Wrist and finger movements
Movements at the wrist joint and hand joints are ensured by the coordinated contraction of strictly defined muscle groups. Failure of any one of them makes it impossible to perform specific tests.
- Radial deviation of the hand (abduction towards the radius) occurs upon contraction of the extensor carpi radialis longus and brevis (m. extensor carpi radialis longus et brevis), as well as the abductor pollicis longus and extensor pollicis brevis (m. abductor pollicis longus et m. extensor pollicis brevis).
- Ulnar deviation (adduction towards the ulna) requires synchronous action of the extensor carpi ulnaris and flexor carpi ulnaris (m. extensor carpi ulnaris et m. flexor carpi ulnaris).
- Opposition of the thumb is impossible without the opponens pollicis (m. opponens pollicis). The flexor pollicis brevis and abductor pollicis brevis also participate in this movement.
- Reposition of the thumb is carried out by the abductor pollicis longus coupled with the extensor pollicis longus and brevis (m. abductor pollicis longus + m. extensor pollicis longus/brevis).
To assess the function of the deep branch of the ulnar nerve, Froment's sign (the key pinch test) is used. In lesions of this nerve, weakness of the adductor pollicis muscle (m. adductor pollicis) occurs. It is also important to remember that the index finger and little finger have their own extensors: m. extensor indicis and m. extensor digiti minimi, respectively.
Anatomical snuffbox
This topographic area on the dorsum of the hand is of critical clinical importance in diagnosing wrist trauma.
- Lateral boundary is formed by the tendons of the first compartment: m. abductor pollicis longus and m. extensor pollicis brevis.
- Medial boundary is represented by the tendon of m. extensor pollicis longus.
- Floor is formed by the scaphoid (os scaphoideum) and trapezium bones.
The radial artery (a. radialis) passes through this region, allowing easy palpation of the pulse. If the patient experiences localized pain upon pressure on the floor of the snuffbox, this is a classic sign of a scaphoid fracture.
The first extensor compartment is frequently subject to inflammation, developing tenosynovitis known as de Quervain's disease. To confirm this diagnosis in clinical practice, Finkelstein's test is used (eliciting pain upon specific ulnar deviation of the wrist).
Cubital fossa: boundaries and contents
The anterior region of the elbow joint is well visualized after removal of the skin and superficial fascia. Knowledge of its boundaries is essential for venipuncture and access to the neurovascular bundle.
Boundaries of the cubital fossa:
- Laterally is the brachioradialis muscle (m. brachioradialis).
- Medially the fossa is bounded by the pronator teres (m. pronator teres).
- Floor (base) is lined by the brachialis (m. brachialis) and supinator (m. supinator).
- Roof consists of skin, superficial fascia (containing the median cubital vein — v. mediana cubiti), the bicipital aponeurosis (bicipital aponeurosis), and deep fascia.
Deformities in nerve and tendon lesions
Damage to major nerve trunks and the tendinous apparatus leads to typical, easily recognizable pathological hand postures:
- Lesion of the median nerve (n. medianus) in the distal forearm/wrist causes atrophy of the thenar eminence. An "ape hand" deformity develops due to the loss of opposition.
- Trauma to the ulnar nerve (n. ulnaris) leads to a "claw hand" deformity due to impairment of the third and fourth lumbricals and the interosseous muscles.
- Damage to the deep branch of the radial nerve (n. radialis) manifests as a "wrist drop" symptom due to paralysis of the extensor muscles.
Additionally, isolated ruptures of the dorsal digital expansion at the finger level result in characteristic deformities: mallet finger and boutonnière deformity.
Briefly: answers to topical questions
Which nerves innervate the thenar muscles of the hand?
The thenar muscles are innervated by branches of the median and ulnar nerves. Distribution of innervation:
- Median nerve (n. medianus) — innervates most thenar muscles; the motor branch originates in the "forbidden zone" at the border of the upper and middle thirds of the plica thenaris.
- Ulnar nerve (n. ulnaris) — its deep branch (ramus profundus n. ulnaris) innervates the adductor pollicis and the deep head of the flexor pollicis brevis.
To memorize the boundaries of the cubital fossa: "The pronator faces inward (medially), and the brachioradialis faces outward (laterally)" — they form a V shape, the floor of which is formed by the brachialis and supinator.
Class and exam questions
How to test the function of the adductor pollicis muscle?
Froment's sign is used for this. The patient is asked to hold a flat object (key pinch) between the thumb and index finger. In muscle weakness, the test reveals pathology of the deep branch of the ulnar nerve.
What does pain in the anatomical snuffbox region indicate?
Pain upon palpation of the floor of this area most commonly indicates a scaphoid fracture (os scaphoideum).
What is Finkelstein's test used for?
The test detects tenosynovitis of the first extensor compartment (de Quervain's disease), through which the tendons of the m. abductor pollicis longus and m. extensor pollicis brevis pass.
What else to study on this topic
- Anatomy of the dorsal digital expansion
- Course and branching of the radial artery (a. radialis) in the hand
- Topography and branches of the deep branch of the ulnar nerve
- Functions and innervation of the lumbricals and interosseous muscles of the hand
- Topography of the first extensor compartment of the wrist
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