imaging of the shoulder is a common investigation requested in patients presenting with shoulder pain and functional disabilities . a wide variety of etiologies , from rotator cuff pathologies to calcifying tendinosis , synovitis , acromioclavicular arthritis , and cervical radiculopathy may lead to similar symptoms . shoulder arthrography and magnetic resonance imaging have been the imaging modalities commonly used to distinguish among these conditions.[12 ] the development of musculoskeletal ultrasonography , based on advanced ultrasound ( us ) capabilities , has enabled this technique to be included as a primary imaging investigation among the battery of available diagnostic tests . knowledge of optimal techniques , normal anatomy , dynamic maneuvers , and pathological conditions is essential for correct us imaging and interpretation . comparison between the damaged and the contralateral sides may aid in reaching diagnostic conclusions . this pictorial essay aims to illustrate the technical performance , normal anatomy , and main pathologies related to the rotator cuff and beyond , as well as pitfalls in the us examination of the shoulder . modern us systems , offering high resolution multifrequency linear array transducers ranging from 4 to 7 , 3 to 9 , 5 to 12 and 5 to 17 mhz , and color doppler capabilities , enable optimal definition of anatomical structures . bone surface , tendons , bursae , ligaments , and muscles can be clearly demonstrated . a checklist protocol is proposed for a systematic shoulder us examination [ table 1 ] . proposed checklist for shoulder us examination shoulder ultrasound starts by examining the bicipital groove ( bg ) and long head of the biceps brachii tendon . the patient is seated facing the operator in a neutral position , his / her hand placed palm up on the thigh . a short axis image is performed by positioning the transducer over the proximal humeral metaphysis perpendicular to the humerus . the long axis image of the tendon is obtained by rotating the transducer to a position parallel to the humeral shaft [ figure 1 ] . patient 's arm is fixed on the flank and the forearm abducted in external rotation . the infraspinatous and teres minor tendons are examined from a posterior view of the shoulder the patient is rotated 90 , his / her hand placed over the opposite shoulder and the transducer oriented in the axial plane over the head of the humerus [ figure 3 ] . the glenohumeral joint and the spinoglenoid notch are also examined on a posterior view of the shoulder . the transducer is now moved medially and caudally in the transverse plane until the posterior margin of the glenohumeral joint is seen and then , further medially to show the spinoglenoid notch [ figure 4 ] . patient 's arm is placed in a posterior position , the dorsal hand on the opposite iliac wing or the palmar hand on the ipsilateral iliac wing . patient 's arm is abducted with the elbow flexed to 90 , or / and the arm is extended anteriorly [ figure 5 ] . the transducer is positioned over the shoulder top in a coronal plane [ figure 6 ] . the normal biceps tendon is a rounded echogenic structure ( arrows ) surrounded by a thin sonolucent area representing a small amount of fluid in the synovial sheath ; the echogenic transverse ligament is seen superficial to the tendon . the bicipital groove ( bg ) is identified at the anterior aspect of the humeral head as a concave echogenic line . ( b ) the position of the transducer on the bicipital groove of the humerus . ( c ) long axis image shows the fine fibrillar structure of the biceps tendon ( arrows ) . ( d ) the position of the transducer along the humeral shaft to view the long head of the biceps tendon . subscapularis tendon . a fibrillar pattern is seen along the tendon ( arrows ) , which inserts into the lesser tuberosity ( ls ) . ( b ) the transducer is placed in an axial plane for a long view of the tendon . ( c ) short axis view of the tendon shows a series of hyperechoic fibers and hypoechoic clefts , due to interposed muscle fibers among the tendon fibers ( arrows ) . ( d ) the transducer is placed in a sagittal plane for a short view of the tendon . ( a ) the infraspinatous tendon ( arrow ) is seen lying superficial to the echogenic cortical bone of the humeral head and deep to the echogenic bursal fat stripe . ( b ) the position of the transducer in an axial plane over the infraspinatus fossa . the image shows the humeral head ( h ) covered by the thin hypoechogenic articular cartilage ( long arrow ) , the glenoid margin ( g ) and a homogeneously echogenic triangular structure- the fibrocartilagenous posterior labrum ( short arrow ) . ( b ) the transducer is positioned slightly lower and medially in an axial plane . the image shows the suprascapular nerve together with the artery and vein running