What Are the Most Common Causes of Carpal Tunnel?

Carpal Tunnel Syndrome is the most common peripheral nerve entrapment disorder, and it is also the most common surgical treatment for hand surgeons. There are many non-surgical treatments for carpal tunnel syndrome, including bracing and corticosteroid injection. If conservative treatment does not relieve the patient's symptoms, surgery should be considered.

Liu Bo	(Deputy Chief Physician)	Beijing Jishuitan Hospital Hand Surgery
Chen Shanlin	(Deputy Chief Physician)	Beijing Jishuitan Hospital Hand Surgery
Tian Guanglei	(Chief physician)	Beijing Jishuitan Hospital Hand Surgery

Western Medicine Name: Carpal tunnel syndrome

English name: Carpal Tunnel Syndrome
Affiliated Department: surgical-

Carpal tunnel syndrome disease

Carpal Tunnel Syndrome is the most common peripheral nerve entrapment disorder, and it is also the most common surgical treatment for hand surgeons. The pathological basis of carpal tunnel syndrome is the compression of the median nerve in the carpal tunnel of the wrist. Its incidence is about 0.4% in the United States, and there is no clear statistics in China.

Dr. Paget first described the clinical manifestations of median nerve entrapment in two patients with distal radius fractures in 1854. In 1913, French scholars Marie and Dr. Foix reported for the first time the neuropathological examination results of patients with low median nerve entrapment symptoms, and proposed that if early diagnosis and incision of the transverse carpal ligament of the wrist, neuropathy may be avoided. In 1933, Learmouth reported a case of surgical incision of the flexor muscle support band to treat carpal tunnel nerve entrapment. In 1953, Kremer first used the term "carpal tunnel syndrome" in public publications to name the disease, and it has been used to this day ^[1] .

Causes of carpal tunnel syndrome

Carpal tunnel syndrome occurs due to increased pressure in the carpal tunnel leading to compression of the median nerve. The carpal tunnel is a bone fiber duct composed of the wrist bones and flexor support bands. The former constitutes the radial, ulnar, and dorsal side walls of the carpal tunnel, and the latter constitutes the side wall of the palm. The top of the carpal tunnel is the flexor support band that spans the ulnar hamstring, triangular bone, and radial scaphoid, most of the horn bones. The median nerve and flexor tendons pass through the carpal tunnel (the long flexor hallucis longus, 4 superficial flexor tendons, and 4 deep flexor tendons). Although the carpal tunnel has open inlets and outlets at both ends, the tissue fluid pressure is stable. The narrowest point in the carpal tunnel is about 50px from the carpal tunnel margin. This anatomical feature is consistent with the median neuromorphological performance of patients with carpal tunnel syndrome during the incision. The median nerve runs under the flexor support band, and is close to the flexor support band. At the distal end of the flexor support band, the median nerve issues recurrent branches that dominate the short abductor hallucis, the superficial head of the short flexor hallucis, and the hallux palmus. The terminal branch refers to the nerve, which innervates the semi-radial skin of the thumb, index, middle finger, and ring finger ^[2] .

Whether the content of the carpal tunnel increases or the volume of the carpal tunnel decreases, the pressure in the carpal tunnel can increase. The most common cause of increased pressure in the carpal tunnel is idiopathic hyperplasia and fibrosis of the perianal synovial membrane in the carpal tunnel. The mechanism of its occurrence is unknown. Sometimes there are other rare causes, such as low flexor muscle abdomen, rheumatoid synovitis inflammation, trauma or degenerative changes leading to abnormal carotid bone structure entrapment nerves, soft tissue masses such as tendon sheath cysts.

Some studies suggest that excessive use of fingers, especially repetitive activities, such as prolonged mouse or typing, can cause carpal tunnel syndrome, but this view remains controversial. Carpal tunnel syndrome is also prone to occur in pregnant and lactating women. The mechanism is unknown. Some people believe that it is related to tissue edema caused by estrogen changes, but many patients still have no relief after the end of pregnancy.

