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Feb 13, 2012 - ABSTRACT: We evaluated coracoacromial ligament (CAL) displacement during motion in shoulders with supraspinatus tendon tears.

Dynamic Ultrasonography to Evaluate Coracoacromial Ligament Displacement during Motion in Shoulders with Supraspinatus Tendon Tears Chueh-Hung Wu,1 Ke-Vin Chang,2 Po-Hsien Su,2 Wen-Hsiu Kuo,2 Wen-Shiang Chen,2 Tyng-Guey Wang2 1

Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Yun-Lin Branch, Yunlin, Taiwan, ROC, Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, Taipei, Taiwan, ROC

2

Received 26 September 2011; accepted 16 January 2012 Published online 13 February 2012 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/jor.22084

ABSTRACT: We evaluated coracoacromial ligament (CAL) displacement during motion in shoulders with supraspinatus tendon tears by dynamic ultrasonography (US). Twenty subjects with unilateral, full-thickness supraspinatus tendon tears (SST group) and 20 subjects with intact supraspinatus tendons (control group) underwent dynamic US. The CAL displacement in their bilateral shoulders was measured in the transverse US view during passive and active shoulder abduction and internal rotation (SAIR). In the SST group, the CAL displacement was significantly greater in the affected shoulders than in the intact ones (1.9 mm  0.8 mm vs. 1.5 mm  0.5 mm, p ¼ 0.01) during passive SAIR, but was not significantly different between the shoulders (1.7 mm  0.7 mm vs. 1.7 mm  0.4 mm, p ¼ 0.81) during active SAIR. In the control group, no difference in the CAL displacement between the shoulders was noted during passive and active SAIR. Thus, dynamic US revealed greater CAL displacement in shoulders with supraspinatus tendon tears than in intact ones during passive SAIR. Dynamic US may help to detect abnormal kinematics in shoulders with such injury. ß 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 30:1430–1434, 2012 Keywords: ultrasound; coracoacromial ligament; rotator cuff tear; shoulder impingement

Supraspinatus tendon tears are a common cause of shoulder pain and dysfunction.1 Shoulder impingement syndrome may partially contribute to the development or progression of such an injury.2 Various factors result in impingement syndrome, including anatomical and biomechanical factors.3 In addition to bony deformities and soft tissue pathologies, abnormal kinematics of the glenohumeral joint (e.g., excessive superior or anterior humeral head translation) and scapulothoracic articulation (e.g., decreased posterior tilt, upward rotation, and external rotation of the scapula) cause narrowing of the subacromial spaces.3 Despite evidence showing that superior head translation rather than abnormal scapular kinematics primarily causes impingement,4 both mechanisms may contribute to subacromial tissue encroachment.3 Previous studies using serial plain radiographs, electromyographic analyses, and electromagnetic motion capture systems showed abnormal translation of the head in patients with supraspinatus tendon tears5–7 and altered scapular kinematics in those with impingement.8,9 However, patient exposure to radiation or complicated instrumentation has prevented the use of these tools in daily practice. Ultrasonography (US) is an easily accessible imaging tool for detecting supraspinatus tendon tears without radiation.10 Dynamic US has been used to detect coracoacromial ligament (CAL) displacement during shoulder elevation.11 The extent of CAL displacement may result from compression of the subacromial structures due to anatomical and biomechanical factors

Correspondence to: Tyng-Guey Wang (T: þ886-2-2312345667588; F: þ886-2-23832834; E-mail: [email protected]) ß 2012 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.

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causing shoulder impingement syndrome.3,11 Young overhead athletes with symptoms of shoulder impingement exhibit greater CAL displacement in the painful shoulder than in the asymptomatic one.12 During shoulder abduction, the superiorly directed force of the deltoid muscle pulls the humeral head upward. In normal circumstances, this movement is counteracted by the compressive and downward action of the supraspinatus muscle-tendon elements.4 In abnormal circumstances, such as with supraspinatus tendon tears, excessive superior head translation may exert pressure to the coracoacromial arch, causing CAL displacement. Therefore, CAL displacement may be altered in shoulders with supraspinatus tendon tears; however, the extent of CAL displacement during shoulder motion in such cases has not been investigated. We evaluated CAL displacement during motion in shoulders with supraspinatus tendon tears by dynamic US. We hypothesized that shoulders with supraspinatus tendon tears would have greater CAL displacement than intact ones.

