Anatomy and Imaging of the Shoulder Joint

J. Rudolph and J. Mäurer

1 Anatomy and Imaging of the Shoulder Joint

Macroscopic Functional Anatomy

The head and the glenoid fossa articulate in the shoulder joint (glenohumeral joint). Functionally, it is a ball-and-socket joint that enables movement in three degrees of freedom. The shoulder is the most mobile of the major joints. Its high mobility, together with its limited osseous embracement accounts for its high rate of injury.

Osseous Structures

Humerus

Articular surface of the humeral head covered hemispherically with hyaline cartilage

Rotation of the humeral head around a central point in the depth of the head

Important markers of the proximal humerus: major and minor tuberosities as well as bicipital groove

Anatomical neck: Transition of the proximal humerus to the humeral head

Surgical neck: Frequent fracture site

Scapula

Gliding and rotation of the scapula on the thoracic surface with arm movement

The glenoid fossa is perpendicular to the body of the scapula

The osseous glenoid fossa is markedly smaller than the humeral head (ratio about 1:4)

According to Bigliani (1982), three different acromial types can be observed in the coronal plane:

– Type I: Flat acromion

– Type II: Curved acromion

– Type III: Hooked acromion with inferior nose

Clavicle

Flat, sinuous, bridging the upper ribs

Medial articulation with the sternum at the sternoclavicular joint (SC joint)

Lateral connection with scapula with the acromioclavicular joint (AC joint)

Soft Tissues

Glenoid Labrum

Since the incongruent osseous articular surfaces alone cannot provide structural and functional integrity of the shoulder joint, it is largely stabilized by the glenoid labrum.

Circular enlargement of the articular surface

Fibrous cuff of fibrocartilage reinforcing the joint capsule

Vascular supply through capsular vessels

“Transitional zone” (hyaline cartilage) between labrum and osseous glenoid fossa

Four labrum segments: anterosuperior and posterosuperior, as well as anteroinferior and posteroinferior quadrants

Surgical localization of the labral lesions following the dial of the clock: right anterior positions 12 to 6 o’clock (left posterior positions 12 to 6 o’clock!)

Numerous normal variants of the labrum (see Chapter 2, Traumatology)

Fig. 1.1 Types of capsular insertion according to Moseley and Övergaard (1962).

Diagram of the different insertions of the anterior capsule as seen on the axial plane (arrowheads).

Bi	Biceps tendon
Hu	Humerus
Gle	Glenoid process

Capsuloligamentous System

The capsuloligamentous system contributes relatively little to the static stability of the shoulder. The joint is further supported by an intra-articular negative pressure.

Capsular insertion with fibrous and synovial component in the region of the osseous glenoid fossa

Three glenohumeral ligaments (superior, medium, and inferior glenohumeral ligaments) to enforce the anterior capsule

Wide variability of course, insertion, and caliber of the three ligaments

The inferior ligament is most important for shoulder stability

Variable anterior capsular insertion at the glenoid fossa; according to Moseley and Övergaard (1962), three capsular insertions can be distinguished in the axial plane (Fig. 1.1):

– Type I: Insertion at the tip or basis of the anterior labrum

– Type II: Insertion of the capsule not more than 1 cm medial to the labrum

– Type III: Insertion of the capsule more than 1 cm medial to the labrum

Type III should predispose to or be the result of anterior dislocation

Musculature of the Rotator Cuff

Since osseous and ligamentous support is inadequate, stability is achieved by soft tissues. Dynamic stability is primarily provided by the muscles of the rotator cuff together with the deltoid muscle.

Four muscles: Anteriorly the subscapular muscle (origin at the minor tuberosity), posteriorly the supraspinatus muscle (origin at the major tuberosity), the infraspinatus muscle and the teres minor (origin at the major tuberosity)

Fibrous “tendon cap” of the rotator cuff around the humeral head

“Critical zone” within the tendon of the supraspinatus muscle (1–1.5 cm proximal to its origin) presumably predisposes to degeneration with subsequent rupture

Additional stabilization of the joint provided by muscular compression through pull of the rotator cuff

Bursae of the Shoulder Joint

Several bursae (fluid-containing sacs lined with synovial membrane) serve as gliding layers to facilitate free motion of the shoulder joint and partially communicate with the joint cavity.

