Traumatic Anterior Shoulder Dislocation Research Articles

Simple bilateral anterior shoulder dislocation: A case report and review of the literature

Bilateral shoulder dislocations are usually of the posterior type, which is commonly associated with seizures, electrocution or electroconvulsive therapy. Bilateral anterior shoulder dislocations are very rare and usually result from significant trauma. Simple bilateral anterior shoulder dislocations without associated fracture are much rarer and not many cases have been reported in the literature. We present a traumatic bilateral simple anterior shoulder dislocation in a 24-year-old male without any features of ligamentous laxity, and review the international literature on simple bilateral anterior shoulder dislocations. From the review we conclude that seizures are as important an aetiology of simple bilateral anterior shoulder dislocation as is trauma. Moreover, this injury is not as rare as was considered in the past.

Flexion Adduction External Rotation (FADER) method for reduction of anterior shoulder dislocation: a study of 30 cases

Objective: To assess the success rate of Flexion Adduction External Rotation (FADER) technique in reducing anterior shoulder dislocation and to report our experience. Methods: A prospective study included 30 patient, with 21 male and 9 female associated with acute anterior dislocation of shoulder treated by FADER in a medical college attached hospital. Results: The FADER technique was used to reduce 30 cases of anterior dislocation shoulder during the study period. 27 cases were first time dislocations and 3 cases second time recurrent dislocations. Fracture of greater tuberosity was present in 2 cases. Reduction is achieved in first attempt in 28 cases, in second attempt in 1 case, and 1 case was reduced under general anaesthesia. No complications were noted. Overall success rate was 96.6% Conclusion: we report the successful use of FADER technique for reduction of traumatic anterior shoulder dislocations, mainly without traction, exhaustion, second assistant, anaesthesia, sedation and uncomfortable position. We believe that FADER may also be applied by inexperienced physicians, as it is simple, easily understood and reproducible with success Keywords: Anterior, Shoulder, Dislocation, FADER, Reduction.

"8 plate": an alternative device to fix highly recurrent traumatic anterior gleno-humeral instability in patients with severe impairment of the anterior capsule.

Background: There is still debate about the best treatment option for highly recurrent anterior shoulder dislocation in patients with severe impairment of the anterior capsule and/or recurrence after either arthroscopic or open capsulorrhaphy. Materials and Methods: The clinical and radiological findings of 7 patients treated with an open capsulorrhaphy stabilized with an “8 plate” for a highly recurrent traumatic anterior shoulder dislocation with severe impairment of the anterior capsule and a large Bankart lesion were retrospectively reviewed. Follow-up evaluation included VAS for pain, Constant-Murley, Simple Shoulder Test, ASES, UCLA, Quick DASH, Rowe, Walsch-Duplay scores, as well as X-rays of the operated shoulder. Results: At follow-up none of the patients reported subsequent dislocations. Range of motion of the shoulder was complete in all cases, but one. Results of the functional scoring systems were satisfactory. X-rays showed no osteolysis and good position of the plate. Conclusion: To our knowledge, this is the first report in the literature about an open capsular tensioning and Bankart lesion repair performed with an “8 plate”. We believe that this is a reliable and effective procedure to address traumatic anterior re-dislocation of the gleno-humeral joint when the capsule is extensively torn and frayed or in revision cases. Moreover the “8 plate” is ideal to be applied in such a narrow space on the slant surface of the scapular neck close to the glenoid rim.

Does External Rotation Bracing for Anterior Shoulder Dislocation Actually Result in Reduction of the Labrum?

Background: External rotation (ER) bracing has been shown to improve labral reduction in cadaveric studies, but this has not translated to universal improvement in re-dislocation rates in clinical series. Purpose: To systematically review and critically appraise the literature that investigates how well the labrum is actually reduced by ER in patients who have had an anterior shoulder dislocation. Study Design: Systematic review. Methods: We conducted a systematic review of the literature using the online databases Medline, EMBASE, and the Cochrane Controlled Trial Register. Studies were included if they reported on the difference in labral reduction after ER and internal rotation bracing in patients who had a traumatic anterior shoulder dislocation. Results: Of the 6 studies included, 5 assessed labral reduction on magnetic resonance imaging and 1 arthroscopically. Each study reported an overall improvement in labral reduction with ER, but anatomic reduction was not commonly achieved. This was despite the use of extreme positions that are unlikely to be well tolerated. Conclusion: External rotation results in anatomic reduction of the labrum in only 35% of cases. We postulate that failure to reduce the labrum may be a contraindication to ER bracing and propose further study to determine whether acute MRI could be used to help identify patients in whom ER achieves labral reduction in a comfortable position. This approach also has the advantage of avoiding the significant inconvenience of ER bracing in those in whom the labrum does not reduce and are therefore theoretically less likely to benefit. However, it is a novel strategy with significant resource implications and therefore warrants further study.

