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ORIGINAL ARTICLE

Evaluating Displacement of the Coracoacromial Ligament in Painful Shoulders of Overhead Athletes Through Dynamic Ultrasonographic Examination Chueh-Hung Wu, MD, Yi-Chiang Wang, MD, Hsing-Kuo Wang, PT, PhD, Wen-Shiang Chen, MD, PhD, Tyng-Guey Wang, MD ABSTRACT. Wu C-H, Wang Y-C, Wang H-K, Chen W-S, Wang T-G. Evaluating displacement of the coracoacromial ligament in painful shoulders of overhead athletes through dynamic ultrasonographic examination. Arch Phys Med Rehabil 2010;91:278-82. Objective: To evaluate displacement of the coracoacromial ligament (CAL), using dynamic ultrasonography (US), for detecting instability-related impingement caused by overhead activities. Design: Between-group survey. Setting: Department of Physical Medicine and Rehabilitation in a tertiary care center. Participants: Volunteer high school volleyball players with unilateral shoulder pain (n⫽10) and volunteer asymptomatic high school volleyball players with identical training activities as control subjects (n⫽16). Interventions: Not applicable. Main Outcome Measure: The displacement of the CAL was measured during throwing simulation using dynamic US. Both shoulders of all subjects were evaluated. Results: During throwing simulation, the displacement of the CAL in the painful shoulders of overhead athletes increased significantly greater than the displacement in the asymptomatic shoulder (3.0⫾0.7mm and 2.2⫾0.4mm, respectively; P⫽.017). No difference was identified between the displacements of the CALs of bilateral shoulders of the control group subjects. Conclusions: Dynamic US, by measuring the displacement of the CAL during simulation of throwing, may be helpful in detecting abnormal humeral head upward migration in overhead athletes. Key Words: Athletic injuries; Rehabilitation; Shoulder impingement syndrome; Ultrasonography. © 2010 by the American Congress of Rehabilitation Medicine

From the Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital (Wu, Wang Y-C, Chen, Wang T-G) and the School and Graduate Institute of Physical Therapy (Wang H-K), College of Medicine, National Taiwan University, Taipei, Taiwan, ROC. Presented as a poster to the 5th World Congress of the International Society of Physical and Rehabilitation Medicine, June 15, 2009, Istanbul, Turkey. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit on the authors or on any organization with which the authors are associated. Reprint requests to Tyng-Guey Wang, MD, Dept of Physical Medicine and Rehabilitation, National Taiwan University Hospital, College of Medicine, National Taiwan University, 7 Chan-Shan S Rd, 100, Taipei, Taiwan, ROC, e-mail: tgw@ ntu.edu.tw. 0003-9993/10/9102-00666$36.00/0 doi:10.1016/j.apmr.2009.10.012

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HOULDER PAIN IS COMMON among elite athletes who S carry out overhead activities. Acute or chronic shoulder pain may interfere with performance and reduce competitive1

ness. If untreated or incorrectly treated, it may lead to permanent damage to the rotator cuff and functional loss.2 Various etiologies may cause shoulder pain in overhead activity athletes, and SIS is considered to be the most common and most important of these.3,4 SIS can arise from structural abnormality or from dynamic instability.3,5,6 SIS caused by anatomic narrowing commonly affects older, nonathletic people and is classified as “primary impingement.”7 SIS arising from shoulder instability is usually seen in young athletes who engage in repetitive overhead activities and is classified as “secondary impingement.”6,8 Timely and accurate diagnosis for both primary and secondary impingement is critical for appropriate treatment to take place. It remains a diagnostic challenge to identify the existence and the nature of secondary impingement.9 The diagnosis of shoulder impingement is based on clinical evaluation and imaging. Disease history and physical examination findings provide valuable preliminary information, but their diagnostic power for shoulder pathophysiologies is insufficient.10,11 Where clinical findings are insufficient or contradictory, imaging is especially important. MR imaging is an excellent technique for detecting primary impingements such as acromial spurs, degeneration or tear of the rotator cuff, arthropathy, and labral lesions.12 However, MR imaging is limited as a diagnostic tool for secondary impingement because patients with secondary impingement usually present no static structural abnormality.13 Dynamic recording of shoulder motion may be more useful for accurately identifying and assessing this type of disorder. US is already in use for evaluating the pathology of the shoulder joint. However, it has had limited use to date in diagnosing secondary impingement.8,14 As well as detecting abnormalities in the static structures of the shoulder joint, US can visualize relations within the CAL, the supraspinatus tendon, and the greater tuberosity of the HH during various shoulder movements. US thus has potential as an imaging tool for recording CAL displacement during overhead activities,15 and therefore as a key diagnostic tool for identifying secondary impingement. Previous studies have shown abnormal upper translation of the HH in patients with SIS.16,17 Abnormal supe-