The subacromial bursa and subdeltoid bursa often communicate with each other, but usually not with the joint capsule (important for rotator-cuff tears!)

The subtendinous bursa of the sub-scapular muscle and the subcoracoid bursa communicate with the joint anteriorly

Normal bursae are not visualized by conventional radiology, only by ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI)

Conventional Radiology

Standard Projections

Like all other joints, the shoulder is first examined by obtaining a baseline study consisting of two views perpendicular to each other. Many special projections are available for different clinical questions (Table 1.1), but their diagnostic contribution has diminished following the introduction of CT and MRI.

Table 1.1 Recommended radiographic projections of the shoulder joint (please refer to text for technical factors)

Clinical question	Projections
Baseline	AP view Axial view
Degeneration	AP view Axial view 90° abduction view
Special impingement	Schweden stage I–III View of the intertubercular groove Supraspinatus outlet view Rockwood view
General trauma	AP view Axial view
Impaired mobility	Transthoracic view Y-projection Velpeau view
Dislocation	AP view Axial view
Special Bankart lesion	West Point view Glenoid rim view according to Bernageau Apical oblique view
Special Hill-Sachs defect	AP view in 60° internal rotation Stryker view Hermodsson view
AC joint	AC joint view AP AC joint view AP with weight bearing Supraspinatus outlet view Rockwood view

Anteroposterior View/Tangential View of the Glenoid Fossa

Caution: The joint space is superimposed on the straight anteroposterior (AP) view!

Indication

Initial workup for suspected

Fractures (location and extent, determination of fracture type, orientation of fracture lines, articular involvement, position of fracture fragments)

Dislocations

Inflammatory conditions

Degenerative changes

Neoplasms

Technique

Shoulder in contact with the cassett

Patient sitting with the arm in neutral position (palms up)

Caudal angulation of the central ray by about 20°

Centered to the coracoid process

Alternatively:

Patient lying with elevation of the contralateral shoulder

Caudal angulation of the central ray

Centered to the coracoid process

Glenoid Tangential View

Orthograde projection of the joint space free of superimposition

The patient is rotated 30–45° to the right (→ scapula parallel to the cassette!)

As on the AP view, centered to the coracoid process

Radiographic Anatomy (Fig. 1.2)

Visualization of the glenohumeral articulation: narrow ovoid or linear (orthogonal) fossa

Apex of the coracoid process in projection of the humeral head

Fig. 1.2 AP view

As initial view of the glenohumeral articulation with the humerus superimposed on the glenoid fossa. The joint space is not exactly seen tangentially.

Fig. 1.3 Axial view.

Location of the humeral head in relation to the glenoid process with the upper arm in 90° abduction, as second plane of the diagnostic workup.

Alternatively:

Craniocaudal Projection

Patient sitting

Position the arm with the flexed elbow lateral on the examination table

Cassette placed in the axilla, better “saddle (curved) cassette”

Perpendicular craniocaudal central ray centered to the joint

Axial View

Caution: Axial view is contraindicated if an acute fracture or dislocation is suspected!

Indication

Second plane of the initial view

Technique

Caudocranial Projection

Patient supine, head and shoulder slightly elevated

About 90° abduction of the arm, external rotation of the upper arm with flexion of the elbow

Place the cassette against the top of the shoulder

Perpendicular craniocaudal central ray parallel to the thoracic wall centered to the axilla

Radiographic Anatomy (Fig. 1.3)

Position of the humeral head relative to the glenoid fossa

Superimposition of the AC joint on the humeral head

Special Projections for Impingement

Since the subacromial space and bicipital (intertubercular) groove are inadequately visualized on both standard views, the following views are used.