METHODS Subjects Individuals with full-thickness supraspinatus tendon tears (SST group, 10 men and 10 women) were consecutively recruited from a tertiary medical center. The inclusion criteria were: (1) presence of a unilateral, full-thickness tear 40 years; (4) ability to understand verbal commands to perform shoulder movements; and (5) 3 or more positive findings in 5 tests—the Neer impingement test, Hawkins–Kennedy impingement test, empty can test, painful arc between 608 and 1208, and external rotation resistance test—for confirming subacromial impingement syndrome.14 Exclusion criteria were based on a history of: (1)

CAL DISPLACEMENT IN SUPRASPINATUS TENDON TEARS

trauma or fracture of the shoulder girdle, (2) adhesive capsulitis, (3) subacromial bursitis, (4) cervical radiculopathy, and (5) systemic musculoskeletal or rheumatic disease. Twenty volunteers (10 men and 10 women) without shoulder pain were recruited as the control group. Inclusion criteria were: (1) age >40 years and (2) ability to understand verbal commands to perform shoulder movements. Exclusion criteria were: (1) any shoulder pain or injury within the past 1 year; (2) US-based diagnosis of subacromial bursitis or any supraspinatus tendon tear; and (3) history of adhesive capsulitis, cervical radiculopathy, or systemic musculoskeletal or rheumatic disease. The study protocol was approved by the Research Ethics Committee of our hospital. Written informed consent was obtained from every subject. US Evaluation US was performed by 2 of the authors together (C.-H. Wu, with 3 years experience, and P.-H. Su with experience in 1,000 cases). A linear array transducer (7–14 MHz) fitted in an ultrasound system (Xario, Model SSA-660A; Toshiba, Japan) was used for static and dynamic US of both shoulders of every subject. A full-thickness tear was diagnosed if a hypoechoic or anechoic cleft extended through the entire thickness of the supraspinatus tendon. The tear size was measured in the transverse view at the level of the rotator interval. During static US, each subject was asked to sit upright with both the forearms supinated and resting on the ipsilateral thigh. The CAL was identified with a transducer placed between the coracoid process and the acromial tip, perpendicular to the skin. The length and thickness of the CAL and the shortest distance between the CAL and the humeral head (CAL-HH) were measured (Fig. 1). During dynamic US, the shoulder was placed in 908 abduction and 908 external rotation with the elbow in 908 flexion. It was then internally rotated to 908 passively as fast as possible but avoiding shoulder pain. This maneuver (shoulder abduction and internal rotation, SAIR), simulating a throwing motion, produces the most prominent CAL displacement.11,15 Each subject was fully relaxed during passive SAIR. The CAL was traced throughout the range of internal rotation. During this examination, CAL displacement with

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Figure 2. Measurement of the displacement of the coracoacromial ligament (CAL). During internal rotation of the shoulder, the CAL bulged. A line was drawn from the bony origin of the CAL on the acromion to the insertion on the coracoid process. The extent of CAL displacement was measured vertically from the vertex of the bulge to the line. A, acromion; C, coracoid process; HH, humeral head.

various degrees of superior convexity could be seen, and the process was recorded with animated films at a rate of 30 frames/s. The displacement was measured from the vertex of the CAL convexity to a line connecting the acromion and coracoid process at the CAL attachment and reviewed repeatedly by using the dynamic films; finally, the maximal displacement was recorded11 (Fig. 2). The maximal CAL displacement was measured three times for each shoulder; the average value was used for analysis. Each subject also underwent US examination while performing SAIR actively. Statistical Analysis We used the paired t-test and Mann–Whitney U-test to compare the characteristics and results of static US between the groups, as appropriate. We used the paired t-test to compare the differences in the US results of the bilateral shoulders in each group. The data are expressed as the mean  standard deviation. A p-value < 0.05 was considered significant.

RESULTS Table 1 shows the demographic data and results of static US. The SST and control groups exhibited no differences in age, weight, height, CAL length and thickness, and CAL-HH.

Table 1. Demographic Data and Results of Static US between the Study Groups Parameter

Figure 1. Static ultrasonography (US) of the coracoacromial ligament (CAL). The length (asterisks) and thickness (arrows) of the CAL and the shortest distance between the CAL and the humeral head (CAL-HH, 2-way arrow) were measured in the transverse US view. A, acromion; C, coracoid process; HH, humeral head.

