Download e-book for kindle: Imaging Anatomy: Musculoskeletal by B. J. Manaster MD PhD FACR, Julia R. Crim MD

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The coracohumeral ligament blends with the supraspinatus tendon at the attachment. 44 Shoulder MR Atlas Shoulder AXIAL T1 MR, LEFT SHOULDER Coracoacromial and coracoclavicular ligaments Deltoid muscle Supraspinatus muscle and tendon Suprascapular vessels Scapular spine Coracohumeral ligament Coracoid process Deltoid muscle Subscapularis muscle Supraspinatus muscle Humeral head Infraspinatus tendon Suprascapular vessels Scapular spine (Top) This image is through the superior aspect of the coracoid process of the scapula.

The middle glenohumeral ligament is outlined by fluid. (Middle) External rotation at the same level empties the anterior recess and decreases the conspicuity of the middle glenohumeral ligament, which moves closer to subscapularis. Posterior recess is now filled with contrast and appears redundant. (Bottom) Extreme external rotation accentuates the normal posterior joint recess. The middle glenohumeral ligament is stretched and taut, paralleling the subscapularis tendon. 35 Shoulder Shoulder MR Atlas ANATOMY IMAGING ISSUES Imaging Approaches "Spaces" of Particular Interest Around Shoulder • Magnetic resonance (MR) imaging ○ Patient positioning – Supine, arm neutral to slight external rotation, avoid internal rotation – Arm at side and slightly away from side of body ○ Axial gradient-echo or T2 FS from acromion through inferior glenoid fossa ○ Coronal oblique T2 FS or proton density and T1 sequences oriented parallel to supraspinatus tendon – From subscapularis muscle anteriorly through infraspinatus muscle posteriorly ○ Sagittal oblique T2 FS oriented perpendicular to supraspinatus tendon – Scapular neck through lateral border of greater tuberosity • Quadrilateral or quadrangular space ○ Superior border: Teres minor ○ Inferior border: Teres major ○ Lateral border: Surgical neck of humerus ○ Medial border: Long head of triceps muscle ○ Contents: Axillary nerve and posterior circumflex humeral artery – Axillary nerve supplies teres minor muscle, deltoid muscle, posterolateral cutaneous region of shoulder and upper arm – Can have complications that are purely neurologic, purely vascular, or both ○ Axillary neuropathy – Due to abnormalities in quadrilateral space (paralabral cyst, fibrous band, glenohumeral joint dislocation, humeral fracture, extreme or prolonged abduction of arm during sleep) – Results in atrophy of teres minor muscle; may affect deltoid • Coracoacromial arch ○ Superior border: Acromion ○ Posterior border: Humeral head ○ Anterior border: Coracoacromial ligament, coracoid process ○ Contents: Subacromial-subdeltoid bursa, supraspinatus muscle/tendon, long head of biceps ○ Space/contents affected by os acromiale – Normal variant anatomy (unfused acromial process) in 5% – Normally fused by age 25 – May be mobile, decreasing coracoacromial space during shoulder motion, predisposing to impingement • Rotator interval ○ Triangular space between inferior border of supraspinatus muscle/tendon and superior border of subscapularis muscle/tendon ○ Medially border: Coracoid process ○ Laterally border: Transverse humeral ligament ○ Anterior border: Coracohumeral ligament, superior glenohumeral ligament, and joint capsule • Suprascapular notch ○ Roof of notch covered by superior transverse scapular ligament ○ Contents: Suprascapular nerve – Arises from brachial plexus superior trunk (4th-6th cervical nerve roots) composed of both motor and sensory fibers – Supplies supraspinatus and infraspinatus muscles – Anterior compression causes supraspinatus and infraspinatus atrophy – Posterior compression causes infraspinatus atrophy • Spinoglenoid notch ○ Located inferior to suprascapular notch, between scapular spine and posterior surface of glenoid body ○ Contents: Infraspinatus branch of suprascapular nerve ○ Supplies infraspinatus muscle Imaging Pitfalls • Magic angle phenomenon on MR ○ 55° to main magnetic field when image echo time (TE) < 30 ms ○ Increases signal intensity in otherwise normal structures ○ Most often seen in supraspinatus tendon, commonly in “critical zone,” 1 cm from greater tuberosity ○ Can be seen in glenoid labrum and biceps tendon proximal to bicipital groove ○ Avoid pitfall by comparing with images acquired with longer TE • Interdigitation of muscle or fibrous tissue between supraspinatus and infraspinatus tendons ○ Simulates increased T2 MR signal within supraspinatus tendon ○ Exaggerated if imaged in internal rotation • Volume averaging of rotator interval contents on coronal oblique images ○ Simulates increased T2 MR signal within supraspinatus tendon • Normal flattening or slight concavity of posterolateral humeral head ○ Proximal to teres minor tendon insertion ○ Can be confused with Hill-Sachs lesion, which is located more proximally, above level of coracoid process • Acromial pseudospurs mimicking osteophytes ○ Fibrocartilaginous hypertrophy at insertion of coracoacromial ligament on inferior acromion ○ Superior and inferior tendon slips of deltoid muscle • Anterolateral branch of anterior circumflex humeral artery and vein in lateral bicipital groove ○ Can be mistaken for biceps tendon longitudinal tear • Hyaline cartilage undercutting of superior labrum simulating labral tear • General imaging artifacts ○ Motion artifact can be decreased by positioning arm away from patient’s body ○ Avoid superior to inferior phase encoding to decrease artifact from axillary vessels ○ Metal susceptibility artifact – Increase bandwidth on all sequences – Fast spin-echo preferred to conventional spin-echo 36 CLINICAL IMPLICATIONS Shoulder MR Atlas Shoulder GRAPHICS, SUPERFICIAL SHOULDER DISSECTION Acromion process Posterior belly deltoid muscle Coracoid process Musculocutaneous nerve Supraspinatus tendon Transverse humeral ligament Subscapularis muscle Anterior circumflex humeral artery Biceps muscle and tendon, long head Biceps muscle and tendon, short head Circumflex scapular artery Teres major muscle Latissimus dorsi muscle Coracobrachialis muscle Brachial artery Median nerve Supraspinatus muscle Acromion process Anterior belly deltoid muscle Scapular spine Infraspinatus muscle Teres minor muscle Supraspinatus tendon Infraspinatus tendon Teres minor tendon Teres major muscle Triceps muscle and tendon, lateral head Latissimus dorsi muscle Triceps muscle and tendon, long head (Top) Anterior graphic of the shoulder shows a superficial scapulohumeral dissection.

MGHL is adjacent to the posterior border of subscapularis tendon, with which it merges slightly more inferiorly. (Middle) The anterior labrum is larger than the posterior labrum. The intermediate signal intensity hyaline cartilage extends beneath the labrum both anteriorly and posteriorly. (Bottom) At the inferior margin of the joint, the inferior labrum is seen superficial to the hyaline cartilage. A prominent posterior joint recess adjacent to the labrum is a normal finding. 27 Shoulder Shoulder Radiographic and Arthrographic Anatomy SAGITTAL: LATERAL TO MEDIAL Infraspinatus tendon Teres minor tendon Supraspinatus tendon Leading edge of supraspinatus tendon Supraspinatus tendon Infraspinatus tendon Subchondral cysts Coracohumeral ligament Biceps tendon, long head Supraspinatus tendon Infraspinatus tendon Coracohumeral ligament Subscapularis tendon Biceps tendon, long head Bicipital recess (Top) First of 9 selected sagittal PD FS MR arthrogram images from lateral to medial shows normal bicycle tire rim appearance of the rotator cuff around the superior and posterior portions of the humeral head.

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