List of Abbreviations CAL HH ICC MR SIS US

coracoacromial ligament humeral head intraclass correlation coefficient magnetic resonance shoulder impingement syndrome ultrasonography

DYNAMIC ULTRASONOGRAPHY IN DETECTING CORACOACROMIAL LIGAMENT DISPLACEMENT, Wu

rior translation of the HH exerts an upward-directed force on the CAL and may cause temporal narrowing of the subacromial space, therefore leading to the displacement of the ligament, causing secondary impingement.3,18,19 By using US to measure CAL displacement during the course of shoulder movement, we aimed to compare the displacement of CAL between affected and unaffected shoulders of overhead activity athletes with a clinical diagnosis of SIS, and between dominant and nondominant shoulders of overhead activity athletes with no history of shoulder pain or injury. METHODS Ten high school volleyball players with unilateral shoulder pain participated in this study between March 2008 and August 2008. They received high-level training and had been involved in regular competition for at least 5 years before the commencement of the study. All the players underwent a physical examination before joining the study to confirm their eligibility to participate as SIS subjects. The physical examination included empty-can, Speed’s, lift-off, sulcus, anterior apprehension, relocation, Neer’s impingement, and Hawkins-Kennedy impingement tests. All 10 subjects had been experiencing shoulder pain with overhead reaching for more than 3 months before the beginning of the study, and had either a positive Hawkins-Kennedy sign or a positive Neer’s impingement sign while having negative findings on other tests. Any subjects with adhesive capsulitis, cervical radiculopathy, arthritis, fracture of the shoulder girdle, systemic musculoskeletal disease, or a history of corticosteroid injection or surgery to the shoulder were excluded from this study based on clinical information. Sixteen high school volleyball players comprised the control group. They underwent a similar intensity and duration of training and competition as the symptomatic group. They had no shoulder pain or any other shoulder disease. They underwent the same physical examination as the study group, and all of the tests showed negative findings. Personal profiles (age, weight, height, handedness, training duration) were obtained for both groups. Informed consent was obtained from all the subjects. The study protocol was presented to the Research Ethics Committee of National Taiwan University Hospital and was approved before this study was initiated. US was performed by the same examination team (C-H Wu with 500 cases and Y-C Wang with 2 years’ experience). A linear array transducer (7–14MHz), fitted in a Toshiba machine,a was used. Each subject initially underwent a routine sonographic examination in accordance with the Mack and Crass method.20,21 The biceps tendon, subdeltoid-subacromial bursa, supraspinatus tendon, subscapularis tendon, infraspinatus tendon, teres minor tendon, and labrum were all examined during this procedure. During the static examination, each subject sat upright with both forearms supinated and resting on the ipsilateral thigh. The CAL was identified with a probe placed perpendicularly on the skin between the coracoid process and acromial tip. The length and thickness of the CAL and the shortest distance between the CAL and the HH (CAL-HH) were measured. The thickness of the supraspinatus tendon was measured 15mm posterior to the tendon of the biceps brachii long head in the horizontal view.22 During the dynamic examination, the shoulder was placed in 90° abduction and 90° external rotation with the elbow in 90° flexion. It was then internally rotated to 90° in a passive manner at an angular velocity of about 20°/s. This motion simulated shoulder movement during throwing.15,23 Each subject was fully relaxed during this throwing simulation. We traced the CAL by US throughout the full range of internal