The Comparison of Results of Early and Late Rehabilitation Following Arthroscopic Bankart Repair with Knotless Anchor in Recurrent Traumatic Anterior Shoulder Dislocation

Objectives:The aim of this study was to compare the clinical and functional results of early and late rehabilitation of patients who had undergone arthroscopic Bankart repair with knotless anchor for recurrent shoulder dislocation and to define the most appropriate rehabilitation time and the effect of this on recurrence.Methods:34 patients (32 male and 2 female) were included in this study. The patients were diagnosed with recurrent anterior shoulder dislocation with Bankart lesion in our institution. The exclusion criteria in this study were multi-directional shoulder instability, wide osseous Bankart lesion, wide Hill-Sachs lesion or rotator cuff tear. All patients underwent arthroscopic Bankart repair. Knotless anchor was used in all patients. The patients were grouped into 2 groups postoperatively according to the immobilization period and rehabilitation regimen. Both groups equally consisted of 17 patients. (Group 1; early rehabilitation group, Group 2; late rehabilitation group) All patients were examined retrospectively. Gender, age, dislocated side, dominant hand, recurrence, presence of additional pathologies, time of first and last dislocations preoperatively and numbers of dislocations were the demographic data recorded. At the final follow-up; the restriction in external rotation was measured by comparative goniometry and clinical evaluation was made using the Constant and Rowe scores. One-sample T-test, Mann-Whitney U Test, Crosstabs Chi Square Test and Shapiro-Wilk Tests used for statistical analysis.Results:The mean age of the patients in Group 1 was found to be 25.1 ± 6.5 ( 17-43) years and in Group 2, 30.8 ± 6.8 (21-46) years. After a mean follow-up period of 14.7 months, no patients in Group 1 experienced a recurrence, whereas in Group 2 over the mean follow-up period of 38.5 months, there was dislocation, following episodes of subluxation, in only 1 patient (5.8%). When the parameters of first dislocation, last dislocation and number of dislocations were evaluated separately in two groups, no statistical difference was observed between the groups in the relevant parameters (n.s.). A statistically significant difference was determined between the groups in respect to the restriction in external rotation (p<0.05). There was no statistically significant difference between the groups in respect to the Constant and Rowe scores (n.s.).Conclusion:The most important result of this study was that the early beginning of rehabilitation yielded less external rotation restriction than late beginning of rehabilitation. The absence of recurrence in the group of early beginning of rehabilitation reminds the question “does early rehabilitation reduce recurrence rates?” The findings in this study should be confirmed with further prospective, randomized and longer follow-up studies.

Incidence of and risk factors for traumatic anterior shoulder dislocation: an epidemiologic study in high-school rugby players

The incidence of reinjuries due to glenohumeral instability and the major risk factors for primary anterior shoulder dislocation in youth rugby players have been unclear. The purpose of this study was to investigate the incidence, mechanisms, and intrinsic risk factors of shoulder dislocation in elite high-school rugby union teams during the 2012 season. A total of 378 male rugby players from 7 high-school teams were investigated by use of self-administered preseason and postseason questionnaires. The prevalence of a history of shoulder dislocation was 14.8%, and there were 21 events of primary shoulder dislocation of the 74 overall shoulder injuries that were sustained during the season (3.2 events per 1000 player-hours of match exposure). During the season, 54.3% of the shoulders with at least one episode of shoulder dislocation had reinjury. This study also indicated that the persistence of glenohumeral instability might affect the player's self-assessed condition, regardless of the incidence during the current season. By a multivariate logistic regression method, a history of shoulder dislocation on the opposite side before the season was found to be a risk factor for contralateral primary shoulder dislocation (odds ratio, 3.56; 95% confidence interval, 1.27-9.97; P = .02). High-school rugby players with a history of shoulder dislocation are not playing at full capacity and also have a significant rate of reinjury as well as a high risk of dislocating the other shoulder. These findings may be helpful in deciding on the proper treatment of primary anterior shoulder dislocation in young rugby players.

