MRI Anatomy of the Shoulder

Functional AnatomyGlenohumeral joint is a ball and socket synovial. Glenoid cavity inherently unstable.

Stability provided by:

i)Static constraints - 3 glenohumeral ligaments- glenoid labrum - joint capsule

•Dynamic constraints, - rotator cuff muscles

counteract the action of the deltoid by preventing the head of the humerus from moving superiorly when the arm is raised

The glenohumeral joint has the following supporting structures:

SuperiorlyCoraco-acromial archLong head of the biceps tendonTendon of supraspinatus muscle

AnteriorlyAnterior labrum3 Glenohumeral ligaments-SGHL, MGHL, IGHL (anterior band)Subscapularis tendon

PosteriorlyPosterior labrumPosterior band of the IGHLInfraspinatus tendonTeres minor tendon

Articular surfacesThe shoulder joint is composed of 3 bones and five articulations.

Bones:ScapulaHumerusClavicle

Articulations:Glenohumeral jointAcromio-clavicular jointScapulothoracic joint Sternoclavicular joint Coracoclavicular joint

Joint capsule

• Attached proximally to the glenoid labrum

• Attached distally to the anatomical neck of the humerus

• Capsule is thickened anteriorly by glenohumeral ligaments

• Herniation of synovial membrane through an anterior defect in capsule & glenohumeral ligaments forms the subscapular bursa

BursaeSubdeltoidBetween joint capsule anddeltoid muscle

SubcoracoidBetween joint capsule andcoracoid process

CoracobrachialBetween subscapularis andcoracobrachialis

SubacromialBetween joint capsule andacromion

Subscapular bursaBetween joint capsule andsubscapularis tendon

Rotator Interval

• Triangular space between the supraspinatus and subscapularis tendons– Contains long head of biceps and SGHL– Acts to prevent anterior dislocation of the shoulder

Ligaments• 3 glenohumeral ligaments– Superior– Middle– Inferior

• Coracohumeral ligament

• Transverse humeral ligament– Between greater and lesser tuberosities of

humerus, maintains long head of biceps in bicipital groove

Superior glenohumeral ligament

Coracohumeral ligament

Long head biceps tendon

SGHL Sagittal

SGHL Axial

Middle glenohumeral ligamant

MGHL Sagittal

MGHL Axial

Inferior glenohumeral ligament

Axillary recess

Subacromial-subdeltoid bursa

Glenoid labrum• The glenoid labrum is a

fibrocartilaginous structure that attaches to the glenoid rim and is about 4 mm wide.

• increases the superior-inferior diameter of the glenoid by 75% and the anterior-posterior diameter by 50%

• Anteriorly, the glenoid labrum blends with the anterior band of the inferior glenohumeral ligament.

• Superiorly, it blends with the biceps tendon and the superior glenohumeral ligament.

• It is usually rounded or triangular on cross-sectional images.

Labral anatomy: Axial

• The normal labrum demonstrates low signal intensity on all pulse sequences, due to the lack of mobile protons in this dense fibrocartilage.

• On cross sectional imaging, the normal labrum is most commonly triangular, but can also be round, cleaved, notched, flat, or absent.

Labral Anatomy: Coronal

• A fat suppressed oblique coronal T2-weighted MR image demonstrates homogeneously low signal intensity in the normal superior labrum.

Labral variants• These normal variants are all located in the

11-3 o'clock position.

• It is important to recognise these variants, because they can mimick a SLAP tear.

• These normal variants will usually not mimick a Bankart-lesion, since these are located at the 3-6 o'clock position, where these normal variants do not occur.

Sublabral recess

There are 3 types of attachments of the superior labrum:Type I No recess between glenoid cartilage and labrumType II Small recess.Type III Large sublabral recess.

Synovial recess between the superior labrum and the glenoid rim created by the attachment of the biceps tendon on the supraglenoid tubercle. Because of this recess, the labrum does not attach to the glenoid rim at the 12 o'clock position.

Sublabral Foramen

An unattached anterosuperior labrum at the 1-3 o'clock position.

Anterior to biceps tendonIt is seen in 11% of individuals. Not to be confused with a sublabral recess or SLAP-tear, which are also located in this region.

Differences between an sublabral recess and a SLAP-tear: A recess more than 3-5 mm is always abnormal and should be regarded as a SLAP-tear.

Buford complex Congenital labral variant

2 Features:Anterosuperior labrum is absent in the 1-3 o'clock position Middle glenohumeral ligament is usually thickened. It is present in approximately 1.5% of individuals.

Os AcromialeResults from failure of one of the acromial ossification centers to fuse.5% of the population. Usually an incidental finding, regarded as a normal variant. May cause impingement because if it is unstable, it may be pulled inferiorly during abduction by the deltoid, which attaches here.

On MR an os acromiale is best seen on superior axial images.

Acromion: 3 types

Type 1 is a flat undersurface with a high angle of inclination.

Type 2 is a curved arc and decreased angle of inclination.

Type 3 is hooked anteriorly with a decreased angle of inclination.

Axial Anatomy

The axillary artery begins at the lateral border of the first rib as a continuation of the subclavian artery. It changes its name to brachial

artery at lower inferior border of the teres major muscle (8).

