The surgical treatment of acromioclavicular joint dislocation is often very difficult because of its high failure rate, especially for high-level dislocation. The previous surgical methods such as Weaver-Dunn will cause a high unplanned secondary surgery rate (8). Therefore, at present, clinical researchers have proposed many methods to solve acromioclavicular joint dislocation, which can be divided into three categories: Endobutton plate suspension to reconstruct coracoclavicular ligament, hook plate or Kirschner wire rigid fixation and coracoclavicle + acromioclavicular joint capsule repair, among which hook plate or Kirschner wire rigid fixation is gradually eliminated due to its many postoperative and long-term complications and the need for secondary removal of internal fixation (8–10). At present, it remains controversy regarding the clinical application of Endobutton plate suspension surgery for the reduction of acromioclavicular dislocation. Through computer simulation of finite element analysis combined with biomechanical research, many scholars consider that additional augmentation suture repair of acromioclavicular ligament after reconstruction of coracoclavicular ligament can significantly improve the postoperative posterior displacement and rotation stability of acromioclavicular joint (11–13). However, some researchers carried out biomechanical analysis of cadaveric specimens simulating surgically treated acromioclavicular joint dislocation, and found that the effect of an additional acromioclavicular cerclage on the stability of acromioclavicular joint seemed to be negligible (14). Therefore, they do not recommend to use additional acromioclavicular cerclage. However, these studies are limited to cadaver specimens or computer simulation, and there are few reports on clinical follow-up studies combined with finite element simulation. In our study, we found that anatomical reconstruction of coracoclavicular ligament with Endobutton plate suspension combined with the reconstruction of acromioclavicular ligament is helpful to improve the horizontal and vertical stability of acromioclavicular joint, recover the function of acromioclavicular joint as soon as possible, effectively reduce surgical trauma, avoid secondary surgery to remove the internal fixation device, and improve the satisfaction of patients.
At present, there are big differences in the selection of surgical techniques for Endobutton plate suspension reconstruction, mainly including the following four aspects: 1. Whether acromioclavicular joint capsule is concerned or not. 2. Differences in the selection of clavicle and coracoid process tunnels. 3. Differences in the selection of suspension materials. 4. The choice of open surgery or arthroscopic surgery.
Most researchers pay more attention to coracoclavicular ligament than acromioclavicular ligament. In fact, acromioclavicular ligament is very important for the stability of acromioclavicular joint. In recent years, acromioclavicular ligament has gained more and more attention in clinical investigators. Many biomechanical studies have shown that although acromioclavicular ligament is thin, the superior and posterior articular ligaments can limit the posterior displacement of the distal clavicle, and the inferior articular ligament can limit the anterior displacement of the distal clavicle. When the acromioclavicular ligament is damaged, the anterior-posterior displacement of the distal clavicle increases significantly (15–18). Simultaneously, many clinical studies have confirmed the importance of acromioclavicular joint ligaments. Cisneros (19) believes that 20% of patients have acromioclavicular joint horizontal instability after surgery, and suggests to increase the augmentation repair of acromioclavicular joint ligament. In the treatment of chronic acromioclavicular joint dislocation, Jensen et al. (20) incised the acromioclavicular joint capsule to strengthen the repair of tendon while they were performing arthroscopy-assisted reconstruction of the coracoclavicular ligament, so as to increase the horizontal stability of acromioclavicular joint. Tauber et al. (21) compared anatomic triple-bundle coracoclavicular ligament and acromioclavicular ligament reconstruction using autologous tendon graft with nonanatomic single-bundle coracoclavicular ligament reconstruction using autologous tendon graft, and confirmed that triple-bundle reconstruction enhanced the horizontal stability of acromioclavicular joint due to the additional repair of acromioclavicular ligament. These results suggest that surgeons should pay more attention to the importance of acromioclavicular ligament and repair acromioclavicular ligament while reconstructing coracoclavicular ligament.
