Background Treatment methods for acromioclavicular joint dislocation of Rockwood type V are numerous. The commonly used is the open surgery with large trauma (by clavicular hook plate fixation). In recent years, some scholars use clavicle-coracoid screws fixation method under arthroscopy, but the screws need to be removed after 6 weeks; there are also scholars using arthroscopic double Endobutton loops single bundle fixation method with good effect, but they found suture rupture between the Endobutton, redislocation or fracture, bone absorption under the loops in some patients. This article investigates the method of arthroscopic procedure with four-tunnel quadruple double-bundle Endobutton double-bundle fixation via self-designed positioning apparatus in the treatment of acute acromioclavicular joint (ACJ) Rockwood Ⅴ degree dislocations and their short-term therapeutic effect.Methods (1)Patient selection:12 patients (9 male and 3 female) with acute acromioclavicular joint dislocation of Rockwood type V were selected from October 2010 to June 2013. Their average age is 28.2 years. with sports injury in 10 cases and fall injury in 2 cases. All patients received surgical repair within 2 weeks after injury. The operations were performed by the same senior surgeon.(2)Preoperative bone tunnel positioning design:All patients had CT scan in the position of 90° internal rotating of bilateral shoulder joint (palm down). Measure the angle of scapular long axis and coronal section (A) separately, make the line in the coracoid neck parallel to the long axis of scapula (S), and then measure the width of parallel line in the part of coracoid neck (P). The midpoint of the coracoid neck is the center between the two preparatively drilled bone tunnels. Make the cross line vertical to line P, and the bone tunnels are located in the I and II quadrant. The distance between two bone tunnels is 6 mm.(3)Surgical techniques:According to the data of preoperative measurement of bone tunnel, the self-designed 4-tunnel double-bundle locator is applied. The 4-tunnel double-bundle acromioclavicular joint fixation is carried out with the method of two Endobutton loops in each of two groups. The technique includes the following 5 parts: ① Acromioclavicular joint exploration and exposure of subcoracoid surface: make the routine posterior approach of acromioclavicular joint with arthroscope of 70°, 4.5 mm and guide the anterior approach. Gradually separate the anteromedial joint capsule with radiofrequency coblation from the inside of the subscapularis tendon above to the subcoracoid surface. Clean the soft tissue on its lower surface to expose the coracoid neck.② Acromioclavicular joint exploration, acromioclavicular joint disc excision and partial excision and plasty of the clavicular lateral end: make a 2-3 cm transverse incision above the acromioclavicular joint parallel to the clavicle, layered the cut, expose the acromioclavicular joint, remove ruptured joint disc, and rub the clavicular lateral end. Afterwards, reduce the acromioclavicular joint and fix it temporarily with Kirschner wire.③ The self-designed locator (Patent No. ZL 201320217047.4) is adopted. Put the head of the locator on the lower surface of coracoid neck, and the transverse bar and 2.4 mm guide pin are arranged on the clavicular surface. The guide pin is inserted into the hole A, drilling through the subcoracoid surface with a 3.5 mm hollow drill for reaming. Adjust the transverse bar to the pre-determined angle of scapular axis and coronal section 6 mm away from hole A, and then ream the hole B with 2.4 mm guide pin inserted.④ After connecting the ring with an Endobutton button plate and 3 Utra-braid sutures (Smith & Nephew, Andover, Ma), pull in the 3 line from hole A below the coracoid process, and then pull out from the bone tunnel on the clavicular end to maintain the Endobutton plate on the subcoracoid surface. The Utra-braid suture penetrates into the other piece of Endobutton plate and then gets pulled out. Tighten and fix it on the clavicular end and then make a knot. Check the acromioclavicular joint to ensure satisfactory fixation. Complete the process of hole B fixation with the same method.⑤ Use C arm X-ray machine for fluoroscopy to understand the effect of fixation and situations of internal fixator. Aggressive postoperative rehabilitation program was applied, and the follow-up time ranged from 6 to 30 months.(4)Postoperative rehabilitation:After operation the acromioclavicular joint was externally fixed in 0° of external rotation, and 48 hours later the patient was encouraged to take appropriate acromioclavicular joint passive activities of abduction less than 90°, flexion and external rotation. Active exercise was allowed 6 weeks after operation, and 3 months later the patient began to return to normal life, work and limited recovery movement.(5)Postoperative evaluation:The VAS score (out of 10) of postoperative acromioclavicular joint pain, recovery of range of movement for acromioclavicular joint and recovery time, Constant score (out of 100), and Karlsson acromioclavicular joint score (A, B, C three grades) were applied for postoperative evaluation.(6)Statistical analysis:SPSS 18.0 statistical software was applied, and χ² test and t test were adopted respectively for statistical process.Results (1)Results of preoperative measurement:Preoperative contralateral CT measurement was conducted in 12 cases of acute acromioclavicular joint dislocation with Rockwood type V. The angle between the scapula and coronal section was (32.33±5.24)°, the angle between the coracoid and scapular axis was (26.35±1.55)°, the diameter of coracoid neck was (2.05±1.12) cm, and the central location of coracoid bone tunnel (the original point of clavicular bone tunnel) in the projection of clavicle are (2.30±0.69) cm from the distal clavicle, (8.92±0.32) cm from the front edge of the clavicle, and (10.89±2.39) cm from trailing edge of the clavicle.(2)Intraoperation:Intraoperative positioning and preoperative measurement have the same result in 10 cases. 2 patients are younger than 20 years old and their anchor points are a bit forward in the projection of clavicle, which makes it difficult to drill the bone tunnels. The oblique positioning method of shifting anchor point backward is applied to move the points 5-6 mm back on the clavicle, and both the positions are good under intraoperative fluoroscopy and postoperative radiological examination.(3)Post operation:11 patients were followed up after operation for 6 to 30 months with an average of 24.2±6.8 months. Postoperative X-ray films and 3D-CT indicated that Endobutton titanium plate was in good position without withdrawal or rupture. No dislocation or subluxation relapse was seen after the operation. 8 male patients and 1 female patient restored pre injury sports level in 3 to 5 months after surgery, including resistive and excessive movement. The other 2 patients returned to normal life but gave up previous sports due to other reasons.The VAS score in 8 patients was less than 3 after operation in a mean of 6.34±3.2 weeks and 4 patients had acromioclavicular joint pain of longer duration (VAS score 4-6), but the VAS score turned less than 3 in 12-18 weeks later. The recovery time was 6.32±2.11 weeks in the postoperative range of joint movement. The postoperative Constant score was (91.2±1.67) (88-100) and the postoperative Karlsson score were excellent in 10 cases and benign in 1 case. Compared with the preoperative and postoperative scores the differences were statistically significant. All the patients were satisfied with the therapeutic outcomes.Conclusions The method of arthroscopic procedure with four-tunnel quadruple Endobutton double-bundle fixation in the treatment of acute acromioclavicular joint dislocation of Rockwood type V provides stable biological fixation with minimal invasion and avoids demerits such as the over-concentrations of stress on double-loop single bone tunnel, weak and thin of the tension line, etc. and it is a better treatment method for acute acromioclavicular joint dislocation of Rockwood type V.