Dynamic Radiologic Evaluation of Horizontal Instability in Acute Acromioclavicular Joint Dislocations

Transcription

1 Dynamic Radiologic Evaluation of Horizontal Instability in Acute Acromioclavicular Joint Dislocations Mark Tauber,* y MD, Heiko Koller,* MD, Wolfgang Hitzl, z PhD, and Herbert Resch,* MD From the *Department of Traumatology and Sports Injuries, University Hospital of Salzburg, Austria, and the z Research Office for Biostatistics, Paracelsus Medical University, Salzburg, Austria Background: Biplane radiologic evaluation is indispensable for the correct diagnosis of acute acromioclavicular (AC) joint injuries. Thus far, no functional radiographic techniques have been quantified to evaluate horizontal instability in acute AC joint dislocations. Hypothesis: Supine dynamic axillary lateral shoulder views detect horizontal instability of the distal clavicle in patients with acute AC joint dislocations. Study Design: Cohort study (Diagnosis); Level of evidence, 2. Methods: Twenty-five consecutive patients with a mean age of years with acute AC joint injury underwent biplane radiologic evaluation, including a conventional Zanca view and an axillary lateral view in a sitting position. In addition, supine axillary lateral views with the arm in 90 of abduction and 60 of flexion and extension were taken to evaluate the horizontal dynamics of the distal clavicle. The gleno-acromio-clavicular angle (GACA) was introduced and used to quantify the horizontal clavicular dynamics in terms of angle differences. The unaffected shoulders served as the control group. Results: Superior dislocation of the lateral clavicle in the Zanca view was classified as Rockwood type II in 7 patients, type III in 15, and type V in 3. The axillary lateral view in a sitting position showed posterior dislocation of the distal clavicle in 8 patients (Rockwood type IV injury). Dynamic radiologic evaluation revealed an average GACA difference between the neutral and anterior position of the arm of for the unaffected shoulder. In the injured AC joints, 11 patients showed no radiologic evidence of horizontal instability (group A) with a GACA difference of Increased anteroposterior translation was evident in 14 patients (group B) with a GACA difference of (P \.001). Conclusion: Functional axillary radiologic evaluation seems to represent a simple imaging tool to reveal dynamic horizontal instability. Clinical Relevance: Horizontal instability of the distal clavicle in acute AC joint injuries represents an indication for surgical treatment. Dynamic axillary radiologic evaluation may detect previously missed unstable injuries. This evaluation might be relevant when deciding on surgical AC joint stabilization. Keywords: acromioclavicular joint dislocation; horizontal instability; axillary view; dynamic radiologic evaluation The acromioclavicular (AC) joint has attracted increased attention in recent years. Biomechanical 3,7,9,15,17,18,31,33 and radiologic 2,11-14,23 studies dealing with the AC joint have been published, as well as clinical reports focusing on new surgical techniques for AC joint reconstruction. 6,10,16,24,26,28,29,32 y Address correspondence to Mark Tauber, MD, Department of Traumatology and Sports Injuries, Paracelsus Medical University Salzburg, Muellner Hauptstrasse 48, 5020 Salzburg, Austria ( m.tauber@ salk.at). The authors declared that they had no conflicts of interests in their authorship and publication of this contribution. The American Journal of Sports Medicine, Vol. 38, No. 6 DOI: / Ó 2010 The Author(s) Cadenat 5 was the first to describe the pathomechanism leading to AC joint separation as a sequential injury beginning with the AC ligaments, progressing to the coracoclavicular (CC) ligament complex, and finally involving the deltoid and trapezius muscles and fascia. On the basis of the increasing soft tissue injury, Rockwood et al 22 classified AC joint injuries into types I to VI: type I, AC ligament sprain with the AC joint intact; type II, disruption of the AC ligaments with sprain of the CC ligaments; type III, AC and CC ligaments torn with the CC distance increased between 25% and 100% more than in the normal shoulder; type IV, complete dislocation with posterior displacement of the distal clavicle into or through the trapezius muscle; type V, increase of the CC distance 100% to 300% more than in the normal shoulder, including disruption of the 1188

