Ultrasound in Med. & Biol., Vol. 35, No. 8, pp. 1242–1248, 2009Copyright � 2009 World Federation for Ultrasound in Medicine & Biology

Printed in the USA. All rights reserved0301-5629/09/$–see front matter

asmedbio.2009.01.003

doi:10.1016/j.ultr

d Original Contribution

DYNAMIC VISUALIZATION OF THE CORACOACROMIAL LIGAMENT BYULTRASOUND

YI-CHIAN WANG,* HSING-KUO WANG,y WEN-SHIANG CHEN,* and TYNG-GUEY WANG**Department of Physical Medicine and Rehabilitation, National Taiwan University Hospital, College of Medicine, NationalTaiwan University, Taipei, Taiwan; and yGraduate Institute and School of Physical Therapy, College of Medicine, National

Taiwan University, Taipei, Taiwan

(Received 8 July 2008; revised 30 December 2008; in final form 9 January 2009)

ASouth

Abstract—Subacromial impingement syndrome (SIS) is prevalent in athletes who make throwing motions overtheir heads, as well as in the normal population, but it is difficult to diagnose precisely using physical examinationand traditional imaging modalities. Furthermore, the diagnostic testing protocols have not been strictly standard-ized. We used ultrasound to dynamically visualize coracoacromial ligament (CAL) morphology during shoulderimpingement tests: the CAL is the key impinging structure in SIS. Fifty normal shoulders were examined. Withthe transducer placed on the CAL, the shoulders were examined with seven different testing protocols describedin the literature. The degree of CAL bulge from the resting position was measured, and the degree of bulge indifferent testing protocols was compared. We found that the Hawkins-Kennedy impingement test caused moreCAL bulge than the Neer’s impingement test, and the most prominent morphological change in the CAL occurredwith an internally rotated and horizontally abducted shoulder. We conclude that high-resolution ultrasound is anexcellent tool for dynamically inspecting the impinging structures, is applicable in clinical settings, and allows moreaccurate diagnosis of SIS. (E-mail: tgw@ntu.edu.tw) � 2009 World Federation for Ultrasound in Medicine &Biology.

Key Words: Supraspinatus, Shoulder impingement syndrome, Ultrasonography, Rotator cuff.

INTRODUCTION

The clinical subacromial impingement syndrome (SIS) is

produced by the compression of subacromial structures

against the coracoacromial arch (Burns and Whipple

1993) and is prevalent both in athletes who make throwing

motions over their heads (Hawkins and Kennedy 1980)

and in the general population (Brotzman and Wilk

2007). The term covers a collection of diverse rotator

cuff diseases, ranging from simple mechanical irritation

to chronic friction-related degeneration or tear. The cora-

coacromial ligament (CAL), which is the central part of

coracoacromial arch, is an anatomical site of stenosis

(Neer 1972) and the main impinging structure in SIS.

As such, it plays a key role in the patho-etiology of SIS,

especially in patients without bony abnormalities (Fre-

merey et al. 2000). In a chronically impinging shoulder,

the CAL may become thicker, have lower failure load

(Fremerey et al. 2000), developed calcified enthesopathy

(Fealy et al. 2005) and undergo microscopic changes,

ddress correspondence to: Tyng-Guey Wang, 7 Chung-ShanRoad, Taipei 100, Taiwan. E-mail: tgw@ntu.edu.tw

1242

showing variegated cellular content with disarrangements

of the extracellular matrix and fibrofatty tissue infiltration

(Sarkar et al. 1990).

