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Anatomy Intraarticular disc • Synovial joint between• lateral end of clavicle & medial end Acromioclavicular Joint Muscle attachments to• medial clavicle & sternum Ligaments of SC joint • Intraarticular disc • Between medial end of• clavicle & manubrium Sternoclavicular Joint Acromioclavicular (AC)• joint Sternoclavicular (SC)• joint Abbreviations GROSS ANATOMY TERMINOLOGY Articular surface of○ clavicle oriented posterolaterally of acromion Sternohyoid & sternothyroid○ muscles separate great Sternocleidomastoid○ from posterior surface medial 1/3 Pectoralis major from○ anterior aspect medial 2/3 clavicle Costoclavicular ligaments○ Interclavicular ligament○ Capsular ligaments ○ Thickest posterosuperiorly○ (3 mm) Complete or incomplete○ ± perforations Attached to joint capsule○ anteriorly & posteriorly < 1/2 of medial clavicle○ articulates with manubrium Much larger than manubrial○ concavity Medial end of clavicle○ = large & bulbous Synovial sellar-type○ (saddle) joint Maximum thickness of capsule– from bony surface = Maximum width of normal– joint on US = 5 mm if < 35 Angle of inclination between– opposing articular anteromedially whereas articularsurfaceofacromionoriented vessels fromSC joint of clavicle(clavicularhead) (clavicular head) Posterior fibers arise– lateral to anterior fibers & resist Anterior fibers arise – from anteromedial surface of 1st Unite inferior surface– medial end clavicle to upper Prevents excessive upward– motion of clavicle Covers anterosuperior – & posterior aspects of joint Connects superomedial – aspect of clavicle to capsular Anterior stronger than– posterior portion Prevent upward displacement– of medial clavicle, Cover anterosuperior & posterior– aspects of SC joint Stability through capsuloligamentous– structures 2.7 mmif<35years&3.6 if>35years years &<4.4mmif>35 & mixed pattern(20%) & clavicle (25%),clavicleunderridingacromion(5%), (50%), verticalorientationbetweenacromion surfaces varieswithclavicleoverridingacromion downward motion rib & resistupwardmotion surface of1strib ligaments & uppermanubrium which maybecausedbydownwardforceonshoulder Sternoclavicular andAcromioclavicularJoints Ligaments of AC joint • SC or AC joints • Imaging Pitfalls Main clinical presentation• of SC joint is painless lump AC joint laxity can be• assessed by pulling down Align on arm transducer transversely• along SC or AC joints High-resolution linear• transducer Imaging Recommendations ANATOMY IMAGINGISSUES Muscle attachments ○ to lateral clavicle Coracoclavicular ligaments○ Superior AC ligament○ Undergoes rapid degeneration○ beginning in 2nd decade Determine whether AC○ joint is AC joint index = AC○ joint width of uninjured side/AC joint Acromion normally elevates○ from rest position during Should not be interpreted○ as subluxation Normally step-off between○ medial clavicle & manubrium Main clinical presentation○ of AC joint is pain due to Mild degrees of capsular○ thickening is readily apparent Compare with contralateral○ side while observingchangeinjointwidthonUS Trapezius attached to – posterior surface lateral 1/3 of Deltoid attached to anterior– surface lateral 1/3 of Mainly prevents lateral– compression of clavicle against Inserts to trapezoid ridge,– which runs along inferior Trapezoid ligament located– anterolaterally Mainly prevents upward– movement of clavicle Inserts to conoid tubercle,– which is located where Conoid ligament located– posteromedially Vary significantly in – length & width Conoid & trapezoid ligaments– Inserts along lateral – clavicle (8 mm) & medial acromion Stronger & thicker (2.0-5.5– mm) than thin or absent → markeddegenerationofdiscby4thdecade Severely subluxed or dislocated– (clavicle subluxed > Partially subluxed (clavicle– subluxed < 50% depth Not ofsubluxed (similar – to opposite side): Grade 1 width ofinjuredside=1.0normally arm adduction &, tolesserdegree,betweenlateralclavicle&acromion arthropathy, &subluxation/dislocation osteoarthritis, ACjointimpingement,inflammatory Occasionally due to mild– capsular swelling ± mild Clinical swelling often– due to relative forward clinically sincejointjustbeneathskinsurface clavicle clavicle acromion surface oflateral1/3clavicle middle 1/3ofclaviclecurvesintolateral (10 mm) inferior ACligament 50% depthofACjoint):Grade3 AC joint):Grade2 subluxation secondarytoSCosteoarthritis rotation ofuppertrunk positioning ofapparentlyswollenSCjointduetoaxial 5 Anatomy Manubrium, sternum Interclavicular l. Interclavicular l. Manubrium, sternum Clavicle Articular disc 1st costal cartilage Manubrium sternum TRANSVERSE US, STERNOCLAVICULAR JOINT US, STERNOCLAVICULAR TRANSVERSE 1st rib Joint capsule Sternoclavicular and Acromioclavicular Joints Acromioclavicular and Sternoclavicular Interclavicular l. Costoclavicular l. Sternoclavicular joint Medial end of clavicle Medial end of clavicle Anterior sternoclavicular l. Anterior sternoclavicular Graphic shows the anterior aspect of the sternoclavicular joint. Note the joint capsule, articular disc, and interclavicular ligament. (Top) Graphic shows the anterior aspect of the sternoclavicular joint. Note the joint capsule, articular medial clavicle is much larger than (Middle) Transverse grayscale US shows the anterosuperior aspect of the sternoclavicular joint. The to the superior aspect of manubrium, and the articulating surface of the manubrium. The thin interclavicular ligament is closely applied its connection with the medial ends of both clavicles is depicted. (Bottom) Transverse grayscale US shows the superior aspect of the clavicle when the lateral clavicle or sternoclavicular joint. The costoclavicular ligament prevents upward movement of the medial shoulder is depressed. 6

