Why does minimally invasive coracoclavicular ligament reconstruction using a flip button repair technique fail? An analysis of risk factors and complications

Arthroscopy-assisted procedure provides less residual horizontal instability and optimal coracoid tunnel creation with less radiation exposure compared to percutaneous procedure after endo-button fixation of type III AC joint dislocations

PURPOSE

The aim of this study was to evaluate the postoperative radiological and functional results of patients treated with arthroscopy-assisted (AA) and percutaneous (P) procedures using endo-button for type III acromioclavicular joint dislocations with a minimum 1-year follow-up. The study hypothesis was that the AA technique would provide more favourable coracoid tunnels.

METHODS

This retrospective study included patients who underwent surgery between 2017 and 2022. Computed tomography images taken immediately postoperatively of all the patients were analysed to group coracoid tunnels as optimal or suboptimal based on orientation and placement within the coracoid base. Residual horizontal instability was assessed using the bilateral Alexander view at the final follow-up. Shoulder functions were evaluated at the final follow-up examination.

RESULTS

Of the 63 patients, 39 underwent surgery using the percutaneous procedure and 24 with the AA procedure. Surgical duration was significantly longer in the AA group (AA: 61.1 ± 5.9 min; P: 34.7 ± 5.6 min) (p = 0.001; 95% confidence interval [CI]: 23.3-29.3), whereas fluoroscopy time was longer in the percutaneous group (AA: 2.0 ± 0.8 s; P: 15.7 ± 3.9 s) (p = 0.001; 95% CI: -14.9 to 12.3). Optimal coracoid tunnels were more frequently observed in the AA group (p = 0.001; 95% CI: 7.4-137.8). There was no significant difference in functional scores between the groups (n.s.). Postoperative horizontal instability was more common in the percutaneous procedure (p = 0.013; 95% CI: 8.3-39.2).

CONCLUSIONS

Although no difference was detected between the methods in terms of complications and functional results, the higher frequency of residual horizontal instability, the high risk of suboptimal tunnel creation and greater radiation exposure were seen to be the most important disadvantages of the percutaneous technique. During surgery, such technical problems related to the percutaneous method should be kept in mind and care should be taken about the orientation of the coracoid tunnel.

LEVEL OF EVIDENCE

Level III.

Clavicular Tunnel Widening After Acromioclavicular Stabilization Shows Implant-Dependent Correlation With Postoperative Loss of Reduction

PURPOSE

To radiographically describe, quantify, and compare clavicular tunnel widening (cTW) of 2 different types of stabilization devices and investigate a possible correlation between cTW and loss of reduction.

METHODS

In a retrospective analysis of single-center registry data, we compared patients who were treated for an acute AC dislocation (Rockwood types III to V) with either the AC Dog Bone (DB) or low-profile AC (LP) repair systems. On 6-week and 6-month postoperative radiographs, we measured clavicle height and tunnel diameter. We calculated the button/clavicle filling (B/C) ratio to quantify how much of the clavicular tunnel height is covered by the low-profile inlet. The association between B/C ratio and the extent of cTW was defined, and we also compared cTW between treatment groups. Reduction of the AC joint was graded as either stable, partially dislocated or dislocated depending on the AC ratio. A 2-sample t-test was used for comparing cTW progression between the 2 groups. For continuous variables between more than 2 groups, the Kruskal-Wallis test was used.

RESULTS

Of 65 eligible patients, there were 37 and 28 included in the DB and LP groups, respectively. Overall, cTW was conically shaped with transclavicular widening noted in the DB group and cTW developing strictly inferior to the button in the LP group. For both implants, mean maximal cTW was 7.1 mm and located at the inferior cortex; the B/C ratio was not associated with increased inferior cTW (r = -0.23, P = .248). Only LP patients with complete loss of reduction had significantly increased cTW (P = .049).

CONCLUSIONS

Conical-shaped cTW is a common implant-independent phenomenon after AC stabilization using suture-button devices. It occurs only at the suture-bone interface and is less excessive for the LP implant. There is an association between increased cTW and loss of reduction specific to the LP implant only.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Mini-open vs. arthroscopic double tight-rope reconstruction after acute AC-joint dislocation: a comparison in functional outcome and sports activity

INTRODUCTION

In athletes, acromioclavicular joint disruptions account for up to 50% of all shoulder injuries. In high-grade injuries, surgery is favored to ensure a correct restoration of the joint, especially in young athletes. The aim of this study was to compare the clinical, radiological and sport related outcomes of the arthroscopic stabilization with the fixation of the AC joint in a mini-open approach.

MATERIALS AND METHODS

19 patients treated arthroscopically (ASK) and 26 patients with an acute AC-joint dislocation Rockwood V who had undergone the mini-open (MO) surgery were included. Constant Murley Score (CMS), Taft Score (TS) and the Simple Shoulder Tests (SST) were evaluated. The sports activity level was determined according to Valderrabano and the athlete's recovery of their athletic activity level after surgery according to Rhee. Furthermore, all available X-ray images were analyzed.

RESULTS

Patients in the ASK group achieved an average score of 11.7 ± 0.6 points in the SST, 10.3 ± 1.8 points in the TS and 91.2 ± 11.8 points in the CMS. On average, patients in the MO group achieved results of 10.5 ± 1.4 points in the SST, 11.7 ± 0.7 points in the TS and 91.6 ± 9.8 points in the CMS. The ASK group showed significant difference regarding the CC distance in side comparison (Δ = 3.6 mm), whereas no significant difference was found in the MO group (Δ = 0.8 mm). In comparison of both groups, the posterior as well as the combined translation were significantly greater in the ASK group than in the MO group (posterior: ASK: 24.8 mm, MO: 19.3 mm, combined: ASK: 29.1 mm, MO: 20.9 mm). Residual horizontal instability was greater in the ASK group (43%) than in the MO group (32%). Similar results were achieved in sports activity and the recovery of athletic activity (Valderrabano: ASK: 2.8, MO: 2.6; Rhee: ASK: 1.6, MO: 1.5).

CONCLUSIONS

Both techniques prove to be effective for the stabilization of high-grade AC-joint disruptions in athletes and showed excellent clinical results. From a radiographic standpoint, the mini-open procedure appears superior to the arthroscopic technique. After mini-open surgery postoperative loss of correction is less common and greater horizontal stability is achieved. The results also suggest the mini-open technique is superior to the arthroscopic procedure when aiming to restore the athlete's original level of sports activity.

LEVEL OF EVIDENCE: 1

Minimally invasive reconstruction of acute acromioclavicular joint injuries using the TwinBridge button system

INTRODUCTION

Acute acromioclavicular joint (ACJ) injuries are among the most common shoulder injuries in active young adults. The most frequently used surgical treatments include the hook plate implantation and arthroscopic treatment using flip-button systems. The aim of this study was to evaluate the results of treating acute ACJ injuries using a new minimally invasive implant based on a flip-button system.

MATERIAL AND METHODS

From January 2016 to October 2019, a total of 20 patients with acute ACJ injuries (1 × Type III, 3 × Type IV, 16 × Type V) underwent surgery using the Twinbridge implant (Smith & Nephew). It is a prefabricated construct consisting of two Endobuttons connected with an UltraTape. One button is placed under the coracoid using a special aiming device and two buttons are placed on the clavicle. Preoperatively, 1 day postoperatively, 3 months and at least 1 year postoperatively, patients were clinically examined and bilateral stress view and axial radiographs were obtained. At final follow-up, the simple shoulder test (SST), Taft score, Constant score, and ACJ instability (ACJI) score were recorded and a side-to-side ratio of the coracoclavicular (CC) distance was calculated.

RESULTS

All 20 patients were contacted at final follow-up at a mean of 28 (min. 13, max 50) months. Six patients were not willing to come for a clinical and radiographic examination and were contacted via telephone. All six patients were free of complaints. Another two patients free of complaints refused radiographs at final follow-up. The patients presented a mean SST of 99.6% (20 patients, min. 91.7, max. 100), Taft score of 11.6/12 points (12 patients, min. 10, max. 12), ACJI of 85.5/90 points (12 patients, min. 78, max. 90), and a Constant score of 97.1 (14 patients, min. 81.0, max. 100) for the affected shoulder. Preoperative stress view images revealed a mean side-to-side difference of the CC distance with a ratio of 1:2.34 (min. 1:1.80, max. 1:3.33). At final follow-up, CC distance was calculated with a mean ratio of 1:1.12 (min. 1.1, max. 1:1.38). Axial images showed a proper position in all cases. A "perfect" radiological result was achieved in six patients (50%) with a side-to-side CC distance of less than 10% (ratio 1:1.1 or less). A Rockwood type II result was achieved in five patients (42%) with a distance of 10 to 25% (ratio 1.11-1.25). One (8%) presented with a Rockwood type III result with a difference of more than 25% (ratio 1:1.38) and was considered a radiological failure.

CONCLUSIONS

When used correctly, the Twinbridge implant offers good-to-excellent clinical and radiographic results using a minimally invasive surgical technique. Complication rate is comparable to other button-systems.

Evaluation of the coracoid bone tunnel placement on Dog Bone™ button fixation for acromioclavicular joint dislocation: a cadaver study combined with finite element analysis

BACKGROUND

Dog Bone™ button fixation is frequently used to treat acromioclavicular joint (ACJ) dislocation. However, various studies have reported complications after fixation.

