MRI Anatomy Flashcards · MSK

Shoulder Anatomy

Learn to identify every labeled structure on a Shoulder MRI, plane by plane.

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Shoulder anatomy, structure by structure

Shoulder MRI is one of the highest-volume musculoskeletal studies you will scan, and reading it well starts with knowing the normal anatomy cold. This reference walks through every structure in our shoulder flashcard deck across the two workhorse planes (axial and coronal oblique), with a plain-language definition, how each structure looks on MRI, and the pathology you will actually run into at the scanner.

Bones and joints

The bony framework of the shoulder girdle and the two joints that move it. Cortical bone is dark on every sequence; fatty marrow is bright on T1.

Glenoid

The shallow, pear-shaped socket of the scapula that articulates with the humeral head to form the glenohumeral joint.

On MRI: A flat-to-slightly-concave bony surface with a dark cortical rim and bright fatty marrow, capped by darker glenoid cartilage and the surrounding labrum. Seen face-on as a shallow cup on axial and as the medial wall of the joint on coronal oblique.

Common pathology: Glenoid bone loss after recurrent anterior dislocation (bony Bankart), glenoid hypoplasia, and degenerative marginal osteophytes.

Tip: The labrum hugs the bony rim of the glenoid, so trace the glenoid first, then look for the dark triangular labrum perched on each edge.

Humeral Head

The rounded, ball-shaped proximal end of the humerus that sits in the glenoid socket.

On MRI: A large sphere of bright fatty marrow inside a thin dark cortical shell, with a smooth dark cartilage cap along the articular surface. It dominates the lateral side of the coronal oblique image.

Common pathology: Hill-Sachs impaction defect on the posterolateral head after anterior dislocation, avascular necrosis (subchondral signal change), and cysts at the rotator cuff footprint.

Humerus

The long bone of the upper arm; its proximal shaft and tuberosities anchor the rotator cuff tendons below the humeral head.

On MRI: A column of bright fatty marrow within a dark cortical outline extending inferiorly from the humeral head; the greater and lesser tuberosities mark the tendon insertions.

Common pathology: Proximal humeral fractures, greater tuberosity bone bruise or avulsion with cuff injury, and metastatic marrow lesions.

Clavicle

The collarbone, the S-shaped strut connecting the sternum to the acromion that suspends the shoulder from the trunk.

On MRI: A bright fatty-marrow bone with a dark cortical rim seen in cross section on axial and along its length on superior coronal oblique slices; its lateral end meets the acromion.

Common pathology: Distal clavicular osteolysis (weightlifter's shoulder), AC joint arthrosis at its lateral end, and old fractures.

Acromion

The flat, forward-projecting bony shelf of the scapula that forms the roof over the rotator cuff.

On MRI: A plate of bone with bright marrow and a dark cortical rim arching over the supraspinatus; its undersurface and slope set the space available for the cuff.

Common pathology: A hooked (type III) acromion or downsloping morphology narrows the subacromial space and contributes to impingement and supraspinatus tears; os acromiale is an unfused variant.

Tip: On coronal oblique the acromion is the bony roof directly above the supraspinatus tendon; the gap between them is the subacromial space you assess for impingement.

Scapula

The shoulder blade, the flat triangular bone that carries the glenoid socket and provides the broad surface for the rotator cuff muscles.

On MRI: A thin flat bone with bright marrow and a dark cortical outline; its body, spine, and glenoid neck frame the medial aspect of the coronal oblique image.

Common pathology: Scapular body and neck fractures, spinoglenoid notch cysts compressing the suprascapular nerve, and bone lesions.

Acromioclavicular Joint

The small synovial joint between the lateral end of the clavicle and the acromion at the top of the shoulder.

On MRI: A narrow gap between the distal clavicle and the acromion, with thin dark cortical margins and a small fibrocartilage disc; fluid or capsular thickening is bright on fluid-sensitive sequences.

Common pathology: AC joint osteoarthritis with capsular hypertrophy (a cause of impingement), and AC separations after a fall onto the shoulder.

Glenohumeral Joint

The main ball-and-socket joint of the shoulder, formed where the humeral head meets the glenoid.

On MRI: The articular space between the humeral head and glenoid, lined by cartilage and bounded by the labrum and capsule; a small amount of joint fluid is bright on fluid-sensitive sequences, and injected contrast distends it on MR arthrography.

Common pathology: Adhesive capsulitis, osteoarthritis, joint effusion, and the instability lesions (labral and capsular) evaluated on MR arthrography.

Rotator cuff

The four muscle-tendon units that center the humeral head in the glenoid. Healthy tendons are uniformly dark; muscle is intermediate signal with feathery internal striations.

Supraspinatus Tendon

The tendon of the supraspinatus muscle that passes under the acromion and inserts on the top of the greater tuberosity.

On MRI: A uniformly dark band running laterally beneath the acromion to its footprint; best profiled on coronal oblique, where bright fluid signal within or through it signals a tear.

Common pathology: The most common rotator cuff tendon to tear, from partial articular-surface fraying to full-thickness tears with retraction; tendinosis shows intermediate (not fluid-bright) signal.

Tip: Bright fluid signal tracking into the subacromial-subdeltoid bursa above a defect is a strong clue to a full-thickness supraspinatus tear.

Supraspinatus Muscle

The rotator cuff muscle in the supraspinatus fossa above the scapular spine that initiates arm abduction.

On MRI: Intermediate-signal muscle filling the fossa above the scapular spine; on sagittal oblique it is the top of the Y-shaped cuff, where fatty atrophy is graded.

Common pathology: Fatty infiltration and atrophy of the muscle belly after a chronic cuff tear, which helps predict whether a tendon repair will hold.

