Shoulder Joint
The shoulder complex is the most mobile joint in the human body, consisting of four articulations that work together to provide exceptional range of motion while maintaining stability through dynamic muscular control.
Quick Reference
| Property | Details |
|---|---|
| Joint Type | Ball-and-socket (glenohumeral); Plane (AC, SC); Physiological (scapulothoracic) |
| Bones | Humerus, scapula, clavicle |
| Degrees of Freedom | 3 (flexion/extension, abduction/adduction, internal/external rotation) |
| Key Ligaments | Glenohumeral ligaments (superior, middle, inferior), coracohumeral ligament, coracoacromial ligament, AC ligaments, coracoclavicular ligaments (conoid, trapezoid) |
| Key Structures | Glenoid labrum, rotator cuff, subacromial bursa, long head of biceps tendon |
| Stability | Dynamic (muscular) > Static (ligamentous) |
| Common Issues | Impingement, rotator cuff pathology, instability, labral tears, frozen shoulder |
Anatomy
The shoulder complex consists of four distinct articulations that function as an integrated unit:
Glenohumeral (GH) Joint: The primary shoulder joint is a ball-and-socket articulation between the humeral head and the shallow glenoid fossa of the scapula. The glenoid labrum, a fibrocartilaginous rim, deepens the socket and provides attachment for the glenohumeral ligaments. This shallow configuration prioritizes mobility over inherent bony stability.
Acromioclavicular (AC) Joint: A plane synovial joint connecting the lateral clavicle to the acromion process of the scapula. Stabilized by the AC ligaments and coracoclavicular ligaments (conoid and trapezoid), it allows the scapula to rotate and adjust position during arm movements.
Sternoclavicular (SC) Joint: The only true articulation between the upper extremity and the axial skeleton, connecting the medial clavicle to the sternum. Despite appearing simple, it allows movement in three planes and acts as a strut for scapular positioning.
Scapulothoracic Articulation: A physiological "joint" between the scapula and thoracic wall, allowing the scapula to glide, rotate, and tilt on the rib cage. Proper scapulothoracic rhythm is essential for overhead shoulder function.
Supporting Structures:
- Glenoid Labrum: Fibrocartilage ring that deepens the glenoid socket by 50%, enhancing stability and serving as attachment for glenohumeral ligaments
- Rotator Cuff: Four muscles (supraspinatus, infraspinatus, teres minor, subscapularis) that dynamically stabilize the humeral head in the glenoid
- Subacromial Bursa: Reduces friction between the rotator cuff and overlying acromion
- Long Head of Biceps Tendon: Travels through the joint, contributing to anterior stability and humeral head depression
The shoulder sacrifices bony stability for mobility. The humeral head is 3-4 times larger than the glenoid socket, making dynamic muscular stability through the rotator cuff critical for joint health.
Range of Motion
Normal shoulder range of motion varies by individual and can be influenced by activity level, age, and training. Measurements are typically for glenohumeral motion isolated from scapular movement.
| Movement | Normal ROM | Limiting Factors |
|---|---|---|
| Flexion | 180° | Inferior GH ligament, posterior capsule, teres major, latissimus dorsi |
| Extension | 50-60° | Anterior capsule, coracohumeral ligament, anterior deltoid, pectoralis major |
| Abduction | 180° | Inferior GH ligament, adductor muscles, middle GH ligament (early range) |
| Adduction | 50-75° (across body) | Lateral deltoid, supraspinatus, body proximity |
| Internal Rotation | 70-90° | Posterior capsule, infraspinatus, teres minor, posterior deltoid |
| External Rotation | 90° | Anterior capsule, subscapularis, anterior GH ligaments |
| Horizontal Adduction | 130-135° | Posterior capsule, posterior deltoid, infraspinatus |
| Horizontal Abduction | 45° | Anterior structures, pectoralis major |
Total shoulder motion requires coordinated scapulothoracic rhythm. For every 2° of arm elevation, approximately 1° occurs at the glenohumeral joint and 1° from scapular rotation (2:1 ratio). Disrupted scapulohumeral rhythm can lead to impingement and dysfunction.
