A Self‐Designed Endobutton Installation Device for Coracoclavicular Stabilization in Acute Rockwood Type III Acromioclavicular Joint Dislocation

Objective Endobutton technique could provide flexible coracoclavicular (CC) stabilization for acromioclavicular joint (ACJ) dislocation and achieved good clinical outcomes. However, the difficult part of this technique was placement of the Endobutton to the coracoid base. In this study, we designed an Endobutton installation device to place the Endobutton at the coracoid base. And we examined the clinical and radiographic outcomes of patients with acute Rockwood type III ACJ dislocation repaired with Endobutton using this device. Methods We designed an Endobutton installation device to place the Endobutton at the coracoid base to achieve CC stabilization. We retrospectively reviewed 42 patients with acute Rockwood type III ACJ dislocation who underwent CC stabilization with Endobuttons placed either using this novel device (group I, n = 19) or the traditional technique (CC stabilization without using special device, group II, n = 23) from January 2015 to April 2020. The two groups were compared regarding the operative time, intraoperative blood loss, and clinical and radiologic outcomes at final follow‐up. The operation‐related complications were also evaluated. The Student's t test and the Mann–Whitney U‐test were used to compare differences in continuous variables. Differences in categorical variables were assessed with either the Pearson's chi‐squared test or Fisher's exact test. Results Forty‐two patients were clinically followed up for a minimum of 12 months. Compared with group II, group I had a significantly shorter mean operative time (56.05 ± 7.82 min vs. 65.87 ± 7.43 min, p < 0.01) and significantly lesser mean intraoperative blood loss (67.89 ± 14.75 mL vs. 94.78 ± 25.01 mL, p < 0.01). At final follow‐up, there were no significant differences between the two groups in the visual analog scale score for pain, Oxford Shoulder Score, Disabilities of the Arm, Shoulder, and Hand score, and postoperative CC distance of the affected side. Loss of reduction occurred in four patients in group I and three patients in group II (p = 0.68); there were no other operation‐related complications in either group. Conclusions The Endobutton installation device makes placement of the Endobutton at the coracoid base easier and achieves satisfactory clinical and radiologic outcomes without additional complications in acute Rockwood type III ACJ dislocation.


Introduction
A cromioclavicular joint (ACJ) dislocation is a common injury among the active population. 1,2In acute Rockwood type III ACJ dislocation, the coracoclavicular (CC) ligament is completely torn; this disruption of the CC ligament leads to vertical instability because of the downward pull of the weight of the arm and the superior pull of the trapezius muscle. 3,4As a result, nonsurgical treatment of acute Rockwood type III ACJ dislocation may result in high rates of pain and shoulder dysfunction. 5,6Therefore, surgery is recommended for acute Rockwood type III ACJ dislocation, especially in young active patients. 7][10] However, each surgical technique has advantages and disadvantages, and there is no consensus regarding the "gold standard" of fixation for acute Rockwood type III ACJ dislocation. 11CC ligament reconstruction is currently recommended for ACJ dislocation because the CC ligament plays a crucial role in the physiological function of the ACJ. 12,13CC stabilization using Endobuttons placed either via open surgery or arthroscopically reportedly achieves good clinical and radiological outcomes. 14,15However, the difficult part of the Endobutton technique for CC stabilization was placement of the Endobutton at the coracoid base, 16 which often required repeated attempts.Therefore, more soft tissue stripping, the operative time and intraoperative blood loss were needed to finish the CC stabilization.
Herein, we present a self-designed Endobutton installation device designed to place the Endobutton at the coracoid base.The purpose of the present study is to examine the clinical and radiographic outcomes of patients with acute Rockwood type III ACJ dislocation repaired with Endobutton using this device.

