Thumb

The thumb is the first digit of the hand, set apart and opposable to the other four digits of the human hand. It is also known as the pollex. The thumb plays a crucial role in a wide range of tasks, including gripping, pinching, and manipulating objects in a precise manner.

Anatomy

The thumb has two phalanges, a proximal and a distal, compared to three in all of the other fingers. It also has two flexor muscles, rather than three. The thumb also includes a metacarpal bone, the first metacarpal, which is located within the hand.

Bones

The thumb consists of a proximal and distal phalanx, and a metacarpal bone. The proximal phalanx is connected to the metacarpal bone by the metacarpophalangeal joint (MCP joint), and the distal phalanx is connected to the proximal phalanx by the interphalangeal joint (IP joint).

Muscles

The thumb has nine muscles, divided into a flexor group and an extensor group. The flexor group consists of the flexor pollicis longus muscle, the flexor pollicis brevis muscle, and the opponens pollicis muscle. The extensor group consists of the extensor pollicis longus muscle, the extensor pollicis brevis muscle, and the abductor pollicis longus muscle.

Function

The thumb is capable of a wide range of motion, thanks to its unique joint structure. This allows for the thumb to oppose, or come into contact with, the other four fingers, which is crucial for tasks such as gripping and manipulating objects.

Clinical significance

Injuries to the thumb can significantly impact hand function. Common injuries include fractures, sprains, and dislocations. Conditions such as arthritis can also affect the thumb, causing pain and limiting movement.

See also

• Finger
• Hand
• Opposable thumb

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