The diagnosis of SIS traditionally relies on the

history and physical examination. However, the diag-

nostic power of disease histories and special physical

tests are not satisfactory (Calis et al. 2000; Hegedus

et al. 2007; MacDonald et al. 2000; Park et al. 2005;

Tennent et al. 2003). Image modalities have been

used to improve diagnostic accuracy and to uncover

the underlying pathology, such as shoulder X-ray to

reveal a subacromial spur or shoulder magnetic reso-

nance imaging (MRI) for detecting subacromial bursitis

or rotator cuff tendinopathy or tear (Seeger et al. 1988;

Zlatkin et al. 1989). These imaging methods focus prin-

cipally on the acromion and subacromial space, over-

looking the role of the CAL. Moreover, MRI has

been reported to be a nonspecific tool for diagnosing

SIS (Birtane et al. 2001), because its static images

cannot reveal impingement that occurs only during

motion; consequently, although it may reveal secondary

evidence of impingement, it may not directly visualize

the underlying pathology.

US visualization of the coracoacromial ligament d Y.-C. WANG et al. 1243

Ultrasound is the modality of choice for imaging

small ligamentous structures such as the CAL, and it has

the advantage of being able to directly record dynamic

shoulder impingement. Nevertheless, few descriptions of

applications of this technique have been published. Based

on static imaging, Yanai et al. (2006) reported that the

CAL changed its shape in different shoulder positions.

We have developed a dynamic ultrasound examination

approach that can visualize the CAL in detail and in

motion. It displays the central part of the coracoacromial

arch more clearly than MRI can and, being a dynamic

examination, can provide more diagnostic information

on SIS than traditional static imaging modalities. We

compared the degrees of CAL bulge generated by the

different testing protocols described in the literature in

healthy subjects. This is a pilot study of a novel technique

of in vivo and real-time imaging of the CAL using muscu-

loskeletal ultrasonography.

Fig. 1. The position of the participants. During examination, theshoulder was abducted and the transducer was positionedperpendicular to the skin and between the coracoid processand acromial tip. In this picture, the transducer was intentionally

tilted to show the landmark on the skin.

MATERIALS AND METHODS

Twenty-five healthy subjects were recruited. Those

with concurrent shoulder pain or previous shoulder

trauma were excluded. All subjects underwent a screening

ultrasound to ensure the absence of occult abnormalities.

Personal profiles were obtained, including body weight,

body height and handedness. The ultrasound study was

performed by the same experienced examiner (one of

the authors), using a linear transducer of 12–14 MHz

(TOSHIBA Xario Model SSA-660A, Tokyo, Japan).

The examiner completed a dedicated three-month clinical

course in musculoskeletal ultrasound in an academic

hospital and practiced soft-tissue ultrasound examination

on more than 500 patients before undertaking this project.

Both shoulders of each subject were examined. The

subject sat upright, arms hanging beside the trunk, fore-

arm supinated and rested on the ipsilateral thigh. The

transducer was positioned perpendicular to the skin and

between the coracoid process and acromial tip to identify

the CAL (Fig. 1). The length of the CAL was measured.

The thickness of the CAL was measured in the middle

of the ligament. The transducer was then tilted to identify

the humeral head (HH) and to record the shortest distance

from the CAL to the humeral head (CAL–HH) (Fig. 2-1).

The Neer’s impingement sign was performed in four

different ways and the Hawkins-Kennedy impingement

test in three different ways, because these testing protocols

have not been strictly standardized and different versions

have been used in the literature (test details are listed in

Table 1). Each test was done with the subject fully relaxed

and the examiner testing the shoulder at a slow pace to

allow tracking of the CAL. We also instructed subjects

to actively perform Neer’s impingement sign and the

Hawkins-Kennedy impingement test at an angular

velocity of 90�/5 seconds to observe CAL motion during

muscular contraction (conditions that resemble daily

activities better than passive tests). Before the CAL

motion was recorded, the examiner performed each

testing protocol on each participant at least twice (usually

3 to 5 times) to ensure the consistency and quality of the

dynamic imaging. An animated file was then recorded at

a frame rate of 30 frames/seconds.

When the subjects were examined with the different

testing protocols, the CAL bulged out and exhibited

various degree of superior convexity (Fig. 2-2). The

process was filmed, and the size of bulge was measured

on the screen when reviewing the dynamic files. A line

was drawn connecting the CAL insertion sites on the cora-

coid process and acromion (Fig. 2-3). The distance from

this line to the vertex of the CAL convexity was measured.

