The muscles of the hand are responsible for the hand and fingers’ movement. The muscles of the hand are redivided into two groups: the extrinsic muscles and the intrinsic muscle groups. The extrinsic groups are the long flexors and extensors muscles. They are termed extrinsic muscles because the muscle belly is positioned on the forearm. The intrinsic muscles located within the hand itself. The hand muscles are innervated by the radial, median, and the ulnar nerves.
Thenar Muscles
The three thenar muscles are the short muscles positioned at the base of the thumb. The thenar hand muscles are liable for the fine movements of the thumb.
- Abductor pollicis brevis
- Flexor pollicis brevis
- Opponens pollicis
Abductor pollicis brevis: The abductor pollicis brevis is a hand muscle that works as an abductor of the thumb.
- Origin:
- Tubercle of scaphoid, trapezium, flexor retinaculum.
- Insertion:
- The base of proximal phalanx of the thumb.
- Action:
- Abduction of thumb.
- Nerve Supply:
- Median nerve.
Flexor pollicis brevis: The flexor pollicis brevis flexes the thumb. It has both a superficial part and a deep part.
- Origin
- Flexor retinaculum, trapezoid and capitate bones
- Insertion:
- The base of the proximal phalanx of the thumb.
- Action:
- Flexes metacarpophalangeal joint of the thumb.
- Nerve Supply:
- Median nerve. The deep head of the flexor pollicis brevis is supplied by the deep branch of the ulnar nerve.
Opponens pollicis brevis: The opponens pollicis is a triangular small muscle in the hand, which act to oppose the thumb. It is lying deep to the abductor pollicis brevis and lateral to the flexor pollicis brevis muscles.
- Origin:
- Flexor retinaculum.
- Insertion:
- The shaft of the metacarpal bone of the thumb.
- Action:
- Pulls thumb medially and forward across the palm.
- Nerve Supply:
- Median nerve.
Hypothenar Muscles
The hypothenar muscles are of four short muscles located at the ulnar side of the palm. The hypothenar hand muscles control the motion of the little finger.
- Palmaris brevis
- Abductor digiti minimi
- Flexor digiti minimi
- Opponens digiti minimi
Abductor digiti minimi: The abductor digiti minimi muscle situated on the ulnar border of the palm of the hand. Its chief role is to pull the little finger apart from the other fingers.
- Origin:
- Pisiform bone.
- Insertion:
- Base of proximal phalanx of the little finger.
- Action:
- Abducts the little finger.
- Nerve Supply:
- Ulnar nerve.
Flexor digiti minimi: The flexor digiti minimi brevis flexes the little finger at the metacarpophalangeal joint. It is located lateral to the abductor digiti minimi during the hand is in anatomical position.
- Origin:
- Flexor retinaculum.
- Insertion:
- The base of proximal phalanx of the little finger.
- Action:
- Flexes the MCP joint of the little finger.
- Nerve Supply:
- Ulnar nerve.
Opponens digiti minimi: The opponens digiti minimi is a triangular form and placed immediately under the palmaris brevis, abductor digiti minimi and the flexor digiti minimi brevis. It is one of the muscles that control the little finger.
- Origin:
- Flexor retinaculum
- Insertion:
- Medial border of the 5th metacarpal bone
- Action:
- Pulls 5th metacarpal forward as in cupping the palm
- Nerve Supply:
- Ulnar nerve.
Palmaris Brevis: Palmaris Brevis is small, thin muscle, found superficially in the subcutaneous tissue of the hypothenar eminence.
- Origin:
- Originates from the palmar aponeurosis and the flexor retinaculum.
- Insertion:
- Palmaris Brevis inserted into the dermis of the skin on the medial margin of the hand.
- Function:
- Ridges the skin of the hypothenar eminence and develops the curvature of the hand, enhancing the handgrip.
- Nerve Supply:
- Ulnar nerve
Lumbricals Muscles
The four lumbricals hand muscles in the hand, each is associated with the finger movement. Lumbricals muscles are very crucial to finger movement, joining the extensor tendons to the flexor tendons.
- Origin:
- 1st – lateral side of the tendon of 2nd digit
- 2nd – lateral side of the tendon of the 3rd digit
- 3rd – adjacent sides of the tendon of 3rd and 4th digits
- 4th –adjacent sides of the tendon of 4th and 5th digits
- Insertion:
- All are inserted via extensor expansion into the dorsum of bases of distal phalanges.
- Function:
- The lumbrical muscles flex at the MCP joint and extend at the interphalangeal (IP) joints of the individual finger.
- Nerve Supply:
- The ulnar nerve supplies the medial two lumbricals (little and ring fingers). The median nerve supplies the lateral two lumbricals (index and middle fingers).
Interossei Muscles
The interosseous hand muscles are found near the metacarpal bones which serve to control the fingers movement. The interosseous muscles lie in the interosseous spaces within the metacarpal bones. They are voluntary muscles. They are usually divided into two groups-palmar and dorsal.
Palmar Interossei: Palmar interossei are four small, unipennate muscles in the hand that lie within the metacarpal bones and are connected to the index, ring, and little fingers. The Palmar interossei are smaller than the dorsal interossei muscles of the hand.
- Origin:
- 1st: medial side of the base of 1st metacarpal
- 2nd: medial side of 2nd metacarpal
- 3rd: lateral side of 4th metacarpal
- 4th: lateral side of 5th metacarpal
- Insertion:
- 1st – medial side of the base of proximal phalanx of thumb or 1st digit
- 2nd, 3rd, 4th – via extensor expansion into the dorsum of bases of distal phalanges of 2nd, 4th, and 5th digits.
- Function:
- Abduct the fingers at the MCP joint.
- Nerve Supply:
- Ulnar nerve.
Dorsal Interossei: Dorsal interossei are four muscles in the back of the hand that work to abduct the index, middle, and ring fingers apart from hand’s midline and assists in flexion at the metacarpophalangeal joints and extension through the interphalangeal joints of the index, middle and the ring fingers.
- Origin:
- 1st – adjacent sides of 1st and 2nd metacarpals
- 2nd – adjacent sides of 2nd and 3rd metacarpals
- 3rd – adjacent sides of 3rd and 4th metacarpals
- 4th – adjacent sides of 4th and 5th metacarpals
- Insertion :
- All are inserted via extensor expansion into the dorsum of bases of distal phalanges of 2nd, 3rd, and 4th digits
- Function:
- Adducts the fingers at the MCP joint.
- Nerve Supply:
- Ulnar nerve.
One adductor of thumb muscles is adductor pollicis.
Adductor pollicis:
- Origin:
- Oblique head: bases of 2nd -3rd metacarpals
- Transverse head: shaft of 3rd metacarpal
- Insertion:
- The base of the proximal phalanx of the thumb.
- Action:
- Adduction of thumb.
- Nerve Supply:
- Ulnar nerve.
Common Hand Conditions: Rheumatoid Arthritis, De Quervain syndrome, Raynaud syndrome, Trigger finger, Finger clubbing, Complex regional pain syndrome, Carpal Tunnel Syndrome, and certain birth defects.