2 Vol. 38, No. 6, 2010 Diagnosis of Acute AC Joint Dislocations 1189 deltotrapezius fascia; and type VI, complete dislocation with inferior displacement of the distal clavicle into a subacromial or subcoracoid position. For correct diagnosis, an exact radiographic examination is indispensable. The examination should include a trauma series with 2 orthogonal views of the AC joint. In addition to the anteroposterior Zanca view 34 with a10 to 15 cephalic tilt of the x-ray, 34 an axillary lateral view is strongly recommended to reveal any posterior displacement of the distal clavicle. In the literature, there are no clear recommendations regarding the position of the patient when the axillary lateral view is taken. It can be performed in the standing, sitting, or supine position. However, in patients with an acute complete AC joint dislocation, the position during radiography is of crucial importance. A standing or sitting position results in drooping of the affected shoulder, which is associated with inferomedial rotation of the scapula along the chest wall due to the disrupted scapuloclavicular suspension. However, these forces are neutralized in the supine position with the arm abducted 90 in the scapular plane. In this context, Alexander 1 described a modification of the true scapulolateral view to demonstrate the posterior displacement of the clavicle that occurs with AC injuries. With the patient sitting or standing, the shoulders are thrust forward at the time when the radiograph is taken. In cases of AC ligament disruption, the distal clavicle will be superiorly displaced and overlap with the acromion. Even with this special lateral stress view, the problem of drooping of the shoulder and subsequent anteroinferior rotation of the scapula has to be considered. The purpose of this study was to validate a standard protocol for radiologic evaluation of acute AC joint injuries. As a result of our experience with the misdiagnosis of horizontal instability of the distal clavicle through various static methods of axillary lateral radiography, a novel radiologic protocol was introduced, consisting of supine dynamic axillary lateral views to document anteroposterior dynamics of the distal clavicle in terms of horizontal instability. The gleno-acromio-clavicular angle (GACA) was introduced to quantify the horizontal dynamics and allow for statistical analysis. MATERIALS AND METHODS Between January and December 2008, 27 consecutive patients sustaining acute AC joint injuries with radiologically evident incomplete or complete AC separation were treated at the authors institution. The inclusion criteria were (1) AC joint injury within 7 days, (2) no previous injuries or surgical procedures of the affected shoulder, (3) no AC joint injuries of the contralateral shoulder, and (4) no deforming musculoskeletal or neurologic disorders involving the shoulder girdle. According to these criteria, 25 patients were included in this prospective study. There were 18 men and 7 women with a mean (6 standard deviation [SD]) age of years. The left shoulder was affected in 14 patients and the right shoulder in 11. The Figure 1. Standard axillary lateral view of a right shoulder with the patient in a sitting position. The anterior tip of the acromion and the anterolateral edge of the distal clavicle are in line with the acromioclavicular joint in an anatomical position indicating no posterior subluxation or dislocation in terms of horizontal instability. right shoulder was the dominant upper extremity in 12 patients (48%). The mechanism of injury was sportsrelated in 19 patients, a traffic accident in 4, and a level fall in 2. After assessment of medical history and physical examination of the affected shoulder, radiologic examination was performed. A bilateral Zanca view 34 and an axillary lateral view (Figure 1) with the patient in a sitting position represented the previous standard projections for radiologic examination of acute AC joint injuries at the authors institution. The injury was classified according to the classification of Rockwood et al. 22 Undisplaced AC sprains (type I injuries) were excluded. Type II injuries were verified in doubtful cases using stress views by hanging 10-kg weights on the wrists. A type IV injury was diagnosed if the distal clavicle showed evident posterior translation in relation to the anterior tip of the acromion (Figure 2), independent from the degree of AC joint separation in the Zanca view. Clinical and