OBJECTIVE

To investigate the effect of the coracoid bone tunnel location on the treatment of ACJ dislocation through single-tunnel coracoclavicular (CC) ligament fixation with the Dog Bone™ button.

METHODS

Six cadaveric shoulders were used. Each specimen was subjected to five testing conditions in the following order: (1) normal ACJ (Gn); (2) acromioclavicular and CC ligaments were removed (G0); (3) CC ligament reconstruction was performed using the Dog Bone™ technique, and the coracoid bone tunnel was at the center of the coracoid base (G1); (4) reconstruction was performed at 5 mm distal from the G1 site, along the axis of the coracoid (G2); (5) reconstruction was performed at 10 mm distal from the G1 site, along the axis of the coracoid (G3). The angles of pronation and supination of the clavicle under the same load (30 N) were measured. Next, a finite element (FE) model was created using computed tomography (CT) images of the normal shoulder. Model 1 (M1), model 2 (M2), and model 3 (M3) correspond to G1, G2, and G3, respectively. A force of 70 N was applied as a vertical upward load to the distal clavicle. Subsequently, the von Mises stress, the strain LE along the FiberWire, and the displacement nephogram of the three models were obtained.

RESULTS

After single-tunnel CC ligament fixation using the Dog Bone™ technique, the clavicle in the G2 group (20.50 (19.50, 21.25) °, 20.00 (18.75, 21.25) °) had the best rotational stability. The peak von Mises stress, the strain LE along the FiberWire, and the maximum displacement were smaller in M2 than in M1 and M3.

CONCLUSIONS

When the coracoid bone tunnel was located 5 mm anterior to the center of the coracoid base (along the axis of the coracoid), the clavicle showed greater rotational stability.

Implant-dependent behavior of tunnel widening and clavicular button migration after arthroscopic-assisted treatment of acromioclavicular joint instabilities

INTRODUCTION

Despite ongoing discussions for the previous few decades, there is still no consensus regarding the optimal surgical technique for acromioclavicular joint instabilities. The purpose of this study was to determine the impact of various implant materials following arthroscopically assisted stabilization of acromioclavicular joint instabilities on tunnel widening and implant migration. We hypothesized an implant-dependent behavior for tunnel widening and implant migration with differences when comparing acute and chronic acromioclavicular joint instabilities.

METHODS

This study compared 105 patients with acromioclavicular joint instabilities that were managed operatively with coracoclavicular double button constructs. Two of the groups containing acute cases were treated with either a double button construct with a wire (TR) or a tape (D) as a central pillar. The two groups with chronic cases were either treated with a wire (T+) or tape D+ as a central pillar and additional hamstring tendon augmentation (+). One central transclavicular-transcoracoidal drill channel was made in the acute cases, while additional medial and lateral drill channels to augment the central pillar with the hamstring tendon were made. The central drill channel in all cases and the medial/lateral drill channels in chronic cases were subsequently radiologically analyzed immediately postoperatively and at follow-up. Following this, additional radiological analysis of the implant migration of the clavicular button took place.

RESULTS

All groups showed significant tunnel widening of the central drill channel at follow-up (p ≤ 0.001). The TR+ technique demonstrated significant widening in both the medial (p ≤ 0.001) and lateral (p ≤ 0.001) drill channels. The D and D+ group displayed significant higher rates of clavicular button migration to a cortical and intraosseous level (p ≤ 0.002).

CONCLUSION

Tunnel widening and implant migration following arthroscopically assisted management of acromioclavicular joint instabilities are dependent on the chosen implant. The stable tape showed a significantly increased degree of tunnel widening with respect to the central drill channel in comparison with the wire. In contrast, a higher degree of load capacity of the tape ultimately favors a protected intraosseous graft healing for chronic cases, which leads to less tunnel widening of the medial and lateral drill channel. Finally, the D/D+ implant groups showed higher rates of implant migration due to lower contact surface area of the implant at the upper clavicular cortex.

LEVEL OF EVIDENCE IV

An Accuracy Comparison of Minimally Invasive Transclavicular-Transcortical Drilling with Free-Hand, C-Shape and Assembly-Type Guide Device: An In Vitro Study

OBJECTIVES

Ensuring the accuracy of transclavicular-transcoracoid drilling in the anatomical reconstruction of the coracoclavicular ligament complex with minimally invasive incisions remains a major problem for inexperienced surgeons. The purpose of this study was to design an assembly guide device for transclavicular-transcoracoid drilling with minimally invasive incisions, to manufacture the finished product, and to compare its feasibility and accuracy with the existing C-shape guide devices and free-hand techniques.

METHODS

An assembly-type guide device was designed and produced using computer-aided design and three-dimensional printing. The specimen data of 54 human shoulders from 27 gross specimen (14 males and 13 females) treated by free-hand drilling, C-shape device drilling, and assembly-type guide device drilling from October 2018 to January 2021 were analyzed in a controlled laboratory study. Fifty-four human shoulder specimens were randomly assigned into free-hand (n = 18), C-shape (n = 18), and assembly (n = 18) groups by drawing lots for transclavicular-transcoracoid drilling by three inexperienced surgeons. After the drilling procedure was completed and the devices were removed, the operation outcomes were assessed and evaluated. Distances from the tunnel edge to the coracoid's medial (d_m ) and lateral (d_l ) edges, operation time, and tunnel location zones on the coracoid's inferior surface of all specimens in the three groups were measured to evaluate the surgical accuracy and efficiency.

RESULTS

All specimens in the three groups completed the drilling operation successfully and were correctly measured. The distance differences (d_d ) between d_m and d_l in the free-hand, C-shape, and assembly groups were 3.2 ± 1.8 mm, 1.8 ± 1.0 mm, 1.0 ± 0.8 mm, respectively. The d_d of the free-hand group was higher than that of the other two groups (p < 0.001). The tunnel exit points on the inferior coracoid surface located in undesired zones were six (33%), one (6%), and zero in the free-hand group, C-shape group, and assembly-type group, respectively (p = 0.012). The operation time in the free-hand, C-shape, and assembly groups were 198 ± 36 s, 256 ± 64 s, and 353 ± 88 s, respectively. The operation time of each group significantly differed from that of the others (p < 0.001).

CONCLUSION

The assembly-type devices may be the first choice for inexperienced surgeons while both the C shape devices and assembly-type guide devices achieved higher accuracy than free-hand techniques.

Arthroscopically assisted single tunnel reconstruction for acute high-grade acromioclavicular joint dislocation with an additional acromioclavicular joint cerclage

PURPOSE

Purpose of this study was to demonstrate that a single tunnel reconstruction of high-grade acromioclavicular (AC) joint instabilities with implants of the second generation is sufficient for stabilisation, especially in combination with an AC cerclage.

METHODS

Patients with an acute AC-joint dislocation type Rockwood III-B and V were included. Besides clinical follow-up examination, radiographs were analysed. The functional outcome measures were Constant Score (CS), Taft score (TS), ACJI score and patient's satisfaction. Horizontal instability was evaluated by clinical examination and radiological with an Alexander view.

RESULTS

Thirty-five patients with a mean follow-up of 29 months were included. Ninety-seven per cent were satisfied with their result, with an average Subjective Shoulder Value of 90%. The CS averaged at 90 ± 10 points, TS at 11 ± 1 points and ACJI at 78 ± 18 points. Radiologically, 3 of 29 patients (10%) showed a persisting horizontal instability. The coracoclavicular (CC) distance improved from 22 preoperative to 10 mm postoperative, which was comparable to the contralateral side (10 mm, p = 0.103). At follow-up the CC distance increased to 13 mm (p = 0.0001).

CONCLUSION

AC-joint stabilisation with a single tunnel reconstruction using a second-generation implant results in good to excellent clinical results with high patient satisfaction. The additional AC augmentation improves stability in horizontal instable AC-joints and is recommended in all high-grade AC joint stabilisations. Nonetheless, reduction was slightly lost over time due to an elongation or suture failure of the coraco-clavicular fixation.

LEVEL OF EVIDENCE

IV.

Low rate of substantial loss of reduction immediately after hardware removal following acromioclavicular joint stabilization using a suspensory fixation system

PURPOSE

To evaluate immediate loss of reduction in patients undergoing hardware removal after arthroscopically assisted acromioclavicular (AC) joint stabilization using a high-tensile suture tape suspensory fixation system and to identify risk factors associated with immediate loss of reduction.

MATERIALS AND METHODS

Twenty-two consecutive patients with a mean age of 36.4 ± 12.6 years (19-56), who underwent hardware removal 18.2 ± 15.0 months following arthroscopically assisted stabilization surgery using a suspensory fixation system for AC joint injury between 01/2012 and 01/2021 were enrolled in this retrospective monocentric study. The coracoclavicular distance (CCD) as well as the clavicular dislocation/acromial thickness (D/A) ratio were measured on anterior-posterior radiographs prior to hardware removal and immediately postoperatively by two independent raters. Loss of reduction, defined as 10% increase in the CCD, was deemed substantial if the CCD increased 6 mm compared to preoperatively. Constitutional and surgical characteristics were assessed in a subgroup analysis to detect risk factors associated with loss of reduction.