The files were reviewed repeatedly to identify the largest

bulge, which was the point that was measured.

Results are expressed as means 6 standard deviation.

The bulges for the different tests were compared using the

nonparametric related samples test and Spearman’s corre-

lation test. A p-value less than 0.05 was considered statis-

tically significant.

RESULTS

The study included 25 normal healthy subjects

(Table 2). Four of the 25 participants reported an

Table 1. The different testing protocols that have been reported for Neer’s impingement sign and the Hawkins-Kennedyimpingement test

Sign Description

Neer’s impingement sign 1 (Neer1) With the humerus in the neutral position, the shoulder is passively anteriorly flexed above90�. (Ciprioano 2003; Craig 1994; Feinberg and Moley 2005; Holsbeeck and Introcaso2001; Jobe et al. 1996; Krishnan et al. 2004; Lee and Flatow 2005; Magee 2008; Ptasznik2001)

Neer’s impingement sign 2 (Neer2) With the humerus 90� internally rotated, the shoulder is passively anteriorly flexed above90�. (An. 1992; Cohen et al. 2007; Feinberg and Moley 2005; Freedman and Hart 2003;McMahon and Skinner 2003)

Neer’s impingement sign 3 (Neer3) With the humerus in the neutral position, the shoulder is passively flexed in the scapularplane above 90�. (Evans 1994; Ryu and Hurvitz 2007)

Neer’s impingement sign 4 (Neer4) With humerus 90� internally rotated, the shoulder is passively flexed in the scapular planeabove 90�. (McMahon et al. 2000)

Neer’s impingement sign, active Subjects actively perform the Neer4.

Hawkins-Kennedy impingement test 1 (HK1) With the shoulder in 90� anterior flexion and the elbow in 90� flexion, the shoulder ispassively internally and externally rotated through range of motion. (Ciprioano 2003;Krishnan et al. 2004; Magee 2008; Ryu and Hurvitz 2007)

Hawkins-Kennedy impingement test 2 (HK2) With the shoulder in 90� flexion along the scapular plane and the elbow in 90� flexion, theshoulder is passively internally and externally rotated through range of motion. (Feinbergand Moley 2005)

Hawkins-Kennedy impingement test 3 (HK3) With the shoulder in 90� abduction and the elbow in 90� flexion, the shoulder is passivelyinternally and externally rotated through range of motion. (Evans 1994; McMahon et al.2000)

Hawkins-Kennedy impingement test, active Subjects actively perform the HK3.

1244 Ultrasound in Medicine and Biology Volume 35, Number 8, 2009

uncomfortable sensation at the end of the HK1 testing

protocol, which required the shoulders to be flexed anteri-

orly to 90� and maximally internally rotated. In all four

cases, the discomfort took place when contact between

the coracoid process and the greater tuberosity was noted

on ultrasound. We therefore performed the HK1 testing

protocol within a range of motion that did not cause symp-

toms in these four cases, which was about 90� of shoulder

anterior flexion and 60� of internal rotation. Otherwise,

our healthy participants reported no symptoms during

examination.

The CAL bulges measured during the Neer’s impinge-

ment sign and the Hawkins-Kennedy impingement test are

summarized in Table 3. The Wilcoxon rank-sum test indi-

cated that the bulge measurements obtained during the

two tests differed significantly. Variants of the testing proto-

cols also made a difference, with internal rotation and

abduction of the humeral head causing the most compres-

sion of the CAL. Active movements produced significantly

more CAL bulge than passive tests, whether in the Neer’s or

Hawkins-Kennedy protocols. Despite the differences in

degree of bulge in the data, Spearman’s correlation test indi-

cated that all tests correlated well with each other, regardless

of the protocols (Fig. 3).

The CAL invariably appeared to be flat or concave at

rest and exhibited various degrees of bulge from the

resting position when tested with the different impinge-

ment protocols. When performing Neer’s impingement

sign, the biceps tendon and bicipital groove lay under

the acromion and were not visible in the neutral position.