AP View in Three Different Rotations (Impingement Series I–III)

Indication

Localization of pathological processes, such as interarticular loose bodies or calcifications of the rotator cuff

Visualization of fractures

Technique

Patient positioning and projection same as in AP standard projection. In addition:

Internal rotation with elbow in flexion and abduction, hand in supination (I)

External rotation of the slightly abducted arm with the hand in supination (II)

External rotation and elevation with 90° abduction of the arm, rectangular flexion of the elbow (III)

Radiographic Anatomy

Visualization of the humeral head and joint space free of superimposition

Subacromial space and minor tuberosity (I and II)

Acromion superimposed on the humeral head, visualization of the AC joint (III)

90° Abduction View

Indication

Visualization of glenohumeral mobility

Visualization of the AC joint free of superimposition

Technique

Patient standing parallel to the cassette

90° abduction of the arm, flexion of the elbow

AP projection

Centered to coracoid process

Radiographic Anatomy (Fig. 1.4)

Superimposed humeral head and acromion

Direct visualization of the AC joint space

Fig. 1.4 View in 90° abduction (diagram)

Visualization of the humeral head (Hu) superimposed on the acromion (Ak), unobstructed projection of the AC joint space (arrowhead).

Cl	Clavicle
Gle	Glenoid process
Pc	Coracoid process

View of the Intertubercular (Bicipital) Groove

Caution: Requires exact tangential projection of the groove; possibly fluoroscopic guidance.

Indication

Visualization of the intertubercular (bicipital) groove free of superimposition

Technique

Craniocaudal Projection

Patient bending over the examination table

Flexion and supination of the arm resting on the table (→ humerus and forearm form an angle between 75° and 80°)

Cassette placed horizontally on the forearm

Palpation of the sulcus and its course marked on the skin

Craniocaudal central ray perpendicular to the skin marks

Alternatively:

Caudocranial Projection

Patient supine

Cassette placed against the top of the shoulder

Arm slightly abducted and externally rotated

Craniocaudal projection through anterior margin of the humerus

Central ray parallel to the longitudinal axis of the upper arm (→ following the course of the groove)

Radiographic Anatomy

Intertubercular (bicipital) groove seen as indentation between both tuberosities

Supraspinatus Outlet View

Indication

Suspected subacromial pathology:

Visualization of the coracoacromial pathology (supraspinatus outlet)

Visualization of possible subacromial osteophytes

Identification of the acromion types according to Bigliani (see Osseous Structures/Scapula)

Technique

Patient in the oblique position, standing or sitting

Cassette perpendicular to the body of the scapula and parallel to the glenoid fossa

Mediolateral projection along the axis of the scapular spine

Central ray craniocaudally angled by 10–15° and centered to the AC joint

Radiographic Anatomy

Body of the scapula free of superimposed ribs

Humeral head in projection of the Y of the scapula (short limb of the Y: acromion and coracoid process; long limb of the Y: scapular body)

Acromion as “roof” of the subacromial space

Rockwood View

Indication

Suspected subacromial pathology:

Visualization of inferior acromial osteophytes

Calcifications of the coracoacromial ligament

Technique

As in the AP view, but 30° caudal angulation of the central ray

Radiographic Anatomy

Visualization of the subacromial space and the anteroinferior acromion

Special Projections for Restricted Mobility

If pain-restricted mobility (dislocation, fracture) contraindicates an axial view, the following alternative views should be considered.

Transthoracic View

Fig. 1.5 Transthoracic view (diagram)

Humerus (Hu) in projection between spine and sternum (St) (the superimposed ribs have been deleted for the sake of clarity). The auxiliary line according to Moloney (1983) is drawn as a blue line.

Gle	Glenoid
Ak	Acromion
Pc	Coracoid process

Caution: Superimposition can interfere with the interpretation.

Indication

Second plane for the motion-restricted shoulder

Evaluation of the joint in (subcapital) fractures of the humerus and shoulder dislocations

Technique

Patient sitting and standing, with slight posterior rotation of the upper body

Affected shoulder laterally placed on the cassette

Hanging arm in supination

Opposite arm raised and placed over the top of the head (→ to be out of the collimation field of the radiographic projection)

Transthoracic mediolateral projection

Centered directly below the coracoid process

Radiographic Anatomy (Fig. 1.5)

Humerus projected between spine and sternum

Glenoid fossa partially superimposed by the humeral head

Auxiliary line according to Moloney (1983): The scapulohumeral arch formed by the axillary border of the scapula and humeral shaft follows a smooth, uninterrupted course