RESULTS

Postoperatively, the CCD significantly increased from 12.6 ± 3.7 mm (4.8-19.0) to 14.5 ± 3.3 mm (8.7-20.6 mm) (p < 0.001) while the D/A ratio increased from 0.4 ± 0.3 (- 0.4-0.9) to 0.6 ± 0.3 (1.1-0.1) (p = 0.034) compared to preoperatively. In 10 cases (45%), loss of reduction was identified, while a substantial loss of reduction (> 6 mm) was only observed in one patient (4.5%). A shorter time interval between index stabilization surgery and hardware removal significantly corresponded to immediate loss of reduction (11.0 ± 5.6 vs. 30.0 ± 20.8 months; p = 0.007), as hardware removal within one year following index stabilization was significantly associated with immediate loss of reduction (p = 0.027; relative risk 3.4; odds ratio 11.67).

CONCLUSIONS

Substantial loss of reduction after hardware removal of a high-tensile suture tape suspensory fixation system was rare, indicating that the postoperative result of AC stabilization is not categorically at risk when performing this procedure. Even though radiological assessment of the patients showed a statistically significant immediate superior clavicular displacement after this rarely required procedure, with an increased incidence in the first year following stabilization, this may not negatively influence the results of ACJ stabilization in a clinically relevant way.

LEVEL OF EVIDENCE

IV.

Position of Coracoid Button Predicts Loss of Reduction in Acromioclavicular Joint Dislocation Patients Treated With the Suture-Button

BACKGROUND

Loss of reduction is the most common complication after acromioclavicular (AC) joint dislocation treated with the suture-button. Some predictors of it are known, but finding new predictors is an ongoing process. In this study, we evaluate the importance of the position of the coracoid button.

MATERIALS AND METHODS

Between April 2010 and February 2017, 186 patients with AC joint dislocation were identified. All patients were managed with the same surgical technique and postoperative protocol. The position of the coracoid button was determined immediately after surgery by anterior-posterior views of the operated shoulder and was classified as medial (Group A, 42 cases), central (Group B, 85 cases) and lateral (Group C, 59 cases) positions. The main outcome measurement was loss of reduction. The main analysis was the association between the coracoid button position and loss of reduction.

RESULTS

No significant difference was found in the baseline characteristics among 3 groups. During follow-up, there were 15 cases (35.7%) developing loss of reduction in Group A, 5 cases (5.9%) in Group B and 26 cases (44.1%) in Group C. The rate of loss of reduction in Groups A and C were higher than that in Group B (p < .05). Moreover, there was no significant difference in the rate of reduction loss between lateral and medial positions of the coracoid buttons (p > .05).

CONCLUSION

Our results indicated that both lateral and medial positions of the coracoid buttons could predict loss of reduction in AC joint dislocation patients treated with the suture-button.

Grade III Acromioclavicular Separations Treated With Suspensory Fixation Techniques: A Systematic Review of Level I Through IV Studies

Purpose

To perform a systematic review comparing clinical outcomes, radiographic outcomes, and complication rates after acute (surgery ≤6 weeks from injury) versus chronic (surgery >6 weeks from injury) acromioclavicular joint reconstructions for grade III injuries using modern suspensory fixation techniques.

Methods

We performed a systematic review of the literature examining acute versus chronic surgical treatment of Rockwood grade III acromioclavicular joint separations using the Cochrane registry, MEDLINE database, and Embase database over the past 10 years according to PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analyses) guidelines. The inclusion criteria included techniques using suspensory fixation, a minimum study size of 3 patients, a minimum follow-up period of 6 months, human studies, and English-language studies. The methodology of each study was evaluated using the Methodological Index for Non-randomized Studies (MINORS) tool for nonrandomized studies and the revised Cochrane risk-of-bias (RoB 2) tool for randomized controlled trials.

Results

The systematic review search yielded 20 studies with a total of 253 patients. There were 2 prospective randomized controlled trials, but most of the included studies were retrospective. On comparison of acute surgery (≤6 weeks) and chronic surgery (>6 weeks), individual studies reported a range of Constant scores of 84.4 to 98.2 and 80.8 to 94.1, respectively. The ranges of radiographic coracoclavicular distances reported at final follow-up also favored acute reconstructions, which showed improved reduction (9.2-15.7 mm and 11.7-18.6 mm, respectively). The reported complication rates ranged from 7% to 67% for acute reconstructions and from 0% to 30% for chronic reconstructions.

Conclusions

The ranges in the Constant score may favor acute reconstructions, but because of the heterogeneity in the surgical techniques in the literature, no definitive recommendations can be made regarding optimal timing.

Level of Evidence

Level IV, systematic review of Level I through IV studies.

Comparison of clinical efficacy between arthroscopically assisted Tight-Rope technique and clavicular hook plate fixation in treating acute high-grade acromioclavicular joint separations

INTRODUCTION

The purpose of this study was to compare the results of arthroscopically assisted reduction of acute acromioclavicular (AC) joint separations with the Tight-Rope technique with results of clavicular hook plate fixation.

MATERIALS AND METHODS

The 28 patients with acute high-grade AC joint dislocation were treated with arthroscopic assisted fixation using the Tight-Rope system, the arthroscopic evaluation and treatment of glenohumeral lesions were performed before AC ligament reconstruction. Each Tight-Rope technique group patient was matched with three controls that underwent clavicular hook plate fixation, and preoperation and postoperative visual analogue scale (VAS) and functional recovery (Constant Score) of the shoulder joint was assessed,. Furthermore, the demographics and clinical characteristics were compared between the two groups.

RESULTS

All patients had clinical and radiological results available at 2 years or greater (mean: 34; range: 24-72 months), they were statistically significant improvement in the constant score and VAS score at the end of follow-up respectively (P < 0.001). Compared with the clavicular hook plate group, Tight-Rope system group patients were incurred significant statistically lower skin incision, hospitalization time and estimated blood loss (P < 0.001), and the constant score and VAS score at the end of follow-up was significantly higher in the Tight-Rope group (P < 0.001). Patients who underwent clavicular hook plate had a higher incidence of fixation failure [10 cases (11.9%) versus 2 cases (7.1%)] than those of the Tight-Rope system group.

CONCLUSIONS

The Tight-Rope technique is advantageous for treating these patients because it is a minimally invasive procedure with low complications and superior clinical outcomes.

Long-term stability of coracoclavicular suture fixation for acute acromioclavicular joint separation

PURPOSE

The optimal (SBJI) surgical treatment for acute acromioclavicular (AC) joint disruption remains controversial. What is being presented is the long-term functional outcomes of a double cross-looped coracoclavicular (CC) suture technique with the intention of restoring both anteroposterior and superior displacement of the clavicle.

METHODS

Between 2007 and 2016, 81 patients underwent surgical reconstruction for acute acromioclavicular joint (AC) disruption in two orthopaedic centers. Two patients died for reasons unrelated to the treatment, and seven missed the final follow-up appointment, leaving 72 patients (67 males; 5 females; age 37 ± 12.4; range 15-64 years) for clinical and radiological assessments. All cases were classified according to the Rockwood classification as type III (n = 34), IV (n = 14) or V (n = 24). The dislocation was repaired with double cross-looped CC fixation using four Ethibond sutures passing underneath the coracoid and through a 4.5 mm drill hole in the clavicle in opposing directions to control both anteroposterior and vertical displacement. Radiological investigation preoperatively and at the last follow-up included anteroposterior and/or Zanca views, axillary or Alexander views, and comparative stress radiography of both AC joints. Patients were evaluated clinically with the Constant-Murley score (CMS) and Acromio Clavicular Joint Instability Score (ACJIS). Loss of reduction, subluxation, CC ligament ossification, post-traumatic arthritis, and peri-implant fractures were also recorded.

RESULTS

Seventy-two patients were available for the last clinical and radiological evaluations. At a median follow-up period of 6.3 ± 2.1 years (range 3-12 years), the CMS and ACJIS were 92.1 ± 7.2 (range 60-100 points) and 90.4 ± 8.6 (range 45-100 points), respectively. Complications included 9 (12.5%) patients with slight loss of reduction, 2 (1.7%) with dislocation recurrence, 1 (1.3%) with superficial infection, 1 (1.3%) with a fracture of the lateral end of the clavicle, and 2 (1.7%) with persistent tenderness in the AC joint. The incidence of periarticular ossification was 22.4% and did not affect the final outcome.

CONCLUSIONS

This technique represents an effective and low-cost treatment for acute AC joint separations.

LEVEL OF EVIDENCE

IV.

Biologic and synthetic ligament reconstructions achieve better functional scores compared to osteosynthesis in the treatment of acute acromioclavicular joint dislocation

PURPOSE

To systematically review the outcomes of surgical treatments of acute acromioclavicular joint dislocation.

METHODS

Studies were identified by electronic databases (Ovid, PubMed). All studies reporting functional and radiological outcomes of surgical treatments of acute acromioclavicular joint dislocations were included. Following data were extracted: authors and year, study design, level of evidence, number of patients, age, classification of acromioclavicular joint dislocation, time to surgery, surgical technique, follow-up, clinical and imaging outcomes, complications, and failures. Descriptive statistics was used, when a data pooling was not possible. Comparable outcomes were pooled to generate summary outcomes reported as frequency-weighted values. Quality appraisal was assessed through the MINORS checklist.

RESULTS

One hundred and thirty-three studies were included for a total of 4473 shoulders. Mean age of participants was 36.9 years. Mean follow-up was 42.06 months. Arthroscopy showed better ASES (p < 0.0001) and lower VAS pain score (p = 0.0249) compared to an open approach. Biologic and synthetic reconstructions demonstrated better results over osteosynthesis techniques. Biologic techniques showed overall better Constant (p = 0.0001) and DASH (p = 0.0215) scores, while synthetic reconstruction showed better UCLA score (p = 0.0001). Among suture buttons, triple button showed overall better results in Constant (p = 0.0001) and VAS (p = 0.0001) scores, while better results in DASH score (p = 0.0003) were achieved by 2 double button techniques. Overall, the level of evidence was low.