in this notch ( arrow ) . the tendon has a homogeneous pattern of medium - level echoes and a convex beak - like shape . from superficial to deep , note the echogenic skin and subcutaneous fat , the hypoechogenic deltoid muscle , the echogenic fat stripe , the hypoechogenic fine subacromial - subdeltoid bursa ( arrows ) and the supraspinatous tendon lying over the hypoechogenic cartilage of the humeral head , the echogenic cortex of the humeral head and the greater tuberosity . ( b ) position of the transducer , in a sagittal plane lateral to the bicipital groove . the tendon lies between the humeral cartilage below and the subacromial subdeltoid bursa above ( sasdb ) . note the short axis view of the biceps tendon medially to the supraspinatous , appears as an oval echogenic structure ( small arrow ) . plot shows supraspinatous tendon and subacromial bursa ( arrow ) lateral to the acromion ( a ) right plot : during dynamic maneuvers , the supraspinatous tendon and subacromial bursa are scanned while gliding beneath the subacromial space ( a ) . ( f ) the transducer is positioned over the acromion while the patient raises his / her arm . ( a ) the medial edge of the acromium ( a ) , clavicular edge ( c ) and joint capsule ( arrows ) are seen . ( b ) the transducer is positioned in a coronal plane , over the acromion . examiners must be aware of anisotropy- a common artifact and potential pitfall in us of tendons , making them appear hypoechoic when the incident ultrasound beam angle is not perpendicular to the tendon . this phenomenon can be avoided by ensuring that the transducer is correctly positioned.[56 ] rotator cuff tears are the most common pathology found in shoulder us examinations . tendon tears may be classified according to the extent of fiber failure , ranging from complete tears [ figure 7 ] , full - thickness tears [ figures 8 , 9 ] , partial - thickness tears [ figures 1012 ] , and intrasubstance tears [ figure 13 ] . an acute tear is usually accompanied by joint or bursal effusion [ figure 12].[79 ] absence of effusion is usually related to chronic tears . in a meta - analysis on the accuracy of mri , mr arthrography , and us in the diagnosis of rotator cuff tears , us offered high sensitivity and specificity for the assessment of full - thickness rotator cuff tears ( 92.3 and 94.4% , respectively ) with 85.1% and 92% , respectively for all tears . partial thickness tear appears as a hypoechoic defect or cleft in the tendon , affecting only part of its thickness , while a full - thickness tear extends from the bursal to the articular surface of the tendon . a complete tear is a full - thickness tear affecting the full width of the tendon . the tendon retracts medially , the amount of retraction depending on the age of the tear . in chronic ruptures , the tendon dissapears beneath the coracoacromial arch , leaving the humeral head uncovered by the supraspinatous , the so - called  naked head  sign . the image shows a sonolucent defect ( arrows ) extending across the width of the supraspinatous tendon . tear at the greater tuberosity attachment of the supraspinatous tendon , appears as a sonolucent gap ( cursors ) . note the echogenic line below the tear ( arrow ) represents the articular cartilage edge , which is well visualized due to fluid in the above tendon tear . the image shows the tear at the articular side of the supraspinatous tendon as a hypoechoic defect with echogenic boundary ( arrows ) . the image shows a sonolucent defect at the bursal side of the supraspinatous tendon ( large arrows ) . note flattening of the acromio clavicular bursa at the level of the tear ( small arrow ) . the image shows a large sonolucent defect in the bursal side of the supraspinatous tendon ( cursors ) . fluid in the subscapularis subdeltoid bursa is seen , secondary to an acute tear ( arrow ) . the most commonly found nontear - related pathologies of the rotator cuff are rotator cuff tendinosis [ figure 14 ] , rotator cuff calcifying tendonitis [ figure 15 ] , and subacromial tendon impingement [ figure 16 ] . it is worthwhile noting that in such cases , tears may develop due to tendon weakness [ table 2 ] . rotator cuff tendinosis or tendinopathy presents as swelling of the tendon with a heterogeneous hypoechoic tendon echotexture . rotator cuff calcifications appear as hyperechoic foci , either with welldefined posterior shadowing ( type i ) or with a faint ( type ii ) or absent ( type iii ) shadow . type i corresponds to the formative phase and types ii and iii to the resorptive phase , in which they change to semi or totally liquid deposits of calcium . in subacromial impigment , tendon gliding in the subacromial space during abduction and anterior elevation of the arm is absent . the image reveals supraspinatous tendon degeneration as tendon widening