The wrist connects the hand to the forearm and is essential for hand movements such as waving or writing. The wrist joint, or radiocarpal joint, facilitates flexion/extension as well as abduction (movement away from the body) and adduction (movement toward the body) of the wrist.
These movements are made possible by the forearm muscles that run across the forearm and attach with their tendons to different parts of the hand.
The forearm muscles that move the hand are grouped as follows:
- Flexor muscles which are organized into a superficial, intermediate and deep layer and primarily flex the hand and pronate the forearm
- Extensor muscles which are organized into a superficial and deep layer and primarily extend the hand and supinate the forearm
All of these muscles are located at the forearm and span across the wrist to move the hand.
However, the hand also has intrinsic muscles that allow movements of the fingers as well as fine adjustments for complex and more precise tasks.
The hand muscles are organized into five groups:
- Thenar muscles: Abductor pollicis brevis, adductor pollicis, flexor pollicis brevis and opponens pollicis. The thenar muscles are located at the palmar side of the base of the thumb and allow flexion, abduction, adduction and opposition of the thumb.
- Hypothenar muscles: Abductor digiti minimi, flexor digiti minimi, opponens digiti minimi and palmaris brevis. The hypothenar muscles make up the fleshy part of the palmar base of the 5th finger (hypothenar eminence) and allow flexion, abduction, lateral rotation and opposition of the 5th finger.
- Lumbricals are positioned between the metacarpal bones and provide flexion in the metacarpophalangeal joint and extension in the interphalangeal joints.
- Palmar interossei lie between the metacarpal bones and attach to the 2nd, 4th and 5th finger to provide finger adduction and support both flexion and extension.
- Dorsal interossei are located on the adjacent sides of the metacarpal bones 1-4 to abduct the digits 2-4 and assist with flexion and extension.
Discover the anatomy of these muscles with interactive diagrams below. Learn even faster with this forearm muscle revision guide.