Hand and Finger Movements
Movements at the radiocarpal and hand joints are produced by the coordinated contraction of strictly defined muscle groups. The loss of function of any single group makes specific clinical tests impossible.
- Radial deviation of the wrist (abduction toward the radius) is produced by the contraction of the m. extensor carpi radialis longus and brevis, along with the m. abductor pollicis longus and m. extensor pollicis brevis.
- Ulnar deviation requires the synchronized action of the m. extensor carpi ulnaris and m. flexor carpi ulnaris.
- Opposition of the thumb is impossible without the m. opponens pollicis. The short flexor and short abductor muscles also assist in this movement.
- Reposition of the thumb is performed by the m. abductor pollicis longus paired with the m. extensor pollicis longus and brevis.
To evaluate the function of the deep branch of the ulnar nerve, Froment's sign (the key pinch test) is used. A lesion of this nerve causes weakness of the m. adductor pollicis. It is also important to remember that the index finger and little finger have their own independent 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 injuries.
- Lateral boundary is formed by the tendons of the first dorsal compartment: m. abductor pollicis longus and m. extensor pollicis brevis.
- Medial boundary is formed by the tendon of the m. extensor pollicis longus.
- Floor is formed by the scaphoid (os scaphoideum) and trapezium bones.
The radial artery (a. radialis) traverses this area, allowing for easy pulse palpation. If a patient experiences localized pain upon palpation of the floor of the snuffbox, it is a classic sign of a scaphoid fracture.
The first extensor compartment is frequently subject to inflammation, leading to tenosynovitis known as De Quervain disease. Finkelstein's test is used in clinical practice to confirm this diagnosis (pain provocation with specific ulnar deviation of the wrist).
Cubital Fossa: Boundaries and Contents
The anterior region of the elbow joint is well visualized after the removal of skin and superficial fascia. Knowledge of its boundaries is essential for venipuncture and accessing the neurovascular bundle.
Boundaries of the cubital fossa:
- Laterally, it is bounded by the brachioradialis muscle (m. brachioradialis).
- Medially, it is bounded by the pronator teres muscle (m. pronator teres).
- The floor (base) is formed by the brachialis muscle (m. brachialis) and supinator muscle (m. supinator).
- The 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
Injuries to major nerve trunks and the tendon apparatus lead to characteristic, 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" (mano simia) deformity forms due to the loss of opposition.
- Trauma to the ulnar nerve (n. ulnaris) results in a "claw hand" (main en griffe) deformity because the function of the 3rd and 4th lumbricals and interosseous muscles is impaired.
- Damage to the deep branch of the radial nerve (n. radialis) manifests as "wrist drop" due to paralysis of the extensor muscles.
Additionally, isolated ruptures of the dorsal digital expansion lead to characteristic deformities: mallet finger and boutonnière deformity.