Axial

Deltoid1)Anterior clavicular fibres – arise from superior anterior aspect of lateral clavicle

1)Lateral acromial fibres – arise from superior aspect of acromion process

1)Posterior fibres – arise from posterior border of spine of scapula

AxialSupraspinatus muscle

Relatively small muscle

Runs from the supraspinatous fossa of scapula to the greater tubercle of the humerus

The supraspinatus tendon is the most important structure of the rotator cuff and subject to tendinopathy and tears. Tears of the supraspinatus tendon are best seen on coronal oblique and ABER-series.In many cases the axis of the supraspinatus tendon (arrowheads) is rotated more anteriorly compared to the axis of the muscle (yellow arrow). When you plan the coronal oblique series, it is best to focus on the axis of the supraspinatus tendon.

Axis of supraspinatous tendon

The attachments of the 3 rotator cuff muscles that insert onto the greater tubercle of the humerus

can be abbreviated SIT when viewed from superior to inferior:

SupraspinatusInfraspinatusTeres minor

SITS inlcudes Subscapularis which inserts onto the lesser tubercle of the humerus

Sagittal

post

post

Axial

Supraspinatus inserts most superiorly to greater tuberosity humeral head

Pec major

Deltoid anterior

Deltoid posterior

Pec minor

Infraspinatus

Subscapularis

Infraspinatus (SIT)• Thick triangular muscle which

occupies most of the infraspinatous fossa

• Attaches medially to the infraspinatus fossa and laterally to the middle facet of the greater tubercle of the humerus

• Trapezoidal insertion of infraspinatus onto humerus is much larger than the insertion of the supraspinatus

*Tip*Coronal oblique MRI

• Supraspinatus – fibres run horizontally

• Infraspinatus – fibres have a slightly oblique orientation

SubscapularisLarge triangular muscle which fills the subscapular fossa Inserts onto the lesser tubercle of the humerus

Subscapular fossa = anterior

Infraspinatous fossa = posterior

ant

post

Axial

Coracobrachialis

Deltoid as one

Coracobrachialis is the smallest of the three muscles that attach to the coracoid process. The other 2 muscles are pectoralis minor and biceps brachii. Distal insertion upper medial aspect of arm

Teres minor

Teres minor(SIT)

Origin:Superior part of lateral border of scapula

Insertion:Inferior facet of greater tuberosity of humerus

AxialThe short head of the biceps originates from the coracoid process (2)

The long head originates from the supraglenoid tubercle (3)

Tendon of long head passes down along the intertubercular/bicipital groove of the humerus into the joint capsule

Both heads arise on the scapula and join to form a single muscle belly which is attached to the upper forearm.

When the humerus is in motion, the tendon of the long head is held firmly in place in the bicipital groove by the greater and lesser tubercles and the overlying transverse humeral ligament.

Long head forms biceps-labral complex with superior glenohumeral ligament

Coronal Long head

Coronal anatomy

Coronal

Posterior humeral circumflex artery and axillary nerve Teres major

Trapezius

extends longitudinally from the occipital bone to the lower thoracic vertebrae and laterally to spine of the scapula

Triceps

Teres major

(Teres minor)

It arises from the dorsal surface of the inferior angle of the scapula

Inserts onto intertubercular sulcus of humerus

Coronal

Triceps

Infraspinatus

Teres minor

Teres major

Coronal

Subscapularis

Teres major

Supraspinatus

Sagittal Anatomy

SagittalP A

Acromioclavicular jointAxial: Clavicle medialAcromion lateral

Sagittal: Acromion posteriorCoracoid anterior

The undersurface of the acromion should align with the undersurface of the clavicle

Ac

Ant Co

Cl

Post

Sagittal: SIT

MR shoulder arthrogram• Technique whereby injection of contrast media into

the joint allows for evaluation of capsule and internal joint structures.

• Originally performed using plain radiography.

• Now injection of gadolinium allows MR arthrography.

• CT arthrograms can also be performed.

Advantages

• Joint distension, outlining intra-articular structures

• Improved detection of tears, including articular surface partial tears

• Demonstration of communication between joint and extra-articular abnormalities eg. Paralabral cysts and bursae.

Disadvantages and pitfalls

• Risks assoc with needle placement into joint: infection, haemorrhage, synovial reaction.

• Avoid oblique position – glenoid in profile – aiming for joint space places the labrum at risk

• Correct needle positioning is essential– Extra articular contrast can complicate findings on

MR and simulate tears

Technique

• Fluoroscopically guided anterior approach is most widely performed.

