The median nerve is superficial in the wrist and is easily injured by sharp objects. Supracondylar fractures and lunate dislocations of the humerus are often combined with median nerve injuries, mostly contusions or crush injuries. If the dislocation is secondary to a shoulder dislocation, it is a strain injury. In addition, the median nerve may be affected by hypertrophy of the transverse carpal ligament or hypertrophy of the anterior rotator muscle, resulting in chronic nerve compression.
Disease description
The median nerve consists of fibers from the cervical 5-8 and thoracic 1 nerve roots. The lateral head is divided from the lateral bundle of the brachial plexus and the medial head from the medial bundle, and the two heads unite to form the median nerve. In the upper arm, the median nerve is accompanied by the brachial artery, and the median nerve has no branches in the upper arm. In the elbow fossa, the median nerve passes between the two heads of the pronator teres muscle. In this area, the median nerve emanates from the following muscular branches: the anterior rotator teres muscle branch; the anterior interosseous nerve that innervates the long thumb flexor, the deep flexor digitorum superficialis, and the anterior rotator teres. In the forearm, the median nerve is located on the radial side of the superficial flexor tendon of the finger and on the deep side of the long palmar tendon, entering the hand via the carpal tunnel.
It branches in this segment as follows.
Muscular branch: innervates the radial flexor carpi radialis, palmaris longus, superficial flexor digitorum longus and radial half of deep flexor digitorum.
Metacarpal branch: Emanating from the radial side of the wrist, it is a cutaneous branch that is distributed in the skin of the middle of the palm and the interphalangeal area, sometimes absent.
In the hand, it emanates sequentially from the distal border of the transverse carpal ligament
(i) Motor branch, which innervates the short thumb adductor, thumb to palmar muscle, and short thumb flexor (radial head).
(ii) The radial intrinsic nerve of the thumb, which is distributed in the radial half of the skin of the thumb.
(iii) The 1st common finger nerve, which is divided into 2 branches, 1 branch distributed in the ulnar half of the skin of the thumb and 1 branch distributed in the radial half of the skin of the index finger. The latter gives off 1 or 2 small branches to the 1st earthworm muscle.
④The 2nd common finger nerve, which is distributed in the skin of the ulnar and radial halves of the index finger, emits 1 to 2 small branches to the 2nd earthworm muscle or is innervated by the ulnar nerve.
⑤ The 3rd common finger nerve, which is divided into 2 branches, is located in the skin of the ulnar side of the middle finger and the radial half of the ring finger.
Injuries to the median nerve occur more frequently, mostly in the wrist or forearm, and less frequently in the upper arm or axilla.
Strain injuries: the most common. Most are caused by the arm being caught in a machine.
Crush injuries: mainly fractures or scar contractures in the forearm, often accompanied by severe and extensive soft tissue injuries.
Cutting injuries: glass cuts that occur in daily life or at work, or accidental injuries during forearm surgery.
Gunshot wounds or injuries caused by accidental injection of drugs into the nerve trunk: these two types of injuries are less common compared to the above injuries. [4]
Clinical manifestations
(1) Movement: The three interphalangeal muscles, i.e., thumb to palmar muscle, thumb short extensor muscle and thumb short flexor muscle, are paralyzed at the superficial head, so the thumb cannot be palmarized, cannot form a 90° angle with the palmar plane, and cannot touch other fingertips with the thumb. Atrophy of the greater interosseous muscle forms the ape hand deformity. The short thumb flexor is sometimes supplied by the abnormal ulnar nerve.
(2) Sensation: median nerve injury has the greatest effect on the sensation of the hand. After injury, there is loss of sensation in the radial half of the thumb, index, middle finger and ring finger on the palmar side, and in the distal segment of the index finger and middle finger on the dorsal side. Due to the loss of sensation, hand function is seriously affected, easy to drop things, no physical sense, easy to be traumatized and burned.
(3) Nutritional changes: There are significant nutritional changes in the skin and nails of the hand, the finger bones atrophy, and the finger ends become small and pointed.
The median nerve at the wrist is completely severed
Motor: three interfiscial muscles, i.e. thumb to palmar muscle, thumb short extensor muscle and thumb short flexor muscle, are paralyzed at the superficial head, so the thumb cannot be palmarized, cannot form a 90° angle with the palmar plane, and cannot touch other finger tips with the thumb. Atrophy of the greater interosseous muscle forms the ape hand deformity. The short thumb flexor is sometimes supplied by the abnormal ulnar nerve.