Clinical manifestations of carpal tunnel syndrome

Carpal tunnel syndrome is more common in women than men, but the cause is unknown. Common symptoms include paresthesia and / or numbness in the median innervation zone (thumb, thumb, middle and ring halves). Finger numbness at night is often the first symptom of carpal tunnel syndrome, and many patients have experienced finger awakening at night. The numbness of many patients' fingers can be relieved to some extent by changing the posture of the upper limbs or shaking their hands. Patients engaged in certain activities during the day can also cause numbness of fingers, such as needlework, driving, holding a phone for a long time or reading a book for a long time. In some patients, only the numbness of the middle or middle fingertips was felt in the early stage, but the thumb was felt in the later stage. Some patients may have numbness or paresthesia in the forearm or even the entire upper extremity, and even feel these symptoms as the main discomfort. With the worsening of the disease, patients may have a clear sensation of loss or loss of finger sensation, atrophy of the abductor hallucis and hallux palm muscles or weakness. Patients may have atrophy of the most radial muscles of the big fish, the thumb is inflexible, the pinching force with other fingers decreases, and the pinching action cannot be completed ^[4] .

Diagnosis and differential diagnosis of carpal tunnel syndrome

The diagnosis of carpal tunnel syndrome is mainly based on clinical symptoms and characteristic physical examination results, and the diagnosis requires electrical diagnostic examination. The most important diagnosis is that the patient has typical clinical symptoms, that is, numbness in the median nerve distribution area, which worsens at night. In addition to subjective symptoms, objective examination is also important. It is clear that the decline or loss of finger sensation and the atrophy of the great intermuscular muscles are serious symptoms, and treatment interventions should be performed before these symptoms appear. Objective tests based on evoked diagnostic tests are also helpful in helping diagnosis, including the Tinel sign, the Phalen test, and the median nerve compression test.

Walking along the median nerve, tapping from the forearm to the distal end, if the numbness discomfort in the median nerve innervation area occurs when tapping in the carpal tunnel area, it is positive for Tinel sign. However, due to the low sensitivity and specificity of this test, it cannot be used as a basis for diagnosis alone.

The Phalen test is to keep the patient's wrist in the most flexed position. If the numbness of the three fingers on the radial side occurs within 60 seconds, it is positive. 66% -88% of patients with carpal tunnel syndrome can be positive for the Phalen test, but 10-20% of normal people will also be positive for the Phalen test.

Dr Durkan described a median nerve compression test specifically for the diagnosis of carpal tunnel syndrome. The examiner pressed the carpal tunnel with his thumb, and if the numbness of the skin in the median innervation area appeared within 30 seconds, it was positive. Durkan reported positive median nerve compression tests in 87% of patients with carpal tunnel syndrome, and the authors reported higher rates. Therefore, this test is an important physical test for the diagnosis of carpal tunnel syndrome ^[5] .

Nerve conduction tests and EMG results can help determine the diagnosis, exclude other neurological disorders, and also reflect the severity of the compression, which is of great reference value for the development of appropriate treatment strategies. However, due to the false negative and false positive results of the electrical diagnostic tests, the diagnosis cannot be determined solely by the electrical diagnostic tests.

When skeletal abnormalities around the carpal tunnel are suspected to cause compression of the median nerve, radiographs of the tangential position of the carpal tunnel can help determine whether there is a change in carpal tunnel volume.

Most patients with carpal tunnel syndrome have typical symptoms and signs, but there are still some atypical patients that need to be distinguished from other neurological disorders. The main differential diagnoses include: intracranial tumors, multiple sclerosis, nerve root cervical spondylosis, cervical spinal cavity disease, thoracic outlet syndrome, peripheral nerve tumors, idiopathic brachial plexus neuritis, subbranchial trunk or other median neuropathy ^{[ 6]} .

Carpal Tunnel Syndrome Treatment

Non-surgical treatment of carpal tunnel syndrome

There are many non-surgical treatments for carpal tunnel syndrome, including bracing and corticosteroid injection.

Doctors often recommend that patients use bracing to control the progress of the condition and relieve symptoms. Commonly used are prefabricated braces. After wearing, the wrist joint is controlled at 30 degrees of dorsal extension. However, such a back extension angle increases the pressure in the carpal tunnel. Studies have confirmed that patients with carpal tunnel syndrome have an increase in the pressure inside the carpal tunnel, and the pressure increases further when the wrist is stretched back. The most effective position for controlling symptoms is the neutral position. Fixing the wrist joint in the neutral position can reduce the pressure in the carpal tunnel, but the position of the wrist joint that is most conducive to the function of the hand is 30 degrees of dorsiflexion. Considering that the neutral position is not conducive to manual performance, the general recommendation is not to fix it during the day, and use a brace to fix the wrist joint in the neutral position at night.

