The Nice knot has advantages such as sliding locking, easy operation and reliable fixing power. Boileau[13] reports on the versatility of the nice knot for arthroscopic repair of tendon and ligament injuries, for binding post-osteotomy fractures and for repositioning and fixing butterfly fractures in fractures, as well as for repairing the separation of the inferior tibiofibular joint in fixation. Mengcun Chen[20] applied nice knot to comminuted patella fracture and achieved good clinical results. P Collin[14] analyzed the biomechanics of the nice knot in the repair of rotator cuff injuries and concluded that the knot provided good sliding lock and significantly reduced the risk of knot elongation during dynamic strain. On the application of nice knot in acromioclavicular dislocation, Zhongxing Ma[21] proposed a modified double endobutton technique in combination with Nice knot for the treatment of Rockwood III-V acromioclavicular dislocation, and achieved good clinical results. We have modified the Endobutton technique by replacing the double-endobutton with a single-endobutton and using the nice knot to treat Rockwood III-V acromioclavicular dislocations, making it easier and more convenient to reposition the acromioclavicular dislocation intraoperatively.
There are various surgical options for dislocation of the acromioclavicular joint, such as fixation with pins, screws or plates, as well as reconstruction of the rostral or acromioclavicular ligaments or distal clavicle resection. More complications associated with internal fixation of the acromioclavicular joint dislocation with Clinique pins[22, 23]. The most commonly used surgical procedures are the clavicle hook plate fixation[24], the Endobutton technique[21, 25, 26] and the Tightrope[27, 28] coracoid collateral ligament repair and reconstruction.
Clavicle hook plate internal fixation is the current treatment for acromioclavicular joint dislocation[24]. Clavicle hook plate provides mechanical stability in the longitudinal and horizontal directions. However, there is a high incidence of complications, including postoperative shoulder pain, limited shoulder movement, foreign body sensation, rotator cuff injury, acromion impingement syndrome, osteolysis of the acromion, distal clavicle fracture and plate fracture[29–34]. In addition, the patient will need to remove the internal fixation device a second time.
The double-Endobutton technique for the treatment of acromioclavicular dislocations was first reported by Struhl[26] in 2007 and has since been widely used. Endobutton system consisting of titanium plates, coils and sutures. During the operation, the acromioclavicular joint was repositioned and temporarily fixed with a Kirschner pin. The base of coracoid process and clavicle were drilled successively. The two titanium plates of the Endobutton are fixed by coils above the clavicle and below the coracoid. The reconstruction of the conical and trapezius ligaments was achieved by drilling holes in various parts of the distal clavicle. The double Endobutton technique significantly improves the patient's early shoulder pain, range of motion in shoulder abduction supination and forward flexion supination. However, biomechanical studies[35] have shown that the Endobutton technique fails mainly because the strength of the coils is greater than the strength of the bone under overload conditions, resulting in bone damage. The main complications of this technique are fractures of the clavicle or rostral process, loss of repositioning, calcification of the rostral-clavicular ligament and traumatic acromioclavicular arthritis[35–37]. In addition, the Endobutton technique only limits the up and down displacement of the clavicle and lacks horizontal stability[38].
The Tightrope technique is a new system that has emerged in recent years to reconstruct the rostro-clavicular ligament and can be considered an improved upgrade to the Endobutton system. It combines the advantages of the Endobutton system and can be adjusted to the length of the coil as required. Studies[35, 39] have shown that the Tightrope technique offers significant advantages in terms of stability and postoperative clinical outcomes. However, it is still at risk of acromion fracture[40].
According to the characteristics of Endobutton technology, we improve the technology in the following aspects: (1) Intraoperative 4.5 mm bone tracts are no longer used. We believe that the 4.5 mm bone channel is too large for the plate to sink into the bone channel. Intraoperative positioning at the central base of the coracoid is particularly difficult, especially in the absence of arthroscopic surveillance, and if the position is shifted intraoperatively, the fracture at the base of the coracoid is easily fractured and fixation fails[12, 41]. Two 2mm channels are drilled in the distal clavicle at 1.5cm and 3cm medially, the coil is passed through the channel and around the base of the coracoid, and the plate is placed on the clavicle and fixed with a nice knot. This not only reduces the risk of fracture from drilling the rostral process, but also reduces the diameter of the process and prevents the plate from sinking into the bone. The surgical incision is minor and does not have to rely on arthroscopic assistance. (2) We drill two bone channels in the clavicle, which is equivalent to reconstructing the vertebral and oblique ligaments at the same time, without additional operations. (3) After the dislocation of acromioclavicular joint was reduced intraoperatively, the clavicle was fixed with Nice Knot. The main feature of the nice Knot is that it can be slid and locked. The knot can be tightened during surgery and then the acromioclavicular joint can be reduced by fluoroscopy. In this group, we treated 16 patients with Rockwood III acromioclavicular dislocation using the nice knot combined with the modified Endobutton technique. No complications such as coracoid fracture, re-dislocation of the acromioclavicular joint or vascular nerve injury were observed after surgery. Post-operative follow-up showed a significant improvement in the function of the affected shoulder compared to the pre-operative period. In the treatment of Rockwood III-V acromioclavicular dislocation with the nice knot assisted modified Endobutton technique, we believe that attention should be made to the following:(1) This technique is not recommended for elderly patients with osteoporosis as there is a risk of fracture of the coronoid due to wire loop cutting. (2) The technique involves wrapping the thread around the base of the coracoid. The limb should be placed in the medial position and the anterior ring introduced against the base of the coracoid and the underlying bone to avoid damage to the brachial plexus nerve and the axillary sheath below the coracoid process. (3) The soft tissues around the acromioclavicular joint and clavicular area scar within 4–6 weeks after surgery. Therefore, a forearm sling should be used for 4 weeks postoperatively to avoid excessive abduction leading to loss of reduction.
Although our data showed good clinical results in terms of operative time, intraoperative fluoroscopy time, intraoperative bleeding, and satisfaction with repositioning, there are still some shortcomings in this study:(1) This study is a single-center retrospective clinical case analysis with a low level of evidence and a small number of cases, and a multi-center, large sample case analysis is required to confirm the results of this study. The practicality and feasibility of the nice knot combined with the modified single-endobutton technique for Rockwood III acromioclavicular dislocations needs to be studied in a large sample. (2) The variables in this study are not unique and there is some selection bias. (3) Although the clinical and imaging results of nice knot are good, more long-term follow-up results are needed to determine whether there are long-term complications.