Joint Actions
- Flexion/Extension
- Abduction/Adduction
- Rotation
- Horizontal Plane
Flexion (raising arm forward/overhead):
- Prime Movers: Anterior deltoid, clavicular head of pectoralis major, coracobrachialis
- Assistors: Biceps brachii (especially with supination), middle deltoid (later range)
- Stabilizers: Rotator cuff (centering humeral head), serratus anterior (upward scapular rotation)
Extension (moving arm backward):
- Prime Movers: Latissimus dorsi, posterior deltoid, teres major
- Assistors: Long head of triceps, teres minor
- Stabilizers: Rotator cuff, rhomboids, lower trapezius
Abduction (raising arm to side):
- Prime Movers: Middle deltoid, supraspinatus (initiation and first 15-30°)
- Assistors: Anterior/posterior deltoid (later range), long head of biceps
- Stabilizers: Rotator cuff (humeral head depression), serratus anterior and trapezius (scapular rotation)
Adduction (lowering arm to side):
- Prime Movers: Latissimus dorsi, pectoralis major, teres major
- Assistors: Anterior deltoid (with flexion), posterior deltoid (with extension)
- Stabilizers: Rotator cuff
Internal Rotation:
- Prime Movers: Subscapularis, pectoralis major, latissimus dorsi, teres major
- Assistors: Anterior deltoid
- Stabilizers: Other rotator cuff muscles, scapular stabilizers
External Rotation:
- Prime Movers: Infraspinatus, teres minor
- Assistors: Posterior deltoid
- Stabilizers: Subscapularis (anteriorly), supraspinatus (superiorly), scapular stabilizers
Horizontal Adduction (moving arm across chest):
- Prime Movers: Pectoralis major, anterior deltoid
- Assistors: Coracobrachialis, short head of biceps
- Stabilizers: Rotator cuff, serratus anterior
Horizontal Abduction (moving arm backward at shoulder height):
- Prime Movers: Posterior deltoid, infraspinatus, teres minor
- Assistors: Latissimus dorsi, teres major (with extension)
- Stabilizers: Rotator cuff, scapular retractors (rhomboids, middle trapezius)
Muscles Acting On It
Shoulder function requires coordinated action across multiple muscle groups. The rotator cuff provides dynamic stability while larger muscles generate force for movement.
| Muscle Group | Prime Movers | Synergists | Stabilizers |
|---|---|---|---|
| Rotator Cuff | Supraspinatus (abduction initiation), Infraspinatus/Teres minor (ER), Subscapularis (IR) | All RC muscles work synergistically | Primary dynamic stabilizers of GH joint |
| Deltoid | Anterior (flexion), Middle (abduction), Posterior (extension, horizontal abduction) | Assists in multiple planes | Helps center humeral head |
| Pectoralis Major | Flexion (clavicular), Adduction, IR, Horizontal adduction | Assists shoulder flexion | Anterior stability |
| Latissimus Dorsi | Extension, Adduction, IR | Assists in multiple pulling motions | Posterior-inferior stability |
| Teres Major | Extension, Adduction, IR | Works with lat dorsi | Posterior stability |
| Biceps Brachii | Shoulder flexion (long head), Stabilizes humeral head | Assists flexion and supination | LHBT stabilizes anteriorly |
| Triceps (Long Head) | Shoulder extension | Assists extension and adduction | Inferior stability |
| Coracobrachialis | Flexion, Adduction | Assists in flexion | Minimal |
| Scapular Muscles | Serratus anterior (upward rotation), Trapezius (rotation), Rhomboids (retraction) | Essential for all overhead movements | Scapular stability = GH function |
The rotator cuff muscles are not primarily movers but stabilizers. Their primary function is to maintain the humeral head centered in the glenoid during movement, allowing the larger muscles (deltoid, pecs, lats) to generate force efficiently.