with internal echostructure heterogeneity ( arrow ) . the image shows calcium deposition as intrasubstance hyperechoic foci with posterior acoustic shadowing ( arrows ) type i calcific tendonitis . left plot : the patient abducts the shoulder while the arm is in internal rotation . the supraspinatous tendon is seen bunching up lateral to the acromion . rotator cuff pathologies gleno - humeral joint effusion [ figure 17 ] , subacromial - subdeltoid bursa effusion [ figure 18 ] , calcifying bursitis [ figure 19 ] , acromio - clavicular joint arthropathies and dislocation [ figure 20 ] , biceps tendon tear [ figure 21 ] , synovitis [ figure 22 ] , and dislocation [ figure 23 ] are the main nonrotator cuff - related pathologies seen in shoulder us [ table 3].[89 ] us is sensitive for the detection of glenohumeral joint effusion and subacromial subdeltoid bursal effusion , even in small amounts . subluxation or dislocation of the acromioclavicular joint appears as widening of the joint cavity and bulging of the superior capsule and ligament . rupture of the long head of the biceps brachii tendon typically generates a lump in the anterior arm , known as  popeye sign  . tendon disruption occurs usually at the intrarticular level with distal retraction , leaving an empty groove . in acute tears medial biceps tendon dislocation is diagnosed with us on transverse scans , which depict the bicipital sulcus and the tendon overlying the lesser tuberosity . gleno - humeral joint effusion.the image shows fluid distending the glenohumeral joint capsule ( long arrow ) . hyperechoic posterior labrum ( small arrow ) adjacent to the glenoid edge ( g ) is separated from the humeral head ( h ) by synovial fluid . the subacromial - subdeltoid bursa is distended ( cursors ) and filled with fluid and echogenic material ( arrows ) , ( b ) bursal hematoma . mixed sonolucent and echogenic material filling the bursa in a patient after acromioplasty , ( c ) clear bursa synovial fluid . the axial image shows sonolucent fluid in the bursa , over the bicipital tendon in the bicipital groove . ( a ) the image shows hyperechoic material within the subacromial subdeltoid bursa compatible with calcific deposits , most commonly calcium hydroxyapatite crystal , distension of the bursa ( small arrows ) by the extensive bursal calcification . few deposits generate acoustic shadowing ( large arrow ) , ( b ) wide posterior acoustic shadow in calcific bursitis . transverse scan over the right acromio - clavicular joint shows slight widening of the joint space between the acromion ( lower long arrow ) and the distal end of the clavicle ( upper long arrow ) . increase in soft tissue width interposed between bone ends of the joint ( short arrow ) and associated irregularity of the articular surfaces are consistent with subluxation secondary to degenerative arthropathy . marked widening of the joint space between lateral end of the clavicle ( c ) and acromion ( a ) in a patient with chronic traumatic dislocation of the left acromioclavicular joint , confirmed by plain films ( not shown ) . . longitudinal scan of the bicipital groove shows proximal retraction of the biceps muscle ( long arrow ) . a fluid - filled gap with echogenic clots ( small arrow ) at the myotendinous junction . axial scan of the biceps tendon shows fluid and synovial thickening ( arrow ) surrounding the biceps tendon sheath . the biceps tendon ( arrow ) lies medially , anterior to the lesser tuberosity of the humerus . a small amount of fluid is seen in the tendon sheath . non - rotator cuff pathologies beyond the benefits of us as a diagnostic tool , interventional procedures under us guidance , such as local anesthetic and steroid injection therapy , fluid aspiration in synovial processes , and biopsies of masses , may be accurately performed . us guidance allows precise needle location thus avoiding the risks of intratendinous steroid injection [ figure 2426 ] . ( a ) echogenic soft tissue oval mass in the subcutaneous fat at the proximal arm , with multiple foci of calcification ( b ) needle biopsy performed with a 16-g tru - cut needle ( small arrows ) under ultrasound guidance . after firing , the needle tip is seen as a strong echogenic dot ( larger arrow ) . the patient suffered from breast carcinoma and had recently been diagnosed with papillary cystoadenocarcinoma of the ovary . ( a ) calcific tendonitis , ( b ) a 20-g spinal needle is directed into the calcific material in the tendon ( arrow ) . using to and fro movements of the needle , ( a ) subacromial - subdeltoid bursa synovitis in a patient with septic arthritis , ( b ) a 20-g spinal needle is guided into the bursa ( arrow ) and fluid is aspirated . modern us systems , offering high resolution multifrequency linear array transducers ranging from 4 to 7 , 3 to 9 , 5 to 12 