Remplissage: An Arthroscopic Technique for Management of The Engaging Hill-Sachs Lesion

Following a traumatic anterior shoulder dislocation, the treating physician is challenged not only with management of this injury extremely but also with the goal of preventing recurrent instability episodes. Although arthroscopic Bankart repair has been shown to significantly decrease the prevalence of recurrent instability, some patients remain significantly at risk for failed operative management owing to the presence of anterior glenoid and posterior humeral head bony loss that may remain unrecognized or unaddressed at the time of surgical intervention. In patients with these posterior-lateral humeral head defects (Hill-Sachs lesions), arthroscopic posterior capsulotenodesis, or remplissage, is an arthroscopic procedure that can be used to supplement arthroscopic Bankart repair. The remplissage procedure offers an effective and valuable technique for some patients with Hill-Sachs lesions and has been demonstrated to reduce the risk of recurrent instability.

Evaluation of a treatment algorithm for acute traumatic osseous Bankart lesions resulting from first time dislocation of the shoulder with a two year follow-up

BackgroundStudies dealing with acute osseous Bankart lesions and corresponding treatment strategies are rare. The purpose of this study is to analyze the results after applying our treatment algorithm for acute glenoid rim fractures caused by first time traumatic anterior shoulder dislocations.Methods25 patients were included in this retrospective case series. All patients sustained a first time shoulder dislocation caused by ski or snowboard accidents. An osseous Bankart lesion was detected in all shoulders. Operative therapy was performed in patients with osseous defects of 5% or more, otherwise conservative therapy was initiated. Primary study outcome parameter was the Rowe score. Additionally, the outer rotation deficit and operative complications were analysed.Results12 patients showed a defect size of less than 5% and were treated conservatively. The average lesion size was 2%. For these patients, the Rowe score was excellent in 58%, good in 25%, and moderate in 17% of patients. Three patients (25%) complained about a feeling of instability. 13 patients had a lesion size of more than 5%, average 15%, and were treated operatively. The Rowe score for this group was excellent in 54%, good in 31%, and moderate results in 15% of patients. One patient (8%) complained about a feeling of instability, without recurrent dislocations. There were no statistically significant differences between both study groups (ROWE score: p = 0.98).ConclusionsApplying our treatment algorithm for acute osseous Bankart lesions consisting of a conservative strategy for small defect sizes and a surgical approach for medium-sized and large defects leads to encouraging mid-term results and a low rate of recurrent instability in active patients.

Immobilization in internal or external rotation does not change recurrence rates after traumatic anterior shoulder dislocation

The objective of this study was to systematically review and quantitatively synthesize the data on recurrence rates after shoulder immobilization in internal versus external rotation in first-time, traumatic shoulder dislocations. We performed a systematic search of the keywords "(((external rotation) OR internal rotation) AND immobilization) AND shoulder" in the online databases PubMed, EMBASE, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Library. Random-effects models were used to calculate the cumulatively pooled risk ratios (RRs) of recurrent shoulder dislocations. All analyses were also stratified by age. We included 5 studies with a total of 471 patients (230 internal rotation and 241 external rotation) published between 2001 and 2011 in English. The pooled random-effects RR for recurrence of shoulder dislocations at all ages was 0.74 (95% confidence interval [CI], 0.44-1.27; P = .278). The RR was 0.70 (95% CI, 0.38 to 1.29; P = .250) for patients aged 30 years or younger and 0.78 (95% CI, 0.32 to 1.88; P = .579) for those aged older than 30 years. The current best evidence does not support a relative effectiveness of immobilization in external rotation compared with internal rotation to avoid recurrent shoulder dislocations in patients with traumatic anterior shoulder dislocations.

Posterior Dislocation of Long Head of Biceps Tendon following Traumatic Anterior Shoulder Dislocation: Imaging and Intra-operative Findings

A case of posterior dislocation of the long head of biceps tendon, a rare occurrence following traumatic anterior glenohumeral dislocation, along with complete rotator cuff rupture and large haemarthrosis is presented with imaging and intra-operative findings. The interposed tendon prevented complete reduction. Appearances at MRI were diagnostic and directed the surgical approach.

