# Shoulder MRI: Rotator Cuff and Labral Pathology

## Overview

### Indications

Shoulder MRI is indicated for suspected rotator cuff tear (weakness, pain with overhead activities), shoulder instability (recurrent dislocation, labral pathology), impingement syndrome refractory to conservative management, and pre-operative planning for rotator cuff repair or labral surgery.

### Imaging Protocols

**Conventional MRI** is the standard for rotator cuff evaluation at 1.5T or 3T. **MR arthrography (MRA)**, which involves intra-articular gadolinium injection, is superior for labral tears, partial-thickness articular surface cuff tears, and SLAP lesions. The standard imaging planes are coronal oblique (parallel to the supraspinatus), sagittal oblique (perpendicular to the supraspinatus), and axial.

## Rotator Cuff Anatomy

### Muscles and Insertions (SITS)

The **supraspinatus** is the most commonly torn rotator cuff muscle. It inserts on the superior facet of the greater tuberosity and is responsible for abduction. The **infraspinatus** inserts on the middle facet of the greater tuberosity and performs external rotation. The **teres minor** inserts on the inferior facet of the greater tuberosity and also performs external rotation. The **subscapularis** inserts on the lesser tuberosity, performs internal rotation, and is the largest of the cuff muscles.

### Critical Zone

The critical zone is a hypovascular area near the supraspinatus insertion, approximately 1 cm from the footprint. Most tears initiate in this zone, which corresponds to the anterior fibers of the supraspinatus and the rotator cable/crescent concept.

### Rotator Cable and Crescent

The **rotator cable** is a thick fibrous band spanning from the infraspinatus to the anterior supraspinatus. The **rotator crescent** is the thin tissue between the cable and the greater tuberosity insertion. Cable-dominant tears may maintain cuff function despite crescent tears, which has implications for surgical decision-making.

## Rotator Cuff Tears

### Full-Thickness Tears

A full-thickness tear is a complete disruption extending from the bursal to the articular surface. On MRI it appears as a fluid signal gap through the tendon on coronal oblique images (on T2 fat-saturated or PD fat-saturated sequences), with associated tendon retraction and fluid in the subacromial-subdeltoid bursa. The report should include the tear size (AP and ML dimensions), degree of tendon retraction, and muscle quality.

### Partial-Thickness Tears

**Articular-surface partial tears** are more common than bursal-surface tears and are best seen on MR arthrography. **Bursal-surface partial tears** are less common and are associated with impingement. **Interstitial (intratendinous) tears** represent delamination within the tendon substance. Partial tears are graded as low-grade (less than 25% thickness), moderate (25-50%), or high-grade (greater than 50%).

### Muscle Atrophy and Fatty Infiltration

#### Goutallier Classification (Modified for MRI)

| Goutallier Grade | Description | Surgical Implication |
|-----------------|-------------|---------------------|
| 0 | Normal muscle, no fat | Good candidate for repair |
| 1 | Some fatty streaks | Good candidate for repair |
| 2 | Fat present but less than muscle | Fair candidate |
| 3 | Equal fat and muscle | Poor outcome predicted; generally irreversible |
| 4 | More fat than muscle | Poor outcome predicted; generally irreversible |

The Goutallier classification grades fatty infiltration of the rotator cuff muscles. **Grade 0** is normal muscle with no fat. **Grade 1** shows some fatty streaks. **Grade 2** shows fat present but less than muscle. **Grade 3** shows equal amounts of fat and muscle. **Grade 4** shows more fat than muscle. Grade 3-4 fatty infiltration predicts poor surgical outcome and is generally considered irreversible.

#### Tangent Sign

The tangent sign is assessed on the most lateral sagittal oblique image showing the scapular spine. If the supraspinatus muscle belly does not cross above a line drawn along the superior border of the scapular spine and the superior margin of the coracoid, the tangent sign is positive, indicating significant atrophy.

## Shoulder Impingement

### Subacromial (External) Impingement

Subacromial impingement results from mechanical compression of the supraspinatus between the humeral head and the coracoacromial arch. Acromion morphology is classified using the Bigliani system: Type I is flat, Type II is curved, and Type III is hooked (carrying the highest impingement risk). Associated findings include subacromial-subdeltoid bursal fluid and thickening, and acromioclavicular joint hypertrophy with inferior osteophytes.

### Internal Impingement

**Posterior-superior internal impingement** occurs in overhead athletes during abduction and external rotation, producing a combined posterior superior labral tear and partial articular surface supraspinatus or infraspinatus tear. **Subcoracoid impingement** causes subscapularis impingement between the coracoid and lesser tuberosity.

## Labral Pathology

### Normal Labral Anatomy

The labrum is a fibrocartilaginous ring attached to the glenoid rim that appears as low signal on all sequences with a triangular shape on axial images. The superior labrum has a more variable attachment and may be meniscoid. Anterior labrum variants are common and must not be overcalled as tears.

