adductor pollicis, which has two heads:

• Oblique head originates on the bases of the 2nd and 3rd metacarpals and the capitate
• Oblique head inserts on the medial side of the base of the proximal phalanx of the thumb;
• Transverse head originates on the anterior surface of the third metacarpal;
• Transverse head inserts with the oblique head on digit 1.
• Together, the oblique and transverse heads adduct the thumb.