During the initial degree of forward flexion, the CAL

deformed slightly, and then returned to the resting position

after the forearm was flexed beyond 60�. If the humerus

was internally rotated, the biceps and bicipital groove

appeared beneath the CAL, and the greater tuberosity

pushed the CAL out from beneath, producing even further

CAL deformity. Likewise, the CAL flattened after the

forearm was flexed over 60�.When performing the Hawkins-Kennedy impinge-

ment test, we found that the lesser tuberosity first entered

the subacromial space when the humeral head was rotated

inwardly from an external start point, followed by the

biceps long-head tendon, the greater tuberosity and finally

the supraspinatus tendon. When the shoulder was inter-

nally rotated and the greater tuberosity and supraspinatus

tendon were brought in the subacromial space, they

pushed the CAL from beneath. Some of the subjects could

not rotate the supraspinatus tendon into the subacromial

space, because this required more than 70� internal rota-

tion of the humeral head. If the humerus was inwardly

rotated to 90�, the greater tuberosity approached the cora-

coid process, and some subjects reported mild discomfort.

DISCUSSION AND SUMMARY

This research suggests that ultrasound examination

may be an ideal imaging tool to evaluate impingement

in the shoulder. In static MRI studies, with the shoulder

in the Hawkins-Kennedy position, there may exist either

a bony contact between the inferior border of anterolateral

acromion and greater tuberosity (De Wilde et al. 2003) or

thickened rotator cuff tendons and relative subacromial

Fig. 2. Measurement of coracoacromial ligament (CAL) bulge.2-(1): The CAL, spanning the acromion (A) and coracoid process(C), is flat or concave at rest. When the transducer is tilted toview the humeral head (HH), the CAL–HH distance can bemeasured. 2-(2): The CAL (arrow) bulged when the Hawkins-Kennedy impingement test was performed. 2-(3): A line wasdrawn connecting the bony insertions of the CAL and the defor-mity degree measured from the vertex of bulge vertically to the

line.

US visualization of the coracoacromial ligament d Y.-C. WANG et al. 1245

stenosis (Roberts et al. 2002). These imaging studies are

done with subjects fixed in a preset position, which may

not be helpful in SIS because for most patients the

impingement occurs during shoulder motion, rather than

in a certain static position. Crucially, high-resolution

ultrasound permits dynamic study, and is therefore the

modality of choice.

Ultrasound also provides good resolution. In a cadav-

eric study (Fealy et al. 2005), the CAL dimensions were

reported to be 31 6 4.7 mm long, 7.9 6 3.4mm wide

and 0.88 6 0.6 mm thick. In our study, the CAL length

but not the CAL thickness measured by ultrasound agreed

with the results of this study. One explanation for the

discrepancy may be that the echogenic paraligamentous

areolar tissue, which forms the superior and inferior

border of the CAL during ultrasound examination, may

have been dissected away in the cadaveric study. Peters-

son and Redlund-Johnell (1984), using X-rays, reported

that the average subacromial space was 9–10 mm. Using

3-D MRI, Graichen et al. (2001) reported that the average

acromion–humeral head distance was 7–8 mm. Our study

is the first to measure the CAL–humeral head distance

using soft-tissue ultrasound, and the data (7.5 6 1.5

mm) are comparable with other published results, despite

possible racial discrepancies.

We found that the Hawkins-Kennedy impingement

test, but not the Neer’s impingement sign, stressed the

CAL. This accords with a previous report (Holsbeeck

and Introcaso 2001). When Hawkins and Kennedy

(1980) first proposed the Hawkins-Kennedy impinge-

ment test for the diagnosis of SIS, anterior flexion and

internal rotation of shoulder were recommended. Later,

other shoulder testing positions have been considered.

In our investigation, abduction and internal rotation of

the humerus produced the most prominent CAL defor-

mity. If the humerus was flexed anteriorly and internally

rotated, the humeral greater tuberosity approached the

coracoid process, and the CAL was less deformed.