The interobserver reliability in diagnosing osseous lesions after first-time anterior shoulder dislocation comparing plain radiographs with computed tomography scans

Recurrence after first-time traumatic anterior shoulder dislocation is frequent. The prevalence of glenoid bone loss ranges from 41% after a first-time dislocation to 86% with recurrent dislocation. Postoperative recurrence can occur in up to 10% of cases. Thus, misdiagnosis of bony glenoid rim lesions has been assumed a major cause for failure. We evaluated the interobserver reliability of radiologic diagnoses after first-time traumatic shoulder dislocation based on radiographs and computed tomography (CT) images. Digital radiographs before and after reduction and CT images after reduction of 20 patients with a first-time shoulder dislocation were assessed by 6 observers. It was recorded whether they diagnosed a lesion at the greater tuberosity, a lesion at the glenoid rim, a Hill-Sachs lesion, or any other skeletal pathology. The average agreement among the investigators was evaluated, and radiographic diagnoses were compared with those based on CT images. Of the 10 cases that presented with a glenoid rim fracture, each investigator had overlooked at least 1 fracture (range, 1-4) on the radiographs. No investigator had diagnosed all 8 Hill-Sachs lesions on the presented images. The average overall agreement among the investigators and corresponding sensitivity and specificity were calculated. Agreement of diagnoses based on radiographs with those based on CT images was lowest for glenoid rim fractures and Hill-Sachs lesions. Radiographs seem inferior to CT scans for assessing osseous lesions especially at the glenoid rim. We suggest performing a CT scan of the shoulder after primary dislocation to apply the correct treatment early and potentially avoid further dislocations.

Travmatik anterior omuz çıkıklarında artroskopik bankart tamiri

Arthroscopic bankart repair in the traumatic anterior shoulder dislocation Objective: To analyze the results of arthroscopic Bankart repair for recurrent anterior shoulder dislocations. Material and Method: 16 patients who were performed arthroscopic Bankart repair due to recurrent anterior shoulder dislocation were included in the study. There were four females and 12 males. X ray and Magnetic resonans imaging was admitted for all patients. Results were evaluated according to Rowe and Constant scores. Results: The mean number of dislocations was 10.2, mean Rowe score was 90.6 and mean Constant score was 94.3. Concomitant superior labral anterior and posterior repair was performed for two patients. Three patients had Hill Sachs defects and three patients had defects on the glenoid rim. One patient was detected with traumatic redislocation 15 months after the operation and was reoperated. One patient was reoperated because of intraarticular penetration of the anchor. Mean follow up time was 32.6 months. Conclusion: Arthroscopic bancart repair has good clinical outcome. Increased number of preoperative dislocations may increase the frequency of redo surgery; this should be kept in mind for these

ROLE OF CT SCAN IN PREDICTING RECURRENCE FOLLOWING PRIMARY TRAUMATIC SHOULDER DISLOCATION

BackgroundShoulder dislocation is a common sporting injury. Glenoid deficiency is thought to be a risk factor for recurrent shoulder dislocations. This study was performed to assess the role of CT...

Evaluation of immobilization in external rotation after primary traumatic anterior shoulder dislocation: 5-year results

It is still not clear which method is the most efficient for treating primary traumatic anterior shoulder dislocation. Immobilization in external rotation has become increasingly discussed within the last 10 years. The aim of this study was to evaluate the rate of recurrence and clinical outcome of the immobilization in external rotation after primary traumatic anterior dislocation within a midterm period of 5 years. Additionally, a summary of literature is given according to the present knowledge of this issue. From May 2004 to May 2006, 28 patients with primary traumatic anterior shoulder dislocations were included in a prospective MRI-controlled study. After a follow-up of 5 years, the recurrence rate and clinical outcomes of the patients were evaluated using clinical scores (Constant and Murley score, Western Ontario Shoulder Instability Index, Rowe score). After 5 years, 26 patients (93 %; males, n = 25; female, n = 1; mean age, 29.3 years) were interviewed concerning re-dislocations. In the meantime, four patients (15 %) experienced a re-dislocation (ø 12.2 months) after the end of the immobilization. Overall, 21 patients (75 %) were included in a clinical follow-up (CM score: ø 92.8 points; Western Ontario Shoulder Instability Index: ø 87 %; Rowe score (in 17 patients): ø 94.2 points). Upon clinical examination, unidirectional anterior instability was found in one patient, which corresponds to an overall instability rate of 19 % within the examined patient population including the re-dislocations. Immobilization in external rotation shows satisfactory results after 5 years in regard to recurrence and instability rates and clinical outcomes. The data show that with immobilization in external rotation, re-dislocations occur within the first 2 years.