Sensation: Median nerve injury has the greatest effect on the sensation of the hand. After injury, sensation is lost in the radial half of the thumb, index and middle fingers and ring finger on the palmar side, and in the distal segment of the index and middle fingers on the dorsal side. Due to the loss of sensation, hand function is severely affected, easy to drop things, no physical sensation, easy to be traumatized and burned.
Nutritional changes: the skin and nails of the hand have significant nutritional changes, the finger bones are atrophied, and the finger ends become small and pointed
Examination of the median nerve and the manifestation of injury.
A, B. thumb abduction to palm is normal; C, D. median nerve injury after the thumb can not be to palm, thumb, show, middle finger can not be flexed; E, F. sensory hypoesthesia or loss of area.
Median nerve injury at the elbow
Motor: In addition to the above changes, there is also paralysis of the anterior circular muscle, anterior rotary muscle, radial carpal flexor, superficial finger flexor, radial half of the deep finger flexor, long thumb flexor and long palmar muscle, so the thumb and index finger cannot be flexed, and the thumb and index finger are still straight when clenching a fist. In some cases, the middle finger can be partially flexed. [5]
Disease diagnosis
Definite history of trauma, radial hemisensory deficit of the hand, thumb to palm inability, “ape-like hand”. Thumb flexion is impaired, and electromyography is performed if necessary. The diagnosis can be confirmed.
Disease examination
Electromyography can help determine the presence and extent of nerve damage.
Treatment
General treatment: The following conditions should be used ① The median nerve injury is mild, muscle and sensory impairment is mainly reduced, and there is no major motor dysfunction. (2) Nerve injury within 3 months, with signs of gradual recovery of function.
Surgical indications.
① Closed nerve injury without recovery after 3 months of conservative treatment.
②Open nerve injury.
Surgical method: Median nerve surgical exposure.
The incision of the median nerve in the upper arm is made along the anterior axillary margin and the medial edge of the biceps tendon up to the elbow joint, and then turned laterally from the transverse elbow palmar line to the middle of the elbow fossa, and then folded to the midline of the forearm. The brachial fascia is incised to reveal the brachial nerve vascular bundle. The median nerve is located lateral to the brachial artery in the upper arm and gradually moves anteriorly from the brachial artery to the medial brachial artery and then inferiorly along the medial border of the biceps to the anterior elbow joint.
(2) The revealing incision of the median nerve in the forearm is made from the anterior midline of the elbow downward, in the midline of the forearm distally to the wrist. The branches of the median nerve that branch off near the pronator teres muscle are divided from the ulnar side of the nerve trunk, so it is safer to separate the median nerve on the radial side. Before the median nerve enters the pronator teres, it first divides into two thicker branches to this muscle, then passes between the deep and superficial heads of this muscle, and then branches to other flexors.
(iii) When the median nerve is revealed at the wrist, the median nerve is incised along the transverse carpal and piriformis lines, and the transverse carpal ligament and palmar fascia need to be incised. Separation by the ulnar border of the median nerve will prevent injury to the lateral branch innervating the piriformis muscle. Depending on the nature of the injury, the appropriate nerve surgery is chosen.
Prevention
How should median nerve injury be prevented? Because median nerve injury not only affects thumb flexion and palmar function, but also has a great impact on the function of the hand due to the loss of solid sensation, so it is very important to restore sensory function. For sensory hypersensitivity, desensitization therapy should be used, i.e., patients should be taught to use sensitive areas more often, to self-massage sensitive areas, to stimulate sensitive areas with objects of different materials, etc. Patients should be taught to protect the sensory impaired areas and not to touch dangerous objects with the affected hand to prevent burns, puncture wounds, pressure ulcers, and when finger muscle strength is restored to level 3, patients should be instructed to do more hand When the finger muscle strength has recovered to level 3, the patient should be instructed to do more fine motor exercises and ADL exercises.
Complications
What diseases can be complicated by median nerve injury? There is no branch of median nerve on the elbow, and the injury can be divided into high level injury (supra-elbow) and low level injury (wrist). The clinical manifestations are mainly thumb to palm dysfunction and radial hemianesthesia of the hand, especially loss of sensation in the distal segment of the index and middle fingers. If treatment is not timely, excessive adhesion of nerves and tendons as well as muscle atrophy and joint stiffness may occur.