Shoulder Joint Anatomy, Stability, ROM & Arthrokinematics

What are the four shoulder articulations?

Glenohumeral (GH), acromioclavicular (AC), sternoclavicular (SC), and scapulothoracic (ST).

What is the primary role of the GH joint?

Provides most shoulder mobility through a ball-and-socket articulation.

What type of joint is the GH joint?

Ball-and-socket synovial joint with three degrees of freedom.

What are the three degrees of freedom of the GH joint?

Flexion/extension, abduction/adduction, and internal/external rotation.

Which GH joint surface is convex?

Humeral head.

Which GH joint surface is concave?

Glenoid fossa.

What is the function of the glenoid labrum?

Deepens the glenoid socket and contributes to the joint seal and stability.

Where does the long head of the biceps attach?

Superior glenoid labrum.

What contributes to GH joint stability?

Bony shape, labrum, capsule, ligaments, negative intra-articular pressure, rotator cuff compression, and concavity-compression.

What is concavity-compression?

Rotator cuff muscles compress the humeral head into the glenoid to help maintain joint stability.

What happens when the labrum, capsule, or glenoid is injured?

The joint seal may weaken, decreasing GH stability.

What is the superior GH ligament responsible for?

Helps limit inferior translation when the arm is at the side.

What is the middle GH ligament responsible for?

Helps limit anterior translation, especially as the arm moves into abduction.

What is the inferior GH ligament complex responsible for?

Provides important stability when the arm is elevated; anterior and posterior bands limit excessive rotation.

What is the loose-packed position of the GH joint?

Approximately 55° abduction and 30° horizontal adduction.

What is the close-packed position of the GH joint?

Full abduction and external rotation.

What is the GH capsular pattern?

External rotation most limited, followed by abduction, then internal rotation.

What is the total shoulder rotation arc?

Approximately 160-170°.

What is the approximate GH flexion ROM?

100-115°.

What is the approximate shoulder-complex flexion ROM?

165-180°.

What is the approximate GH extension ROM?

20-25°.

What is the approximate shoulder-complex extension ROM?

50-60°.

What is the approximate GH abduction ROM?

90-125°.

What is the approximate shoulder-complex abduction ROM?

170-180°.

What is the approximate GH external rotation ROM?

80-90°.

What is the approximate shoulder-complex external rotation ROM?

90-100°.

What is the approximate GH internal rotation ROM?

50-60°.

What is the approximate shoulder-complex internal rotation ROM?

70-90°.

What is the convex-on-concave rule at the GH joint?

The convex humeral head rolls in the direction of movement and glides in the opposite direction.

During GH abduction, which direction does the humeral head roll?

Superiorly.

During GH abduction, which direction does the humeral head glide?

Inferiorly.

Which GH mobilization improves restricted GH abduction?

Inferior glide of the humeral head.

Why is inferior glide important during GH abduction?

It helps maintain the humeral head centered in the glenoid as the arm elevates.

Why compare GH ROM with total shoulder-complex ROM?

To determine whether motion restriction is coming primarily from the GH joint or other shoulder articulations.

What type of joint is the AC joint?

Plane synovial joint.

What does the AC joint connect?

Lateral clavicle and acromion.

What is the primary function of the AC joint?

Allows the scapula to move relative to the clavicle.

What stabilizes the AC joint?

AC ligament and coracoclavicular ligament, consisting of conoid and trapezoid portions.

What type of joint is the SC joint?

Saddle-shaped synovial joint.

What does the SC joint connect?

Medial clavicle, sternum, and first costal cartilage.

What movements occur at the SC joint?

Clavicular elevation/depression, protraction/retraction, and rotation.

What is the importance of the SC joint?

It is the bony connection between the upper limb and axial skeleton.

What structures support the SC joint?

Capsule, articular disc, sternoclavicular ligaments, and costoclavicular ligament.

What is the approximate distance of the scapular vertebral border from the spine?

Approximately 5 cm.

Between which ribs is the scapular vertebral border located?

Ribs 2-7.

Where is the superior angle of the scapula?

Near T2.

Where is the scapular spine?

Near T4.

Where is the inferior angle of the scapula?

Approximately T7-T9.

What is the typical resting scapular upward rotation?

Approximately 10-20°.

What is the typical resting scapular internal rotation?

Approximately 30-45°.

What is the typical resting scapular anterior tilt?

Approximately 10-20°.

What three movements does the scapula generally perform during arm elevation?

Upward rotation, elevation, and posterior tilt.

