MRI Shoulder

MRI of the shoulder is the best test for the rotator cuff tendons, glenoid labrum, glenohumeral ligaments, biceps tendon, cartilage, bone marrow and surrounding muscles. It is the main imaging test for shoulder pain and instability after radiographs and ultrasound.

The study uses a 1.5 or 3 tesla scanner with a dedicated shoulder coil. The arm is placed at the side in neutral or slight external rotation. Slices are 3 to 4 mm thick. The examination takes 20 to 30 minutes.

The core sequences are oblique coronal (parallel to the supraspinatus tendon), oblique sagittal and axial proton density or T2-weighted fast spin echo images with fat suppression, and T1-weighted oblique coronal images.

Direct MR arthrography (diluted gadolinium 1 to 2 mmol/L injected into the joint under imaging control) or indirect arthrography (intravenous contrast with exercise) is used for labral and partial thickness cuff tears in selected patients. The abduction external rotation position shows the inferior capsule and labrum.

Shoulder pain affects up to 1 in 5 adults at some time. Rotator cuff tears are present in about 20% of the general population and over 50% of people over 80, and many are symptom free.

MRI has a sensitivity and specificity of over 90% for full thickness cuff tears. For partial tears and labral tears, direct arthrography is more accurate than non-contrast studies.

Indications.

• Shoulder pain or weakness not explained by radiographs and ultrasound, especially before surgery.
• Suspected rotator cuff tear, and assessment of size, retraction and muscle quality.
• Shoulder instability and recurrent dislocation, including labral tear and bone loss.
• Suspected biceps tendon lesion (long head tear, instability).
• Impingement and subacromial disease with failed conservative treatment.
• Adhesive capsulitis (frozen shoulder) when atypical.
• Fracture not seen on radiographs (greater tuberosity, glenoid), and avascular necrosis of the humeral head.
• Infection, inflammatory arthritis and crystal arthropathy.
• Tumours and soft tissue masses.
• Muscle atrophy, nerve entrapment (suprascapular nerve, quadrilateral space) and brachial neuritis.
• Post-operative assessment of repair, failed repair and arthroplasty.

Not indicated as the first test in uncomplicated shoulder pain with a clear impingement picture and normal radiographs.

Contraindications and precautions.

• The usual MRI safety screen. Anchors and metal fixation cause artefact. Most are safe.
• Gadolinium: renal precautions. Intra-articular injection needs sterile technique and avoidance of infection in the joint.
• Pregnancy: non-contrast MRI is acceptable.
• Claustrophobia: shoulder studies keep the head partly outside the bore in some scanners.
• Patients who cannot lie flat or raise the arm for the abduction external rotation view.

Preparation and technique.

No preparation is needed for the non-contrast study. The patient lies supine with the arm at the side, thumb up or palm up, and the shoulder close to the coil centre.

For direct arthrography, the joint is injected under fluoroscopy or ultrasound with a mixture of diluted gadolinium and local anaesthetic (10 to 15 mL), and the scan follows within 30 minutes.

Oblique coronal, oblique sagittal and axial fat suppressed images are taken. The abduction external rotation series is added for the anterior inferior labrum and inferior glenohumeral ligament.

Normal appearances.

The rotator cuff tendons (supraspinatus, infraspinatus, teres minor, subscapularis) are dark, continuous and uniform. The supraspinatus tendon lies under the acromion and acromioclavicular joint, and inserts on the greater tuberosity.

The glenoid labrum is a dark triangular fibrocartilage rim that is continuous except for a normal sublabral recess at the anterior superior part. The long head of the biceps tendon runs in the bicipital groove and attaches to the superior labrum.

Hyaline cartilage is thin over the humeral head and glenoid. The acromion shape and the acromioclavicular joint are seen. Muscle bulk is symmetrical and fat free.

A small amount of fluid in the subacromial bursa and the biceps sheath is normal.

Interpretation.