Infraspinatus Muscle

The rotator cuff muscle below the scapular spine that externally rotates the arm.

On MRI: Intermediate-signal muscle filling the infraspinatus fossa on the back of the scapula, posterior to the supraspinatus; its tendon inserts on the greater tuberosity behind the supraspinatus.

Common pathology: Fatty atrophy with posterosuperior cuff tears, and denervation edema or atrophy from spinoglenoid notch cysts compressing the suprascapular nerve.

Subscapularis Muscle

The largest rotator cuff muscle, lying on the front of the scapula, that internally rotates the arm.

On MRI: Intermediate-signal muscle filling the subscapular fossa anterior to the scapula on axial; its tendon crosses to insert on the lesser tuberosity, forming the front wall of the rotator interval.

Common pathology: Subscapularis tears (often with biceps instability), and the tear pattern seen after anterior dislocation.

Tip: Axial slices best show subscapularis and its tendon; a torn subscapularis often lets the biceps tendon slip medially out of its groove.

Labrum and biceps

The fibrocartilage rim that deepens the socket and the biceps tendon anchored to its top. Normal labrum is uniformly dark and triangular; the biceps is a dark tendon in its groove.

Anterior Glenoid Labrum

The front portion of the fibrocartilage rim around the glenoid that deepens the socket and stabilizes the joint anteriorly.

On MRI: A small dark triangle on the anterior edge of the glenoid on axial images; MR arthrography distends the joint so contrast outlines any tear or detachment.

Common pathology: Bankart lesions (anteroinferior labral tear) after anterior dislocation, and anterior labral variants that can mimic a tear.

Posterior Glenoid Labrum

The back portion of the fibrocartilage rim around the glenoid that stabilizes the joint posteriorly.

On MRI: A dark triangle on the posterior edge of the glenoid on axial images, mirroring the anterior labrum across the socket.

Common pathology: Posterior labral tears (reverse Bankart) from posterior instability, and tears in throwing athletes.

Superior Glenoid Labrum

The top portion of the fibrocartilage rim where the long head of the biceps tendon anchors to the glenoid.

On MRI: A dark triangle at the top of the glenoid on coronal oblique images, blending with the biceps anchor; a normal sublabral recess here can mimic a tear.

Common pathology: SLAP (superior labrum anterior to posterior) tears at the biceps anchor, a classic overhead-athlete and traction injury best shown on MR arthrography.

Tip: Coronal oblique through the biceps anchor is the key plane for SLAP tears; a normal sublabral recess follows the glenoid contour, while a tear extends laterally into the labrum.

Inferior Glenoid Labrum

The bottom portion of the fibrocartilage rim, continuous with the attachment of the inferior glenohumeral ligament.

On MRI: A dark triangle along the lower glenoid rim on coronal oblique images, just above where the inferior capsule attaches.

Common pathology: Inferior extension of a Bankart lesion and HAGL-related injury patterns of the inferior capsulolabral complex.

Long Head of Biceps Tendon

The tendon of the long head of the biceps that runs in the bicipital groove and anchors to the top of the glenoid labrum.

On MRI: A small round dark structure within the bicipital groove between the tuberosities on axial images; trace it up into the joint to the superior labral anchor.

Common pathology: Biceps tendinosis and tears, and medial dislocation out of the groove when the subscapularis or its sling is torn.

Tip: On axial, find the dark dot of the biceps tendon sitting in the bony groove; if it is empty or the tendon lies medial to the groove, suspect a subscapularis tear.

Other muscles

Superficial muscles outside the rotator cuff that move and support the shoulder girdle.

Trapezius Muscle

The large superficial muscle of the upper back and neck that elevates and stabilizes the scapula.

On MRI: Intermediate-signal muscle draping over the top and back of the shoulder girdle, superficial to the supraspinatus and scapular spine on axial and coronal oblique images.

Common pathology: Strains and contusions, and atrophy or denervation from spinal accessory nerve injury after neck surgery or trauma.

Frequently asked questions

What structures are seen on a shoulder MRI?

A standard shoulder MRI shows the bones and joints (glenoid, humeral head and humerus, clavicle, acromion, scapula, the acromioclavicular joint, and the glenohumeral joint), the four rotator cuff muscles and the supraspinatus tendon, the glenoid labrum (anterior, posterior, superior, inferior) with the long head of the biceps tendon, and surrounding muscles such as the trapezius. This page labels each one with its MRI appearance.

Which planes are used for shoulder MRI?

Shoulder MRI is read primarily in three planes prescribed off the glenohumeral joint: axial, coronal oblique (parallel to the supraspinatus tendon), and sagittal oblique (perpendicular to it). This deck focuses on the axial and coronal oblique planes. Axial best shows the labrum and the biceps tendon in its groove, while coronal oblique best profiles the supraspinatus and the superior labrum.

What is the best way to evaluate the rotator cuff on MRI?

Use fluid-sensitive sequences such as fat-suppressed T2 or proton density, and profile the supraspinatus tendon on coronal oblique. A healthy tendon is uniformly dark; bright fluid signal extending through it, especially up into the subacromial-subdeltoid bursa, indicates a tear. Sagittal oblique images are used to grade muscle fatty atrophy, which affects whether a repair will hold.

Why is MR arthrography used for the labrum?

Injecting dilute contrast into the glenohumeral joint distends the capsule and pushes fluid into any labral tear, making detachments and SLAP and Bankart lesions far easier to see. It is the preferred study for shoulder instability and suspected labral injury, particularly in younger and athletic patients.

Do I need an account to use these shoulder MRI flashcards?

No. The interactive flashcards and this full labeled reference are open to use, with no account required to start. Creating an account lets you save your progress across devices and track which packs you have mastered.

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Shoulder Anatomy