CONCLUSION

Biological and synthetic reconstructions achieved better functional scores compared to osteosynthesis. Among suture buttons, the triple button showed better functional performance.

LEVEL OF EVIDENCE

IV.

Locking plate combined with titanium cable for Neer type II distal clavicle fractures

Background

There is controversy about the optimal strategy treatment of unstable distal clavicle fractures. We explored use of a surgical strategy: combination of a distal clavicle locking plate and a titanium cable. The purpose of this retrospective case series study was to evaluate the clinical outcomes of this new strategy in treating Neer type II distal clavicle fractures.

Methods

Twenty-one patients with Neer type II distal clavicle fracture were treated with a distal clavicle locking plate and a titanium cable. All patients were followed for at least one year. We retrospectively collected and reviewed follow-up data. The clinical outcomes were assessed for union rate, functional score, and complication rate.

Results

All patients achieved bony union within 6 months. The average follow-up period was 20.6 months (range12–48 months). The mean Constant score at one-year follow-up was 94.6 ± 3.3 (range 84–98), and the mean UCLA (University of California, Los Angeles) score was 33.3 ± 2.6 (range 27–35). Only one complication (wound infection) was observed during follow-up. Two patients received another operation for implant removal due to local irritation.

Conclusions

Use of a distal clavicle locking plate in combination with a titanium cable for treatment of Neer type II fractures results in high union rate, a low complication rate, and good shoulder function. This combined surgical strategy can be considered an effective method for treating unstable distal clavicle fractures.

[Arthroscopically-assisted treatment of acute and chronic dislocations of the acromioclavicular joint : A prospective clinical trial]

BACKGROUND

Injuries of the acromioclavicular joint (ACJ) are frequent and often occur during sports. While arthroscopically-assisted stabilization of acute injuries of the ACJ is a well-established procedure, there is not much data available for arthroscopically-assisted stabilization of chronic injuries of the ACJ.

OBJECTIVES

This study assesses clinical and radiological results of arthroscopically-assisted stabilization of acute and chronic injuries of the ACJ.

MATERIALS AND METHODS

Thirty-six patients with acute and chronic injuries of the ACJ were assessed in a prospective clinical trial. Twenty-five patients with acute injuries (group A) and eleven patients with chronic injuries (group B) were included in this study. Patients of group A were operated using two suture-button systems, while patients of group B received one suture-button system and an autologous gracilis tendon graft.

RESULTS

In group A, the mean preoperative Constant score rated 38, and the ASES score rated 34. At follow-up the Constant score (92) and the ASES score (89) had improved. Panorama views revealed an increased coracoclavicular distance of the affected shoulder (15.8 mm) in comparison to the contralateral shoulder (10.9 mm). In group B, the preoperative Constant score measured 57. It improved to 72 points at follow-up. The ASES score improved from 39 to 72 points in the same period. Panorama views revealed an increased coracoclavicular distance of the affected shoulder (18.9 mm) in comparison to the contralateral shoulder (12.4 mm).

CONCLUSIONS

Stabilization of acute injuries of the ACJ with two suture-button systems is related to very good shoulder function after one year. The native coracoclavicular distance cannot be restored with this procedure. Stabilization of chronic injuries of the ACJ with a suture-button system and an autologous gracilis tendon graft is related to improved shoulder function after one year. However, shoulder function cannot be fully restored with the stabilization technique presented.

Risk factors related to the loss of reduction after acromioclavicular joint dislocation treated with the EndoButton device

Background

Anatomic ligament reconstruction using the EndobutBon device has been proven an effective technique for the management of acute acromioclavicular (AC) joint dislocation. The aim of this study was to analyze the risk factors causing loss of reduction after AC joint dislocation treated with the EndoButton device for open procedures.

Methods

A total of 107 patients who met the inclusion and excluded criteria finally were enrolled. We retrospectively analyzed the clinical tests, imaging data, and postoperative rehabilitation of patients in a stable reduction group and a loss of reduction group.

Results

Among all patients included in the study, the incidence of reduction failure was 14%. Univariate analysis identified that the time between injury to surgery, double or triple EndoButton, coracoid EndoButton position, weight-bearing time of the upper limb, and osteolysis had statistically significant associations with loss of reduction for the AC joint (P=0.022, 0.002, 0.000, 0.000, and 0.000 respectively). By using multivariate logistic regression analysis, we found that coracoid EndoButton position (P=0.002), weight-bearing time of the upper limb (P=0.011), and osteolysis (P=0.036) were the significant independent risk factors related to the loss of reduction after AC joint dislocation treated with the EndoButton device used with open procedures.

Conclusions

In order to reduce the incidence of reduction failure and improve the prognosis of patients, more accurate placement of EndoButton plates in surgery and guidance for patients in completing planned rehabilitation training are needed.

Early clinical and radiographic results of fixation with the TightRope device for Rockwood type V acromioclavicular joint dislocation: A retrospective review of 15 patients

OBJECTIVE

The aims of this study were, first, to assess the loss of reduction after fixation of Rockwood type V acromioclavicular joint dislocation (ACJD) with the TightRope device (Arthrex, Naples, FL, USA) and, second, to present the functional and radiological outcomes of this treatment.

METHODS

We retrospectively reviewed the medical records of 15 patients (12 males; mean age=39.2 years; age range=23-61) with Rockwood type V ACJD who were treated by the TightRope fixation device. The mean follow-up period was 19.3 (range=12-30) months. Functional status was assessed using the Constant-Murley score (CMS) at the final follow-up examination. To determine the reduction loss of ACJ, we measured and compared the coracoclavicular (CC) distance using radiographs with Zanca view in the early postoperative period and at the final follow-up examination. The fixation procedures were performed with an open technique using the TightRope fixation device.

RESULTS

The mean CMS at the final follow-up was 93.2 (range=82-100) points. All the patients experienced full recovery of the shoulder's range of motion, were able to return to the activities of daily living, and were satisfied with the treatment. ACJ reduction was successfully achieved in all the patients using the TightRope technique. Postoperative radiographs revealed no reduction loss in the ACJ, and the CC distance was well maintained. The mean CC distance was 19.95 (range=13.1-28.3) mm before surgery. The mean CC distance was 7.47 (range=4.2-11.5) mm in the early postoperative radiographic measurements. This difference was statistically significant (p=0.001). The mean CC distance at the final follow-up examination was 7.70 (range=4.5-11.7) mm. At the final follow-up visit, the shoulders of all the patients were still completely reduced, with a mean difference in the CC of 0.23 (range=0-1.3) mm compared with that in the early postoperative period. The difference in the CC between the early postoperative and final follow-up intervals was not statistically significant (p=0.055). No patient experienced recurrence or required an operation for hardware removal.

CONCLUSION

It seems that the TightRope device can provide anatomical restoration in patients with acute type V ACJD without subluxation at the final follow-up examination.

LEVEL OF EVIDENCE

Level IV, Therapeutic study.

Early clinical results of minimally invasive coracoclavicular ligament reconstruction can be maintained at a minimum of five years' follow-up

AIMS

There is a lack of long-term data for minimally invasive acromioclavicular (AC) joint repair. Furthermore, it is not clear if good early clinical results can be maintained over time. The purpose of this study was to report long-term results of minimally invasive AC joint reconstruction (MINAR) and compare it to corresponding short-term data.

METHODS

We assessed patients with a follow-up of at least five years after minimally invasive flip-button repair for high-grade AC joint dislocation. The clinical outcome was evaluated using the Constant score and a questionnaire. Ultrasound determined the coracoclavicular (CC) distance. Results of the current follow-up were compared to the short-term results of the same cohort.

RESULTS

A total of 50 patients (three females, 47 males) were successfully followed up for a minimum of five years. The mean follow-up was 7.7 years (63 months to 132 months). The overall Constant score was 94.4 points (54 to 100) versus 97.7 points (83 to 100) for the contralateral side showing a significant difference for the operated shoulder (p = 0.013) The mean difference in the CC distance between the operated and the contralateral shoulder was 3.7 mm (0.2 to 7.8; p = 0.010). In total, 16% (n = 8) of patients showed recurrent instability. All these cases were performed within the first 16 months after introduction of this technique. A total of 84% (n = 42) of the patients were able to return to their previous occupations and sport activities. Comparison of short-term and long-term results revealed no significant difference for the Constant Score (p = 0.348) and the CC distance (p = 0.974).

CONCLUSION

The clinical outcome of MINAR is good to excellent after long-term follow-up and no significant differences were found compared to short-term results. We therefore suggest this is a reliable technique for surgical treatment of high-grade AC joint dislocation. Cite this article: Bone Joint J 2020;102-B(7):918-924.

Radiographic features and complications following coracoclavicular ligament reconstruction

OBJECTIVE

To report radiographic features and complications of coracoclavicular ligament reconstruction and the association of radiographic features with symptomatology.

MATERIALS AND METHODS

Retrospective picture archiving and communication system query (1/2012-8/2018) identified subjects with prior coracoclavicular ligament reconstruction. Post-operative radiographs were reviewed with attention to the following: (1) acromioclavicular alignment, (2) coracoclavicular width, (3) distal clavicular osteolysis, (4) osseous tunnel widening, and (5) hardware complication or fracture. Medical records were reviewed to determine purpose of imaging follow-up (symptomatic versus routine). Statistical analysis determined associations between binary features and outcomes, and inter-reader agreement.