radiologic observations led to doubts regarding the detection of horizontal instability of the distal clavicle when the axillary lateral view was taken in the sitting position. Disruption of the ligaments (mainly the AC but also the CC) results in increased anteroposterior translation of the lateral clavicular end. 9 The slight leaning position of the body in the sitting position, the pathologic anterior rotation of the scapula related to the position of the arm, and the inclination of the x-ray beam may disguise posterior subluxation or dislocation of the distal clavicle in the axillary lateral view, leading to the misdiagnosis of horizontal instability (Rockwood type IV injury). To eliminate these influencing factors, we decided

3 1190 Tauber et al The American Journal of Sports Medicine Figure 2. Standard axillary lateral view of a right shoulder (type II injury in the Zanca view 34 ) with the patient in a sitting position showing a type IV injury according to the classification of Rockwood et al. 22 Notice the considerable posterior dislocation of the distal clavicle. Figure 3. Patient positioning for the axillary lateral view. The patient is supine with the arm in 90 of abduction (position 0). The cassette is placed superior to the shoulder and the x-ray tube is placed inferior to the axilla with an upward tilt of 10 to 15 and a lateral inclination of 30. The dynamics of the distal clavicle are documented in 60 of flexion (position 1) and 60 of extension (position 2). to perform the axillary lateral view with the patient supine and the arm abducted to 90 (position 0). The cassette was placed superior to the shoulder and the x-ray tube was placed inferior to the axilla with an upward tilt of 10 to 15 and a lateral inclination of 30 (Figure 3). In addition, axillary lateral views with the arm in 90 of abduction, 60 of flexion (position 1), and 60 of extension (position 2) were taken to evaluate the horizontal dynamics of the distal clavicle in regard to the acromion in terms of anteroposterior AC instability. If the patient experienced pain during active maneuvers, the arm was held by the physician. Figure 4. Three-dimensional graph of an axillary lateral shoulder view with the humeral head subtracted. The broken lines mark the gleno-acromio-clavicular angle (GACA), which is defined by a line drawn through the glenoid articular surface and the line between the anterior acromial edge and the anterolateral clavicular edge. To quantify the dynamics of the distal clavicle in the axillary lateral view with respect to the anterior acromial edge while the arm was in different positions (90 of abduction, 60 of flexion, neutral, and 60 of extension), the GACA was measured. This angle allows for measurement of the horizontal displacement of the distal clavicle. The rationale for using an angle rather than a distance for measurement purposes is that there is less susceptibility to error, based on the trigonometric rules. The GACA is defined by the line drawn through the glenoid articular surface and the line between the anterior acromial edge and the anterolateral clavicular edge (Figures 4 and 5). In the case of horizontal instability, the GACA increases with the arm in position 1 (Figures 6 and 7) and decreases with the arm in position 2 (Figure 8). To exclude the influence of interindividual anatomical skeletal differences, the same protocol for measurement of the GACA was completed in the 3 various arm positions. Measurements were also completed in the unaffected upper extremity for direct comparison. Anteroposterior translation (in terms of horizontal mobility of the distal clavicle) was calculated using the GACA differences between positions 1 and 0. The physiologic range of horizontal mobility was defined by the values of the unaffected shoulders. All measurements of the GACA were performed by 3 independent examiners (M.T., H.K., and H.R.) who were blinded to patient data. Interobserver differences were evaluated using an intraclass correlation coefficient (ICC). 27 The ICC was calculated by comparing the results of the 3 examiners. An ICC score from 0 to 0.4 was rated poor, 0.41 to 0.75 was fair or moderate, and more than 0.75 was excellent. Two examiners (M.T. and H.K.) performed a second measurement of the GACA 4 weeks later for assessment of intraobserver reliability. Access to the first measurement or to other examiner s assessments was never available during the evaluation process.