This observation is compatible with the findings of

Gerber et al. (1985), who used computed tomography

scanning to analyze shoulders in different Hawkins-

Kennedy positions.

In our scrutiny of Neer’s impingement sign using ultra-

sound, CAL bulge was not found if the humerus was flexed

beyond 90�. Previous studies with MRI (Roberts et al. 2002)

and stereophotogrammetry (Flatow et al. 1994) revealed no

subacromial narrowing or tissue compression in Neer’s

position. Pappas et al. (2006) used MRI to evaluated Neer’s

position and found mild subacromial space narrowing, but

there was still no tissue contact. A positive Neer’s impinge-

ment sign may therefore be explained by glenohumeral joint

instability (Beaulieu et al. 1999; Pappas et al. 2006), gleno-

humeral cartilage lesions (Guntern et al. 2003), supraspina-

tus impingement from the superior–posterior glenoid and

Table 2. Demographic data and baseline coracoacromialligament dimensions

CategoriesAverage 6 standard

deviation (range)

Sex Male: 12Female: 13

Age (y) 29.5 6 4.3 (22–41)Body weight (kg) 59.5 6 4.0 (46.0–79.0)Body height (cm) 165.4 6 8.4 (151.0–180.0)Shoulder width (cm) 38.5 6 3.4 (34.0–44.0)CAL length (mm) 31.20 6 2.99 (24.8–37.8)CAL thickness (mm) 1.97 6 0.49 (1.1–3.2)CAL–humeral head distance (mm) 7.48 6 1.89 (5.1–13.5)

CAL 5 Coracoacromial ligament.

1246 Ultrasound in Medicine and Biology Volume 35, Number 8, 2009

labrum (Hodge et al. 2001) or an anterior subacromial spur

(Uhthoff et al. 1988).

By definition, SIS refers to symptoms during active

motion. In contrast, impingement tests are done passively

by clinicians. An important question raised by our study is

whether passive impingement tests can reproduce real-life

impingement, because the CAL was significantly more

deformed in active motion than in passive tests. This

phenomenon might be explained by supraspinatus muscle

contraction and increased muscle volume, causing relative

stenosis of subacromial space.

In our study, an anterior–superior ultrasound view

visualized the central part of the coracoacromial arch

(the space below CAL), but not the lateral part (the space

below the acromion) or medial part (the space below the

coracoid process), because of extensive ultrasound atten-

uation produced by the bone structures in front of the cor-

Table 3. The largest bulge of the coracoacromial ligament duridescription of

Neer’s impingement sign Av

Neer’s impingement sign 1 (Neer1)y

Neer’s impingement sign 2 (Neer2)y

Neer’s impingement sign 3 (Neer3)y

Neer’s impingement sign 4 (Neer4)y

Neer’s impingement sign, activey

Averaged CAL extrusion of Neer1-Neer4*Hawkins-Kennedy impingement test

H-K impingement test 1 (HK1)z

H-K impingement test 2 (HK2)z

H-K impingement test 3 (HK3)z

H-K impingement test, activez

Averaged CAL extrusion of HK1- HK3*

*The Hawkins-Kennedy impingement test caused significantly more bulge oftest, p , 0.001; yThe CAL bulged significantly more when the Neer’s impingemthe scapular plane (Neer4), or with the subject actively performing Neer’s impikins-Kennedy impingement test, the CAL bulged the most when the Hawkins-Kizontally (HK3), followed by the humerus flexed in the scapular plane (HK2performed the Hawkins-Kennedy impingement test, more CAL deformity was

acoacromial arch. This would limit its usefulness if the

impingement occurred at the undersurface of the acromion

or coracoid process. Another limitation of this study is that

only normal subjects were recruited. To compare the

differences between normal subjects and patients with

clinical impingement, further studies are needed. The

width of the CAL may contribute to measurement inaccur-

acy if the transducer is tilted or misaligned, but the error is

acceptable considering the small size of CAL (Yanai et al.

