Radial nerve entrapment is relatively common in clinical practice and is highly susceptible to occur under external compression, injury, tumor, scarring, etc. due to the anatomic structural characteristics of radial nerve travel.
First, there are three common sites of radial nerve compression in the upper arm.
The first site is at the axillary arm angle: the radial nerve is located just medial to the humeral neck and the upper end of the humeral stem at this site. When resting, the axillary part is placed on the back of the chair and is prone to occur, or inappropriate use of crutches walking, all the weight through the axillary part pressed on the crossbar of the crutches, it is easy to happen radial nerve compression and injury.
The second site is on the lateral side of the upper arm, the radial nerve sulcus: the radial nerve turns from the posterior to the lateral part, in this section the radial nerve is located on the lateral side of the humerus close to the humerus, when lying on the side the ipsilateral upper limb is pressed under the body is easy to damage the radial nerve, the author almost every year to diagnose 7 to 8 such patients. This is especially true on the weekends when one is lying on one’s side after a drunken meal, pressing one’s arm underneath one’s body to sleep, and upon awakening one may not be able to extend the wrist and fingers, hence the Western term “weekend syndrome”, which, fortunately, often recovers on its own within 2-4 weeks.
The third site is where the radial nerve penetrates the lateral interval: this site is located about 10 cm from the lateral epicondyle of the humerus, where the radial nerve is often wrapped by the crossed tendon muscles, which means that the radial nerve is relatively fixed here and is in a ring of tendon tissue that can easily suffer compression, especially after strenuous activity of the upper extremity, which can easily damage the nerve.
The disease has a tendency to recover on its own. If it does not recover after 2-3 months of clinical observation, surgical treatment may be considered.
In addition, the growth of bone reed after internal fixation of humeral stem fracture and the scar healing of surrounding soft tissue can also cause radial nerve entrapment.
Diagnostic points: medical history, clinical physical examination, electromyography.
Elbow radial nerve entrapment
Elbow joint dislocation, fracture, hematoma, tumor, etc. may also cause radial nerve entrapment at the elbow.
The radial nerve is located between the biceps, brachialis and brachioradialis muscles and continues down to about 3-5 cm above the lateral epicondyle of the humerus to innervate the brachioradialis and radial extensor carpi radialis longus muscle branches. In anatomic studies, it was found that 20% of cadaveric radial nerves emanate at this level to innervate the brachialis muscle, and then the radial nerve bifurcates. The branch of the radial nerve that innervates the radial extensor carpi radialis longus muscle may originate from the main radial nerve trunk or from the superficial branch of the radial nerve.
Diagnostic points
Injury to the supra-elbow radial nerve results in drooping wrist and thumb deformity, while injury to the inferior elbow results in normal function of the brachioradialis and radial longissimus carpi radialis muscles. Moreover, there are differences of opinion about the superficial branch of radial nerve being a sensory nerve.
Third, the deep branch of the radial nerve – posterior interosseous nerve entrapment
The so-called posterior rotator canal, that is, the deep branch of the radial nerve (posterior interosseous nerve) crosses a muscular gap in the posterior rotator muscle, where the fibers of the posterior rotator muscle are aligned from the proximal radial side to the distal ulnar side, and the muscle fibers around the nerve are wrapped around the nerve in a semi-loop.
This arch, may cause interosseous posterior nerve entrapment here. It may be related to repeated forearm wrist movements. The radial extensor carpi radialis shortis, on the other hand, often has a sickle fiber tendinous rim that is capable of compressing the interosseous dorsal nerve before it enters the Frohse arch, or it may be superficial to the Frohse arch, exacerbating the compression of the interosseous dorsal nerve by this arch.
The superficial branch innervates the ulnar carpal extensors, the common extensor digitorum profundus, and the intrinsic extensor digitorum minor. The deeper branch sends out the long thumb extensor, the long thumb extensor, the short thumb extensor, and the intrinsic extensor of the index finger, while the dorsal interosseous nerve, after sending out the last branch, is the terminal branch, which travels close to the interosseous membrane and travels in the deepest radial and deepest layer of the fourth extensor sheath, crossing the radial carpal joint at the dorsal aspect of the navicular-lunar capsule and the capitellar-lunar capsule, which is slightly expanded and sends out several fine branches to both sides, deep and distal, and disappears in these fibrous tissues.
The terminal branch of the interosseous dorsal nerve in the fourth extensor sheath is covered by a layer of fascial tissue and is often not visible without separation. Interosseous dorsal nerve closure can be used to determine if wrist disease is due to irritation of the terminal branch, and interosseous dorsal nerve severance at the wrist can also be used to treat wrist pain.
Four, the superficial branch of the radial nerve in the forearm is stuck
In essence, the superficial branch of the radial nerve in the forearm is not uncommon, as long as the possibility of the patient is often thought of clinically, and the presence of the disease can often be detected by routine examination of sensory function in patients with manual atrophy. It should be noted that the superficial branch of the radial nerve has multiple sensory branches innervating deeper tissues on the dorsal side of the wrist and the dorsal side of the palm. This can also cause distension and discomfort in the wrist.
Anatomic points
The superficial branch of the radial nerve branches off from the main radial nerve trunk and is located deep down in the brachioradialis muscle. The nerve penetrates from the deep fascial layer to the subcutis at the junction of the middle and lower 1/3 of the forearm between the sharp tendon gap at the junction of the radial extensor carpi radialis longus and the tendon belly of the brachioradialis muscle. The dorsal fascia tissue of the two tendons at the site of this nerve penetration is tightly wrapped together.
Diagnostic points
When the forearm is rotated forward, the radial extensor carpi radialis longus approaches the brachioradialis tendon and even crosses to the superficial layer of the brachioradialis tendon, which makes the superficial branch of the radial nerve located between the two tendons vulnerable to compression or aggravates the original compression, especially when the wrist joint is also palmarly flexed when the superficial branch of the radial nerve is stretched tightly and then squeezed, which may produce more serious symptoms. When the wrist joint is radially deviated or dorsally extended, the superficial branch of the radial nerve is relaxed, while when it is ulnarly deviated, it is stretched tightly. When the hand is repeatedly knocked with a hammer, the superficial branch of the radial nerve is repeatedly stretched, and if one is engaged in such an occupation, one is prone to superficial radial nerve syndrome.
When this syndrome is suspected, making the patient bend the wrist and make a fist, ulnar deviation, or rotate the front can induce numbness and pain in the back of the hand. The superficial branch of the radial nerve does not only innervate sensation in the dorsum of the thumb and tiger’s mouth, but also in the proximal interphalangeal plane of the index and middle fingers and part of the ring finger.