Shoulder Complex Anatomy Quiz

4 joints: glenohumeral, acromioclavicular, sternoclavicular, scapulo-thoracic (not a real one) 4 bones: sternum, clavicle, scapula, humerus.

The scapula is a triangular bone with a spine, acromion, coracoid process, glenoid fossa, and various other features.

The four joints of the shoulder are the glenohumeral, sternoclavicular, acromioclavicular, and scapulothoracic (functional, not a true joint).

The sternoclavicular (SC) joint is a synovial, bi-concave saddle joint located between the sternum and clavicle.

During elevation, the clavicle is convex and slides in the opposite direction. During Protraction/Retraction, the clavicle is concave and slides in the same direction.

Convex, opposite

Concave

Concave, same

Elevation/depression, protraction/retraction, and rotation of the clavicle (upon shoulder flexion).

A Concave surface moves on a Convex Surface, and rolls and slides in the SAME Direction.

A convex surface moves on a Concave Surface, and rolls and slides in Opposite Directions.

The acromioclavicular (AC) joint is a simple joint where the bony projections of the scapula and clavicle meet at the top of the shoulder.

Small movements of anterior/posterior tilt, involved in protraction/retraction & abduction/adduction, rotation of scapula, and upward/downward rotation.

Internally rotates

Tilt anteriorly, downwardly rotates

Upwardly rotates

A functional joint, not a true joint, involving the articulation plane between the scapula and thorax.

The plane of the scapula is slightly anterior tilted (10 degrees) and internally rotated (35 degrees).

Elevation, depression, retraction, protraction, upward rotation, downward rotation.

ST: upwardly rotates, SC: elevates, AC: upward rotation

Glenohumeral: Flexion/extension, Abduction/adduction, Internal/external rotation

Sternoclavicular: Elevation/depression, Protraction/retraction, Rotation of clavicle

Acromioclavicular: Rotation of the scapula, Protraction/abduction, Retraction/adduction, Upward/downward rotation

Scapulothoracic: Elevation/depression, Protraction/retraction, Upward/downward rotation, Winging, Tipping

The glenohumeral (GH) joint is a synovial ball-and-socket joint between the convex humeral head and concave glenoid fossa, with very little congruency.

The humerus is angled 30 degrees forward from the coronal plane, and the glenoid fossa is upwardly tilted.

Fibrous capsule, capsular ligaments, rotator cuff muscles (SITS), long head of biceps, and glenoid labrum.

The fibrous capsule surrounds the GH joint, allowing mobility and slackening at rest.

The capsular ligaments limit extreme GH movements on the opposite side and get taut during movement.

Supraspinatus, infraspinatus, teres minor, subscapularis.

The long head of biceps restricts anterior translation and is important in abduction.

The glenoid labrum is a fibrocartilage ring that deepens the glenoid fossa.

The Superior Capsular Structures (SCS) include the supraspinatus tendon, superior capsular ligament, and coracohumeral ligament.

The SCS pushes the head of the humerus into the glenoid fossa, which is upwardly tilted, preventing subluxation.

A partial dislocation which could occur in the shoulder if the force coupling system fails.

Three degrees of freedom: Flexion and Extension, Abduction and Adduction, Internal Rotation and External Rotation, and a fourth motion: Horizontal Adduction/Abduction.

Rotation of the humerus in the sagittal plane. Flexion to 120 degrees, to reach 180 requires scapular upward rotation.

Anteriorly

Rolls posterior, slides anterior.

Rolls anterior, slides posterior.

Superior roll, inferior glide.

Active shoulder abduction to 180 degrees occurs with 120 degrees GH Abduction, with 60 degrees ST upward rotation.

Innervation for the Upper Extremities. C5-T1 nerve roots

• Upper trunk: C5-C6
• Middle trunk: C7
• Lower trunk: C8-T1

Muscles that originate on the spine, ribs, or cranium and insert on the scapula or clavicle.

Muscles that originate on the scapula and clavicle and insert on the humerus or forearm.

Upper Trapezius, Rhomboids, Levator Scapulae

Pecs Minor, Latissimus Dorsi, Lower Traps

Pecs Minor and Serratus Anterior

Trapezius: Middle and lower traps, Rhomboids

Upper Traps, Lower Traps, Serratus Anterior

Deltoid, Supraspinatus

Supraspinatus. If paralyzed, the deltoid will struggle to do full abduction.

Supraspinatus. The other rotator cuff muscles stabilize and rotate the humerus, ensuring the greater tubercle clears the acromion.

Phase 1: Resting phase Phase 2: 0-30 degrees abduction Phase 3: 30-90 degrees abduction (2:1 ratio - 60 degrees GH movement, 30 degrees ST movement) Phase 4: 90-180 degrees abduction (2:1 ratio continues)

During abduction, the ST joint upwardly rotates, the SC joint elevates, and the AC joint upwardly rotates.

Biceps, Anterior Deltoid, Pecs Major

Latissimus Dorsi, Teres Major, Posterior Deltoid, Pecs Major, Triceps

Rhomboid, Pecs Minor, Levator Scapulae

Teres Major, Subscapularis, Latissimus Dorsi, Anterior Deltoid, Pecs Major

Teres Minor, Deltoid (posterior), Infraspinatus