You're staring at a shoulder MRI. The images are grainy, the anatomy is stacked in ways that don't match the textbook, and somewhere in there — maybe — is the reason your patient can't sleep on their right side.
Been there. Still there most Tuesdays Worth keeping that in mind..
Reading a shoulder MRI isn't about memorizing checklists. It's about building a mental 3D model from 2D slices, knowing where pathology hides, and — this is the part nobody teaches — recognizing when something looks wrong but isn't the problem.
What Is a Shoulder MRI
Magnetic resonance imaging of the shoulder uses strong magnetic fields and radiofrequency pulses to generate detailed soft-tissue contrast. In practice, no ionizing radiation. Even so, great for tendons, labrum, cartilage, marrow, and fluid. Less great for cortical bone detail — that's still CT territory.
Most studies are done at 1.5T or 3T. Three-tesla gives better signal-to-noise, which matters when you're hunting for a 2-millimeter SLAP tear. But a good 1.5T with a dedicated shoulder coil beats a bad 3T every time And it works..
Sequences matter. You'll typically see:
- T1-weighted (anatomy, fat bright)
- T2-weighted fat-suppressed or STIR (fluid bright, edema sensitive)
- PD-weighted fat-suppressed (the workhorse — great tendon detail, fluid still bright)
- Sometimes T1 post-contrast if there's an arthrogram component
Planes: axial, coronal oblique, sagittal oblique. That distinction saves lives. "Oblique" means aligned to the scapula, not the body. Or at least saves you from missing a posterior labral tear.
Why It Matters / Why People Care
Shoulder pain is the third most common musculoskeletal complaint in primary care. MRI is the go-to advanced imaging — but it's overordered, overinterpreted, and occasionally misleading.
Here's the uncomfortable truth: asymptomatic people have rotator cuff tears, labral tears, and AC joint arthritis on MRI. A lot of them. Think about it: one study found full-thickness cuff tears in 28% of pain-free adults over 60. Labral "tears" in 72% of asymptomatic volunteers.
So the scan doesn't diagnose the patient. Here's the thing — the scan informs the diagnosis. Your job is to correlate.
Miss a massive retracted cuff tear? Overcall a degenerative labral fray as a tear? Worth adding: the patient gets an unnecessary arthroscopy. Underestimate glenoid bone loss? Worth adding: the surgeon plans a repair that won't hold. The instability recurrence rate skyrockets.
This isn't academic. It changes what happens in the OR.
How to Read a Shoulder MRI — A Systematic Approach
Don't scroll randomly. Still, build a routine. Do it the same way every time. Muscle memory prevents the "oh no I forgot to check the suprascapular notch" moment at 11 PM.
1. Start with the localizer and series labels
Confirm laterality. Confirm planes. Make sure the coronal obliques are truly perpendicular to the supraspinatus tendon — not the scapular spine. A 15-degree rotation error makes a normal tendon look torn Most people skip this — try not to..
2. Bones and marrow — the "boring" stuff that isn't
Scan the humeral head, glenoid, scapular body, clavicle, proximal humerus. Look for:
- Marrow edema (bright on fluid sequences) — fracture, contusion, AVN, tumor, infection
- Subchondral cysts — osteoarthritis, rheumatoid, post-traumatic
- Cortical irregularity — Hill-Sachs, Bennett lesion, old fracture
- Sclerosis — chronic stress, degenerative change
Don't skip this. A "cuff tear" referral might actually be a humeral head insufficiency fracture. Seen it twice this year Simple, but easy to overlook..
3. Rotator cuff — the main event
Go tendon by tendon. Coronal obliques are primary. Sagittals confirm.
Supraspinatus — most commonly torn. Check the critical zone (1 cm from insertion). Look for:
- Focal thinning
- High signal on T2/PD extending to both surfaces = full-thickness tear
- High signal on one surface only = partial tear (articular > bursal usually)
- Fluid in the subacromial-subdeltoid bursa = full-thickness tear with communication
- Retraction: grade it. Patte classification: grade 1 (at tendon footprint), grade 2 (mid-humeral head), grade 3 (glenoid level). Medial retraction > 3 cm = poor repair prognosis.