and 5 to 17 mhz , and color doppler capabilities , enable optimal definition of anatomical structures . bone surface , tendons , bursae , ligaments , and muscles can be clearly demonstrated . a checklist protocol is proposed for a systematic shoulder us examination [ table 1 ] . proposed checklist for shoulder us examination shoulder ultrasound starts by examining the bicipital groove ( bg ) and long head of the biceps brachii tendon . the patient is seated facing the operator in a neutral position , his / her hand placed palm up on the thigh . a short axis image is performed by positioning the transducer over the proximal humeral metaphysis perpendicular to the humerus . the long axis image of the tendon is obtained by rotating the transducer to a position parallel to the humeral shaft [ figure 1 ] . patient 's arm is fixed on the flank and the forearm abducted in external rotation . the infraspinatous and teres minor tendons are examined from a posterior view of the shoulder the patient is rotated 90 , his / her hand placed over the opposite shoulder and the transducer oriented in the axial plane over the head of the humerus [ figure 3 ] . the glenohumeral joint and the spinoglenoid notch are also examined on a posterior view of the shoulder . the transducer is now moved medially and caudally in the transverse plane until the posterior margin of the glenohumeral joint is seen and then , further medially to show the spinoglenoid notch [ figure 4 ] . patient 's arm is placed in a posterior position , the dorsal hand on the opposite iliac wing or the palmar hand on the ipsilateral iliac wing . patient 's arm is abducted with the elbow flexed to 90 , or / and the arm is extended anteriorly [ figure 5 ] . the transducer is positioned over the shoulder top in a coronal plane [ figure 6 ] . the normal biceps tendon is a rounded echogenic structure ( arrows ) surrounded by a thin sonolucent area representing a small amount of fluid in the synovial sheath ; the echogenic transverse ligament is seen superficial to the tendon . the bicipital groove ( bg ) is identified at the anterior aspect of the humeral head as a concave echogenic line . ( b ) the position of the transducer on the bicipital groove of the humerus . ( c ) long axis image shows the fine fibrillar structure of the biceps tendon ( arrows ) . ( d ) the position of the transducer along the humeral shaft to view the long head of the biceps tendon . a fibrillar pattern is seen along the tendon ( arrows ) , which inserts into the lesser tuberosity ( ls ) . ( b ) the transducer is placed in an axial plane for a long view of the tendon . ( c ) short axis view of the tendon shows a series of hyperechoic fibers and hypoechoic clefts , due to interposed muscle fibers among the tendon fibers ( arrows ) . ( d ) the transducer is placed in a sagittal plane for a short view of the tendon . ( a ) the infraspinatous tendon ( arrow ) is seen lying superficial to the echogenic cortical bone of the humeral head and deep to the echogenic bursal fat stripe . ( b ) the position of the transducer in an axial plane over the infraspinatus fossa . the image shows the humeral head ( h ) covered by the thin hypoechogenic articular cartilage ( long arrow ) , the glenoid margin ( g ) and a homogeneously echogenic triangular structure- the fibrocartilagenous posterior labrum ( short arrow ) . ( b ) the transducer is positioned slightly lower and medially in an axial plane . the image shows the suprascapular nerve together with the artery and vein running in this notch ( arrow ) . the tendon has a homogeneous pattern of medium - level echoes and a convex beak - like shape . from superficial to deep , note the echogenic skin and subcutaneous fat , the hypoechogenic deltoid muscle , the echogenic fat stripe , the hypoechogenic fine subacromial - subdeltoid bursa ( arrows ) and the supraspinatous tendon lying over the hypoechogenic cartilage of the humeral head , the echogenic cortex of the humeral head and the greater tuberosity . ( b ) position of the transducer , in a sagittal plane lateral to the bicipital groove . the tendon lies between the humeral cartilage below and the subacromial subdeltoid bursa above ( sasdb ) . note the short axis view of the biceps tendon medially to the supraspinatous , appears as an oval echogenic structure ( small arrow ) . plot shows supraspinatous tendon and subacromial bursa ( arrow ) lateral to the acromion ( a ) right plot : during dynamic maneuvers , the supraspinatous tendon and subacromial bursa are scanned while gliding beneath the subacromial space ( a ) . ( f ) the transducer is positioned over the acromion while the patient raises his / her arm . ( a ) the medial edge of the acromium ( a ) , clavicular edge ( c ) and joint capsule ( arrows ) are seen . ( b ) the transducer is positioned in a coronal plane , over the acromion . examiners must be aware of anisotropy- a common artifact and potential pitfall in us of tendons , making them appear hypoechoic when the incident ultrasound beam angle is not perpendicular to the tendon . tendon tears may be classified according to the extent of fiber failure , ranging from complete tears [ figure 7 ] , full - thickness tears [ figures 8 , 9 ] , partial - thickness tears [ figures 1012 ] , and intrasubstance tears [ figure 13 ] . an acute tear is usually accompanied by joint or bursal effusion [ figure 12].