4 Vol. 38, No. 6, 2010 Diagnosis of Acute AC Joint Dislocations 1191 Figure 5. Axillary lateral radiographic view of a left shoulder with the arm in 90 of abduction (position 0). The glenoacromio-clavicular-angle (GACA) is No horizontal dislocation or subluxation of the acromioclavicular joint is evident in this neutral position. Figure 7. With the arm in 90 of abduction and 60 of flexion (position 1), posterior dislocation of the distal clavicle can be observed in horizontally unstable acromioclavicular joint injuries. This is the same patient as shown in Figure 5. The GACA increases to 85.7, which corresponds to a gleno-acromioclavicular angle (GACA) difference of 26.5 between position 1 and position 0. Figure 8. With the arm in 90 of abduction and 60 of extension (position 2), an anterior subluxation of the distal clavicle is evident because of horizontal acromioclavicular joint instability. Accordingly, the gleno-acromio-clavicular angle (GACA) decreases to Figure 6. Three-dimensional graph of an axillary lateral shoulder view with the humeral head subtracted in a type IV injury according to the classification of Rockwood et al. 22 The distal clavicle shows posterior translation in terms of horizontal instability. The institutional review board approved the study and all patients signed an informed consent form before undergoing radiologic examination. Statistical Analysis Descriptive statistics with paired and unpaired t tests were used to analyze the data. A receiver operating characteristic (ROC) curve together with its area under the curve was computed to estimate a cutoff value for GACA differences, which maximizes both sensitivity and specificity. A P value less than.05 was considered statistically significant. For all statistical analyses, the absolute values of the angle measurements or angle differences were used.

5 1192 Tauber et al The American Journal of Sports Medicine TABLE 1 Radiologic Findings Regarding Horizontal Instability of the Distal Clavicle With the Axillary View in a Sitting Position and Using Dynamic Evaluation Injury Type According to Rockwood et al 22 in the Coronal Plane Horizontal Instability Axillary View Sitting Dynamic Evaluation II (n 5 7) 1 3 III (n 5 15) 4 8 V(n53) 3 3 Total (n 5 25) 8 14 TABLE 2 Gleno-acromio-clavicular Angle Measurements a GACA in in in Unaffected shoulder (n 5 25) Group A (n 5 11) Group B (n 5 14) Figure 9. Diagram showing a receiver operating characteristic (ROC) curve together with its area under the curve allowing for defining the cutoff with maximal sensitivity and specificity. A cutoff value of 12.3 for the gleno-acromioclavicular angle (GACA) difference is associated with a sensitivity of 93% and a specificity of 92%. a Mean values in degrees and standard deviation. GACA, gleno-acromio-clavicular-angle. All analyses were done with STATISTICA, version 6.1 (StatSoft, Tulsa, Oklahoma) and SPSS for Windows, version 16.1 (SPSS Inc, Chicago, Illinois). RESULTS Superior dislocation of the distal clavicle in the Zanca view 34 was classified according to the classification of Rockwood et al. 22 Type II injury was diagnosed in 7 patients, type III in 15, and type V in 3. The standard axillary view taken in the sitting position revealed posterior dislocation of the distal clavicle (type IV injury) (Figure 2) in 8 patients (Table 1). GACA Measurements In the unaffected shoulders, the average GACA difference between position 0 and position 1 was Between position 0 and 2 it was and between position 1 and 2 it was (Table 2). In the injured shoulder, the average GACA difference between position 0 and position 1 was , between position 0 and position 2 it was , and between position 1 and position 2 it was A comparison of the averages of the unaffected and injured shoulders yielded statistical significance (P ). The injured AC joints were analyzed by focusing on the horizontal instability of the distal clavicle. Because the GACA differences were statistically significant for all positions, only the differences between position 1 and position 0 were used in further calculations. When the GACA differences between position 1 and position 0 in the injured shoulder significantly exceeded the corresponding values in the contralateral shoulder, they were defined as pathologic. Thus, 2 groups were formed and compared: group A, with normal values for the GACA difference, and group B, with increased values compared with the unaffected shoulders. The mean GACA difference between position 1 and position 0 was in group A and in group B (P \.0001) (see Tables 2 and 3 for group comparison and subgroup distribution). If the GACA difference was compared between the normal shoulders and group A, no statistical difference was observed (P 5.14). A comparison between the normal shoulders and group B yielded statistical significance (P ). Statistical analysis computing a ROC curve together with its area under the curve determined a cutoff between groups A and B of 12.3 (Figure 9). This means that a GACA difference between position 0 and position 1 exceeding 12.3 corresponds to a horizontally unstable AC joint injury. With this cutoff value of 12.3, a sensitivity of 93% and a specificity of 92% are obtained. For horizontally unstable AC joint injuries, this cutoff permits a true positive diagnosis in 93% of all cases. Regarding the horizontally stable injuries, the diagnosis using this cutoff is true-negative in 92% and false-negative in 8%. The area under the ROC curve is 0.98 (95% confidence interval: ), which indicates a particularly high separation power of the GACA difference between both groups.