- Muscle quality: Goutallier/Fuchs grading on T1 sagittals. Grade 0 = normal. Grade 1 = some fat. Grade 2 = fat < muscle. Grade 3 = fat = muscle. Grade 4 = fat > muscle. Grade 3+ = think twice about repair.
Infraspinatus — posterior. Tears often extend from supraspinatus. Isolated tears = think suprascapular nerve entrapment at the spinoglenoid notch. Check for cyst there Less friction, more output..
Subscapularis — anterior. Best seen on axials and sagittals. Look at the superior fibers (most commonly torn). "Bare area" of the humeral neck is normal — don't overcall. Biceps tendon subluxation medially? That's a subscap tear sign That's the part that actually makes a difference..
Teres minor — often forgotten. Atrophy = suprascapular nerve or quadrilateral space syndrome.
4. Long head biceps tendon
Track it from the supraglenoid tubercle, through the bicipital groove, to the musculotendinous junction.
- Subluxation/dislocation: medial = subscap tear. Lateral = rare, usually trauma.
- Tenosynovitis: fluid sheath > 3 mm or circumferential fluid.
- Tendinosis: thickened, intermediate signal on all sequences.
- Rupture: empty groove, retracted tendon distally ("Popeye" sign clinically).
- SLAP tears often involve the biceps anchor — more on that next.
5. Labrum — the ring that isn't a ring
The glenoid labrum is fibrocartilage. Here's the thing — triangular in cross-section. Plus, variable signal normally — can be intermediate, not always dark. Don't overcall signal as tear.
Superior labrum (12 o'clock) — SLAP tears. Types I-IV (and beyond). Type II = detached biceps anchor. Most common clinically relevant. Look for:
- Fluid undercutting the biceps anchor on coronal/sagittal
- Biceps anchor displacement
- Glenoid articular cartilage signal changes (chronic)
- Paralabral cyst at spinoglenoid notch = strong secondary sign
Anterior-inferior (3–6 o'clock) — Bankart lesions. Anterior band of IGHL + labrum detached. Look for:
- "Double line" sign (fluid between labrum and glenoid)
- Medialized labrum
- Glenoid bone loss (bony Bankart)
- ALPSA lesion — labrum healed medially, stripped periosteum
- HAGL — humeral avulsion of IGHL (rare, axials key)
Posterior (6–9 o'clock) — posterior labral tears, Kim lesions (marginal tear without detachment), reverse Bankart. Common in posterior instability, linemen, weightlifters.
Paralabral cysts — track them. Spinoglenoid notch = suprascapular nerve compression. Suprascapular notch = proximal compression. Both cause infraspinatus +/- supraspinatus atrophy.
6. Capsule and ligaments
6. Capsule and ligaments
The glenohumeral ligaments (GHL) are thickenings of the anterior capsule, not separate structures. They matter most in instability patterns.
Superior GHL (SGHL) — extends from the supraglenoid tubercle to the lesser tuberosity. It's the most variable ligament and often absent. Thickening can be seen in adhesive capsulitis or as an anatomic variant — don't overcall.
Middle GHL (MGHL) — the most consistent of the three. Runs from the anatomic neck to the lesser tuberosity, anterior to the subscapularis tendon. It's the primary restraint to anterior translation at lower degrees of abduction Simple as that..
Inferior GHL (IGHL) — the workhorse of glenohumeral stability. It has three parts:
- Anterior band — runs from the anteroinferior glenoid to the lesser tuberosity. Key restraint to anterior instability.
- Posterior band — runs from the posteroinferior glenoid to the humeral neck posteriorly. Key restraint to posterior instability.
- Axillary pouch — the lax interval between the two bands. Volume matters — a tight pouch restricts all motion; a redundant pouch permits instability.