Mobility Work
Stretches
Posterior Capsule Stretch (Sleeper Stretch)
- Lie on affected side, arm at 90° forward
- Use opposite hand to internally rotate forearm toward floor
- Targets: Posterior capsule, infraspinatus, teres minor
- Hold: 30-60 seconds, 2-3 reps
Doorway Pec Stretch
- Forearm on doorframe, elbow at 90°
- Step forward until stretch in anterior shoulder/chest
- Vary arm height (low, 90°, high) to target different fibers
- Targets: Pectoralis major, anterior capsule
- Hold: 30-60 seconds per position
Cross-Body Stretch
- Bring arm across body at shoulder height
- Use opposite hand to pull arm closer to chest
- Targets: Posterior deltoid, posterior capsule
- Hold: 30-60 seconds, 2-3 reps
Lat Stretch with Rotation
- Reach arm overhead and across to opposite side
- Lean into stretch, adding slight rotation
- Targets: Latissimus dorsi, teres major
- Hold: 30-60 seconds each side
Mobilizations
Wall Slides
- Back against wall, arms in "goal post" position
- Slide arms up wall maintaining contact
- Purpose: Scapular upward rotation, overhead mobility
- Sets: 2-3 sets of 10-15 reps
Thread the Needle
- Start in quadruped position
- Reach arm under body, rotating thoracic spine
- Purpose: Thoracic rotation, internal rotation mobility
- Sets: 10-12 reps per side
Shoulder CARs (Controlled Articular Rotations)
- Create tension throughout shoulder complex
- Move arm through full available ROM slowly and controlled
- Purpose: Full ROM assessment and maintenance, motor control
- Sets: 5 rotations each direction
Banded Distraction
- Attach band to fixed point, loop around shoulder joint
- Lean away, creating joint space
- Move arm through various positions
- Purpose: Joint capsule mobilization, pain reduction
- Duration: 1-2 minutes with movement
Dowel/Broomstick Pass-Throughs
- Hold stick wide grip in front of body
- Rotate arms overhead and behind body
- Gradually narrow grip as mobility improves
- Purpose: Full shoulder ROM, scapular mobility
- Sets: 10-15 reps
Avoid aggressive stretching into painful ranges, especially with overhead positions. Shoulder pain with stretching may indicate impingement or instability patterns that require assessment before progressing mobility work.
Common Issues
Subacromial Impingement Syndrome
Description: Compression of rotator cuff tendons and/or subacromial bursa between humeral head and acromion during overhead movements.
Common Causes:
- Poor scapular control and positioning
- Rotator cuff weakness (inadequate humeral head depression)
- Tight posterior capsule causing anterior-superior humeral head migration
- Acromion morphology variations
- Overuse in overhead activities
Signs/Symptoms:
- Pain with overhead reaching (60-120° arc)
- Positive impingement tests (Neer's, Hawkins-Kennedy)
- Night pain, especially lying on affected side
- Weakness with abduction/external rotation
Management Approach:
- Rotator cuff strengthening (especially external rotators)
- Scapular stabilization exercises
- Posterior capsule stretching
- Activity modification (avoid painful arc)
- Address kinetic chain dysfunction (thoracic mobility, core stability)
Rotator Cuff Tears
Description: Partial or full-thickness tear of one or more rotator cuff tendons, most commonly supraspinatus.
Common Causes:
- Acute trauma (fall, sudden load)
- Chronic degeneration (age-related tendon changes)
- Impingement leading to tendon breakdown
- Repetitive overhead activities
Signs/Symptoms:
- Weakness in specific planes (abduction, external rotation)
- Positive drop arm test, lag signs
- Pain with specific resisted movements
- Possible atrophy of affected muscle(s)
- Night pain
Management Approach:
- Many partial tears respond to conservative treatment
- Physical therapy focusing on compensatory strengthening
- Modification of aggravating activities
- Full-thickness tears may require surgical consideration
- Post-surgical rehabilitation is lengthy (6-12 months)
Labral Tears
Description: Tear in the glenoid labrum, often classified as SLAP lesions (Superior Labrum Anterior to Posterior) or anterior/posterior tears.