[79 ] absence of effusion is usually related to chronic tears . in a meta - analysis on the accuracy of mri , mr arthrography , and us in the diagnosis of rotator cuff tears , us offered high sensitivity and specificity for the assessment of full - thickness rotator cuff tears ( 92.3 and 94.4% , respectively ) with 85.1% and 92% , respectively for all tears . partial thickness tear appears as a hypoechoic defect or cleft in the tendon , affecting only part of its thickness , while a full - thickness tear extends from the bursal to the articular surface of the tendon . a complete tear is a full - thickness tear affecting the full width of the tendon . the tendon retracts medially , the amount of retraction depending on the age of the tear . in chronic ruptures , the tendon dissapears beneath the coracoacromial arch , leaving the humeral head uncovered by the supraspinatous , the so - called  naked head  sign . the image shows a sonolucent defect ( arrows ) extending across the width of the supraspinatous tendon . tear at the greater tuberosity attachment of the supraspinatous tendon , appears as a sonolucent gap ( cursors ) . note the echogenic line below the tear ( arrow ) represents the articular cartilage edge , which is well visualized due to fluid in the above tendon tear . the image shows the tear at the articular side of the supraspinatous tendon as a hypoechoic defect with echogenic boundary ( arrows ) . the image shows a sonolucent defect at the bursal side of the supraspinatous tendon ( large arrows ) . note flattening of the acromio clavicular bursa at the level of the tear ( small arrow ) . the image shows a large sonolucent defect in the bursal side of the supraspinatous tendon ( cursors ) . fluid in the subscapularis subdeltoid bursa is seen , secondary to an acute tear ( arrow ) . the most commonly found nontear - related pathologies of the rotator cuff are rotator cuff tendinosis [ figure 14 ] , rotator cuff calcifying tendonitis [ figure 15 ] , and subacromial tendon impingement [ figure 16 ] . it is worthwhile noting that in such cases , tears may develop due to tendon weakness [ table 2 ] . rotator cuff tendinosis or tendinopathy presents as swelling of the tendon with a heterogeneous hypoechoic tendon echotexture . rotator cuff calcifications appear as hyperechoic foci , either with welldefined posterior shadowing ( type i ) or with a faint ( type ii ) or absent ( type iii ) shadow . type i corresponds to the formative phase and types ii and iii to the resorptive phase , in which they change to semi or totally liquid deposits of calcium . in subacromial impigment , tendon gliding in the subacromial space during abduction and anterior elevation of the arm is absent . the image reveals supraspinatous tendon degeneration as tendon widening with internal echostructure heterogeneity ( arrow ) . the image shows calcium deposition as intrasubstance hyperechoic foci with posterior acoustic shadowing ( arrows ) type i calcific tendonitis . gleno - humeral joint effusion [ figure 17 ] , subacromial - subdeltoid bursa effusion [ figure 18 ] , calcifying bursitis [ figure 19 ] , acromio - clavicular joint arthropathies and dislocation [ figure 20 ] , biceps tendon tear [ figure 21 ] , synovitis [ figure 22 ] , and dislocation [ figure 23 ] are the main nonrotator cuff - related pathologies seen in shoulder us [ table 3].[89 ] us is sensitive for the detection of glenohumeral joint effusion and subacromial subdeltoid bursal effusion , even in small amounts . subluxation or dislocation of the acromioclavicular joint appears as widening of the joint cavity and bulging of the superior capsule and ligament . rupture of the long head of the biceps brachii tendon typically generates a lump in the anterior arm , known as  popeye sign  . tendon disruption occurs usually at the intrarticular level with distal retraction , leaving an empty groove . in acute tears medial biceps tendon dislocation is diagnosed with us on transverse scans , which depict the bicipital sulcus and the tendon overlying the lesser tuberosity . gleno - humeral joint effusion.the image shows fluid distending the glenohumeral joint capsule ( long arrow ) . hyperechoic posterior labrum ( small arrow ) adjacent to the glenoid edge ( g ) is separated