RESULT

Review of 55 charts identified 32 subjects (23 male, 9 females; age range 24-64; imaged 1-34 months following surgery) meeting inclusion criteria. Loss of acromioclavicular reduction was the most common imaging finding (n = 25, 78%), with 76% progressing to coracoclavicular interval widening. Distal clavicular osteolysis was seen in 21 cases (66%) and was significantly associated with loss of acromioclavicular joint reduction (p = 0.032). Tunnel widening occurred in 23 patients (82%) with more than one follow-up radiograph. Six (19%) had hardware complication or fracture. No radiographic feature or complication had significant correlation with symptomatology (p values 0.071-0.721). Inter-reader agreement was moderate to substantial for coracoclavicular interval widening and hardware complication, fair to substantial for tunnel widening, and fair to moderate for loss of acromioclavicular reduction and distal clavicular osteolysis.

CONCLUSION

Loss of acromioclavicular joint reduction, coracoclavicular interval widening, distal clavicular osteolysis, and tunnel widening are common radiographic features after coracoclavicular ligament reconstruction; however, they do not necessarily correlate with symptomatology.

What Regions of the Distal Clavicle Have the Greatest Bone Mineral Density and Cortical Thickness? A Cadaveric Study

BACKGROUND

Osteosynthesis of distal clavicle fractures can be challenging because of comminution, poor bone quality, and deforming forces at the fracture site. A better understanding of regional differences in the bone structure of the distal clavicle is critical to refine fracture fixation strategies, but the variations in BMD and cortical thickness throughout the distal clavicle have not been previously described.

PURPOSE

/questions (1) Which distal clavicular regions have the greatest BMD? (2) Which distal clavicular regions have the greatest cortical thickness values?

METHODS

Ten distal clavicle specimens were dissected from cadaveric shoulders. Eight specimens were female and two were male, with a mean (range) age of 63 years (59 to 67). The specimens were selected to match known epidemiology, as distal clavicular fractures occur more commonly in older patients with osteoporotic bone, and clavicular fractures in older patients are more common in females than males. The clavicles were then imaged using quantitative micro-CT to create 3-D images. The BMD and cortical thickness were calculated for 10 regions of interest in each specimen. These regions were selected to represent locations where distal clavicular fractures commonly occur and locations of likely bony comminution. Findings were compared between different regions using repeated measures ANOVA with Geiser-Greenhouse correction, followed by Bonferroni method multiple comparison testing. Effect size was also calculated to estimate the magnitude of difference between regions.

RESULTS

The four most medial regions of the distal clavicle contained the greatest BMD (anterior intertubercle space 887 ± 31 mgHA/cc, posterior intertubercle space 879 ± 26 mgHA/cc, anterior conoid tubercle 900 ± 21 mgHA/cc, posterior conoid tubercle 896 ± 27 mgHA/cc), while the four most lateral regions contained the least BMD (anterior lateral distal clavicle 804 ± 32 mgHA/cc, posterior lateral distal clavicle 800 ± 38 mgHA/cc, anterior medial distal clavicle 815 ± 27 mgHA/cc, posterior medial distal clavicle 795 ± 26 mgHA/cc). All four most medial regions had greater BMD than the four most lateral regions, with p < 0.001 for all comparisons. For the BMD ANOVA, η was determined to be 0.81, representing a large effect size. The four most medial regions of the distal clavicle also had the greatest cortical thickness (anterior intertubercle space 0.7 ± 0.2 mm, posterior intertubercle space 0.7 ± 0.3 mm, anterior conoid tubercle 0.9 ± 0.2 mm, posterior conoid tubercle 0.7 ± 0.2 mm), while the four most lateral regions had the smallest cortical thickness (anterior lateral distal clavicle 0.2 ± 0.1 mm, posterior lateral distal clavicle 0.2 ± 0.1 mm, anterior medial distal clavicle 0.3 ± 0.1 mm, posterior medial distal clavicle 0.2 ± 0.1 mm). All four most medial regions had greater cortical thickness than the four most lateral regions, with p < 0.001 for all comparisons. For the cortical thickness ANOVA, η was determined to be 0.80, representing a large effect size. No differences in BMDs and cortical thicknesses were found between anterior and posterior regions of interest in any given area.

CONCLUSIONS

In the distal clavicle, BMD and cortical thickness are greatest in the conoid tubercle and intertubercle space. When compared with clavicular regions lateral to the trapezoid tubercle, the BMD and cortical thickness of the conoid tubercle and intertubercle space were increased, with a large magnitude of difference.

CLINICAL RELEVANCE

Distal clavicular fractures are prone to comminution and modern treatment strategies have centered on the use of locking plate technology and/or suspensory fixation between the coracoid and the clavicle. However, screw pullout or cortical button pull through are known complications of locking plate and suspensory fixation, respectively. Therefore, it seems intuitive that implant placement during internal fixation of distal clavicle fractures should take advantage of the best-available bone. Although osteosynthesis was not directly studied, our study suggests that the best screw purchase in the distal clavicle is available in the areas of the conoid tubercle and intertubercle space, as these areas had the best bone quality. Targeting these areas during implant fixation would likely reduce implant failure and strengthen fixation. Future studies should build on our findings to determine if osteosynthesis of distal clavicular fractures with targeted screw purchase or cortical button placement in the conoid tubercle and intertubercle space increase fixation strength and decreases construct failure. Furthermore, our findings provide consideration for novel distal clavicular locking plate designs with modified screw trajectories or refined surgical techniques with suspensory fixation implants to reliably capture these areas of greatest bone quality.

Analysis of risk factors for loss of reduction after acromioclavicular joint dislocation treated with the suture-button

BACKGROUND

The most commonly reported complication after acromioclavicular (AC) joint dislocation treated with the Suture-button is loss of reduction. Loss of reduction is a major factor influencing the patient's joint function and subjective satisfaction. The objective of this study is to analyze the risk factors causing loss of reduction after AC joint dislocation treated with the Suture-button.

METHODS

One hundred and thirty patients with AC joint dislocation who were surgically treated the Suture-button in our hospital from February 2009 to February 2015, were recorded their age, sex, BMI, time from injury to surgery, Rockwood's classification, with or without osteoporosis, double or triple button technique, position of the clavicle tunnel, tunnel diameter, coracoid button position, alignment of the button, acromioclavicular ligament repair or not, different methods of postoperative limb immobilization, and so on. Mean comparisons or chi-square test was used for univariate analysis of the above factors, and then multivariate logistic regression analysis was performed to predict risk factors.

RESULTS

Reduction was lost in 23.1% of the patients. Univariate analysis showed that button alignment, double or triple button technique, coracoid button position, position of the clavicle tunnel, acromioclavicular ligament repair or not and osteoporosis had statistically significant association with loss of reduction for AC joint (P = 0.031, 0.034, 0.000, 0.042, 0.047 and 0.000 respectively). Multivariate logistic regression analysis demonstrated that osteoporosis (P = 0.003), position of the clavicle tunnel (P = 0.032) and coracoid button position (P < 0.001) were the risk factors that significantly associated with the loss of reduction after AC joint dislocation treated with the Suture-button.

CONCLUSIONS

Clavicle tunnel location using relative ratio method, accurate placement of button plate under coracoid process (inside or outside deviation <20°), various reinforcement operations for patients with osteoporosis are important factors in preventing loss of reduction.

Current Concepts in the Operative Management of Acromioclavicular Dislocations: A Systematic Review and Meta-analysis of Operative Techniques

BACKGROUND

Acromioclavicular (AC) instability is a frequent injury affecting young and athletic populations. Symptomatic, high-grade dislocations may be managed by a myriad of operative techniques that utilize different grafts to achieve reduction. Comparative data are lacking on the ability of these techniques to achieve excellent patient outcomes and stable AC reduction and to minimize complications.

PURPOSE

To systematically review the outcomes and complications of different techniques of AC joint reconstruction.

STUDY DESIGN

Systematic review and meta-analysis.

METHODS

The MEDLINE, Scopus, Embase, and Cochrane Library databases were accessed to perform a systematic review of the scientific literature from 2000 to 2018 using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) criteria with the following keywords: "acromioclavicular" and "reconstruction." Included articles were evaluated for loss of reduction, complication rate, revision rate, and change in coracoclavicular distance. Articles were stratified by graft and surgical material used: suture only, Endobutton with suture, TightRope, GraftRope, synthetic artificial ligament, tendon graft, and Weaver-Dunn coracoacromial ligament transfer. These outcomes were pooled using a random-effects model and stratified by surgical technique and arthroscopic versus open reconstruction.

RESULTS

Fifty-eight articles were included in the analysis, with 63 homogeneous populations composed of 1704 patients. The mean age was 37.1 years (range, 15-80 years) with a mean follow-up of 34.3 months (range, 1.5-186 months). The overall failure rate was 20.8% (95% CI, 16.9%-25.2%). The overall pooled complication rate was 14.2% (95% CI, 10.5%-18.8%). The most common complications were infection (6.3% [95% CI, 4.7%-8.2%]), fracture to the coracoid or distal clavicle (5.7% [95% CI, 4.3%-7.6%]), and hardware/button failure (4.2% [95% CI, 3.1%-5.8%]). There were no differences between arthroscopic and open techniques in regard to loss of reduction (P = .858), overall complication rate (P = .774), and revision rate (P = .390). Open surgery had a greater rate of clavicular/coracoid fractures than arthroscopic surgery (P = .048). Heterogeneity, best assessed from the pooled loss of reduction, was measured as I² = 64.0%.