2006). The correlations between each of the many testing

protocols were high, convincing us that this ultrasound

examination method is potentially applicable in clinical

settings. However, more studies are required to prove its

intrarater reliability, interrater reliability and diagnostic

accuracy.

To summarize, we developed a new method of

imaging the subacromial space using high-resolution

ultrasonography. The coracoacromial ligament and suba-

cromial structures were visualized effectively and dynam-

ically during various impingement tests. The

measurements of CAL bulge were compatible with

previous clinical, cadaveric and imaging studies. Based

on its accessibility, small cost and high-resolution power,

ultrasound examination can bridge the gap between the

physical special tests and traditional static imaging modal-

ities, improving our ability to diagnose subacromial

impingement syndrome. We suggest further research on

the applicability of this examination method to the patient

population.

Acknowledgements—This research was approved by the Research EthicsCommittee of the National Taiwan University Hospital, and all

ng different impingement tests (see Table 1 for a detailedthe tests)

Bulge (mm)

erage 6 standard deviation (range) Median

0.37 6 0.79 (0–3.5) 00.49 6 0.77 (0–2.7) 00.24 6 0.55 (0–1.9) 00.81 6 1.03 (0–3.6) 01.79 61.18 (0–5.0) 1.80.47 6 0.82 (0–3.6) 0

0.62 6 1.04 (0–4.1) 01.20 6 1.17 (0–4.3) 1.051.61 6 1.17 (0–4.5) 1.652.10 6 1.01 (0–5.0) 2.101.14 6 1.10 (0–4.5) 0.90

the CAL more than the Neer’s impingement sign did. Wilcoxon rank-sument sign was performed with the humerus rotated internally and flexed in

ngement sign. Kendall’s W test, p , 0.001; zWhen tested with the Haw-ennedy impingement test was performed with the humerus abducted hor-) and the humerus flexed anteriorly (HK1). When the subject activelyobserved than for any passive test. Kendall’s W test, p , 0.001.

Fig. 3. Spearman’s correlation test indicated good correlationbetween the Hawkins-Kennedy impingement test and Neer’s

impingement sign. Correlation value 0.637, p , 0.001.

US visualization of the coracoacromial ligament d Y.-C. WANG et al. 1247

volunteers gave informed consent. No commercial party having a director indirect interest in the subject matter of this article has conferred or willconfer a benefit upon the author or upon an organization with which theauthor is associated.

REFERENCES

An HS. Synopsis of Orthopaedics. New York: Thieme MedicalPublishers; 1992.

Beaulieu CF, Hodge DK, Bergman AG, Butts K, Daniel BL, Napper CL,Darrow RD, Dumoulin CL, Herfkens RJ. Glenohumeral relation-ships during physiologic shoulder motion and stress testing: Initialexperience with open MR imaging and active imaging-plane registra-tion. Radiology 1999;212:699–705.

Birtane M, Calis M, Akgun K. The diagnostic value of magnetic reso-nance imaging in subacromial impingement syndrome. YonseiMed J 2001;42:418–424.

Brotzman SB, Wilk KE. Handbook of Orthopaedic Rehabilitation. Phil-adelphia: Mosby Elsevier, 2007.

Burns WC, Whipple TL. Anatomic relationships in the shoulderimpingement syndrome. Clin Orthop Relat Res 1993;96–102.

Calis M, Akgun K, Birtane M, Karacan I, Calis H, Tuzun F. Diagnosticvalues of clinical diagnostic tests in subacromial impingementsyndrome. Ann Rheum Dis 2000;59:44-47.

Ciprioano JJ. Photographic Manual of Regional Orthopaedic and Neuro-logical Tests. Philadelphia: Lippincott Williams & Wilkins, 2003.

Cohen BS, Romeo AA, Bach BR Jr. Shoulder injury. In: Brotzman SB,Wilk KE, (eds). Handbook of Orthopaedic Rehabilitation. ed 2. Phil-adelphia: Mosby Elsevier, 2007: 173–374.