Kinesthetically guided reaching accuracy in individuals with a history of traumatic anterior shoulder dislocation

Background: The purpose of the study was to investigate whether individuals with a history of traumatic anterior shoulder dislocation show larger reaching errors than those with healthy shoulders and to determine if they implement different reaching strategies to protect the injured shoulder. Methods: Ten people with a history of traumatic anterior shoulder dislocation and 15 with healthy shoulders volunteered for this study. After viewing targets in space, participants pointed with the unconstrained arm to remembered target locations in space without visual guidance. Nine different targets were located in various planes and heights. Endpoint reaching errors were determined by comparing the finger endpoint position without visual guidance to the target location. Shoulder rotation angle at the endpoint was also compared between groups. Results: Participants with injured shoulders were able to point voluntarily to visually specified targets as accurately as participants with healthy shoulders (1 cm difference). However, participants with injured shoulders showed less shoulder external rotation (average 12° difference) at the target location when compared with healthy shoulders. This difference was consistent over a large range of target locations. Conclusion: Individuals with a history of traumatic anterior shoulder dislocation have sufficient kinesthetic information about their upper limb orientation to point accurately to visually specified targets in space. However, individuals with injured shoulders acquired a new motor strategy to reach with less shoulder external rotation, presumably to protect the injured shoulder from recurrent injuries.

The Cost-Effectiveness Of Arthroscopic Bankart Repair Versus Non-Operative Treatment For First-time, Traumatic, Anterior Shoulder Dislocations

Objectives:Prior studies have demonstrated excellent results after acute arthroscopic stabilization of first-time, traumatic, anterior shoulder dislocations in young patients. However, this treatment has not been widely accepted as first line management of this injury. Surgeons may point to the initial direct costs of surgical management as one rationale for conservative management of these injuries. The purpose of this study is to determine whether surgical stabilization of first time traumatic anterior shoulder dislocation represents a cost effective treatment alternative when compared to non-operative treatment with physical therapy.Methods:A decision-analytic model was constructed to assess the cost-effectiveness of arthroscopic bankart repair compared with non-operative treatment with physical therapy based on the incremental cost-effectiveness ratio (ICER). A threshold ICER of less than $100,000/quality adjusted life year gained was set to define a cost-effective treatment modality. Health state utilities for treatment outcomes of a recurrently dislocating shoulder and a stable shoulder were collected prospectively by surveying fifty patient volunteers using a time trade-offMethod:The probabilities of the various treatment outcomes and the costs associated with treatment were derived from the orthopaedic literature and adjusted Medicare reimbursement rates.Results:The incremental cost-effectiveness ratio (ICER) for arthroscopic bankart versus non-operative treatment was $43,500. The estimated cost of surgical treatment must increase from approximately $11,000 to over $24,000 for surgery to no longer be cost-effective. The one-year probability of dislocation after bankart repair must increase from approximately 4% to 7%, or the probability of dislocation after non-operative treatment must decrease from 17% to approximately 11% for surgery to no longer be cost-effectiveConclusion:Using currently available probabilities, estimated costs, and prospectively collected health state utilities, arthroscopic bankart repair represents a cost-effective treatment alternative for first-time, traumatic anterior shoulder dislocations in young patients. These results are robust when the costs, probabilities, and utilities are widely varied. Further studies should focus on identifying patient populations who fall within the threshold values identified in this analysis.