6 Vol. 38, No. 6, 2010 Diagnosis of Acute AC Joint Dislocations 1193 TABLE 3 Characteristics of Group A (Horizontally Stable) and Group B (Horizontally Unstable) With GACA Measurements for Various Subgroups According to the Classification of Rockwood et al 22a Injury Type According to Rockwood et al 22 in the Coronal Plane For comparison purposes, the GACA differences (position 1 and position 0) between the unaffected and the injured shoulder were subtracted. This difference was for group A and for group B (P \.001). Regarding the superior dislocation of the distal clavicle in the coronal plane, both groups were comparable. Group A consisted of 4 type II and 7 type III injuries and group B included 3 type II, 8 type III, and 3 type V injuries (Table 3). Two patients with type II injuries and 4 patients with type III injuries in the coronal plane had normal axillary views in the sitting position. These patients were determined to have anteroposterior instability using the functional axillary views. This corresponds to 24% of the entire study population. The 8 patients with type IV injuries already diagnosed on the standard axillary views with the patient in a sitting position were confirmed as having horizontally unstable injuries using the dynamic radiologic evaluation. Interobserver and Intraobserver Reliability The interobserver reliability of the 3 independent raters in respect to the GACA was excellent, with an ICC of The ICC for the intraobserver reliability was also rated as excellent. The 2 observers had ICC values of 0.78 and 0.81, respectively. DISCUSSION No. of Patients Group A GACA No. of Patients Group B GACA P Value II \.001 III \.001 V Total \.001 a GACA difference 5 difference of the gleno-acromio-clavicularangle (mean values and standard deviation in degrees) between position 0 and position 1. The classification system of AC joint injuries according to Rockwood et al 22 exactly quantifies the extent of dislocation of the distal clavicle in the frontal plane. However, the posterior dislocation in type IV injuries has not been defined quantitatively. Interindividual variations or positiondependent factors may considerably influence the radiologic relations between the distal clavicle and the acromion. However, the lack of international standards in radiologic viewing techniques may lead to misdiagnosis of acute AC joint injuries and incomparable radiographs. Personal observations resulted in a critical analysis of the radiologic viewing techniques in acute AC joint injuries, especially the axillary views. Disruption of the scapuloclavicular ligaments leads to anteroposterior AC instability, which may not be radiologically evident with a static view. Depending on the position of the arm, an AC joint injury on the axillary view may appear normal, leading to an incorrect diagnosis and inadequate therapy. Ligamentous joint instability cannot always be diagnosed by standard radiographs (as seen in other joints, such as the knee, ankle, or spine). Stress or functional views have to be obtained to detect ligamentous insufficiency. Out of this rationale, we developed a simple method of dynamic radiologic evaluation of acute AC joint injuries in the axillary plane, which should allow for detection and quantification of anteroposterior AC instability that otherwise would be missed by a static axillary view. A major purpose of this study was to introduce a standardized technique of axillary radiography. This represents a fundamental prerequisite for angle measurements and allows for intraindividual and interindividual comparisons and statistical analysis. Rockwood et al 22 did not define the position of patients during the axillary view. Furthermore, no international consensus exists regarding the position. During the study we performed a survey at 20 radiology departments at university hospitals asking about the patient s position when obtaining the axillary view; 19 departments performed the axillary