Nerves Flashcards
Median nerve lesions at elbow
Damaged at the Elbow
Mechanism of injury: Supracondylar fracture of the humerus.
Motor functions: The flexors and pronators in the forearm are paralysed, with the exception of the flexor carpi ulnaris and medial half of flexor digitorum profundus. The forearm constantly supinated, and wrist flexion is weak (often accompanied by adduction, because of the pull of the flexor carpi ulnaris).
Flexion at the thumb is also prevented, as both the longus and brevis muscles are paralysed.
The lateral two lumbricals are affected, and the patient will not be able to flex at the MCP joints or extend at IP joints of the index and middle fingers.
Sensory functions: Lack of sensation over the areas that the median nerve innervates.
Characteristic signs: The thenar eminence is wasted, due to atrophy of the thenar muscles. If patient tries to make a fist, only the little and ring fingers can flex completely. This results in a characteristic shape of the hand, known as hand of benediction.
Median nerve lesions at wrist
Mechanism of injury: Lacerations just proximal to the flexor retinaculum.
Motor functions: Thenar muscles paralysed, as are the lateral two lumbricals. This affects opposition of the thumb and flexion of the index and middle fingers.
Sensory functions: Same as an injury at the elbow.
Characteristic signs: The hand is held in the same position as damage at the elbow, but the forearm is unaffected (not supinated or adducted, wrist flexion likely unaffected, depending on the location of the lesion).
Ulnar nerve lesions at elbow
Mechanism of injury: Trauma at the level of the medial epicondyle (e.g. isolated medial epicondyle fracture, supracondylar fracture). It can also be compressed in the cubital tunnel.
Motor functions:
All the muscles of innervated by the ulnar nerve are affected.
Flexion of the wrist can still occur, but is accompanied by abduction (due to paralysis of flexor carpi ulnaris and medial half of flexor digitorum profundus).
Abduction and adduction of the fingers cannot occur (due to paralysis of the interossei).
Movement of the 4th and 5th digits is impaired (due to paralysis of the medial two lumbricals and hypothenar muscles).
Adduction of the thumb is impaired, and the patient will have a positive Froment’s sign (due to paralysis of adductor pollicis).
Sensory functions: All sensory branches are affected, so there will be a loss of sensation over the areas that the ulnar nerve innervates.
Characteristic signs: Patient cannot grip paper placed between fingers, positive Froment’s sign, wasting of hypothenar eminence.
Ulnar nerve lesions at wrist
Mechanism of injury: Lacerations to the anterior wrist.
Motor functions:
Only the intrinsic muscles of the hand are affected.
Abduction and adduction of the fingers cannot occur (due to paralysis of the interossei).
Movement of the 4th and 5th digits is impaired (due to paralysis of the medial two lumbricals and hypothenar muscles).
Adduction of the thumb is impaired, and the patient will have a positive Froment’s sign (due to paralysis of adductor pollicis).
Sensory functions: The palmar branch and superficial branch are usually severed, but the dorsal branch is unaffected. This results in sensory loss over palmar side of medial one and a half fingers only.
Characteristic signs: Patient cannot grip paper placed between fingers, positive Froment’s sign, wasting of hypothenar eminence.
Radial nerve lesions at axilla
The radial nerve can be damaged in the axilla region by a dislocation at the shoulder joint, or a fracture of the proximal humerus. Occasionally, it is injured via excessive pressure on the nerve within the axilla (e.g. a badly fitting crutch).
Motor functions – the triceps brachii and muscles in posterior compartment are affected. The patient is unable to extend at the forearm, wrist and fingers. Unopposed flexion of wrist occurs, known as wrist-drop.
Sensory functions – all four cutaneous branches of the radial nerve are affected. There will be a loss of sensation over the lateral and posterior arm, posterior forearm, and dorsal surface of the lateral three and a half digits.
Radial nerve lesions in radial groove
The radial nerve is tightly bound within the spiral groove of the humerus. Thus, it is most susceptible to damage with a fracture of the humeral shaft.
Motor functions
The triceps brachii may be weakened, but is not paralysed (branches to the long and lateral heads of the triceps arise proximal to the radial groove).
Muscles of the posterior forearm are affected. The patient is unable to extend at the wrist and fingers. Unopposed flexion of wrist occurs, known as wrist-drop.
Sensory functions – the cutaneous branches to the arm and forearm have already arisen. The superficial branch of the radial nerve will be damaged, resulting in sensory loss to the dorsal surface of the lateral three and half digits and the associated area on the dorsum of the hand.