Modified transglenoid sutures for bankart repair for the treatment of recurrent anterior shoulder instability

BackgroundRecurrent shoulder dislocation is a challenging orthopedic problem. Bankart lesion is the main pathological abnormality in cases of traumatic anterior shoulder dislocation. Many procedures have been performed for treatment, both open and arthroscopic. Transglenoid sutures were used in the past before the use of the anchors.ObjectivesThe aim of this study was to evaluate the results of the modified transglenoid sutures for recurrent anterior shoulder instability.Patients and methodsNineteen patients, with a mean age of 25.4 years (range 20-44 years), had been treated by a modified technique using 2-3 labral sutures using #5 PDS sutures and passing the ends of the sutures through two holes in the glenoid, the first at 4 o'clock on the right side (8 o'clock on the left) and the second at 1 o'clock on the right side (11 o'clock on the left), and tied over the soft tissue and the bone bridge through a small posterior skin incision. They were followed up for a mean of 39.2 months (range 24-54 months).ResultsThe mean Rowe score was changed from 27.9 preoperatively to 96.8 postoperatively. All patients were satisfied by the final results of the operation. This procedure reduced the cost of the operation.ConclusionThe transglenoid suture technique with the modification is suitable for the treatment of recurrent traumatic shoulder instability, especially in developing societies. However, this is still a preliminary study and it should be conducted on more patients.

Paper 31: Arthroscopic Management of First-time Traumatic Anterior Shoulder Dislocation in Young Athletes: Evaluation and Results in 100 Cases with 7.4 years Follow-up

In the literature several publications show the advantages of the early arthroscopic stabilization after the first episode of traumatic shoulder dislocation. Nevertheless it is still considered by some authors a controversial topic. The purpose of this paper is a retrospective evaluation of our first 100 cases treated with arthroscopic stabilization. Between September 1989 and May 2005 100 arthroscopic stabilization of first time dislocation were performed in athletes. Mean age at surgery moment was 22 years. 78% of the patients were rugby players. Until October 1995 we used the Transglenoid suture technique in 23 cases and the others 77 cases were stabilized with Suture Anchor technique. The mean follow-up was 7.4 years (range: 3-19 years). Capsular tear with complete labrum detachment (type III lesion) was the most frequent surgical finding. Minor Bony Bankart lesions (<25%) were found in 19 cases. 75 cases (75%) of osteochondral Hill-Sachs lesions and 15 cases (15%) of bone HillSachs lesions were identified. We treated 2 cases of Humeral Avulsion of Glenohumeral ligament (HAGL) with arhtoscopic and mini open technique. According to the Rowe scale we obtained excellent and good results for 96% (74 cases) of the patients treated with the Suture Anchor Technique and in 87% (20 cases) of the patients treated with the Transglenoid technique. Return to sport was allowed after the 4th month, being at pre-injury level for all cases. The average time was 5.3 months (4-7). Many studies have shown a high percentage of redislocation after non-surgical treatment. Younger patients and practicing contact sports, over head sports or sports of high speed (snow skiing, motocross) increase this risk.

Paper 21: Primary Repair versus Conservative Treatment After First Time Traumatic Anterior Shoulder Dislocation

Paper 21: Primary Repair versus Conservative Treatment After First Time Traumatic Anterior Shoulder Dislocation

Calculating anterior glenoid bone loss using the Bernageau profile view

To determine if it is possible to measure glenoid bone loss by using the Bernageau view and to compare it to a 3D CT scan. Fifty healthy subjects with a mean age of 34 ± 8 years old and 31 (62 %) male were submitted to the Bernageau view X-ray of both shoulders. Three blinded evaluators measured the distance between the posterior and anterior glenoid rim. Ten patients with multiple episodes of unilateral traumatic anterior shoulder dislocation with a mean age of 34 ± 9.1 years old and 90 % male were submitted to the same X-ray technique to determine the percentage of glenoid bone loss. They were also submitted to a bilateral 3D CT scan to be compared to the radiographs. In the 50 asymptomatic subjects, the AP distance was 24.48 mm ± 3.32 mm in the left shoulder and 24.82 mm ± 3.16 mm in the right shoulder. Comparing the X-ray study and the 3D CT scan of the ten patients with multiple episodes, there was no significant statistical difference of the AP normal distance in both methods (p = 0.646), the AP erosion distance (p = 0.386), as well as the percentage of bone loss (p = 0.513). Moreover, the differences between the percentages of bone loss in the X-ray, compared with the 3D CT scan were, on average 2.28 % (range 0 to 6.05 %). The Bernageau radiographic view is an accurate and reproducible technique for measuring the presence of glenoid erosion, with similar results when compared to the 3D CT scan.