SST Group

Age (years) Height (cm) Weight (kg) CAL length (mm) CAL thickness (mm) CAL-HH (mm)

58.0 162.4 67.6 27.8

   

8.2 6.9 12.2 3.0

Control Group 60.8 162.9 62.8 29.1

   

p-Value

5.1 8.8 7.3 4.0

0.19 0.86 0.14 0.11

1.0  0.1

1.0  0.2

0.22

7.7  2.1

7.9  1.2

0.68

US, ultrasonography; SST, supraspinatus tendon tear; CAL, coracoacromial ligament; HH, humeral head. JOURNAL OF ORTHOPAEDIC RESEARCH SEPTEMBER 2012

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Table 2. Comparison of the Results of Static and Dynamic US of Both Shoulders in the Study Groups SST Group Parameter CAL length (mm) CAL thickness (mm) CAL-HH (mm) CAL displacement during passive SAIR (mm) CAL displacement during active SAIR (mm)

Affected Shoulder 27.8 1.0 7.8 1.9

   

2.9 0.1 2.1 0.8

1.7  0.7

Control Group

Intact Shoulder

p-Value

   

3.2 0.1 2.2 0.5

0.91 0.31 0.74 0.01

1.7  0.4

0.81

27.8 1.0 7.6 1.5

Dominant Shoulder 29.4 1.0 7.8 1.5

   

4.2 0.2 1.4 0.5

1.6  0.5

Nondominant Shoulder

p-Value

   

4.0 0.1 1.1 0.4

0.20 0.21 0.72 0.25

1.7  0.3

0.11

28.7 1.0 7.9 1.6

US, ultrasonography; SST, supraspinatus tendon tear; CAL, coracoacromial ligament; HH, humeral head; SAIR, shoulder abduction and internal rotation.

All the full-thickness supraspinatus tendon tears occurred in the dominant shoulders. In the SST group, the bilateral shoulders showed no differences in CAL length, CAL thickness, and CAL-HH. During dynamic US, the CAL displacement was significantly greater on the affected side than on the intact side (1.9  0.8 mm vs. 1.5  0.5 mm, p ¼ 0.01) in passive SAIR, but was not significantly different between the shoulders (1.7  0.7 mm vs. 1.7  0.4 mm, p ¼ 0.81) in active SAIR. In the control group, no significant differences in CAL length and thickness, CAL-HH, and CAL displacement during passive and active SAIR were noted between shoulders (Table 2).

DISCUSSION Factors that contribute to CAL displacement include the viscoelastic properties of the CAL, the thickness and compliance of the soft tissue within the subacromial space, and the extent of superior translation of the humeral head.3,16,17 Given that the acromion, coracoid process, and humeral head are bony structures, compressive force within the subacromial space during shoulder motion may cause deformation of the most yielding structure, the CAL. We found no differences in CAL thickness, CAL length, and CAL-HH between the shoulders with and without supraspinatus tendon tears. Therefore, the significantly greater CAL displacement in the affected shoulders may represent a greater increase in the extent of superior translation of the humeral head. Dysfunction of static glenohumeral stabilizers, such as labral detachment, loss of tension in the glenohumeral ligaments, and injury to the capsular mechanism, may lead to abnormal head translation.18 The greater CAL displacement that occurred during passive motion only in the cuff tear patients may imply that these static glenohumeral stabilizers may be impaired. However, this functional impairment was not so severe that activation of dynamic stabilizers could compensate for it. One study investigating the effect of passive and active loading on humeral head translation during glenohumeral abduction showed that head translation decreases with muscle loading,19 which may support this argument. JOURNAL OF ORTHOPAEDIC RESEARCH SEPTEMBER 2012

Further, the similar CAL displacement between the shoulders of each control subject in this study supports the view that the CAL displacement was related to supraspinatus tendon tear rather than to shoulder dominance. The finding of greater CAL displacement in the shoulders with supraspinatus tendon tears only during passive SAIR has two possible explanations: (1) compensation due to muscle activation or (2) avoidance of further internal rotation because of pain, reducing CAL displacement. The former is more likely because all subjects were instructed to perform internal rotation relatively slowly and achieved similar ranges of motion compared to the intact side. Although this relatively slow shoulder motion is different from that performed in real-life situations, it implies that compensation occurs during slow active shoulder motion. An individual with pain during shoulder motion should be instructed to avoid moving the affected shoulder too fast. A prior study revealed compensatory scapular elevation to reduce impingement during arm elevation in athletes with shoulder impingement.20 We believe that the dysfunction of the supraspinatus muscletendon elements, which depresses the humeral head, may be sufficiently compensated for by some mechanism in the shoulders when incomplete supraspinatus tendon tears are present. For instance, serratus anterior and lower trapezius act to produce scapular upward rotation, acromioclavicular joint posterior tilting, and external rotation, which normalize the shoulder movement pattern and compensate for the reduced subacromial space.2,20 Activation of these muscles may protect the subacromial structures from compression, thus reducing CAL displacement. The facts that none of the patients underwent surgery and that their symptoms subsided under medication and physiotherapies supports this viewpoint. However, it may also imply that, in these patients with incomplete supraspinatus tendon tears, impingement under the CAL may not be a significant part of the pathology, since it can be compensated for with active motion. CAL displacement represents an interaction between superior head translation and surrounding soft

