Carpal tunnel syndrome (CTS) is the most common focal peripheral nerve disease, which is a group of clinical syndromes caused by damage to median nerve in the carpal tunnel. Its clinical manifestations include mainly numbness, tingling and hypoesthesia of the area supplied by median nerve and atrophy and strength decline of thenar muscles. The pathogenesis of CTS is still uncertain. At present, it is believed that there are two main causes of CTS. One is the mechanical compression caused by the thickened transverse carpal ligament causing ischemic injury of median nerve.The other is the increase of pressure in carpal tunnel caused by the excessive proliferation of synovium and the injury of inflammatory reaction.Surgical intervention should be taken for patients with CTS who are unable to respond to conservative treatment. Traditionally, carpal tunnel open decompression method is the mainstay of surgical treatment for CTS, however with the development of endoscopic technology, endoscopic minimally invasive decompression surgery is becoming more common. There is a lack of guidance for the selection of surgical methods. The current classification of CTS is mainly based on severity. Some researchers have proposed a classification, in which patients with synovial hyperplasia are named as synovial hyperplasia type CTS. For these patients, carpal tunnel open decompression and synovium clearance surgery has achieved satisfied curative efficacy. However, there are no comparison between synovial hyperplasia type CTS and the other types. The purpose of this study is to explore the clinical efficacy of different surgical methods for different types of CTS, and to further clarify the significance of classification on guiding treatment and affecting prognosis.

(1) General information: From January 2014 to July 2018, a total of 84 cases (13 males and 71 females, 108 hands ) with CTS underwent surgical intervention who had no respond to conservative treatment for at least three months. They ranged in age from 20 to 82 years, with an average age of (57±10.4) years; 44 cases had bilateral CTS (20 of them underwent unilateral surgery only) , and 40 cases had unilateral CTS. Of them, 87 hands underwent open carpal tunnel releasing and 21 hands underwent endoscopic carpal tunnel releasing. All patients underwent preoperative electromyography (EMG) examination to assist in definitive diagnosis. (2) Surgical methods and postoperative rehabilitation: All patients received brachial plexus anesthesia, supine position, abduction of affected limbs, and proximal tourniquet. Carpal tunnel open decompression surgery: A 3-5 cm L-shaped incision was made from thenar crease to wrist transverse stria on the volar side of the wrist. Skin, subcutaneous tissue and palmar aponeurosis were cut layer by layer to expose and cut off the transverse carpal ligament. The median nerve and the recurrent branch of median nerve were protected during the surgery. The median nerve and tendons in the carpal tunnel were then separated and protected. If severe synovial hyperplasia and nerve hyperaemia were seen, the synovial tissue with hyperplasia would be cleared. According to the toughness of epineurium, it was decided whether or not to undergo epineurilysis.At last,strict wound hemostasis, detaining drainage strip and suturing palmar aponeurosis, subcutaneous tissue and skin layer by layer were performed. The excised synovial tissue was sent for pathological examination. Endoscopic (2.7 mm in diameter, Stryker Corporation, USA) carpal tunnel releasing: A transverse incision of 2-3 cm proximal to the transverse carpal ligament and 1 cm ulnar length of the palmar longus tendon was taken.Skin, superficial and deep fascia were incised layer by layer. An endoscope was inserted subcutaneously between the palmar longus tendon and the flexor carpi ulnaris tendon to reach the interspace under the transverse carpal ligament. The distal edge of the transverse carpal ligament was determined under the endoscope. The hook knife was pulled upward from far to near. The transverse carpal ligament was completely cut off and the skin was sutured. Within 24-48 hours after surgery, the drainage strip was removed, and the flexion and dorsal extension of fingers were performed under the guidance of doctors to prevent tendon adhesion. At night, the affected limbs were raised to reduce swelling. The stitches were removed 14 days after surgery. Mecobalamin 0.5 mg 3 times a day (Mecobalamin, Eisai Co., Ltd.) were taken orally for 4 weeks. After 4-6 weeks, patients were allowed to resume normal activity. (3) Evaluation index, classification and statistical analysis: Kelly evaluation criteria (excellent: symptoms disappeared completely; good: symptoms relieved significantly; general: symptoms lightened; poor: symptoms unchanged or aggravated) were used to evaluate the effect of operation. According to the medical records and follow-up inquiries, all patients were asked to determine whether there was a history of awakening from numbness and pain symptoms at night before surgery.All of the patients were divided into two types according to the above-mentioned preoperative clinical manifestations. The patients who had the typical preoperative symptoms were defined as synovial type CTS (nerve injury mainly caused by synovial hyperplasia, increased pressure and inflammation stimulating in carpal tunnel) . The other group was defined as compression type CTS (nerve injury mainly caused by mechanical compression of thickened transverse carpal ligament) . SPSS 20.0 software was used for statistical analysis. The measurement data were expressed by ±s, and the comparison between groups was performed by Independent-Sample T test. The counting data were expressed as percentages, and the Chi-square test was used for comparison between groups. P<0.05 was considered statistically significant.