Self-Designed Endobutton Installation Device
The difficult part of Endobutton technique for CC stabilization was placement of the Endobutton to the coracoid base.Therefore, we designed an Endobutton installation device to easily place the Endobutton at the coracoid base for CC stabilization.The self-designed Endobutton installation device is composed of a cannula and a pushing rod (Patent number: ZL201821603597.9).The cannula is 100 mm long and has outer and inner diameters of 4.3 mm and 4.1 mm, respectively, through which the Endobutton (12 mm long, 3.75 mm wide, 1.5 mm thick; Johnson & Johnson, Piscataway, NJ, USA) can pass.The pushing rod is 150 mm long and has a rectangular handle (30 mm long, 10 mm wide, 2.0 mm thick), cylindrical part (110 mm long, 2.0 mm diameter), and rectangular end (10 mm long, 2.5 mm wide, 1.5 mm thick) (Figure 1).The Endobutton installation device is made of medical stainless steel and was produced by Double Medical Technology Inc., Xiamen, China (Figure 2).

Study Population
This retrospective study included patients with acute Rockwood type III ACJ dislocation who received CC stabilization using either the Endobutton installation device (group I) or the traditional Endobutton placement technique (group II) from January 2015 to April 2020.The inclusion criteria were (1): acute Rockwood type III ACJ dislocation that occurred within 2 weeks of surgery; (2) consent for surgical treatment; (3) postoperative follow-up of at least 12 months.The exclusion criteria were: (1) age younger than 18 years; (2) history of surgery on the affected shoulder; (3) concomitant fracture around the affected shoulder; (4) chronic ACJ dislocation; (5) severe osteoporosis.Surgery was recommended for patients with high activity levels.Forty-two patients with acute Rockwood type III ACJ dislocation consented to surgical treatment and were included in this study.All surgeries were performed by two surgeons (J.M. and X.W.) at a single institution.This study was approved by the Ethics Committee of the hospital (approval number: SH9H-2023-T89-1).

Surgical Technique
After the induction of general anesthesia, the patients were placed in the beach-chair position.A 5-cm transverse incision was made over the lateral third of the clavicle extending toward the ACJ.The ACJ reduction was achieved and maintained by temporary K-wire fixation across the ACJ.The anterior deltoid muscles were bluntly dissected along the deltoid fibers from the clavicle to the tip of the coracoid.The soft tissue under the coracoid base was then pushed away with the surgeon's fingers.A director was placed from the middle of the clavicle (20-30 mm from the distal end of the clavicle) to the middle of the coracoid base under X-ray guidance.
In group I, a 4.6-mm bony tunnel was drilled through the director.The cannula was inserted into the bony tunnel from the clavicle surface to the coracoid base.A suture was placed through the Endobutton loop, and the Endobutton was then put into the cannula.Under X-ray guidance, the Endobutton was placed at the coracoid base by the pushing rod.The Endobutton loop was brought to the clavicle surface by pulling the suture.Another Endobutton was inserted through the Endobutton loop to reconstruct the CC ligament (Figure 3).In group II, a 4.2-mm bony tunnel was drilled through the director.A stainless steel suture (M649G, Ethicon Inc., Somerville, NJ, USA) was folded into double strands.The middle fold of the steel suture was passed through the bony tunnel to the coracoid base and was taken to the incision site by vascular forceps.No. 1 Ethibond suture (Ethicon Inc.) was then passed through the loop of the Endobutton and through the middle fold of the steel suture.The Endobutton was placed at the coracoid base and the loops were brought to the surface of clavicle by pulling the middle fold of the steel suture and the Ethibond suture.Another Endobutton was inserted through the Endobutton loop to reconstruct the CC ligament (Figure 4).

Postoperative Rehabilitation
Patients were encouraged to begin passive movement of the shoulder, including pendulum exercises, self-assisted circumduction exercises, and gradual passive range of motion (ROM) exercises on the first day postoperatively.Active ROM of the shoulder was encouraged at 1 week postoperatively when the pain was sufficiently relieved.A shoulder sling was used for 4 weeks postoperatively.Patients were instructed to avoid lifting, carrying, pushing, and pulling with strong force for 8 weeks postoperatively.