• Perform routine preparation– Correct patient– Correct side– No iodine allergies– Explain procedure to patient, obtain consent– Confirm indication

Indications

• Assessment of integrity of rotator cuff• Evaluation of shoulder instability• Diagnosis of labral pathology• Diagnosis of adhesive capsulitis

Technique

• Sterile procedure• Fluoroscopically guided• Obtain control images of shoulder– Patient supine, AP view– Arm in external and internal rotation– Angle tube to view acromion in profile – clear

visualisation of sub-acromial space– Evaluate for calcium deposition in tendons

Patient Positioning• Supine position creates oblique

orientation of glenoid surface.• Posterior glenoid overlaps

humeral head on AP• Anterior glenoid lies medial to

humeral head• Thus needle directed AP at

humeral head will not injure anterior labrum

• External rotation exposes a larger articular surface anteriorly

• Placing a sandbag in the patient’s hand may help maintain the position

Technique• Determine skin entry site

using fluoroscopy• Just lateral to the medial

cortex of the humeral head (never medial)

• At junction of middle and lower third of humeral head

• Ideally central in fluoroscopic image

• Locally anaesthetise skin and subcutaneous tissue

Technique• Prepare contrast whilst allowing local anaesthetic to take effect (can

also be done before procedure starts)

• Bloem protocol:– 20 ml syringe– 10 ml sterile water– 5 ml iodine based non-ionic LOCM (eg.Ultravist, Omnipaque)– 5 ml lignocaine– 0.1 ml gadolinium

• Other:– Test injection with 1-2 ml of lignocaine– Contrast: 10 ml saline, 10 ml Iodine LOCM, 0.1 ml gadolinium, 0.3 ml

1:1000 adrenaline

• Syringe connected to connecting catheter(line)

• Advance needle (usually 20G spinal needle with stylet) in direct AP direction posteriorly.

• Continue until contact with humeral head.

• Consider test injection with lignocaine.

• Should only meet low resistance when in joint space

• If high resistance – possibly in hyaline cartilige – carefully manipulate needle by rotation and minimal retraction (few mm)

• Loss of resistance indicates either intra-articular or bursal location

Technique

• Inject iodinated contrast to distinguish between intra-articular and bursal location

• Intra-articular contrast will collect in glenohumeral joint space

• If intra-articular position is confirmed, continue with proper contrast injection

• Usually inject 14 – 16 ml of contrast, depending on patient and pathology.

Technique

Alternative: Posterior approach

• When suspecting anterior pathology. • Avoids the interpretative difficulties that may be associated with

anterior extracapsular contrast extravasation • Aim for the inferomedial quadrant of humeral head within

boundary of anatomic neck (interrupted line).

Other techniques• Inject only water, no gadolinium

– Achieves effect of distension– Need to use T2 sequences– Disadvantage:

• Difficult to distinguish between small full thickness and partial tears

• Indirect arthrogram– 1 mmol/kg Gd IV– Exercise joint for 5 to 5 minutes– Gd passes into joint space– Can perform T1 images– Disadvantages:

• Joint not distended• Extra-articular structures will also enhance

MR technique• Three plane T1 with fat sat• T2 with fat sat axial and coronal oblique (Consider Ax

GRE to evaluate for calcification)• Sagittal oblique T1/PD without fat suppression• Some protocols suggest pre contrast T2 sequences.

– Detection of intra-substance and bursal surface tears.– Pre-existing fluid collections and cysts

• Coronal oblique parallel to supraspinatus tendon (not muscle)

• Sagittal oblique perpendicular to glenoid surface• (ABER – Abduction and External rotation sometimes

used for evaluation of anterior and inferior GHL’s)

Labral tearsThe abduction external rotation (ABER) view is excellent for assessing the anteroinferior labrum at the 3-6 o'clock position, where most labral tears are located. Inferior glenohumeral ligament stretched resulting in tension on the anteroinferior labrum, allowing intra-articular contrast to get between the labral tear and the glenoid.

Rotator cuff tearsVery useful for both partial- and full-thickness tears of the rotator cuff. Releases tension on the cuff relative to the normal coronal view obtained with the arm in adduction.

Images in the ABER position are obtained in an axial way 45º off the coronal plane (figure). In that position the 3-6 o'clock region is imaged perpendicular.

ABER view

Rotator cuff tears• Arthrography improves detection of

tears as the joint is being distended and contrast forced into small defects.

• T1 (quicker) sequences with improved SNR can be used

• Diagnoses full thickness tears and articular surface partial thickness tear

• Not of value in intra-substance or bursal surface partial thickness tears

• Full-thickness tear will demonstrate the gadolinium contrast solution extending first through a defect in the cuff and then into the subacromial-subdeltoid bursa.

• Articular-surface partial-thickness tears show a focal extension of the contrast solution into the substance of the tendon.

• Fat suppression is necessary as peribursal fat may mimic contrast.

References• Ryan S, McNicholas M, Eustace S. Anatomy for diagnostic imaging.• CT and MR Arthrography of the Normal and Pathologic Anterosuperior

Labrum and Labral-Bicipital Complex. October 2000 RadioGraphics, 20, S67-S81.

• www.radiologyassistant.nl Radiology Assistant: MR Shoulder Part I.• http://musculoskeletal-radiology.blogspot.com/2006/09/glenohumoral-li

gaments.html• Jacobson et al. Aids to Successful Shoulder Arthrography Performed with

a Fluoroscopically Guided Anterior Approach. Radiographics. 2003; 23:373–379

• Beltran et al. MR Arthrography of the Shoulder: Variants and Pitfalls. Radiographics. 1997; 17:1403-14 12