CAL DISPLACEMENT IN SUPRASPINATUS TENDON TEARS

tissues, which cannot be revealed through radiological examination. In the circumstances of excessive superior translation, the distributed downward-directed forces exerted by the undersurface of the CAL and the distributed upward-directed forces exerted by the upper surface of the head compress the subacromial structures.15 In reaction, the subacromial structures push the CAL upwards, thus causing the CAL displacement, which can be detected by US. Abnormal superior head translation and altered scapular kinematics during shoulder motion were demonstrated in patients with supraspinatus tendon tears and shoulder impingement.5–9 However, previous researchers used serial radiographs or complicated instruments to demonstrate these abnormal movements. They also focused on shoulder abduction or flexion at different angles, representing only a part of the complexity of shoulder motion. In our study, the SAIR was similar to a real-life throwing motion and could be assessed by dynamic US. Furthermore, subjects were not exposed to radiation. The more prominent CAL displacement in the shoulders with supraspinatus tendon tears indicated increasing subacromial pressure that resulted from excessive head superior translation during shoulder motion. Although US revealed greater CAL displacement in such cases, we were unable detect any differences in CAL-HH distance during passive and active SAIR. The lower boarder of the CAL or the cortex of the head could not be identified clearly in 30–40% of subjects, possibly due to excessive changes of anatomical relationships between the CAL and the humeral head after internal rotation, or due to blocking of US signals by osteophytes of the coracoacromial arch. However, previous cadaveric studies showed that CAL excision led to an increase in anterosuperior head translation, suggesting that head translation may exert forwardand upward-directed forces on the CAL and cause its displacement.21,22 Therefore, despite this limitation in direct visualization of CAL-HH changes, US measurements of CAL displacement still provided indirect evidence of humeral head superior translation. In addition to superior translation, existence of internal rotation and activation of shoulder muscules may further influence CAL displacement. The CAL displacement measured by US was 1.5–1.7 mm in the control group and 1.5–1.9 mm in the SST group. Increased superior translation of the humeral head (1.0– 1.5 mm) was demonstrated in shoulders with supraspinatus tendon tears during shoulder elevation in the scapular plane,23,24 which was smaller than in our study. However, factors in addition to superior head translation during simple arm elevation may contribute to CAL displacement. Nobuhara reported that the subacromial pressure did not increase markedly during elevation in the scapular plane, but increased markedly with internal rotation in the horizontal plane.25 A recent cadaveric study investigating pressure on the CAL during various shoulder motions

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showed that the pressure increased markedly during shoulder flexion or abduction with internal rotation, but did not increase markedly without internal rotation.26 Therefore, internal rotation may be the key shoulder motion exerting pressure on the CAL. In our study, the SAIR was comprised of abduction plus internal rotation, and may have caused greater subacromial pressure than elevation alone, thus causing greater CAL displacement. These results were compatible with those of Yanai et al.15 On the other hand, activation of shoulder muscules may further influence the extent of CAL displacement. The discrepancy in CAL displacement between passive and the active movements in the SST group implies that sound function of the humeral head depressors (e.g., teres major and latissimus dorsi27) may prevent further impingement. Our results may have further clinical applications. First, since passive SAIR seemed to exert pressure on the subacromial structures, patients should be instructed to limit passive SAIR following repair of subacromial structures. Second, US may be useful in preoperative assessment. A radiological study showed that increased superior head excursion may be related to a higher incidence of extended rotator cuff tears involving subscapularis tendon and lower preoperative functional outcomes measured by Constant scores.7 It has also been suggested that a tear wider than 3 cm should be treated aggressively by open repair.28,29 In our study, dynamic US revealed clear differences in CAL displacement between shoulders with supraspinatus tendon tears 40 years old in concordance with Neer’s stage III of subacromial impingement syndrome, indicating mechanical disruption of the rotator cuff tendons.31 Further studies may provide information about whether individuals with wider or complete supraspinatus tendon tears, asymptomatic persons, or younger individuals with such tears have similar features. Second, because arthroscopy was not performed, no proof exists of supraspinatus tendon tears. JOURNAL OF ORTHOPAEDIC RESEARCH SEPTEMBER 2012

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However, a previous study showed that US has good accuracy for detecting these tears.10 Furthermore, arthroscopy is invasive. Third, because of our cross-sectional study design, we could not determine the cause– effect relationship between supraspinatus tendon tear and CAL displacement; a longitudinal study is warranted. Fourth, the examiners were not blinded to the study groups because US was used for both diagnosis of supraspinatus tendon tear and evaluation of CAL displacement, and electromyography was not used to ensure that subjects remained relaxed during passive SAIR. These possible biases should be considered when interpreting these results.

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