The principle findings of the present study demonstrated that loop suspensory reconstruction resulted in superior clinical outcomes than hook plate fixation, even in patients with residual subluxation. It also yielded fewer acromial complications and no necessity for a second surgery for implant removal, although the surgical duration was greater, the intraoperative blood loss higher, and the proportion of patients with residual displacement greater (Table 2). In light of this comprehensive comparison, we recommend loop suspensory reconstruction for advanced AC dislocation owing to the superior clinical outcomes and fewer postoperative complications, despite the longer surgical duration and greater blood loss than for hook plate fixation, which did not relate to the final outcome. Acromioclavicular joint dislocation is a common injury and frequently occurs in active young males. In our series, the average age was 42.1 years, with male dominance (accounting for 81.1%). The injury mechanism was almost always due to direct force to the AC joint, either in a fall or in a traffic accident in the acute setting. The optimal treatment option for acute AC joint dislocation remains controversial. Various procedures have been described for the treatment of Rockwood type III to type VI AC joint dislocation [21]. In vertical stability restoration, loop suspensory reconstruction is one of the mainstays of surgical treatment, with good reported results [9, 10, 22]. Regarding horizontal stability restoration, the hook plate method is appealing, because it provides a rigid fixation and offers the promise of high-stability AC joint fixation, whilst also maintaining normal biomechanical rotation between the clavicle and the scapula [23]. The advantages of this modality are the rapid stabilization and reliable reduction maintenance [24]; however, acromial complications and postoperative pain were major concerns following the surgery.
In this study, group II demonstrated a significantly shorter surgical duration and less blood loss as compared with group I (101.0 ± 38.0 vs 66.6 ± 26.1 minutes, p = 0.005; 17.5 ± 25.6 vs 43.8 ± 45.6 ml, p = 0.015). The result was compatible with a systemic review and meta-analysis by Alisara et al. [25], which indicated that hook plate fixation required a significantly shorter surgical duration than loop suspensory fixation, at an average of 16.21 minutes. According to a review of the literature, few studies have assessed the intraoperative blood loss in these two groups. We postulated that both the higher blood loss and the longer surgical duration in the loop suspensory reconstruction group resulted from the more extensive anterior deltoid splitting and advanced soft tissue dissection required to allow the curved passer to pass underneath the coracoid process, which is not required in hook plate fixation. However, a blood loss of around 50 ml would not cause major complications in the general population. Regarding neurovascular injury while passing through the coracoid process, no related complications were noted in the present study. However, for patients with multiple trauma or a high anesthesia risk, hook plate fixation might be a better choice owing to the shorter durations of anesthesia and surgery. Kirschner wires or Knowles pins are common implants used to fix the AC joint as an augmentation for temporary stability, and good outcomes have been reported [26]. However, complications such as pin migration or breakage and pin-tract infection are concerns [27]. In our series, no obvious migration of Kirschner wires was noted until removal, but one patient developed pin-tract infection complicated with clavicle osteomyelitis and eventually a frozen shoulder. On the other hand, there was also one case of surgical site infection in the hook plate fixation group developing 2 weeks after the primary surgery. In terms of complications due to infection, there were no significant differences between groups.
Hook plate fixation provided a significantly greater stability of the AC joint than loop suspensory reconstruction according to CCDR analysis (Table 2). There were 9 cases of residual subluxation in group I (39.1%) and 2 in group II (14.3%), which was not statistically significant (p = 0.150). Nevertheless, there were no clinical signs or symptoms of instability, and thus no patient required further revision in either group. This indicated that soft-tissue healing of the CC space in the loop suspensory reconstruction patients could be achieved in a non-anatomic position under the permanent stability provided by non-resorptive suture materials. Meanwhile, some reports have mentioned mechanical failure of this implant, although hook plate fixation is regarded as a rigid fixation [28]. Regarding acromial osteolysis, the lateral portion of the hook plate could cause subacromial impingement; in other words, the stress on the base of acromion increases, which could further result in acromion osteolysis, possibly even complicated by fracture. This poor result usually occurs in patients with a hook plate retention of more than 1 year [17, 29]. This complication could be attributed to an inappropriate size of the implant [16, 29], or interpreted as the force concentration phenomenon due to morphological mismatch between the acromion and hook plate [30]. In our series, there were 4 cases of acromion osteolysis in the hook plate fixation group, although removal of the hook implant was carried out between 3 and 6 months after surgery as previously recommended [16, 17]. The average interval between surgery and implant removal in the present hook plate fixation group was 182.2 ± 63.3 days (range: 114–338 days), whereas the interval in the 4 cases with acromion osteolysis was 229 days. Furthermore, these 4 cases in the hook plate fixation group presented no significant improvement in the Constant-Murley score at the final follow-up (Table 4). These results showed that the longer the implant was retained, the greater the possibility of acromial osteolysis, and soft-tissue healing around the CC space was not strongly related to the duration for which the implant was retained. This finding differed from the results of a study by Eschler et al. [18], which mentioned that acromial osteolysis in the hook plate group had no influence on the final functional result.
A meta-analysis compared these two popular techniques by analysis of the Constant-Murley score (CMS), pain visual analog score (VAS), and rates of postoperative complications. The study demonstrated that loop suspensory reconstruction resulted in a higher postoperative functional score as compared with hook plate fixation, but the surgical duration was longer. There were no differences regarding the postoperative VAS or the complication rate [27]. We adopted the interval of intermittent painkiller usage for pain assessment rather than the VAS, because it reflected the duration of pain that interfered with daily life after surgery. The mean period of painkiller usage was 121.7 ± 174.1 and 235.4 ± 251.8 days in groups I and II, respectively, significantly lower in the loop suspensory reconstruction group (p = 0.031). In addition, the patients in group I revealed significantly superior Constant-Murley scores at the final outpatient follow-up than those in group II (71.7 ± 15.8 versus 61.1 ± 6.7, p = 0.009), which revealed that loop suspensory reconstruction provides a superior clinical outcome in terms of both clinical function and pain reduction.
Limitations of the present study existed. First, the inherent weakness of the retrospective nature of the study and the limited case numbers weakened the strength of the statistical power. Second, the non-randomized control study may have led to selection bias. Third, long-term follow-up (more than 2 years) comparison of these two groups could not be performed in the present study. However, by the combination of a literature review and comprehensive comparison in the present study, we were able to conclude a superior outcome of CC loop suspensory reconstruction over hook plate fixation.