Craig EV. The shoulder and arm. In: Weinstein SL, Buckwalter JA, (eds).Turek’s Orthopaedics: Principals and Their Applications. ed 5. Phil-adelphia: Lippincott, 1994: 359–400.

De Wilde L, Plasschaert F, Berghs B, Van Hoecke M, Verstraete K,Verdonk R. Quantified measurement of subacromial impingement.J Shoulder Elbow Surg 2003;12:346–349.

Evans RC. Illustrated Essentials in Orthopedic Physical Assessment. St.Louis: Mosby, 1994.

Fealy S, April EW, Khazzam M, Armengol-Barallat J, Bigliani LU. Thecoracoacromial ligament: morphology and study of acromial enthes-opathy. J Shoulder Elbow Surg 2005;14:542–548.

Feinberg JH, Moley PJ. The physical examination. In: DeLisa JA,Gans BM, Walsh NE, (eds). Physical Medicine and Rehabilitation:

Principles and Practice. ed 4. Philadelphia: Lippincott Williams &Wilkins, 2005: 52–60.

Flatow EL, Soslowsky LJ, Ticker JB, Pawluk RJ, Hepler M, Ark J,Mow VC, Bigliani LU. Excursion of the rotator cuff under the acro-mion. Patterns of subacromial contact. Am J Sports Med 1994;22:779–788.

Freedman KB, Hart RA. Physical examination. In: Bernstein J, (ed).Musculoskeletal Medicine. Rosemont: IL, American Academy ofOrthopaedic Surgeons, 2003: 291–344.

Fremerey R, Bastian L, Siebert WE. The coracoacromial ligament:Anatomical and biomechanical properties with respect to age androtator cuff disease. Knee Surg Sports Traumatol Arthrosc 2000;8:309–313.

Gerber C, Terrier F, Ganz R. The role of the coracoid process in thechronic impingement syndrome. J Bone Joint Surg Br 1985;67:703–708.

Graichen H, Bonel H, Stammberger T, Englmeier KH, Reiser M,Eckstein F. Sex-specific differences of subacromial space widthduring abduction, with and without muscular activity, and correlationwith anthropometric variables. J Shoulder Elbow Surg 2001;10:129–135.

Guntern DV, Pfirrmann CW, Schmid MR, Zanetti M, Binkert CA,Schneeberger AG, Hodler J. Articular cartilage lesions of the gleno-humeral joint: Diagnostic effectiveness of MR arthrography andprevalence in patients with subacromial impingement syndrome.Radiology 2003;226:165–170.

Hawkins RJ, Kennedy JC. Impingement syndrome in athletes. Am JSports Med 1980;8:151–158.

Hegedus EJ, Goode A, Campbell S, Morin A, Tamaddoni M, MoormanCT, Cook C. Physical Examination Tests of the Shoulder: A System-atic Review with Meta-analysis of Individual Tests. Br J Sports Med2007.

Hodge DK, Beaulieu CF, Thabit GH 3rd, Gold GE, Bergman AG,Butts RK, Dillingham MF, Herfkens RJ. Dynamic MR imagingand stress testing in glenohumeral instability: Comparison withnormal shoulders and clinical/surgical findings. J Magn ResonImaging 2001;13:748–756.

Holsbeeck MTv, Introcaso JH. Musculoskeletal Ultrasound. Philadel-phia: Mosby; 2001.

Jobe FW, Schwab DM, Wilk KE, Andrew JR. Rehabilitation of theshoulder. In: Brotzman SB, (ed). Clinical Orthopaedic Rehabilita-tion. St. Louis: Mosby Year Book, 1996: 91–142.

Krishnan SG, Hawkins RJ, Bokor DJ. Clinical evaluation of shoulderproblems. In: Rockwook Jr, CA, Masten III FA, Wirth MA,Lipitt SB, (eds). The Shoulder, ed 3. Philadelphia: Saunders, 2004:145–186.