Clinical and Radiographic Evaluation
The operative time (minutes) was recorded as the time from skin incision to the closure of the wound.Intraoperative blood loss (ml) was also recorded.The patients were followed up at a minimum of 12 months postoperatively to evaluate the clinical and radiologic outcomes.The clinical outcomes were evaluated using the visual analog scale (VAS) score for pain, Oxford Shoulder Score, and Disabilities of the Arm, Shoulder, and Hand (DASH) score.For the evaluation of radiologic outcomes, the CC distances (CCD) of the affected and contralateral sides were measured on anteroposterior radiographs as described previously. 17Briefly, the CCD was measured between the uppermost border of the coracoid process and the opposing clavicular surface.CCD measurements were performed by two clinicians (J.M. and Y.T.).Operation-related complications such as incision infection, loss of reduction, re-dislocation, implant loosening, pleural injury, neurovascular injury, and iatrogenic fracture were recorded.Loss of reduction and re-dislocation were defined as increases in the CCD with respect to the contralateral side of 50%-100% and >100%, respectively, at final follow-up. 18,19atistical Analysis SPSS software (version 23.0;IBM Corp., Armonk, NY, USA) was used for statistical evaluations.The Student's t test and the Mann-Whitney U-test were used to compare differences in continuous variables.Differences in categorical variables were assessed with either the Pearson's chi-squared test or Fisher's exact test.The level of significance was p < 0.05 for all tests.

Patient Demographics
The patient demographics were detailed in Table 1.There were no significant differences between the two groups in terms of age, sex, affected side, injury type, duration from injury to operation, and duration of follow-up (all p > 0.05).
Of the 42 patients with acute Rockwood type III ACJ dislocation, 19 patients (13 men and six women) were treated using the Endobutton installation device to place the Endobutton at the coracoid base for CC stabilization (group I).In group I, the mean age was 43.26 years (range 28-56 years); the dislocation occurred on the right side in 10 patients and the left side in nine; seven, eight, and four injuries were caused by motor vehicle accidents, falls from a height, and direct traumatic injuries, respectively; the mean time from injury to

Clinical and Radiographic Outcomes
The operative details were summarized in The clinical outcomes were shown in Table 3.At a minimum of 12 months postoperatively, all 42 patients had satisfactory clinical outcomes.At final follow-up in groups I and II, the average VAS scores for pain were 1.1 AE 0.9 (range, 0-3) and 1.3 AE 0.9 (range, 0-3), respectively (p = 0.57), the  The radiologic outcomes were shown in Table 4.All patients achieved satisfactory radiologic outcomes at final follow-up.There were significant differences between the pre-and postoperative CCD on the injured side in both groups I and II (p < 0.01).The mean postoperative CCD of the injured side did not significantly differ between groups I and II ( p = 0.30).

Postoperative Complications
At final follow-up, a loss of reduction was radiographically confirmed in four patients in group I and three patients in group II (p = 0.68).In group I, the mean preoperative CCD of the affected side was 17.55 AE 0.91 mm (range, 17.1-18.5mm), the mean postoperative CCD of the affected side was 13.85 AE 0.89 mm (range, 12.5-14.6mm), and the mean CCD of the contralateral side was 8.55 AE 0.55 mm (range, 8-9 mm).In group II, the mean preoperative CCD of the affected side was 17.87 AE 0.90 mm (range, 17.2-18.9mm), the mean postoperative CCD of the affected side was 13.87 AE 0.81 mm (range, 13.3-14.8mm), and the mean CCD of the contralateral side was 8.4 AE 0.20 mm (range, 8.2-8.6 mm).The VAS score for pain in the injured shoulder was 2-3 (indicating mild pain) in seven patients, but no patients required additional analgesic medication.There was no radiological evidence of re-dislocation or implant loosening at final follow-up in either of the two groups.No patients had incision infection, pleural injury, neurovascular injury, or iatrogenic fracture.

Discussion
Technique Advantages To our knowledge, this is the first report of a self-designed Endobutton installation device for placing the Endobutton at the coracoid base to achieve CC stabilization in acute Rockwood type III ACJ dislocation.In our study, this technique enabled us to easily and effectively place the Endobutton at the coracoid base and achieve satisfactory clinical and radiologic outcomes without severe complications.