shoulder view with the patient in a sitting position. Whereas intact capsuloligamentous structures of the AC joint warrant motions only within physiologic limits, in acute AC joint injuries the position of the patient during the axillary view may be of crucial importance because of the injury-related variable interosseous configuration. Reports in the literature of inconsistent results after nonsurgical treatment of type II and type III AC joint injuries led us to believe that horizontally unstable injuries are missed during primary radiologic examinations. If the injury is not initially classified as unstable in an anteroposterior direction, nonsurgical treatment would be the therapy of choice, according to evidence-based literature. However, at the present time we do not know if all cases showing horizontal instability require surgery. Mouhsine et al 20 reported a 27% failure rate after conservatively treating type I and type II AC joint injuries with secondary surgical treatment at 26 months. Prior authors observed even higher rates of failure. In one study, 25% to 35% of patients had persistent complaints after type II injuries. 4,8 Schlegel et al 25 noted a 20% rate (4 of 20 patients) of suboptimal outcome after conservative treatment of type III AC joint injuries. In a meta-analysis of 1172 patients with type III AC joint dislocations, 13% had unsatisfactory results after nonoperative treatment and 12% after operative treatment. 21 It must be mentioned, though, that there is only little information for the surgical outcomes of AC joint dislocations if the injuries are broken down into types III through V according to the classification of Rockwood et al. 22 Most reports include type III AC joint injuries according to the classification of Tossy et al, 30 which represents a spectrum of pathologic injuries. However, most

7 1194 Tauber et al The American Journal of Sports Medicine reports lack information concerning the primary radiologic evaluation of the axillary view. This plane is crucial in the detection of posterior subluxation or dislocation of the distal clavicle, even in injuries appearing to be type II or III in the coronal plane. This concept is supported by the data of the present study. Some type II and type III injuries show pathologically increased anteroposterior AC translation, whereas others keep within the physiologic limits of horizontal AC joint motion. A possible explanation is provided by Mazzocca et al, 19 who suggest that a spectrum of AC joint injuries exists between type II AC joint disruption (CC sprain) and type III AC joint injuries (CC disruption). In a laboratory study, an attempt was made to quantify the biomechanical level of injury at which the AC ligaments are disrupted and the CC complex sustains a partial injury. They concluded that an increase in distal clavicle mobility may explain some of the variability in the clinical outcomes of type II AC joint injuries. Accordingly, we believe that a continuous and variable spectrum of ligamentous injuries results in various degrees of multidirectional AC joint instability. Partial disruption of the AC ligaments in combination with incomplete CC ligament injury has to be considered. Furthermore, the aponeurosis of the deltoid and trapezoid muscles can partially detach, causing increased horizontal mobility of the distal clavicle. The combination of injuries is clearly defined by the trauma mechanism and may vary between individual patients. This may explain why type II or III dislocations in the Zanca view may have different degrees of horizontal AC joint instability. Some limitations of the study need to be mentioned. The sample size of this study (25 patients) is moderate. Nevertheless, statistical analyses revealed highly significant differences between the horizontally stable (group A) and unstable (group B) groups. In addition, the number of subgroups was small, limiting the statistical meaningfulness. This series presents