What is the purpose of scapular upward rotation?

Turns the glenoid upward to allow continued arm elevation.

What is scapular plane elevation?

Raising the arm slightly forward of the body in line with the scapula's natural orientation.

What is scapulohumeral rhythm?

Coordination between GH and scapular movement during arm elevation.

Which three muscles create the primary scapular upward-rotation force couple?

Upper trapezius, lower trapezius, and serratus anterior.

What may contribute to decreased subacromial space during arm elevation?

Rounded shoulders and a slouched upper back.

What does SITS stand for?

Supraspinatus, Infraspinatus, Teres minor, and Subscapularis.

What is the primary function of the rotator cuff?

Dynamic GH stability through compression and centering of the humeral head in the glenoid.

What is the main action of supraspinatus?

Assists shoulder abduction and helps maintain the humeral head in the glenoid.

What nerve innervates supraspinatus?

Suprascapular nerve, C5-C6.

Which rotator-cuff muscle is most commonly affected by pathology according to the notes?

Supraspinatus.

What is the main action of infraspinatus?

External rotation and GH stabilization.

What is the main action of teres minor?

External rotation and GH stabilization.

What is the main action of subscapularis?

Internal rotation and GH stabilization.

What is the main action of upper trapezius?

Scapular elevation and contribution to upward rotation.

What nerve innervates the upper trapezius?

Spinal accessory nerve, CN XI.

What is the main action of middle trapezius?

Scapular retraction/adduction.

What nerve innervates the middle trapezius?

Spinal accessory nerve, CN XI.

What is the main action of lower trapezius?

Scapular upward rotation and depression.

What nerve innervates the lower trapezius?

Spinal accessory nerve, CN XI.

What is the main action of serratus anterior?

Scapular protraction/abduction and upward rotation.

What nerve innervates serratus anterior?

Long thoracic nerve, C5-C7.

What is the main action of levator scapulae?

Scapular elevation, adduction, and some downward rotation.

What nerve innervates levator scapulae?

Dorsal scapular nerve, C5, and C3-C4 ventral rami.

What is the main action of rhomboid major and minor?

Scapular retraction and downward rotation.

What nerve innervates rhomboid major and minor?

Dorsal scapular nerve, C5.

What is the main action of pectoralis minor?

Scapular protraction/abduction.

What nerve innervates pectoralis minor according to the notes?

Medial pectoral nerve, listed as C8.

What is the main action of anterior deltoid?

Shoulder flexion, some internal rotation, and horizontal adduction.

What nerve innervates the anterior deltoid?

Axillary nerve, C5-C6.

What is the main action of middle deltoid?

Shoulder abduction.

What nerve innervates the middle deltoid?

Axillary nerve, C5-C6.

What is the main action of coracobrachialis?

Shoulder flexion and some horizontal adduction.

What nerve innervates coracobrachialis?

Musculocutaneous nerve, C5-C7.

What is the main action of the clavicular portion of pectoralis major?

Flexion, horizontal adduction, and internal rotation.

What nerve innervates the clavicular portion of pectoralis major?

Lateral pectoral nerve, C5-C6.

What is the main action of the sternocostal portion of pectoralis major?

Horizontal adduction and extension.

What nerve innervates the sternocostal portion of pectoralis major?

Medial pectoral nerve, C6-T1.

What can the long head of the biceps assist with when the shoulder is externally rotated?

Shoulder abduction.

What nerve innervates the long head of the biceps?

Musculocutaneous nerve, C5-C6 according to the notes.

What does SAPS stand for?

Subacromial pain syndrome.

What other terms are used for SAPS?

Impingement and rotator-cuff-related shoulder pain.

What structures may be involved in subacromial pain syndrome?

Supraspinatus tendon, other rotator-cuff tendons, subacromial bursa, long-head biceps tendon, GH capsule, and subacromial arch.

What is the typical pain location for subacromial pain syndrome?

Lateral or anterolateral shoulder, sometimes extending down the outside of the arm toward the elbow.

What activities commonly aggravate subacromial pain syndrome?

Overhead activity and raising the arm.

What is a painful arc?

Shoulder pain occurring during a portion of arm elevation.

What is primary impingement?

Structural changes narrow the subacromial space or tissue enlargement/irritation contributes to compression.

What is secondary impingement?

Instability or poor motor control causes abnormal movement and stresses the rotator cuff.

What is internal impingement?

Posterior rotator-cuff tissue contacts the glenoid, labrum, or capsule during overhead throwing.