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rotation in each subject. The examiner tested the shoulder at a slow pace for clear tracking of the CAL. Both shoulders of each subject were examined. The measurements of superior CAL displacement during throwing simulation were performed at a later date, without knowing which side was symptomatic. During dynamic measurement, maximal superior CAL displacement measured from a line connecting the acromion and the coracoid process at the CAL attachment was recorded (fig 1).15 We measured the maximal displacement of the CAL 3 times in each shoulder, with the average used for statistical analysis. We used the Mann-Whitney U test to compare the characteristics of the shoulder pain group and the control group. We used the paired t test to compare differences in the US parameters of both shoulders in each group. ICC was calculated to determine interrater and intrarater reliability of measurements of displacement of the CAL. Results were expressed as mean ⫾ SD. A P value of less than .05 was considered significant. RESULTS All of the subjects were male. Two of the 10 symptomatic subjects and 2 of 16 asymptomatic subjects were left-handed. Among the symptomatic subjects, the painful shoulders were always on the same side as their dominant hands. In both groups, US revealed no structural abnormalities (for instance, distension bursitis or tendinopathy in the biceps brachii and rotator cuff). Age, height, weight, and training duration were identical in both groups (table 1). The interrater reliability for the raters was found to be an ICC of .905 (95% confidence interval, .666 –.976). The intrarater reliability was found to be an ICC of .951 (95% confidence interval, .816 –.988). CAL thickness, CAL length, CAL-HH, and supraspinatus tendon thickness between both shoulders in both groups were not found to be significantly different. In the shoulder pain group, increases in the CAL displacement that occurred during simulation of throwing in the symptomatic shoulders increased more than in the asymptomatic shoulders (3.0⫾0.7mm and 2.2⫾0.4mm, respectively; P⫽.017). In the control group, no significant difference was identified in the CAL displacement between both shoulders of each subject during the throwing simulation (table 2). Increases in the CAL displacement in the symptomatic shoulders of the shoulder pain group increased more than in the matched (ie, dominant) shoulders of the control group (3.0⫾ 0.7mm and 2.1⫾0.9mm, respectively; P⬍.01). DISCUSSION We found a significantly greater displacement of the CAL in the painful shoulders of overhead athletes during throwing simulation in comparison with their asymptomatic shoulders. This may imply that the symptomatic shoulders may have functional instability. Abnormal superior translation of the HH may cause soft tissue impingement in the subacromial space, causing shoulder pain, and may also result in the displacement of the CAL. No differences were found in other US parameters between both shoulders of the shoulder pain group, indicating that the symptoms were related to functional abnormalities rather than structural factors such as CAL thickness and length, CAL-HH, and supraspinatus tendon thickness. A greater increase in the CAL displacement in the symptomatic shoulders of the shoulder pain group than that in the matched shoulders of the control group further validated that the increases in the CAL displacement were related to the symptoms, rather than due to shoulder dominance. Arch Phys Med Rehabil Vol 91, February 2010

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space, and the degree of superior translation of the HH during shoulder motion.24-26 All the subjects in this study were relatively young, and US examination did not reveal structural abnormalities in their shoulders. Viscoelastic properties of the CAL and compliance of the soft tissue within the subacromial space should not be very different between both shoulders of a young subject without a history of shoulder trauma or surgery. Besides, the thickness of the supraspinatus tendon, which comprised the majority of the soft tissue within the subacromial space, was not different between both shoulders in this study. Therefore, a significantly greater displacement of the CAL in the symptomatic shoulders may be representative of abnormal upper translation of the HH in these painful shoulders. Abnormal upper translation of the HH during shoulder motion has been demonstrated in patients with SIS through radiologic examinations.16,17 This procedure requires serial radiographs and a complicated analysis to demonstrate the abnormal upper translation of the HH. Furthermore, the procedure is time-consuming and exposes subjects to radiation. In addition, this method of research to our knowledge has, to date, focused on shoulder abduction only, which is only one element of the complexity of shoulder movements that comprise the motion of throwing. Our study, by contrast, focused on overhead throwing motion and associated impingement, and performed US dynamically without exposing our subjects to radiation. The CAL displacement represented the interaction between the upper translation of the HH and the surrounding soft tissue, which cannot be detected through radiologic examinations. In this study, the more prominent displacement of the CAL in the painful shoulder provided demonstration of abnormal upper translation of the HH. Thus, US examination seemed to be a better image tool in evaluating the painful shoulders in the patients with SIS. Our study confirmed that US is an effective tool for detecting and measuring dynamic shoulder motions. Radiographs can reveal abnormalities of bony structures. MR imaging, while providing accurate anatomic evaluations of the rotator cuff, coracoacromial arch, and the subacromial-subdeltoid bursa, has only limited use for identifying dynamic instability, as with secondary impingements in the shoulders of athletes, who are generally young, may not have a history of trauma, and are very unlikely to have structural abnormalities. In addition, patients undergoing MR imaging examinations are not usually placed in a position in which impingement will occur.27 US, in contrast with the static nature of MR imaging, has the advantage of dynamic recording during shoulder motion, since there are usually functional rather than anatomic abnormalities in secondary impingement. It is well established that both US and MR imaging have high accuracy rates for identifying rotator cuff lesions.28,29 In addition to rotator cuff and subacromial disease, various studies have focused on evaluating shoulder

Table 1: Demographic Data of Shoulder Pain and Control Groups Fig 1. Measurement of displacement of the CAL. (A) Spanning the acromion and the coracoid process was the CAL, which was flat at rest. We measured the CAL-HH distance by tilting the probe to show the HH. (B) The CAL (arrows) bulged during throwing simulation. (C) A line was drawn from the bony insertions of the CAL on the acromion to the insertion on the coracoid process. The degree of the displacement was measured vertically from the vertex of the bulge to the line. Abbreviations: A, acromion; C, coracoid process.