Technical Characteristic
The following three surgical techniques are frequently used for CC stabilization in clinical practice 8,[20][21][22] : (1) ACJ fixation (static techniques: K-wires [no longer used because of complications]; dynamic techniques: hook plate); (2) CC fixation (static techniques: CC screws; dynamic techniques: Endobuttons); and (3) CC ligament reconstruction.However, each of these surgical techniques has complications and the best treatment strategy for CC stabilization remains controversial.The most commonly used surgical procedure is internal fixation with the Endobutton technique, 23,24 which can be performed either via open surgery, mini-open surgery, or arthroscopically. 15,16,21Endobuttons technique provide flexible CC stabilization for ACJ dislocation. 25,26owever, as described above in the Surgical Technique section (Figure 3), the difficult part of the traditional Endobutton technique for CC stabilization is placement of the Endobutton at the coracoid base, 16 which often requires repeated attempts.The use of the traditional Endobutton technique may be associated with problems such as more soft tissue stripping, operative time, and intraoperative blood loss.However, to our knowledge, no studies have reported the use of special devices for Endobutton placement.We designed an Endobutton installation device to place the Endobutton at the coracoid base for CC stabilization.During the operation, instead of 4.2-mm bony tunnel in the traditional Endobutton technique, a 4.6-mm bony tunnel from the clavicle surface to the coracoid base was needed for the annula pass through.And then, the Endobutton was easily placed at the coracoid base through the annula.

Application of the Technique
In our study, we retrospectively analyzed 19 and 23 patients with acute Rockwood type III ACJ dislocation treated with Endobutton placement using the Endobutton installation device (group I) and the traditional technique (group II), respectively.During the operation, a mini-open technique was used in both groups, with a finger used to protect the neurovascular structures under the coracoid base when the director was placed and the bony tunnel was drilled.This procedure seemed to be safe and simple compared with arthroscopy or surgery under extensive radiographic guidance.Additionally, our results suggest that the Endobutton installation device easily and effectively placed the Endobutton at the coracoid base.And, the operative time and intraoperative blood loss were significantly reduced in group I compared with group II.At final follow-up, all 42 patients achieved satisfactory clinical outcomes, with no significant differences between groups I and II in the mean VAS score for pain, mean Oxford Shoulder Score, and mean DASH score.Moreover, on radiographs obtained at final follow-up, the postoperative CCD was significantly decreased compared with the preoperative CCD of the injured side in both groups, and the postoperative CCD of the injured side was similar in the two groups.There was a similar incidence of loss of reduction in both groups.In both groups, we only reconstructed the conical ligaments, which lacks horizontal stability. 27Therefore, the loss of reduction might have occurred mainly because the reconstruction of the conical ligaments was not able to completely stabilize the ACJ. 18owever, as previously reported, this loss of reduction was not significantly associated with clinical outcomes. 26,28The patients with loss of reduction still achieved satisfactory clinical outcomes, and no further complications occurred in either group in the present study.

Technique Risks and Strategies
Despite the good outcomes achieved in the present study, the Endobutton installation device has some disadvantages.Firstly, the bony tunnels are drilled using a 4.6-mm drill instead of a 4.2-mm drill.Although there were no clavicle and coracoid fractures in our study, the use of a drill with a larger diameter carries a risk of this kind of complication.We think that these complications were prevented because the bony tunnels were drilled through the middle of the distal clavicle and the coracoid base, which are wide enough to drill 4.5-5.0-mmbony tunnels. 29Secondly, there is a theoretical risk that an Endobutton is more likely to move into a 4.6-mm bony tunnel than a 4.2-mm bony tunnel.However, no such complications occurred in our study.We consider that the incidence of implant loosening may have been reduced by implementation of the following two procedures. 1 The Endobutton loop was kept under appropriate tension.
With the aid of direct vision and radiographic monitoring, we confirmed that the ACJ dislocation was completely reduced and maintained by temporary K-wires placed across the ACJ.The bony tunnel was then drilled and the length was carefully measured.Based on this measurement, we chose a loop that was the same size or one size larger than the tunnel length.After the loop was brought to the clavicle surface, another Endobutton was inserted through the loop. 2 The Endobutton was placed horizontally above or below the center of the tunnels in the distal clavicle and the coracoid base.Thirdly, the drilling of a bony tunnel through the coracoid base carries the risk of pleural injury and neurovascular injury.To prevent such injuries, the surgeons used their fingers to push away the soft tissue under the coracoid base.
The surgeons then placed a finger at the coracoid base when the director was placed and the bony tunnels were drilled.These procedures may avoid pleural and neurovascular injuries.