Coracohumeral ligament (CHL) — spans from the coracoid to the greater tuberosity, blending with the supraspinatus and infraspinatus tendons. Thickening or adhesions are seen in adhesive capsulitis ("capsulitis pattern" — axillary pouch effusion, CHL thickening, rotator interval thickening).
Rotator interval — the space between supraspinatus and subscapularis, bridged by the SGHL and CHL. Contains the biceps long head and the superior glenohumeral ligament. Full-thickness rotator interval tears present as a gap between the two tendons on sagittals/axials with fluid signal. These can be subtle and are often missed — look carefully.
Adhesive capsulitis — the MRI picture is nonspecific but characteristic:
- Axillary pouch fluid and thickening (> 4 mm)
- CHL thickening and enhancement
- Rotator interval thickening
- Diffuse synovitis
- Absence of discrete tear
- Glenohumeral joint volume is reduced
- Coracohumeral ligament thickening (> 4 mm) is one of the most reproducible signs
7. Bone and cartilage
Glenoid bone loss — critical to quantify in instability. A bony Bankart lesion (fracture of the anteroinferior glenoid rim) can be measured on axial CT or sagittal MRI. Loss > 20–25% is generally considered significant and changes surgical planning (Latarjet rather than Bankart repair alone). The glenoid track concept — the distance between the glenoid rim and the humeral head articular surface — is a useful parameter: if the humeral head overhangs the glenoid by > 50%, engagement is likely Less friction, more output..
Humeral head articular cartilage — assess on T2 FS or PD sequences. Chondral defects can be full-thickness (subchondral bone exposed) or partial. The humeral head is the most common site of chondral injury in anterior instability (Hill-Sachs lesion is the bony counterpart; the cartilage defect is the "chondral Bankart") Simple, but easy to overlook. Turns out it matters..
Subchondral bone marrow edema — in the humeral head (posterior) and/or glenoid (anteroinferior), this reflects impaction injury and is a marker of instability, not just an incidental finding. It correlates with cartilage damage and can progress to arthritis if instability is untreated.
Fractures — don't miss them. Greater tuberosity fractures can be accompanied by rotator cuff tears (sup
sequently, particularly in older patients or those with osteoporotic bone). Look for cortical disruption, trabecular discontinuity, or associated hematoma. In the setting of acute trauma, always evaluate the labrum for concomitant detachment, as a fracture and a Bankart lesion frequently coexist.
8. Systematic Reporting Checklist
To ensure a comprehensive and high-quality MRI report, follow this structured approach:
- Rotator Cuff: Evaluate each component (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis) for tears (full-thickness vs. partial), tendinosis, or atrophy/retraction.
- Labrum: Inspect the entire circumference (Anterior, Posterior, Superior, Inferior) for fraying, detachment, or paralabral cysts.
- Biceps Tendon/Pulley: Check the long head of the biceps for tendon pathology and the integrity of the rotator interval.
- Capsule and Ligaments: Assess the thickness and signal intensity of the CHL and the axillary pouch to rule out adhesive capsulitis.
- Bone and Cartilage: Quantify glenoid bone loss, identify Hill-Sachs lesions, and assess the articular cartilage integrity.
- Effusion/Edema: Note the presence and location of joint effusion or subchondral bone marrow edema.
Conclusion
MRI remains the gold standard for the non-invasive evaluation of the glenohumeral joint, offering unparalleled detail of the soft tissue structures that define shoulder stability and mobility. By meticulously evaluating the rotator cuff, labrum, capsule, and bony architecture, the radiologist provides the orthopedic surgeon with the critical information necessary to differentiate between conservative management and surgical intervention. Still, while the pathology can be complex—ranging from subtle labral fraying to significant bone loss—a systematic approach is essential. As imaging technology evolves, the integration of quantitative measurements (such as glenoid track analysis) and advanced sequences will continue to refine the precision of shoulder diagnostics Less friction, more output..