The degree of CAL displacement may be related to several factors including viscoelastic properties of the CAL, the thickness and compliance of the soft tissue within the subacromial Arch Phys Med Rehabil Vol 91, February 2010

Variable

Shoulder Pain Group

Control Group

P

Number Sex Age (y) Height (cm) Weight (kg) Training duration (y)

10 All male 16.7⫾0.5 178.5⫾4.6 72.6⫾10.0 6.2⫾1.4

16 All male 16.4⫾0.9 177.4⫾4.7 71.3⫾8.4 6.2⫾0.8

NA NA .40 .58 .73 .98

NOTE. Statistical method: Mann-Whitney U test between groups. Values are mean ⫾ SD. Abbreviation: NA, not applicable.

DYNAMIC ULTRASONOGRAPHY IN DETECTING CORACOACROMIAL LIGAMENT DISPLACEMENT, Wu

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Table 2: Ultrasonographic Parameters of Both Shoulders in Shoulder Pain and Control Groups Shoulder Pain Group Variable

Symptomatic Shoulder

Asymptomatic Shoulder

CAL length (mm) CAL thickness (mm) CAL-HH (mm) Supraspinatus tendon thickness, transverse (mm) Maximum superior CAL displacement (mm)

30.7⫾3.1 1.1⫾0.3 9.0⫾2.0

31.5⫾2.4 1.0⫾0.2 9.0⫾2.1

7.2⫾1.0

6.4⫾0.8

3.0⫾0.7

2.2⫾0.4

Control Group P

Dominant Hand

Nondominant Hand

P

31.3⫾2.9 1.0⫾0.2 8.2⫾1.9

31.7⫾4.6 1.1⫾0.3 8.0⫾1.4

.63 .36 .38

.066

7.9⫾1.6

7.3⫾1.9

.15

.017

2.1⫾0.9

2.3⫾0.9

.30

.21 .53 1.00

NOTE. Statistical method: paired t test within group. Values are mean ⫾ SD.

instability using US.30,31 These studies evaluated glenohumeral laxity by applying a force to the proximal HH, with the shoulders adducted and internally rotated. They did not, however, compare symptomatic and asymptomatic shoulders to evaluate the degree of impingement that occurs during throwing simulation. They could not therefore track and evaluate the occurrence of functional abnormalities in the shoulders during the course of overhead activities, since no shoulder motion took place in their subjects during the examination. Study Limitations There were several limitations to this study. First, we did not assess the morphologic features of the acromion, and the relation between the HH and the acromion by radiology. However, this is only a minor weakness since previous research evaluating acromiohumeral distance and subacromial space has already established that there is a strong correlation between US and radiologic examinations.22,32,33 Second, recording of the impingement under the acromion and the coracoid process was restricted because of the bony barrier against sound beams. In this study, the motion of throwing simulation was similar to the motion carried out in the Hawkins-Kennedy impingement test. Previous research has revealed that the motion in the HawkinsKennedy impingement test compresses the HH against the CAL rather than against the anterior acromion.23,27,34 Therefore, the limitation of inspecting the structures under the acromion and the coracoid process using US did not greatly affect the results in this study. Third, although throwing simulation was carried out, the intensity and speed of this motion were highly different from shoulder motion during a real-life sporting activity. During real-life competition, each episode of shoulder motion is completed in a very short time. For instance, when a baseball pitcher accelerates a baseball from 0 to 90mph, it may take only 50 milliseconds, and the angular velocity of the shoulder can achieve 6100°/s,35 which is much faster than the 20°/s achieved in the throwing simulation in this study. Tracing CAL displacement that occurs in high-velocity motion is difficult. Nevertheless, this study has provided a basis for evaluating shoulder instability during throwing motion. In this study, we focused on measuring the displacement of the CAL by using dynamic US. The displacement in the CAL in the painful shoulders of overhead athletes increased significantly more than the displacement in the contralateral shoulder during throwing simulation. Further research is needed to confirm whether a high joint-compressive load during highvelocity throwing influences shoulder stability. Our positive findings on the effectiveness of US as a diagnostic tool for secondary impingement confirm the value of pursuing this line of research into the dynamics of this often-misdiagnosed condition that so widely affects young athletes.

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