Limitations
O ur study has several limitations.This study was a single-center retrospective study with a low level of evidence and a small number of patients.Thus, the present results require confirmation in a multicenter study with a large sample size.Additionally, there may have been biases related to coding that may have influenced the identification of potentially eligible patients.To control for the bias related to coding, we carefully code the ACJ dislocation based on the Rockwood classification in the future study.

Prospects for Clinical Application
The endobutton installation device may be a good option for placing the Endobutton at the coracoid base to achieve CC stabilization, such as in the ACJ dislocation and Neer type IIB lateral clavicle fractures.It makes placement of the Endobutton at the coracoid base easier with less soft tissue stripping, the operative time and intraoperative blood loss.However, a drill with a larger diameter carries risk of clavicle and coracoid fractures in this surgical procedure.To avoid the intraoperative clavicle and coracoid fractures, the surgeon needed to manipulate carefully to maintain the bony tunnels were drilled through the middle of the distal clavicle and the coracoid base.

Conclusion
I n conclusion, the Endobutton installation device makes placement of the Endobutton at the coracoid base easier and achieves satisfactory clinical and radiologic outcomes without additional complications in acute Rockwood type III ACJ dislocation.

FIGURE 1
FIGURE 1 Illustration of the self-designed Endobutton installation device.(A) The cannula is 100 mm long and its outer and inner diameters are 4.3 mm and 4.1 mm, respectively.(B) The pushing rod is 150 mm long and is composed of a 30 mm long, 10 mm wide, and 2.0 mm thick rectangular handle; a 110 mm long cylindrical part with a 2.0 mm diameter; and a 10 mm long, 2.5 mm wide, and 1.5 mm thick rectangular end.

FIGURE 2 FIGURE 3
FIGURE 2 The self-designed Endobutton installation device used to place an Endobutton at the coracoid base.(A) Lateral view of the cannula, Endobutton, and pushing rod.(B) Transverse view of the cannula and Endobutton.(C) Lateral view of the Endobutton being passed through the cannula using the pushing rod.

FIGURE 4
FIGURE 4 A 46-year-old man with Rockwood type III ACJ dislocation.(A) Preoperative radiographs.(B) The ACJ reduction is achieved and maintained by the placement of temporary K-wires across the ACJ.(C) A director is placed from the middle of the clavicle to the middle of the coracoid base.(D) Illustration showing the stainless steel suture folded into double strands.A 4.2-mm bony tunnel is drilled through the director and the middle fold of the steel suture is passed through the bony tunnel to the coracoid base.(E) Illustration of the middle fold of the steel suture being taken to the incision site by the vascular forceps.(F) Illustration showing the No. 1 Ethibond suture passing through the loop of the Endobutton and through the middle fold of the steel suture.(G) Illustration of the Endobutton placed at the coracoid base and the loop brought to the surface of clavicle by pulling the middle fold of the steel suture and the Ethibond suture.(H) The second Endobutton plate without loops is placed in the loop above the clavicle.(I) Postoperative radiograph obtained to assess the reduction.

TABLE 2
Operation-related factors.
Abbreviations: DASH score, disabilities of the arm, shoulder and hand score; SD, standard deviation; VAS, visual analog scale.