Lee EW, Flatow EL. The shoulder and arm. In: Weinstein SL,Buckwalter JA, (eds). Turek’s Orthopaedics: Principals and TheirApplications, ed 6. Philadelphia: Lippincott Williams & Wilkins,2005. 345–389.

MacDonald PB, Clark P, Sutherland K. An analysis of the diagnosticaccuracy of the Hawkins and Neer subacromial impingement signs.J Shoulder Elbow Surg 2000;9:299-301.

Magee DJ. Orthopedic Physical Assessment. St. Louis: Saunders; 2008.McMahon PJ, Merrill KD, Friedman RJ, Skinner HB. Sports medicine.

In: Skinner HB, (ed). Current Diagnosis & Treatment in Orthopedics,ed 2. New York: Lange Medical Books/McGraw-Hill, 2000:125–175.

McMahon PJ, Skinner HB. Sports medicine. In: Skinner HB, (ed).Current Diagnosis & Treatment in Orthopedics, ed 3. New York:Lange Medical Books/McGraw-Hill, 2003: 155–204.

Neer CS 2nd. Anterior acromioplasty for the chronic impingementsyndrome in the shoulder: A preliminary report. J Bone Joint SurgAm 1972;54:41–50.

Pappas GP, Blemker SS, Beaulieu CF, McAdams TR, Whalen ST,Gold GE. In vivo anatomy of the Neer and Hawkins sign positionsfor shoulder impingement. J Shoulder Elbow Surg 2006;15:40–49.

Park HB, Yokota A, Gill HS, El Rassi G, McFarland EG. Diagnosticaccuracy of clinical tests for the different degrees of subacromialimpingement syndrome. J Bone Joint Surg Am 2005;87:1446-1455.

Petersson CJ, Redlund-Johnell I. The subacromial space in normalshoulder radiographs. Acta Orthop Scand 1984;55:57–58.

1248 Ultrasound in Medicine and Biology Volume 35, Number 8, 2009

Ptasznik R. Sonography of the shoulder. In: Holsbeeck MTv,Introcaso JH, (eds). Musculoskeletal Ultrasound, ed 2. Philadelphia:Mosby, 2001: 465–615.

Roberts CS, Davila JN, Hushek SG, Tillett ED, Corrigan TM. Magneticresonance imaging analysis of the subacromial space in the impinge-ment sign positions. J Shoulder Elbow Surg 2002;11:595–599.

Ryu RKN, Hurvitz GR. The rotator cuff. In: Johnson DH, Pedowitz RA,(eds). Practical Orthopedic Sports Medicine & Arthroscopy. Phila-delphia: Lippincott Williams & Wilkins, 2007: 201–224.

Sarkar K, Taine W, Uhthoff HK. The ultrastructure of the coracoacromialligament in patients with chronic impingement syndrome. ClinOrthop Relat Res 1990:49–54.

Tennent TD, Beach WR, Meyers JF. A review of the special tests asso-ciated with shoulder examination. Part I: The rotator cuff tests. Am JSports Med 2003;31:154-160.

Seeger LL, Gold RH, Bassett LW, Ellman H. Shoulder impingementsyndrome: MR findings in 53 shoulders. AJR Am J Roentgenol1988;150:343–347.

Uhthoff HK, Hammond DI, Sarkar K, Hooper GJ, Papoff WJ. The roleof the coracoacromial ligament in the impingement syndrome. Aclinical, radiological and histological study. Int Orthop 1988;12:97–104.

Yanai T, Fuss FK, Fukunaga T. In vivo measurements of subacromialimpingement: Substantial compression develops in abduction withlarge internal rotation. Clin Biomech (Bristol, Avon) 2006;21:692–700.

Zlatkin MB, Iannotti JP, Roberts MC, Esterhai JL, Dalinka MK,Kressel HY, Schwartz JS, Lenkinski RE. Rotator cuff tears: diag-nostic performance of MR imaging. Radiology 1989;172:223–229.