The acromioclavicular joint (ACJ) is a diarthrodial joint located between the acromion and the clavicle and is supported by the AC and coracoclavicular (CC) ligaments. The AC ligament connects the acromion to the distal clavicle and provides the ACJ with horizontal (anterior–posterior) stability [1-3]. ACJ injury accounts for 9%–12% of shoulder injuries, is most common in people aged 20 to 30 years, and occurs five times more often in men than in women [1,2,4-6]. These injuries are often caused by direct trauma to the shoulder during contact sports (such as cycling, skiing, ice hockey, rugby, and soccer) when the arm is in an inclined position or when falling on an inclined arm [1,2,7,8]. ACJ injuries are usually classified by the Rockwood system into six types based on the damage to the AC and CC ligaments. Recommendations for managing these injuries are usually non-surgical for types I and II, surgical for types IV to VI, and controversial for type III [1,2,9].

More than 60 methods for treating ACJ injuries have been proposed in the literature, indicating disagreement about the best surgical procedure for treating them. Many of the methods focus on vertical instability (disruption of the CC ligaments). Horizontal instability (AC ligament disruption) has received less attention [1,9,10]. There is currently no gold standard surgical treatment for any type of AC injury, especially for horizontal ACJ instability [4,8,10,11]. This study examined the effects of two Ethibond suture techniques, the loop technique and the two holes in the clavicle technique, on the horizontal stability of the ACJ following its complete dislocation. These techniques were used because they are cheaper for patients than other techniques in our country.

This study was approved by the University Ethics Committee (IR.GUMS.REC.1395.307) and is registered at the Iranian Registry of Clinical Trials (IRCT201704087274N12). All patients signed the consent form, and their personal information was kept confidential.

A total of 104 patients entered the study, but two patients were excluded from the two-hole group due to unavailability. Therefore, 50 patients in the two-hole group and 52 patients in the loop group were evaluated. Among the patients undergoing surgery, 79.4% were male. The mean age of the patients was 29.2±5.5 years. The sex distribution (p=0.526) and mean age (p=0.116) of patients did not differ significantly between the two techniques. The percentage of superficial infections in the form of mild discharge from the wound was 25% (n=13) in the loop group and 30% (n=15) in the two-hole group, which was a not significant difference (p=0.06). Each group had one case of loss of reduction, and the loop group had one case of painful ACJ (Fig. 4).

As shown in Table 1, changes in the horizontal stability of the shoulder differed significantly with the two methods (p<0.05) at all the measurement times (3, 6, and 12 months post-surgery), and the incidence of unstable cases with the loop technique was higher than that with the two-hole technique. Repeated-measure ANOVA results are shown in Table 2, along with the effect of time on the scores in the two groups. The CS and TS changes show a significant upward trend over time with both techniques (p_time<0.001). The group effect on the CS (p_group=0.121) and TS (p_group=0.126) was not statistically significant, indicating that the two techniques did not differ. The interaction between time and group for the CS and TS was significant, and those changes were statistically different at some intervals. However, the mean difference was not clinically significant.

The results show a higher degree of horizontal instability with the loop technique than the two-hole technique. Twelve months after surgery, instability was found in 26.9% of the loop group and 8% of the two-hole group (17.6% overall). The changes in shoulder function reported in the CS and TS were similar with the two techniques. Also, the incidence of superficial infections caused by the subcutaneous pins was the same in the two groups. In this study, horizontal dislocations and joint instability were lower in the two-hole group; at 1-year postoperation, instability was more than three times more common in the loop group than the two-hole group (26.9% vs. 8%). However, with the loop technique, additional instability did not occur after 6 months. In other words, joints treated with the loop technique maintained the stability they had achieved at 6 months after surgery. Although the rates of instability and dislocation differed between the two techniques, the resulting shoulder function did not differ between the groups. Kraus et al. [12] showed that instability existed after shoulder joint reduction for grade V injuries with the double-tightrope technique based on either the V-shaped or parallel drill hole method. Shoulder function did not differ with those two methods either, consistent with the findings of this study. In general, it can be argued that horizontal instability does not affect short- or medium-term shoulder function.

In a review of biomechanical and clinical studies, Jordan et al. [16] showed that simultaneous reconstruction of the ACJ and CC joint produces less horizontal instability than isolated CC reconstruction, although the clinical outcomes did not differ. In other words, horizontal instability appears not to affect the functional outcomes of the shoulder.

In the two-hole group in this study, two holes were made in the clavicle, and an Ethibond suture was passed through the holes and looped around the coracoid so that the two ends of the suture could be tied together. In contrast, in the loop technique, the Ethibond suture was looped around the clavicle and the coracoid. In general, passage of the suture through the holes in the clavicle appears to restrict it. In other words, if the clavicle is fixed by passing a suture through holes in its structure, movement restriction is increased, which reduces the horizontal instability of the clavicle. Beitzel et al. [17] also showed that horizontal instability is limited in CC ligament reconstruction using single or double tunneling, which confirms the results of this study, though their surgical procedural details differed from those used here.

Previous studies have shown that several methods can be used for ACJ reconstruction, and no consensus has been reached on the best methods for diagnosing, evaluating, and treating acute or chronic ACJ horizontal instability. Horizontal instability injuries are often overlooked or not well understood, complicating diagnosis and potentially leading to extensive complications and failure after surgical stabilization [1].

Regarding complications, because subcutaneous pins were used for both techniques in this study, mild infections with small secretions were observed in both groups and were controlled with antibiotics. In a study by Liu et al. [13], a patient developed a superficial wound infection 3 weeks after surgery, which healed after routine care. Theopold et al. [18] reported no intraoperative complications and generally no fractures in the clavicle or coracoid area based on radiological examinations. No postoperative infections or wound healing disorders occurred in their study. In a study by Bostrom Windhamre et al. [19], five superficial infections were reported and treated with oral antibiotics, which is comparable to the results in this study, in which 28 people developed superficial infections. In our study, each group had one case of loss of reduction, and the loop group had one case of painful ACJ. In the study of Tauber et al. [20], a vertical re-dislocation with complete loss of reduction and clinically relevant ACJ deformity was observed in four patients. In general, ACJ reconstruction with various surgical techniques appears to have limited and acceptable complications.

Although horizontal stability differed between the two groups over the course of 1 year, functional outcomes did not differ between the groups. A 1-year follow-up might be too short to evaluate shoulder function, and functional outcomes might vary with longer follow-up periods. Also, clavicle instability could cause ACJ arthritis in the long term. None of the participants in this study were professional athletes or relied heavily on shoulder use. Functional outcomes might also differ in those individuals depending on which of the two techniques is used, and that constitutes one of the limitations of this study.

Although functional outcomes did not differ significantly between the two-hole and loop techniques in the short- and medium-term, the improved horizontal stability of the ACJ with the two-hole method suggests that technique as a more suitable option for ACJ reduction.