The Endobutton plate was initially used to reconstruct the cruciate ligament of the knee joint, and then gradually became an implant for the surgical treatment of acromioclavicular joint dislocation. Many clinical investigators have used Endobutton plate for single-bundle coracoclavicular ligament reconstruction, and achieved some short-term therapeutic effects (22–25). However, with the in-depth anatomical study of the stable structure of the acromioclavicular joint, some researchers believe that double-bundle anatomical reconstruction is the key factor for postoperative stability of the acromioclavicular joint and it is necessary to reconstruct the two branches of the coracoclavicular ligament: the trapezoid ligament and the conus ligament. Some of these researchers used double-bundle reconstruction with two tunnels on both clavicle and coracoid process, or used autogenous tendon to bypass the base of coracoid process to form double-bundle ligament (26), which not only can increase the vertical stability of acromioclavicular joint after surgery, but also can enhance the horizontal stability of acromioclavicular joint to some extent (27, 28). However, it has been proposed that coracoid dual-tunnel may greatly increase the risk of iatrogenic fracture and injury of brachial plexus nerve and blood vessels (22). Therefore, we chose to anatomically reconstruct the coracoclavicular ligament with double-tunnel on the clavicle and a single tunnel on the coracoid process. Through measuring fresh cadaver specimens, Rios et al. (29) found that the anatomic location of bone tunnel is very important for the reconstruction of coracoclavicular ligament. The tunnel on the conus ligament should be 30–45 mm medial to the acromioclavicular joint and posterior to the clavicle. The bone tunnel on the trapezium ligament should be 15 mm lateral to the conus tunnel, and more anterior compared with the conus tunnel, which can improve the stability and strength of the reconstructed structure. According to the intraoperative conditions of our patients, we chose 40 mm and 15 mm away from the acromion of clavicle as the start points of standard bone tunnels.
Regarding the selection of suspension materials, PDS suture, autogenous tendon, synthetic ligament, Endobutton loop are all commonly used suspension materials. However, PDS suture alone can easily cause iatrogenic fracture and osteolysis in the long run due to its cutting effect on the bone; autogenous tendon may enlarge the surgical area, increase related complications, and decrease the patients' satisfaction; synthetic ligament is easy to cause infection and rejection due to biocompatibility; because it is difficult to accurately measure the physiological distance of patients' coracoclavicular joints, it is very hard to choose the length of Endobutton's high-strength loop (18, 23, 30–33). Therefore, after comprehensive consideration, we chose No. 2 ultrabraid suture as the suspension material, combined with the use of mini steel plate to reduce some complications caused by the suspension material.
With the popularization of arthroscopy, arthroscopy-assisted reconstruction of ligament for acromioclavicular dislocation has been recommended by more and more surgeons. Under the arthroscope, the surface under the coracoid process can be observed clearly to provide a visual field for the establishment of bone tunnel, which is more conducive to the establishment of bone tunnel and the placement of steel plate (34, 35). Abdelrahman et al. (36) performed open surgery and arthroscopic repair of acromioclavicular dislocation and achieved good clinical outcome. However, the learning curve of arthroscopic technique is long, the cost of patients is high, and the operation time is longer. Gowd et al. (37) carried out a systematic review and meta-analysis and confirmed that there was no significant difference in reduction loss and related complications between open surgery and arthroscopic surgery for acromioclavicular joint dislocation. Moreover, arthroscopic repair of the acromioclavicular ligament is difficult, which requires additional incision and repair (20). Therefore, we believe that reconstruction of acromioclavicular joint under direct vision in a limited incision can also achieve satisfactory clinical outcome.
In addition, on the basis of clinical research, we carried out preliminary computer simulation biomechanical research using finite element analysis to verify the results of the clinical study. We have demonstrated that acromioclavicular ligament augmentation repair combined with coracoclavicular ligament mini plate suspension fixation is more stable than coracoclavicular ligament mini plate suspension fixation alone. This result is consistent with the results of multiple finite element analysis-related literatures (11–13). The finite element analysis study supported and validated our clinical research conclusions from three aspects: 1. The deformation of distal clavicle in coracoclavicular ligament reconstruction combined with acromioclavicular ligament reconstruction group was smaller than that in coracoclavicular ligament reconstruction alone group. 2. In the coracoclavicular ligament reconstruction alone group, the deformation of the distal clavicle in the horizontal direction was obvious, while the deformation of the distal clavicle decreased significantly after the additional reconstruction of the acromioclavicular ligament. 3. Under the mixed movement loading condition, the stress of the suspension suture between clavicle and coracoid process in the Endobutton reconstruction of coracoclavicular ligament combined with the reconstruction of acromioclavicular ligament group was lower than that in the coracoclavicular ligament reconstruction alone group. Because it is considered that the fixation fails when the deformation of the acromioclavicular joint is over 5 mm, (38), these findings also support that reconstruction of coracoclavicular ligament with Endobutton plate alone cannot provide horizontal stability. At present, biomechanical analysis of cadaveric specimens and finite element analysis of computer simulation are the mainstream methods to study different surgical methods of acromioclavicular joint dislocation in vitro. The advantages of finite element analysis are non-invasive, low cost, high efficiency and scientific. However, its limitation lies in that the tests are carried out in vitro, which may not be able to completely duplicate the real in vivo situation. Therefore, after the retrospective analysis of clinical cases, we performed finite element analysis to verify our findings and achieved satisfactory results. As far as we know, this is the computer simulated finite element analysis combined with retrospective clinical study to explore the feasibility of surgical methods for acromioclavicular joint dislocation.