Intrinsic Muscles of the Hand
The intrinsic muscles of the hand include the thenar muscles, hypothenar muscles, lumbrical muscles, and interosseous muscles, which collectively provide the foundation for fine motor control and specialized movements of the hand.
Anatomical Classification
Thenar Muscles
- Abductor pollicis brevis
- Opponens pollicis
- Flexor pollicis brevis
- Adductor pollicis
Hypothenar Muscles
- Abductor digiti minimi
- Flexor digiti minimi brevis
- Opponens digiti minimi
Midpalmar Muscles
- Lumbricals (4 muscles)
- Dorsal interossei (4 muscles)
- Palmar interossei (3 muscles)
Functional Anatomy
Thenar Muscles
- Form the thenar eminence (thumb base)
- Function: Control thumb movement and opposition
- The deep thenar muscles (opponens pollicis, flexor pollicis brevis, and adductor pollicis) actually form a single muscle mass without clear borders 1
- Innervation: Primarily median nerve, with adductor pollicis and deep head of flexor pollicis brevis supplied by the ulnar nerve
Hypothenar Muscles
- Form the hypothenar eminence (base of little finger)
- Function: Control movement of the little finger
- Innervation: Ulnar nerve
Lumbrical Muscles
- Four small worm-like muscles
- Origin: Tendons of flexor digitorum profundus
- Insertion: Extensor expansion (dorsal aponeurosis)
- Function: Flex metacarpophalangeal joints while extending interphalangeal joints
- Architectural design shows extremely high fiber length/muscle length ratio, indicating specialization for high excursion 2
- Innervation: Median nerve (1st and 2nd lumbricals) and ulnar nerve (3rd and 4th lumbricals)
Interosseous Muscles
- Seven muscles arranged in two groups:
- Dorsal interossei (4 muscles): Abduct fingers from midline
- Palmar interossei (3 muscles): Adduct fingers toward midline
- Function: Control finger abduction/adduction, flex metacarpophalangeal joints, and extend interphalangeal joints
- The interosseous muscles can be considered the cornerstone of hand function, providing a foundation for all intrinsic and extrinsic hand movements 3
- Have relatively high physiological cross-sectional areas with low fiber length/muscle length ratios, suggesting adaptation for high force production and low excursion 2
- Innervation: Ulnar nerve exclusively
Clinical Significance
- The intrinsic muscles work in coordination with extrinsic muscles via the dorsal aponeurosis to control precise finger movements 4
- The first dorsal interosseous and adductor pollicis have physiologic cross-sectional areas comparable to extrinsic muscles, indicating their importance in power grip and pinch 2
- MRI is useful for evaluating intrinsic hand muscle abnormalities and correlates well with clinical findings 5
- Dysfunction of intrinsic muscles can lead to significant impairment in hand function, particularly affecting grip strength and fine motor skills
Anatomical Relationships
- The interosseous muscles are arranged in dorsal and palmar layers between the metacarpal bones
- Lumbricals run along the radial side of each finger
- The thenar and hypothenar muscles form the muscular prominences at the base of the thumb and little finger, respectively
- All intrinsic muscles work together with the extrinsic muscles to provide the complex movements required for hand function
Understanding the intrinsic muscles of the hand is essential for diagnosing and treating hand disorders, as they form the foundation for both power and precision movements.