Muscles of the thumb

Muscles of the thumb

The thumb is a highly specialized digit of the hand that plays a crucial role in grip and dexterity. The muscles of the thumb are divided into two main groups: the extrinsic muscles and the intrinsic muscles.

Extrinsic Muscles

The extrinsic muscles of the thumb originate in the forearm and insert into the thumb. These muscles include:

• Flexor pollicis longus: This muscle originates from the radius and the interosseous membrane and inserts into the base of the distal phalanx of the thumb. It is responsible for flexing the thumb at the interphalangeal joint.
• Extensor pollicis longus: Originating from the ulna and the interosseous membrane, this muscle extends the thumb at the interphalangeal joint.
• Extensor pollicis brevis: This muscle originates from the radius and the interosseous membrane and extends the thumb at the metacarpophalangeal joint.
• Abductor pollicis longus: Originating from the ulna, radius, and interosseous membrane, this muscle abducts the thumb at the carpometacarpal joint.

Intrinsic Muscles

The intrinsic muscles of the thumb are located within the hand itself. These muscles include:

• Abductor pollicis brevis: This muscle originates from the scaphoid and trapezium bones and inserts into the lateral side of the base of the proximal phalanx of the thumb. It is responsible for abducting the thumb.
• Flexor pollicis brevis: Originating from the trapezium, trapezoid, and capitate bones, this muscle flexes the thumb at the metacarpophalangeal joint.
• Opponens pollicis: This muscle originates from the trapezium and inserts into the lateral side of the first metacarpal bone. It is responsible for opposition of the thumb.
• Adductor pollicis: This muscle has two heads (oblique and transverse) originating from the capitate and the third metacarpal bone, respectively. It inserts into the medial side of the base of the proximal phalanx of the thumb and is responsible for adducting the thumb.

Function

The muscles of the thumb work together to perform a variety of movements, including flexion, extension, abduction, adduction, and opposition. These movements are essential for tasks such as grasping objects, writing, and manipulating small items.

Clinical Significance

Injuries or conditions affecting the muscles of the thumb can significantly impair hand function. Common conditions include De Quervain's tenosynovitis, trigger thumb, and thumb arthritis. Proper diagnosis and treatment are essential for restoring thumb function and alleviating pain.

See Also

• Hand
• Finger
• Carpal tunnel syndrome
• Tendon
• Ligament