Common Causes:
- Acute trauma (fall on outstretched arm, shoulder dislocation)
- Repetitive overhead activities (throwing, swimming)
- Traction injuries
- Age-related degeneration
Signs/Symptoms:
- Deep shoulder pain, often difficult to localize
- Clicking, catching, or locking sensation
- Pain with overhead activities
- Positive O'Brien's test, anterior apprehension test
- Feeling of instability
Management Approach:
- Conservative management for minor tears
- Focus on dynamic stability training
- Avoid provocative positions initially
- Surgical repair for significant tears with instability
- Gradual return to activity post-surgery
Adhesive Capsulitis (Frozen Shoulder)
Description: Progressive loss of active and passive shoulder range of motion due to capsular inflammation and fibrosis.
Common Causes:
- Idiopathic onset (primary)
- Following injury or immobilization (secondary)
- Associated with diabetes, thyroid disorders, autoimmune conditions
- More common in ages 40-60, females
Signs/Symptoms:
- Progressive loss of ROM (especially external rotation)
- Significant night pain (freezing phase)
- Equal loss of active and passive ROM
- Capsular pattern of restriction (ER > Abd > IR)
Management Approach:
- Natural history: freezing (0-9 months), frozen (4-12 months), thawing (12-24 months)
- Physical therapy emphasizing gentle ROM within tolerance
- Pain management (NSAIDs, possibly corticosteroid injection)
- Patient education about natural course
- Surgical intervention (manipulation, capsular release) for refractory cases
Shoulder Instability
Description: Excessive translation of humeral head in glenoid, ranging from subluxation to complete dislocation.
Types:
- Traumatic: Acute dislocation (usually anterior) from injury
- Atraumatic: Multidirectional instability from capsular laxity, often bilateral
- Microtraumatic: Repetitive overhead activities causing gradual instability
Signs/Symptoms:
- Feeling of shoulder "slipping" or "going out"
- Apprehension with specific positions (typically abduction + external rotation)
- Positive apprehension and relocation tests
- Possible previous dislocation history
- Avoidance of provocative positions
Management Approach:
- Acute dislocation requires immediate reduction and initial immobilization
- Rehabilitation focuses on dynamic stability (rotator cuff, scapular muscles)
- Proprioceptive training
- Activity modification to avoid provocative positions
- Surgical stabilization for recurrent dislocations or significant structural damage
- First-time dislocators under 25 have high recurrence rates
Many shoulder issues share overlapping symptoms. Accurate diagnosis often requires physical examination by a qualified healthcare provider. Self-diagnosis and treatment of shoulder pain should be approached cautiously, especially if pain is acute, severe, or persistent.
Related Joints
The shoulder functions as part of an integrated kinetic chain, with dysfunction in related areas often contributing to shoulder problems.
Cervical Spine
- Connection: Neural innervation (C5-T1), muscle attachments (levator scapulae, upper trap)
- Impact: Cervical dysfunction can cause referred shoulder pain, affect scapular control
- Key Consideration: Cervical radiculopathy can mimic shoulder pathology
Thoracic Spine
- Connection: Scapular resting position, foundation for arm movement
- Impact: Limited thoracic extension/rotation restricts overhead shoulder motion
- Key Consideration: Thoracic mobility is essential for healthy scapulohumeral rhythm; 30-40° thoracic extension needed for full overhead reach
Scapulothoracic Joint
- Connection: Direct mechanical link; scapular position determines glenoid orientation
- Impact: Poor scapular control (dyskinesis) is present in most shoulder pathologies
- Key Consideration: "Setting" the scapula is prerequisite for safe shoulder loading
Elbow
- Connection: Biceps and triceps cross both joints
- Impact: Elbow position affects shoulder muscle length-tension relationships
- Key Consideration: Common flexor/extensor tendon pathology can alter shoulder mechanics
Core and Lower Body
- Connection: Proximal stability for distal mobility; force transfer through kinetic chain
- Impact: Core weakness or hip/ankle limitations reduce force generation, increasing shoulder demand
- Key Consideration: Throwing, swimming, and overhead athletes require full kinetic chain assessment
When addressing shoulder issues, always assess the entire kinetic chain. Restrictions in thoracic spine, hip mobility, or core stability often manifest as shoulder pain or dysfunction. The shoulder is rarely the sole problem.
Sources
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