According to the preoperative clinical symptoms, the patients were defined as synovial type CTS (45 cases, 59 hands) and compression type CTS (39 cases, 49 hands) . Preoperative physical examination showed that the proportion of limbs with decreased motor function in synovial type CTS (42.4%, 25/59 hands) was lower than that in compression type CTS (61.2%, 30/49 hands) (P=0.050) . For cases with complete EMG data, the distal median nerve of synovial type CTS (35 hands) has shorter motor latency[ (5.02±1.31) ms, n=35; (5.37±1.42) ms, n=30; P=0.557], faster motor conduction velocity[ (50.06±4.65 ) m/s, n=35; (49.24±10.76) m/s, n=30; P=0.136]and longer sensory latency[ (4.41±1.26) ms, n=35; (4.08±1.25) ms, n=30; P=0.890], slower sensory conduction velocity[ (32.17±10.00) m/s, n=35; (35.34±12.20) m/s, n=30; P=0.564]than that of compression type CTS (30 hands) ,however,there was no significant statistical difference between these two groups at baseline.In synovial type CTS cases, synovial hyperplasia, nerve congestion and edema could be seen during the open decompression surgery. Pathological examination showed a large number of lymphocyte infiltration.However,in compression type CTS cases, mechanical compression changes were the main manifestations of median nerve injury. 74 cases (98 hands) were followed up[from 3 to 58months, [ (30±19.2) months) and evaluated according to Kelly criteria (excellent:61 hands, good:28 hands, general:7 hands,poor:2 hands; excellent and good rate:90.8%) . The excellent and good rate of carpal tunnel open decompression surgery cases (94.9%, 74/78 hands) was higher than that of endoscopic surgery group (75.0%, 15/20 hands) (P=0.016) . According to the cases of the two types CTS who underwent open decompression surgery, the excellent and good rate was 95.6% (43/45 hands) in synovial type CTS and 93.9% (31/33 hands) in compression type CTS (P=0.749) . There was no statistical difference between them. In synovial type CTS cases, the excellent and good rate of open decompression surgery group (95.6%) was significantly better than that of endoscopic surgery group (62.5%,5/8hands) (P=0.020) , while the difference of the excellent and good rate of patients who underwent open decompression surgery group (93.9%) and endoscopic surgery group (83.3%, 10/12 hands) was not statistically significant (P=0.286) in compression type CTS cases. Although there were fewer cases of two types CTS who underwent endoscopic surgery, the excellent and good rate of compression type CTS cases (83.3%) was higher than that of synovial type CTS cases (62.5%) .

Carpal tunnel open decompression surgery is the effective method for treatment of CTS. Endoscopic surgery can achieve a similar clinical efficacy as open decompression surgery for compression type CTS patients, but not for synovial type CTS patients. So endoscopic transverse carpal ligament cutting off surgery should be carefully selected for synovial type CTS patients.