Oral anti-inflammatory drugs and topical corticosteroid injections are also commonly used, with varying success rates reported in the literature. Celiker et al. Compared the efficacy of corticosteroid injection with non-steroidal anti-inflammatory drugs in brace braking in a randomized controlled study. The results showed a marked improvement in symptoms in both groups. But with only 8 weeks of follow-up, the conclusion was not convincing enough. Both Edgell et al. And Green believe that if local injections can temporarily relieve symptoms, the success rate of surgery is high. There are also reports in the literature about the complications of hormone injection, such as injury to the median nerve. It has been found through rodent test models that even if dexamethasone is injected directly into the nerve, it will not damage the nerve. When all other steroids are injected into the sciatic nerve of rats, they can damage the nerves. Therefore, despite temporary relief, corticosteroid injections are not recommended for routine use ^[7] .

Carpal tunnel syndrome surgical treatment

If conservative treatment does not relieve the patient's symptoms, surgery should be considered. In 1924, Herbert Galloway underwent the first carpal tunnel release operation. Later, a variety of surgical methods appeared, including various incisions, small incision decompression, and endoscopic surgery. Although the purpose of the surgery is to release the median nerve, one or even several bundles of the median nerve may be damaged due to iatrogenic reasons. Therefore, no matter which surgical method is preferred, the median nerve should be fully exposed to prevent injury to the nerve. For patients with damaged wrist structures, space-occupying lesions, synovial lesions, and secondary decompression and decompression, it is best to do open decompression and decompression, and also make long incisions to enable additional surgery. When using a short incision, such as difficult operation, difficult to see directly, etc., the incision should be extended, and the short incision should be changed to a long incision to avoid accidents.

Endoscope technology is a "minimally invasive" surgical treatment method with small incisions and small trauma, which can avoid problems such as postoperative incision discomfort. At present, there are many literatures using various endoscopic techniques, but there are also certain problems, such as iatrogenic nerve damage, poor visual field, inability to distinguish anatomical variations, insufficient loosening, and higher costs. If the field of vision is not sufficient, an incision should be made instead. Some doctors believe that small incision decompression surgery is also a "minimally invasive technique", which can also reduce the rate of postoperative complications.

Endoscopic minimally invasive carpal tunnel release surgery is divided into two categories (Chow method) and single approach (Agee method). The double approach is to make a small incision of about 25px on the proximal and distal sides of the carpal tunnel. Under the guidance of the endoscope, use a small hook knife to cut the flexor support band. In the single approach, only a small incision is made from the proximal side of the carpal tunnel. Under the guidance of the endoscope, a special incision is used to open the flexor support band.

Carpal Tunnel Syndrome Rehabilitation

Postoperative management, the current practice is loose bandaging, to limit wrist movements within 2 days after surgery. After 2 days of dressing change, the patients were instructed to start shoulder, elbow, wrist, hand and finger exercises. Within three weeks after surgery, braces can be used to fix the wrist in a neutral position at night. The sutures were removed 12 to 14 days after the operation. Resume work after 1 month, but limit the load. 6 to 8 weeks after the operation, the activity was completely restored.

Although carpal tunnel release and decompression can be divided into incision and endoscope release and decompression, and there are many kinds of operations, the final curative effect and complications are the same. The only difference is the severity and lightness of complications. Long and short. Short surgical incisions, small tissue trauma, light scars, rapid pain disappearance, and short recovery periods; otherwise, they are heavy, slow, and long, which has become a consensus.

Palm pillar pain is the main reason for prolonging the rehabilitation period. There are many causes. Even if the incision is not on the palm side of the transverse carpal ligament, this complication will still occur. Nathan cut in the palm of the hand near the middle and the proximal side, but the transverse wrists were far away. The decompression surgery was compared. The former was longer than 62.5px and the latter was shorter than 62.5px. They found that short incisions can reduce postoperative pain and shorten the time to return to work, but early postoperative exercise and physical therapy are more important and have a more significant effect. Therefore, if you want to shorten the rehabilitation period, you should also start functional exercise as early as possible.