Anatomy LONGITUDINAL US,STERNOCLAVICULARJOINT dislocation ispresent,astheymay alsobeinjured. posterior tothesternoclavicularjoint andmaygetinjuredinposteriordislocation.Alltendinousattachments shouldbeassessedif well astheclavicleand1stcostal cartilage.(Bottom)LongitudinalgrayscaleUSshowsthe sternoclavicularjoint.Greatvesselslie the upperanteriorsurfaceof manubrium. Thesternohyoidandsternothyroidareattachedtothe posterioraspectofthesternumas the sternoclavicularjointregion.The sternocleidomastoidisattachedtotheuppersurfaceofmedial endoftheclavicleaswell from thesternum,uppercostalcartilages, andupperpartofexternalobliqueaponeurosis.(Middle)LongitudinalgrayscaleUSshows clavicle whenshoulderisdepressed.Pectoralismajormusclearises fromthemedial1/2ofanteriorsurfaceclavicleaswell (Top) LongitudinalgrayscaleUSshowssternoclavicularjoint.Costoclavicular ligamentpreventsupwardmovementofthemedial Sternohyoid, sternothyroid,t. Sternocleidomastoid m. Medial endofclavicle Subclavian a. Subclavian a. Sternoclavicular andAcromioclavicularJoints Sternocleidomastoid m.,sternalinsertion Sternum Sternocleidomastoid m.,sternalend 1st rib Costoclavicular l. Pectoralis majorm. Subclavian v. Medial endofclavicle Sternocleidomastoid, clavicularinsertion 7 Anatomy Coracoclavicular l., trapezoid component Coracoid process Coracoid process Clavicle, distal band Coracoclavicular l., conoid Coracoid process Subscapularis m. Teres major m. US, ACROMIOCLAVICULAR JOINT US, ACROMIOCLAVICULAR Acromion Deltoid m. Humeral head Sternoclavicular and Acromioclavicular Joints Acromioclavicular and Sternoclavicular Coracohumeral l. Supraspinatus m. Coracoacromial l. Coracoacromial l. Latissimus dorsi m. Biceps t., long head Biceps t., short head Transverse humeral l. Lateral end of clavicle Inferior acromioclavicular l. Inferior acromioclavicular Superior acromioclavicular l. Superior acromioclavicular Coracoclavicular l., trapezoid component Coracoclavicular l., trapezoid (Top) Anterior graphic shows the shoulder in superficial dissection. (Middle) Longitudinal grayscale US shows the acromioclavicular joint as it is on MR exam. These ligaments prevent region. The coracoclavicular ligament is demonstrated but is not as clearly depicted on US upward and lateral movement of the clavicle. (Bottom) Transverse grayscale US of the acromioclavicular joint region shows the the coracoacromial ligament during arm coracoacromial ligament. The supraspinatus tendon and intervening bursa can impinge against abduction. 8

Anatomy TRANSVERSE US,ACROMIOCLAVICULARJOINT slightly overridestheacromion.This isanormalconfiguration. vertically aligned.(Bottom)TransversegrayscaleUSshowsthe superioraspectoftheacromioclavicularjoint.Inthisimage,clavicle acromioclavicular joint.Separation oftheclavicleandacromioncanbereadilyappreciated.Notehow opposingbonemarginsarenot is thinwithastrongsupportingsuperioracromioclavicularligament. (Middle)TransversegrayscaleUSshowstheanterosuperior (Top) TransversegrayscaleUSshowstheanterioraspectofacromioclavicular joint.Thejointcapsuleoftheacromioclavicular Sternoclavicular andAcromioclavicularJoints Acromion Acromion Acromion Anterior capsule Clavicle Superior acromioclavicularl. Joint capsule Clavicle Superior acromioclavicularl. Joint capsule Clavicle Superior acromioclavicularl. 9 Anatomy Clavicle Clavicle Clavicle TRANSVERSE US, ACROMIOCLAVICULAR JOINT US, ACROMIOCLAVICULAR TRANSVERSE Acromion Acromion Acromion Joint capsule Joint capsule Joint capsule Sternoclavicular and Acromioclavicular Joints Acromioclavicular and Sternoclavicular Superior acromioclavicular l. Superior acromioclavicular l. Superior acromioclavicular Transverse grayscale US shows the anterosuperior aspect of the acromioclavicular joint with the arm positioned by the side of the (Top) Transverse grayscale US shows the anterosuperior aspect of the acromioclavicular joint with body. Note that the clavicle slightly overrides the acromion. (Middle) Transverse grayscale US shows the acromioclavicular joint with Note how the joint capsule bulges the arm in abducted position. The acromion is now level with the lateral aspect of the clavicle. superiorly, and the opposing bones are approximated with the arm abducted. (Bottom) Transverse grayscale US shows the relative to this lateral end of the clavicle. acromioclavicular joint with the arm in an abducted position. The acromion is now depressed