### Anterior Labral Tears (Instability)

#### Bankart Lesion

The Bankart lesion is a tear or avulsion of the anteroinferior labrum off the glenoid. A **soft Bankart** is a labral-ligamentous avulsion without bony involvement, while a **bony Bankart** includes a fracture of the anteroinferior glenoid rim with labral avulsion. Bankart lesions are associated with anterior shoulder dislocation. On MR arthrography, contrast extends between the labrum and glenoid, and the detached labrum may be displaced.

#### Perthes Lesion

In a Perthes lesion the labrum is stripped from the glenoid but the periosteum remains intact, so the labrum is non-displaced and may reduce and appear normal on conventional MRI. It is best detected on MR arthrography with ABER (abduction-external rotation) positioning.

#### ALPSA (Anterior Labroligamentous Periosteal Sleeve Avulsion)

In an ALPSA lesion the anteroinferior labrum is avulsed and rotated medially along the scapular neck. The periosteum is intact but stripped, and the labrum heals in a medialized position. This creates a bumper-less glenoid that is associated with recurrent instability.

### SLAP Tears (Superior Labrum Anterior to Posterior)

SLAP tears involve the superior labrum at the biceps anchor. **Type I** shows degeneration and fraying without displacement. **Type II** is the most common surgical SLAP and involves detachment of the superior labrum and biceps anchor from the glenoid; MR arthrography shows contrast undermining the labrum. **Type III** is a bucket-handle tear of the superior labrum (meniscoid type). **Type IV** is a bucket-handle tear extending into the biceps tendon. SLAP tears are best evaluated with MR arthrography.

### Normal Variants (Not Tears)

The **sublabral recess (sulcus)** is a smooth cleft between the superior labrum and glenoid that runs medially, differing from a SLAP tear, which extends laterally and has irregular margins. The **Buford complex** is a normal variant consisting of an absent anterosuperior labrum with a thick cordlike middle glenohumeral ligament. The **sublabral foramen** is a focal detachment of the anterosuperior labrum in the 11-to-1 o'clock position and is a normal variant in up to 12% of individuals.

<image>A coronal oblique PD fat-saturated MRI of the shoulder showing a full-thickness supraspinatus tendon tear. The tendon gap is filled with high-signal fluid. The torn tendon is retracted medially approximately 2 cm from the greater tuberosity footprint (arrows). Fluid extends into the subacromial-subdeltoid bursa. A sagittal oblique image inset demonstrates the tangent sign with the supraspinatus muscle belly falling below the reference line, indicating significant muscle atrophy.</image>

<image>An axial T1 fat-saturated MR arthrography image of the shoulder at the level of the anteroinferior glenoid showing a Bankart lesion. The anteroinferior labrum is torn and displaced from the glenoid rim. Contrast (bright signal) fills the space between the detached labrum and the glenoid face. An adjacent axial image shows a bony Bankart variant with a small fracture fragment from the anterior glenoid rim. A diagram inset illustrates the three anterior labral lesion types: Bankart, Perthes, and ALPSA, with arrows showing the direction of displacement.</image>

<image>A coronal oblique MR arthrography image showing a Type II SLAP tear. The superior labrum is detached from the glenoid, and contrast extends beneath the labral-bicipital complex (arrow). An inset shows the normal sublabral recess for comparison, with the smooth medially-oriented cleft that does not extend to the labral margin. A second inset shows the four SLAP tear types (I-IV) in schematic form with the biceps anchor labeled.</image>

## Clinical Pearls

Goutallier Grade 3-4 fatty infiltration is generally considered irreversible and predicts poor functional outcome after rotator cuff repair; this finding should be reported prominently. MR arthrography is superior to conventional MRI for labral pathology and partial articular surface rotator cuff tears, and MRA should be requested when these are the clinical questions. The sublabral recess is the most common mimic of a Type II SLAP tear; a recess is smooth and extends medially, while a SLAP tear has irregular margins and extends laterally toward the labral free edge. After anterior shoulder dislocation, the radiologist should always evaluate for a Bankart lesion (both soft tissue and bony), a Hill-Sachs lesion (posterolateral humeral head impaction), and an associated rotator cuff tear (especially in patients over 40 years). The positive tangent sign on the most lateral sagittal image is a reliable indicator of clinically significant supraspinatus atrophy. In overhead athletes with posterior shoulder pain, internal impingement with a combined posterior superior labral tear and partial articular surface cuff tear should be considered.

## References

- Stoller DW. *Magnetic Resonance Imaging in Orthopaedics and Sports Medicine*. 3rd ed. Lippincott, 2007
- Snyder SJ, et al. "SLAP Lesions of the Shoulder." *Arthroscopy*, 1990
- Goutallier D, et al. "Fatty Muscle Degeneration in Cuff Ruptures." *Clinical Orthopaedics and Related Research*, 1994
- ACR Appropriateness Criteria: Shoulder Pain, 2018