CONCLUSION

Open and arthroscopic AC joint reconstruction techniques have no differences in loss of reduction, the complication rate, and the revision rate based on the available literature. Complications are significant, and profiles vary between surgical techniques, which should be evaluated in the decision making of selecting the technique.

All-Arthroscopic Reconstruction of Severe Chronic Acromioclavicular Joint Dislocations

PURPOSE

To report the outcomes of all-arthroscopic coracoclavicular (CC) ligament reconstruction and simultaneous diagnosis and treatment of glenohumeral pathologies in patients with symptomatic, chronic (>6 weeks), complete (Rockwood type III-V) acromioclavicular joint (ACJ) separations.

METHODS

We prospectively followed up 57 consecutive patients treated arthroscopically for chronic Rockwood type III (n = 11), type IV (n = 19), and type V (n = 27) ACJ dislocations. Previous ACJ surgery failed in 11 (19%). The mean delay between injury and surgery was 39 months (range, 6 months to 17 years). The mean age at surgery was 42 years (range, 19-71 years). After glenohumeral exploration, an arthroscopic modified Weaver-Dunn procedure with CC suture button fixation (Twinbridge) was performed. The CC reduction and tunnel position were analyzed with radiographs and computed tomography. The mean follow-up period was 36 months (range, 12-72 months).

RESULTS

Intra-articular pathology was treated arthroscopically in 27 patients (48%): 17 labral tears, 8 rotator cuff tears (3 partial and 5 complete), and 15 biceps lesions (4 SLAP lesions and 11 subluxations). At last follow-up, 7 patients (12%) experienced recurrent ACJ instability: 2 frank dislocations (1 trauma and 1 infection) and 5 ACJ subluxations. There was no significant correlation between subluxation and clinical outcome. The rate of recurrent ACJ instability was significantly higher in patients with higher-grade ACJ dislocations (P < .01) and/or previous failed surgery (P < .001). Recurrent subluxation was observed in 3 cases of lateral migration of the coracoid button with lateral tunnel placement, as well as 2 cases of anterior migration of the clavicular button with anterior tunnel placement. The Constant score increased from 67 (range, 28-89) to 85.5 (range, 66-100), and the mean Subjective Shoulder Value increased from 54% to 85% (P < .001). At last follow-up, 95% of patients (54 of 57) were satisfied.

CONCLUSIONS

All-arthroscopic treatment allows successful CC ligament reconstruction and simultaneous diagnosis and treatment of frequently associated (48%) glenohumeral lesions. Higher-grade ACJ dislocations, previous ACJ surgery, and misplacement of bone tunnels are risk factors for recurrent instability.

LEVEL OF EVIDENCE

Level IV, case series.

Clinical outcomes of a single-tunnel technique for coracoclavicular and acromioclavicular ligament reconstruction

BACKGROUND

A large number of surgical techniques have been described to treat acromioclavicular (AC) joint separations. Despite the high success rates with double-tunnel reconstruction, this method has been associated with the risk of coracoid and clavicle fractures. This study aimed to evaluate the outcomes of the first cohort of patients who underwent single-tunnel AC and coracoclavicular (CC) ligament reconstruction. It was hypothesized that this technique would result in maintenance of reduction and a minimal risk of fracture of the coracoid and clavicle.

METHODS

All patients who underwent single-tunnel AC joint reconstruction between 2012 and 2015 via the technique with 2-year follow-up were included. Objective outcomes recorded were maintenance of reduction as measured by the CC distance on radiographs, shoulder range of motion, strength, return to sports, and complications. Subjective outcomes included maintenance of reduction on visual inspection and various patient-reported outcomes.

RESULTS

Seventeen patients were included with a mean age of 41 ± 12 years. Separation types included types III, IV, and V. The mean follow-up period was 29 ± 9 months (range, 16-45 months). The CC distance improved from 37.4 to 30.0 mm on plain radiographs (P = .006), the American Shoulder and Elbow Surgeons score improved from 67.0 to 90.1 (P = .094), and the Single Assessment Numeric Evaluation score improved from 30.5 to 91.1 (P = .025). Reduction on visual inspection was maintained in 16 patients (94.1%). Regarding sports participation, 14 patients (82.4%) returned to their preinjury level. The most common complication was a prominent suture knot stack, occurring in 3 patients (17.6%), which was removed in all 3 in a second procedure. There were no clavicle or coracoid fractures.

CONCLUSION

The described technique results in satisfactory objective and patient-reported outcomes and return to sports while avoiding coracoid and clavicle fractures.

New insights in the treatment of acromioclavicular separation

A direct force on the superior aspect of the shoulder may cause acromioclavicular (AC) dislocation or separation. Severe dislocations can lead to chronic impairment, especially in the athlete and high-demand manual laborer. The dislocation is classified according to Rockwood. Types I and II are treated nonoperatively, while types IV, V and VI are generally treated operatively. Controversy exists regarding the optimal treatment of type III dislocations in the high-demand patient. Recent evidence suggests that these should be treated nonoperatively initially. Classic surgical techniques were associated with high complication rates, including recurrent dislocations and hardware breakage. In recent years, many new techniques have been introduced in order to improve the outcomes. Arthroscopic reconstruction or repair techniques have promising short-term results. This article aims to provide a current concepts review on the treatment of AC dislocations with emphasis on recent developments.

Anatomic Coracoclavicular Ligament Reconstruction for the Treatment of Acute Acromioclavicular Joint Dislocation: Minimum 10-Year Follow-up

Background:

The long-term clinical and radiographic outcomes following coracoclavicular (CC) ligament reconstruction for the operative treatment of acute acromioclavicular (AC) joint dislocation remain uncertain. The purpose of the present study was to determine the long-term clinical and radiographic outcomes of CC ligament reconstruction and to identify risk factors for unfavorable outcomes.

Methods:

We reviewed 20 cases of AC joint dislocation in 19 patients (18 male and 1 female; mean age, 32.3 years) that were treated with single-bundle reconstruction. The mean duration of follow-up was 12.7 years. We measured the CC vertical distance (CCD) on the anteroposterior view and compared the affected and unaffected sides (CCD ratio). We divided the patients into those with a CCD ratio of <25% (Group 1) and those with a CCD ratio of ≥25% (Group 2). We radiographically investigated the clavicular tunnel anteroposterior (CTAP) angle, clavicular tunnel ratio, and coracoid tunnel orientation on the basis of the entry and exit points at the base of the coracoid. For the coracoid tunnel orientation, we compared center-center orientation and noncenter-center orientation.

Results:

Group 1 comprised 17 cases (85%), and Group 2 comprised 3 cases (15%). At the time of the latest follow-up, Group 1 had a significantly higher mean Constant score than Group 2 (98.2 compared with 90.7; p = 0.038). Of the 3 radiographic parameters, only the CTAP angle was significantly different between the 2 groups (p < 0.0001). Two (67%) of the 3 cases in Group 2 were associated with posterior AC joint displacement.

Conclusions:

CC ligament reconstruction for the treatment of acute AC joint dislocation resulted in successful long-term clinical and radiographic outcomes. It is important to decrease the CTAP angle and to ensure proper anatomic placement of the clavicular and coracoid tunnels at the time of surgery.

Level of Evidence:

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Open capsular and ligament reconstruction with semitendinosus hamstring autograft successfully controls superior and posterior translation for type V acromioclavicular joint dislocation

PURPOSE

Appropriate surgical management for type V complete acromioclavicular (AC) joint dislocation remains controversial. The purpose of this paper is to retrospectively report the clinical and radiographic outcomes of an open surgical technique consisting for AC joint ligamentous and capsular reconstruction using autologous hamstring tendon grafts and semi-permanent sutures.

METHODS

Between January 2005 and December 2011, 32 consecutive patients with symptomatic type V complete AC joint dislocation underwent surgical treatment using the same technique. The median time from injury to surgery was 45 days (range 24-90). The average median postoperative clinical and radiographic follow-up time was 30 months (range 24-33). Clinical outcomes measures included the ASES score, the visual analog score (VAS), and subjective patient satisfaction score. Minimum follow-up was 2 years.

RESULTS

ASES score increased from a median of 38.2 ± 6.2 preoperative to 92.1 ± 4.7 postoperatively (p ≤ 0.05). The median VAS score improved from 62 mm (range 45-100 mm) preoperatively to 8 mm (range 0-20 mm) at final follow-up (p ≤ 0.05). No patient experienced pain or discomfort with either direct palpation of the AC joint or with cross-body adduction. Final radiographs demonstrated symmetric AC joint contour in 25/32 (78%) patients. Seven patients (22%) radiographically demonstrated superior translation of the distal clavicle relative to the superior margin of the acromion but less than 50% of the clavicular width. 30/32 patients (93%) were able to return to their pre-injury level of work and sports activities.

CONCLUSIONS

This novel surgical technique using a free graft and braided suture for simultaneous coracoclavicular ligament and AC joint capsular reconstruction successfully controls superior and posterior translations after type V AC joint dislocation and minimizes the incidence of persistent postoperative AC joint subluxation.

LEVEL OF EVIDENCE

Retrospective case series, Level IV.