from the humeral head ( h ) by synovial fluid . the subacromial - subdeltoid bursa is distended ( cursors ) and filled with fluid and echogenic material ( arrows ) , ( b ) bursal hematoma . mixed sonolucent and echogenic material filling the bursa in a patient after acromioplasty , ( c ) clear bursa synovial fluid . the axial image shows sonolucent fluid in the bursa , over the bicipital tendon in the bicipital groove . ( a ) the image shows hyperechoic material within the subacromial subdeltoid bursa compatible with calcific deposits , most commonly calcium hydroxyapatite crystal , distension of the bursa ( small arrows ) by the extensive bursal calcification . few deposits generate acoustic shadowing ( large arrow ) , ( b ) wide posterior acoustic shadow in calcific bursitis . transverse scan over the right acromio - clavicular joint shows slight widening of the joint space between the acromion ( lower long arrow ) and the distal end of the clavicle ( upper long arrow ) . increase in soft tissue width interposed between bone ends of the joint ( short arrow ) and associated irregularity of the articular surfaces are consistent with subluxation secondary to degenerative arthropathy . marked widening of the joint space between lateral end of the clavicle ( c ) and acromion ( a ) in a patient with chronic traumatic dislocation of the left acromioclavicular joint , confirmed by plain films ( not shown ) . . longitudinal scan of the bicipital groove shows proximal retraction of the biceps muscle ( long arrow ) . a fluid - filled gap with echogenic clots ( small arrow ) at the myotendinous junction . axial scan of the biceps tendon shows fluid and synovial thickening ( arrow ) surrounding the biceps tendon sheath . the biceps tendon ( arrow ) lies medially , anterior to the lesser tuberosity of the humerus . beyond the benefits of us as a diagnostic tool , interventional procedures under us guidance , such as local anesthetic and steroid injection therapy , fluid aspiration in synovial processes , and biopsies of masses , may be accurately performed . us guidance allows precise needle location thus avoiding the risks of intratendinous steroid injection [ figure 2426 ] . ( a ) echogenic soft tissue oval mass in the subcutaneous fat at the proximal arm , with multiple foci of calcification ( b ) needle biopsy performed with a 16-g tru - cut needle ( small arrows ) under ultrasound guidance . after firing , the patient suffered from breast carcinoma and had recently been diagnosed with papillary cystoadenocarcinoma of the ovary . ( a ) calcific tendonitis , ( b ) a 20-g spinal needle is directed into the calcific material in the tendon ( arrow ) . using to and fro movements of the needle , the calcium is indented by the needle . ( a ) subacromial - subdeltoid bursa synovitis in a patient with septic arthritis , ( b ) a 20-g spinal needle is guided into the bursa ( arrow ) and fluid is aspirated . shoulder us has become the modality of choice for the diagnosis of rotator cuff and non - rotator cuff pathologies , offering a high level of diagnostic specificity and sensitivity along with significant benefits to the examiner and the patient , assuming the study is performed by an experienced examiner with high - capacity equipment . us is noninvasive , relatively inexpensive and allows for easy comparison between the affected shoulder and the contralateral side . strict compliance with procedure protocol , and a comprehensive knowledge of shoulder anatomy , pathologies , and potential technical pitfalls are all needed to make accurate diagnoses . dynamic imaging and color / power doppler us add information unavailable through mri and arthrography . us guidance adds the benefits of accuracy and safety in interventional procedures such as anesthetic and steroid injections .
ultrasound ( us ) of the shoulder is the most commonly requested examination in musculoskeletal us diagnosis . 
 sports injuries and degenerative and inflammatory processes are the main sources of shoulder pain and functional limitations . because of its availability , low cost , dynamic examination process , absence of radiation exposure , and ease of patient compliance , us is the preferred mode for shoulder imaging over other , more sophisticated , and expensive methods . 
 operator dependence is the main disadvantage of us examinations . 
 use of high range equipment with high resolution transducers , adhering to a strict examination protocol , good knowledge of normal anatomy and pathological processes and an awareness of common pitfalls are essential for the optimal performance and interpretation of shoulder us . 
 this article addresses examination techniques , the normal sonographic appearance of tendons , bursae and joints , and the main pathological conditions found in shoulder ultrasonography .