• Tendinosis: increased intermediate signal and thickening without a fluid bright defect.
• Partial thickness tear: fluid bright defect involving the articular or bursal surface, or intrasubstance, with less than full thickness. Report the percent thickness and the location.
• Full thickness tear: fluid bright defect through the whole tendon from the articular to the bursal surface, with a gap, retraction (measured from the humeral footprint), and fluid in the subacromial bursa. Report the width and the retraction of each tendon involved.
• Chronic cuff tear: muscle atrophy and fatty infiltration (T1 bright striations in the muscle), tendon retraction, and loss of muscle bulge over a line drawn through the scapular spine and the coracoid. These predict poor repair results.
• Massive tear: involvement of two or more tendons or retraction to the glenoid, with superior migration of the humeral head and cuff arthropathy.
• Subscapularis tear: often with medial biceps tendon subluxation.
• Impingement and subacromial disease: subacromial bursal fluid, spurs on the undersurface of the acromion, hooked acromion, thickening and degeneration of the acromioclavicular joint and an os acromiale.
• Biceps tendon: tendinosis, partial or full tear, empty bicipital groove, or subluxation medially out of the groove.
• Labral tears: anteroinferior tear with glenoid rim bone injury after anterior dislocation, detached labrum with the anterior band of the inferior ligament, and variants with periosteal stripping. Superior labral tear from anterior to posterior (contrast tracking under the superior labrum beyond a normal sulcus). Posterior labral tears follow posterior dislocation or repetitive loading. Paralabral cysts compress the suprascapular nerve.
• Bone injury: a posterolateral humeral head impaction defect after anterior dislocation, glenoid rim fractures, and bone loss in recurrent instability, assessed on 3D CT when needed.
• Adhesive capsulitis: thickened joint capsule and axillary recess (over 4 mm), thickening of the coracohumeral ligament, and obliteration of the fat triangle under the coracoid.
• Calcific tendinitis: low signal calcification in the tendon with surrounding oedema.
• Arthritis: cartilage loss, osteophytes, subchondral cysts, and humeral head flattening. Rheumatoid disease shows synovitis and erosions.
• Avascular necrosis: serpiginous low signal margin in the humeral head, with later collapse.
• Infection: marrow oedema, effusion, soft tissue collections and enhancement.
• Tumours: osseous (osteochondroma, chondrosarcoma, metastasis) and soft tissue masses.
• Nerve and muscle: denervation oedema of the supraspinatus and infraspinatus (suprascapular nerve), teres minor atrophy (quadrilateral space), and acute brachial neuritis.
• Post-operative: tendon repair integrity (a persistent gap or retraction indicates failure), anchor artefact, and arthroplasty complications.

Critical values and findings needing immediate action.

• Septic arthritis or osteomyelitis: aspiration, drainage and antibiotics.
• Acute full thickness cuff tear in a young active person: early surgical repair gives better outcomes.
• Displaced fracture or locked dislocation: orthopaedic fixation or reduction.
• Aggressive bone or soft tissue tumour: referral to a specialist centre before biopsy.
• Suprascapular nerve compression from a cyst: surgical decompression.
• Acute axillary artery or brachial plexus injury after dislocation: vascular and neurological assessment.

Limitations and artefacts.

• Cuff tears and labral abnormalities are common in asymptomatic older people, so findings must match the symptoms.
• Magic angle effect causes false increased signal in the supraspinatus tendon near its insertion on short echo sequences.
• Partial thickness articular surface tears and small labral tears are better seen with arthrography.
• Normal sublabral recesses, the sublabral foramen, a cord like middle glenohumeral ligament and labral variants mimic tears.
• Metal anchors and staples cause artefact, and post-operative signal changes persist for months.
• Differentiation of tendinosis from partial tear and of partial from small full thickness tear is not exact.
• Motion from breathing and pain limits image quality.
• Muscle fatty infiltration is graded subjectively.
• Dynamic instability and impingement are clinical diagnoses that static images cannot prove.

Special groups.

• Young athletes and people with recurrent dislocation: labral and bone injury, with the abduction external rotation view or arthrography.
• Adolescents: physeal injury, apophysitis and osteochondral lesions.
• Older adults: degenerative tears, cuff arthropathy and calcific disease. MRI changes treatment mainly when surgery is being considered.
• Patients with arthroplasty or repairs: metal artefact reduction sequences, or ultrasound.
• Patients with inflammatory disease: synovitis and erosions.
• Regions: trauma, neglected dislocations, septic arthritis and tuberculosis of the shoulder are common. MRI is scarce, and radiographs and ultrasound are the main tools.

Follow up tests.

• Radiographs (anteroposterior in neutral, internal and external rotation, axillary and outlet views).
• Ultrasound for cuff and biceps tendons and subacromial bursa, with injection if needed.
• CT arthrography or 3D CT for bone loss and for patients who cannot have MRI.
• Joint aspiration for infection and crystals.
• Blood tests: full blood count, inflammatory markers, rheumatoid factor and anti-citrullinated peptide antibody, uric acid.
• Nerve conduction studies and electromyography for nerve lesions.
• Arthroscopy for therapeutic treatment.
• Referral to orthopaedics, sports medicine, rheumatology or physiotherapy.