Early complications of acromioclavicular joint reconstruction requiring reoperation

PURPOSE

Prior studies have reported high complication rates with acromioclavicular joint reconstruction (ACJR). However, many of these reports have suffered from small sample sizes and inclusion of older surgical techniques. The purpose of this study was to determine the rates of early complications requiring reoperation in patients treated with ACJR.

METHODS

From 2007 to 2011, patients who were treated with ACJR were identified using the PearlDiver database, a large insurance database in the USA. The following reoperations were then queried from this patient cohort: irrigation and debridement within 30 days of index surgery, manipulation under anaesthesia (MUA) of the shoulder joint within 3 months of index surgery, and revision ACJR, distal clavicle excision, and removal of hardware within 6 months of index surgery.

RESULTS

In total, 2106 patients treated with ACJR were identified. The reoperation rates for irrigation and debridement, MUA, revision ACJR, distal clavicle excision, and removal of hardware were 2.6, 1.3, 4.2, 2.8, and 6.2 %, respectively. Patients ≥35 years of age and females more likely to undergo a reoperation after ACJR. Specifically, patients ≥35 years of age were more likely to undergo MUA and revision ACJR, while patients ≥50 years of age were more likely to undergo an irrigation and debridement. Females were more likely than males to undergo revision ACJR and distal clavicle excision.

CONCLUSIONS

Older patients and females were more likely to experience postoperative complications requiring reoperations, including revision ACJR, distal clavicle excision, and irrigation and debridement. By analysing a large cohort of patients across multiple centres and providers, this study provides valuable insight into the recent complication profiles of ACJR, allowing surgeons to appropriately counsel patients on the risks of these procedures.

LEVEL OF EVIDENCE

IV.

Axial-Plane Biomechanical Evaluation of 2 Suspensory Cortical Button Fixation Constructs for Acromioclavicular Joint Reconstruction

BACKGROUND

Although numerous suture-button fixation techniques for acromioclavicular (AC) joint reconstruction have been validated with biomechanical testing in the superior direction, clinical reports continue to demonstrate high rates of construct slippage and breakage.

PURPOSE

To compare the stability of a novel closed-loop double Endobutton construct with a commercially available cortical button system in both the axial and superior directions.

STUDY DESIGN

Controlled laboratory study.

METHODS

Six matched pairs of fresh-frozen cadaveric upper extremities were anatomically dissected and prepared to simulate a complete AC joint dislocation. One side of each pair was reconstructed with the double Endobutton (DE) construct and other side with the dog bone button (DB) construct. The specimens were then tested using a materials testing machine, determining initial superior and axial displacements with a preload, and then cyclically loaded in the axial direction with 70 N for 5000 cycles. Displacement was again measured with the same preloads at fixed cycle intervals. The specimens were then loaded superiorly to failure.

RESULTS

At 5000 cycles, the mean axial displacement was 1.7 mm for the DB group and 1.2 mm for the DE group (P = .19), and the mean superior displacement was 1.1 mm for the DB group and 0.7 mm for the DE group (P = .32). Load at failure was similar (558 N for DE, 552 N for DB; P = .96). There was no statistically significant difference in the modes of failure.

CONCLUSION

Biomechanical testing of both constructs showed similar fixation stability after cyclical axial loading and similar loads to failure.

CLINICAL RELEVANCE

The strength of both constructs after cyclical loading in the axial plane and load-to-failure testing in the superior plane validate their continued clinical use for achieving stability in AC joint reconstruction procedures.

Acute high-grade acromioclavicular dislocations treated with triple button device (MINAR): Preliminary results

OBJECTIVE

Describe the clinical and radiological results of triple button device in the treatment of high-grade AC dislocations (Rockwood, type V) and assess whether improves vertical and horizontal stability compared to the techniques previously described.

MATERIAL AND METHODS

This retrospective study included 39 patients with type V acromioclavicular dislocations treated with Twin Tail TightRope™ system (triple button device). Of the 39 patients, 33 (26 men and 7 women) were able to participate in clinical and radiographic follow up. At the time of surgery, the mean age was 25years±7(range, 17-49). All patients underwent bilateral-weighted Zanca (CC distance) and Alexander view (AC distance) as well as the Constant Score (CS) and Acromioclavicular Joint Instability Scoring System (ACJI). Radiological and clinical outcome was assessed during routine follow-up examinations preoperatively, postoperatively, 1, 3, 6 months and every year after the surgery. The presence of calcification, degenerative changes, mobilization of implants and bone resorption were also assessed.

RESULTS

After a mean follow up of 25±4months (range 14-38), the results of the Constant (CS) were 94.1±5,5 (range 76-100) and test ACJI 87.3±9,8 (range 65-100), showing no significant differences with the uninjured shoulder (CS 95.8±2.5, range 83-100; ACJI 94.1±3.7, range 80-100). At final review, we observed that preoperative coracoclavicular distance (Zanca View) improved from 21,75±1.97mm to 8,73mm±0.75 and the acromioclavicular distance (Alexander View) from 12,65mm±1.99 to 0,35±0.3mm. Compared with healthy shoulder, these differences were not significant. There was no loss of reduction with this system in the vertical plane. 4 patients (12.12%) revealed signs of posterior instability with worse clinical test results. The presence of degenerative joint changes (6,06%), calcifications (27,2%) or mobilization of the implant (18,18%) was not associated with worse clinical outcomes.

CONCLUSION

Twin Tail device using minimally invasive technique improves stability in the vertical and, specially in the horizontal plane relative to the previously described techniques without increasing number of complications.

Comparison of Short-term Complications Between 2 Methods of Coracoclavicular Ligament Reconstruction: A Multicenter Study

Background:

Numerous techniques have been used to treat acromioclavicular (AC) joint dislocation, with anatomic reconstruction of the coracoclavicular (CC) ligaments becoming a popular method of fixation. Anatomic CC ligament reconstruction is commonly performed with cortical fixation buttons (CFBs) or tendon grafts (TGs).

Purpose:

To report and compare short-term complications associated with AC joint stabilization procedures using CFBs or TGs.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

We conducted a retrospective review of the operative treatment of AC joint injuries between April 2007 and January 2013 at 2 institutions. Thirty-eight patients who had undergone a procedure for AC joint instability were evaluated. In these 38 patients with a mean age of 36.2 years, 18 shoulders underwent fixation using the CFB technique and 20 shoulders underwent reconstruction using the TG technique.

Results:

The overall complication rate was 42.1% (16/38). There were 11 complications in the 18 patients in the CFB group (61.1%), including 7 construct failures resulting in a loss of reduction. The most common mode of failure was suture breakage (n = 3), followed by button migration (n = 2) and coracoid fracture (n = 2). There were 5 complications in the TG group (25%), including 3 cases of asymptomatic subluxation, 1 symptomatic suture granuloma, and 1 superficial infection. There were no instances of construct failure seen in TG fixations. CFB fixation was found to have a statistically significant increase in complications (P = .0243) and construct failure (P = .002) compared with TG fixation.

Conclusion:

CFB fixation was associated with a higher rate of failure and higher rate of early complications when compared with TG fixation.

Importance of additional temporary pin fixation combined coracoclavicular augmentation using a suture button device for acute acromioclavicular joint dislocation

INTRODUCTION

We evaluated the outcomes of coracoclavicular (CC) augmentation using a suture button device with additional temporary pin fixation for acute acromioclavicular (AC) joint dislocation.

MATERIALS AND METHODS

Thirty-six consecutive cases who underwent CC augmentation using TightRope™ (Arthrex, Naples, FL, USA) were included. We temporarily fixed trans-articular pins in the first 10 cases (TA group) and a trans-spine pin in the next 26 cases (TS group). The radiological and clinical outcomes were evaluated at minimum 2 years postoperatively.

RESULTS

The mean follow-up period was 56.7 months (range, 24-84 months). At the final follow-up evaluation, reduction status showed anatomical reduction in 25 cases (69.4 %), slight loss of reduction in seven cases (19.4 %), partial loss of reduction in two cases (5.6 %), and total loss of reduction in two cases (5.6 %). The mean ASES score, UCLA score, and subjective shoulder value were 92.3, 32.9, and 91.6 %, respectively. There were no significant differences between the two groups with respect to the outcomes. Intraoperative complications occurred in three cases (8.3 %) including two cases of failed reduction and one case of technical failure of the implant. Postoperative complications occurred in three cases (8.3 %) including one case of pin tract infection and distal clavicle fracture at the clavicle-hole, one case of reduction loss by severe subsidence of the clavicular button, and one case of shoulder stiffness.

CONCLUSIONS

CC augmentation using a suture button device with temporary pin fixation yielded satisfactory radiological and clinical outcomes. These results support that temporary pin fixation for the AC joint may help to protect the AC reduction in the early phase of healing and rigid scar formation when performing CC fixation using a suture button device.

LEVEL OF EVIDENCE

Level-IV, Retrospective Case Series, Treatment Study.

Surgical treatment of acute acromioclavicular joint dislocations: hook plate versus minimally invasive reconstruction

PURPOSE

This study was performed to compare the clinical results of a minimally invasive technique for acute acromioclavicular (AC) joint dislocation repair with the traditional hook plate fixation.

METHODS

Forty-four patients with an acute (within 2 weeks after trauma) complete AC joint separation (35 male, nine female; median age 36.2 years, range 18-56) underwent surgical repair with either a minimally invasive AC joint repair or a conventional hook plate. Functional outcome was evaluated using the Constant-Murley Score (CMS), the TAFT score and the AC joint instability score (ACJI). Radiographic evaluation was performed with bilateral anterior-posterior (a.p.) stress and Alexander views.