preliminary data; further investigations including a larger study population may confirm the promising results of the present study. Another concern involves the difficulty of radiologic projection errors. A precise radiologic setup is crucial for exact and comparable measurements to minimize the risk for projection errors. Conventional radiography may be susceptible to projection errors, resulting in measurement inaccuracy. Direct comparison of absolute GACA values between the affected and unaffected shoulders is not permissible. To avoid this problem, the GACA difference between position 1 and position 0 was used for calculations. It can be assumed that for one shoulder, the projection inaccuracy between the 2 positions of the arm is negligible. However, the inaccuracy may be too great from one shoulder to the other. This error is why the GACA differences rather than absolute values were used for comparison purposes between the injured and unaffected shoulders. A further limitation of this study is the fact that this study involves a completely novel measurement parameter to quantify a previously undefined functional abnormality of the AC joint. As a result, no reference values are available for comparison purposes. Overall, this study does not claim to be comprehensive. It is an attempt to establish a classification system and to develop a simple, practical, and available imaging tool to diagnose horizontal AC joint instability. The next reasonable step is the implementation of these radiologic findings into a therapeutic process. This technique could be used to identify patients who need surgical treatment. Furthermore, this technique can reveal dynamic horizontal AC instability independent of the grade of superior dislocation of the distal clavicle in the coronal plane. Further prospective clinical studies are needed to demonstrate the clinical relevance and therapeutic advantage of this novel radiologic classification system. REFERENCES 1. Alexander OM. Dislocation of the acromioclavicular joint. Radiography. 1949;15(179): Alyas F, Curtis M, Speed C, Saifuddin A, Connell D. MR imaging appearances of acromioclavicular joint dislocation. Radiographics. 2008;28(2): Baker JE, Nicandri GT, Young DC, Owen JR, Wayne JS. A cadaveric study examining acromioclavicular joint congruity after different methods of coracoclavicular loop repair. J Shoulder Elbow Surg. 2003;12(6): Bergfeld JA, Andrish JT, Clancy WG. Evaluation of the acromioclavicular joint following first- and second-degree sprains. Am J Sports Med. 1978;6(4): Cadenat F. The treatment of dislocations and fractures of the outer end of the clavicle. Int Clin. 1917;1: Choi SW, Lee TJ, Moon KH, Cho KJ, Lee SY. Minimally invasive coracoclavicular stabilization with suture anchors for acute acromioclavicular dislocation. Am J Sports Med. 2008;36(5): Costic RS, Labriola JE, Rodosky MW, Debski RE. Biomechanical rationale for development of anatomical reconstructions of coracoclavicular ligaments after complete acromioclavicular joint dislocations. Am J Sports Med. 2004;32(8): Cox JS. The fate of the acromioclavicular joint in athletic injuries. Am J Sports Med. 1981;9(1): Dawson PA, Adamson GJ, Pink MM, et al. Relative contribution of acromioclavicular joint capsule and coracoclavicular ligaments to acromioclavicular stability. J Shoulder Elbow Surg. 2009;18(2): Dimakopoulos P, Panagopoulos A, Syggelos SA, Panagiotopoulos E, Lambiris E. Double-loop suture repair for acute acromioclavicular joint disruption. Am J Sports Med. 2006;34(7): Ernberg LA, Potter HG. Radiographic evaluation of the acromioclavicular and sternoclavicular joints. Clin Sports Med. 2003;22(2): Fialka C, Krestan CR, Stampfl P, Trieb K, Aharinejad S, Vecsei V. Visualization of intraarticular structures of the acromioclavicular joint in an ex vivo model using a dedicated MRI protocol. AJR Am J Roentgenol. 2005;185(5): Heers G, Gotz J, Schubert T, et al. MR imaging of the intraarticular disk of the acromioclavicular joint: a comparison with anatomical, histological and in-vivo findings. Skeletal Radiol. 2007;36(1): Heers G, Hedtmann A. Correlation of ultrasonographic findings to Tossy s and Rockwood s classification of acromioclavicular joint injuries. Ultrasound Med Biol. 2005;31(6): Jari R, Costic RS, Rodosky MW, Debski RE. Biomechanical function of surgical procedures for acromioclavicular joint dislocations. Arthroscopy. 2004;20(3): Jiang C, Wang M, Rong G. Proximally based conjoined tendon transfer for coracoclavicular reconstruction in the treatment of acromioclavicular dislocation: surgical technique. J Bone Joint Surg Am. 2008;90(suppl 2 Pt 2): Luis GE, Yong CK, Singh DA, Sengupta S, Choon DS. Acromioclavicular joint dislocation: a comparative biomechanical study of the

8 Vol. 38, No. 6, 2010 Diagnosis of Acute AC Joint Dislocations 1195 palmaris-longus tendon graft reconstruction with other augmentative methods in cadaveric models. J Orthop Surg. 2007;2: Mazzocca AD, Santangelo SA, Johnson ST, Rios CG, Dumonski ML, Arciero RA. A biomechanical evaluation of an anatomical coracoclavicular ligament reconstruction. Am J Sports Med. 2006;34(2): Mazzocca AD, Spang JT, Rodriguez RR, et al. Biomechanical and radiographic analysis of partial coracoclavicular ligament injuries. Am J Sports Med. 2008;36(7): Mouhsine E, Garofalo R, Crevoisier X, Farron A. Grade I and II acromioclavicular dislocations: results of conservative treatment. J Shoulder Elbow Surg. 2003;12(6): Phillips AM, Smart C, Groom AF. Acromioclavicular dislocation: conservative or surgical therapy. Clin Orthop Relat Res. 1998;353: Rockwood CJ, Williams G, Young D. Disorders of the acromioclavicular joint. In: Rockwood CJ, Matsen FA III, eds. The Shoulder. 2nd ed. Philadelphia: WB Saunders; 1998: Sahara W, Sugamoto K, Murai M, Tanaka H, Yoshikawa H. 3D kinematic analysis of the acromioclavicular joint during arm abduction using vertically open MRI. J Orthop Res. 2006;24(9): Salzmann GM, Walz L, Schoettle PB, Imhoff AB. Arthroscopic anatomical reconstruction of the acromioclavicular joint. Acta Orthop Belg. 2008;74(3): Schlegel TF, Burks RT, Marcus RL, Dunn HK. A prospective evaluation of untreated acute grade III acromioclavicular separations. Am J Sports Med. 2001;29(6): Shin SJ, Yun YH, Yoo JD. Coracoclavicular ligament reconstruction for acromioclavicular dislocation using 2 suture anchors and coracoacromial ligament transfer. Am J Sports Med. 2009;37(2): Shrout PE, Fleiss JL. Intraclass correlations: uses in assessing rater reliability. Psychol Bull. 1979;86: Tauber M, Gordon K, Koller H, Fox M, Resch H. Semitendinosus tendon graft versus a modified Weaver-Dunn procedure for acromioclavicular joint reconstruction in chronic cases: a prospective comparative study. Am J Sports Med. 2009;37(1): Tomlinson DP, Altchek DW, Davila J, Cordasco FA. A modified technique of arthroscopically assisted AC joint reconstruction and preliminary results. Clin Orthop Relat Res. 2008;466(3): Tossy JD, Mead NC, Sigmond HM. Acromioclavicular separations: useful and practical classification for treatment. Clin Orthop Relat Res. 1963;28: Walz L, Salzmann GM, Fabbro T, Eichhorn S, Imhoff AB. The anatomic reconstruction of acromioclavicular joint dislocations using 2 TightRope devices: a biomechanical study. Am J Sports Med. 2008; 36(12): Wellmann M, Zantop T, Petersen W. Minimally invasive coracoclavicular ligament augmentation with a flip button/polydioxanone repair for treatment of total acromioclavicular joint dislocation. Arthroscopy. 2007;23(10):1132.e Wellmann M, Zantop T, Weimann A, Raschke MJ, Petersen W. Biomechanical evaluation of minimally invasive repairs for complete acromioclavicular joint dislocation. Am J Sports Med. 2007;35(6): Zanca P. Shoulder pain: involvement of the acromioclavicular joint: analysis of 1,000 cases. Am J Roentgenol Radium Ther Nucl Med. 1971;112(3): For reprints and permission queries, please visit SAGE s Web site at