RESULTS

All patients were available after a median follow-up of 32 months (range 24-51). There were no significant differences in the mean CMS, Taft score and the ACJI between the two groups. The radiological assessment revealed no significant difference in the coracoclavicular distance. In both groups, a slight loss of reduction was observed. Periarticular ossification was seen in 11 patients of the minimally invasive AC joint repair and eight patients of the hook plate group but this did not affect the final outcome. Hook plates were removed after a median interval of 11.9 weeks (range 10-13).

CONCLUSION

Good clinical results can be achieved with both minimally invasive AC joint repair and hook plate fixation. However, in the hook plate group a second operation is mandatory for plate removal.

LEVEL OF EVIDENCE

III.

Continuous Loop Double Endobutton Reconstruction for Acromioclavicular Joint Dislocation

BACKGROUND

Current anatomic methods for reconstruction of the dislocated acromioclavicular (AC) joint show improved clinical results but continue to be associated with significant rates of fixation loss and complications, limiting more widespread use.

PURPOSE

To determine the long-term clinical and radiologic outcomes of a novel surgical technique using a closed-loop double Endobutton device to reconstruct both acute and chronic dislocations.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Between 2003 and 2012, a total of 35 patients (31 men, 4 women) at a mean age of 42 years (range, 25-70 years) were surgically treated for a Rockwood type III or greater AC joint dislocation with the described technique (26 chronic, 9 acute). Imbrication of the AC joint capsule and deltotrapezial fascia was performed in all patients. Biological bridging across the coracoclavicular (CC) interval was performed in all patients by use of coracoacromial (CA) ligament transfer in 28 patients and primary repair of the CC ligament in 7 patients. Complete follow-up information was obtained for 31 of 35 patients.

RESULTS

At a mean follow-up of 5.2 years (range, 27-144 months), the construct remained stable in all but 1 patient. The mean CC interval difference was 1.1 mm (range, -2.5 to 4.0 mm) and was <2 mm in 87% of patients. The mean Constant score was 98; the mean University of California, Los Angeles Shoulder Rating Scale score was 34; and the mean American Shoulder and Elbow Surgeons Shoulder Score was 98. Follow-up MRI evaluation in 10 patients consistently demonstrated a wide band of dense scar tissue between the coracoid and clavicle. No infections, fractures, or perioperative complications occurred.

CONCLUSION

Excellent results were obtained and maintained over long-term follow-up. The continuous loop device eliminated the possibility of knot slippage or breakage. MRI confirmed a robust healing response. The described technique resulted in outcomes that were significantly superior to historical reports of nonsurgical outcomes, and the technique can be recommended both for acute and chronic dislocations.

Minimally Invasive Coracoclavicular Ligament Reconstruction With a Flip-Button Technique (MINAR): Clinical and Radiological Midterm Results

BACKGROUND

Acromioclavicular (AC) joint dislocation is a frequent injury in sports.

HYPOTHESIS

A minimally invasive flip-button technique, MINAR (minimally invasive acromioclavicular joint reconstruction), will achieve good clinical and radiographic results in the surgical treatment of high-grade AC joint dislocations.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

In this study, 96 patients with AC joint dislocation grades III through V and minimally invasive flip-button repair were identified. Radiographic assessment was performed by use of the Alexander view and by anteroposterior stress radiograph. Clinical outcomes were assessed with the Constant and Taft scores. Factors that influenced outcomes, such as age, time from trauma to surgery, and degree of dislocation, were evaluated.

RESULTS

Of the 96 patients, 83 (86.4%; 3 women and 80 men) were able to participate in clinical and radiographic follow-up. The average age of the participants was 39 years (range, 17-80 years). At a mean follow-up of 39 months (range, 12-78 months), clinical assessment revealed excellent results with a mean Constant score of 94.7 (range, 61-100). Clinical and radiological assessment using the Taft score also showed excellent results, with a mean score of 10.8 (range, 3-12). The mean time period from trauma to surgery was 6 days (range, 0-22 days), and mean duration of surgery was 48 minutes (range, 24-98 minutes). Nine patients (10.8%) underwent revision surgery due to recurrent dislocation (n = 8) or wound infection (n = 1). Radiological assessment showed that 18 patients had sustained a loss of reduction defined as subluxation of 50% of the clavicle shaft width in the vertical plane. However, there was no significant correlation (P = .254) with clinical outcome. Patient age was a relevant factor influencing outcome, as significantly higher outcome values were detected for younger patients (P = .024). No significant influence was shown for the time period from trauma to surgery (P = .336) or degree of dislocation after trauma (P = .987).

CONCLUSION

The MINAR technique is a safe procedure and achieves good to excellent clinical and radiographic results in the surgical treatment of high-grade AC joint dislocations. Despite the simplicity of this technique, the surgeon has to overcome the learning curve to minimize the risk of recurrent dislocation.

Biomechanical evaluation of coracoid tunnel size and location for coracoclavicular ligament reconstruction

PURPOSE

The purpose of this study was to determine the effect of coracoid tunnel size and location on the biomechanical characteristics of cortical button fixation for coracoclavicular ligament reconstruction.

METHODS

Thirteen matched pairs of cadaveric scapulae were used to determine the effects of coracoid tunnel size, and 6 matched pairs were used to determine the effects of coracoid tunnel location. For tunnel size, a 4.5-mm hole was drilled in the base of the coracoid of one scapula and a 6-mm hole was drilled in the contralateral scapula. For tunnel location, 2 holes were drilled: (1) The first group received a hole centered in the coracoid base and a hole 1.5 cm distal from the first, along the axis of the coracoid. (2) The second group received holes that were offset anteromedially from the first set of holes (base eccentric and distal eccentric). A cortical button-suture tape construct was placed through each tunnel, and constructs were then loaded to failure.

RESULTS

For tunnel size specimens, load at ultimate failure was significantly greater for the 4.5-mm group compared with the 6-mm group (557.6 ± 48.5 N v 466.9 ± 42.2 N, P < .05). For tunnel location, load at ultimate failure was significantly greater for the centered-distal tunnel group compared with the eccentric-distal group (538.1 ± 70.2 N v 381.0 ± 68.6 N, P < .05).

CONCLUSIONS

A 4.5-mm tunnel in the coracoid provided greater strength for cortical button fixation than a 6-mm tunnel. In the distal coracoid, centered tunnels provided greater strength than eccentric tunnels.

CLINICAL RELEVANCE

When performing cortical button fixation at the coracoid process for coracoclavicular ligament reconstruction, a 4.5-mm tunnel provides greater fixation strength than a 6-mm tunnel. The base of the coracoid is more forgiving than the distal coracoid regarding location.

Chronic acromioclavicular joint dislocations treated by the GraftRope device

BACKGROUND AND PURPOSE

Surgical treatment of chronic acromioclavicular joint dislocations is challenging, and no single procedure can be considered to be the gold standard. In 2010, the GraftRope method (Arthrex Inc., Naples, FL) was introduced in a case series of 10 patients, showing good clinical results and no complications. We wanted to evaluate the GraftRope method in a prospective consecutive series.

PATIENTS AND METHODS

8 patients with chronic Rockwood type III-V acromioclavicular joint dislocations were treated surgically using the GraftRope method. The patients were clinically evaluated and a CT scan was performed to assess the integrity of the repair.

RESULTS AND INTERPRETATION

In 4 of the 8 patients, loss of reduction was seen within the first 6 weeks postoperatively. A coracoid fracture was the reason in 3 cases and graft failure was the reason in 1 case. In 3 of the 4 patients with intact repairs, the results were excellent with no subjective shoulder disability 12 months postoperatively. It was our intention to include 30 patients in this prospective treatment series, but due to the high rate of complications the study was discontinued prematurely. Based on our results and other recent reports, we cannot recommend the GraftRope method as a treatment option for chronic acromioclavicular joint dislocations.

Reconstruction of the coracoclavicular and acromioclavicular ligaments with semitendinosus tendon graft: a pilot study

PURPOSE

this study was conducted to assess the safety and efficacy of a new surgical technique for anatomical reconstruction of the coracoclavicular (CC) and acromioclavicular (AC) ligaments using one single-strand semitendinosus tendon graft.

METHODS

eighteen patients affected by chronic type III-V AC joint dislocations were included in the present study between January 2010 and March 2012. All underwent the same surgical operation and rehabilitation protocol. The semitendinosus tendon was harvested from the ipsilateral knee. The CC and AC ligaments were reconstructed using the graft passed beneath the coracoid and through bone tunnels in the clavicle and in the acromion. The graft was secured with non-absorbable sutures. Radiographic recurrence of AC joint dislocation was the primary outcome. Clinical outcome was assessed using the DASH score and normalized Constant score. Wilcoxon's signed-rank test was used for comparison between pre- and postoperative results. Significance was set at p ≤ 0.05.

RESULTS

the mean follow-up duration was 26.4±2.3 months (range: 24-30 months). On X-ray evaluation, only two patients (11%) showed asymptomatic recurrence of AC joint instability. Comparison between pre- and postoperative DASH and Constant scores showed significant clinical improvement (p<0.001).

CONCLUSION

anatomical reconstruction of CC and AC ligaments using an autologous semitendinosus tendon graft for the treatment of AC joint dislocation provided good and reliable clinical and radiological results with a low failure rate at short-term follow-up.

LEVEL OF EVIDENCE

level IV, therapeutic case series.