Acromioclavicular Joint Pain

Other Names

• AC Joint OA
• Acromioclavicular Joint Osteoarthritis
• Degenerative Joint Disease of the Acromioclavicular Joint
• AC Joint Pain
• Acromioclavicular Joint Pain
• Acromioclavicular Pain
• AC Joint Injury
• Acromioclavicular Joint Syndrome
• AC Joint Arthralgia
• AC Joint Dysfunction
• Distal Clavicle Pain
• AC Joint Arthritis Pain

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Background

• This page refers to atraumatic and/or chronic causes of pain to the Acromioclavicular Joint (AC Joint)
  • Traumatic Acromioclavicular Joint Separation is discussed separately

History

• Hippocrates (460-377 BC) noted that AC joint dislocations were often misdiagnosed as glenohumeral injuries
• First detailed description of AC joint injury pathoanatomy is widely credited to Cadenat in 1917

Epidemiology

• Affects approximately 45 per 100,000 person-years
• AC joint injuries accounting for 11% of all shoulder injuries
• Tends to affect mild aged (20-49 years) males, with 82% of cases ocurring in men
• Sports-related injuries account for 53% of AC joint injuries

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Introduction

Illustration of the acromioclavicular joint

Labeled radiograph of the AC joint

Anteroposterior radiographs providing examples of acromioclavicular osteoarthritis grades (A) 0, (B) 1, (C) 2, and (D) 3, as well as (E) distal clavicular osteolysis. The difference between grades 2 and 3 is primarily with regard to the size of the periarticular osteophytes

A plain radiograph of the shoulder showed joint space widening with acromioclavicular joint osteoarthritis

Anatomy of the AC Joint

General

• AC Joint Pain is a common cause of shoulder pain that can result from traumatic injurise or degenerative osteoarthriitis
• The AC joint connects the clavicle to the acromion and is critical for shoulder stability and motion
• The diagnosis is made clinically and supported by imaging findings
• Patients are initially treated conservatively but may require surgical intervention in refractory cases

Etiology: Primary Osteoarthritis

• Refers to age-related degeneration, typically affecting middle aged individuals
  • Most common cause of AC joint pain
• Intra-articular disc
  • Functions like the meniscus of the knee
  • Prone to fraying, tearing, and forming holes, macerated by defects in the chondral surface
• Inflammatory arthropathies:
  • Rheumatoid Arthritis
  • Gout
  • Pseudogout
• Septic arthritis
  • Uncommon in AC joint but risk factors include trauma, recent surgery, IV drug abuse, immune compromised, and hematogenous seeding among many others

Etiology: Post Traumatic

• Most common in young adult males who play contact sports (football, hockey) or cycling
  • Most commonly occuring with an axial load on an abducted arm
  • Many of thesee athletes will have sustained AC Joint Separation or Dislocation
• Distal clavicle osteolysis
  • Related to repetitive microtrauma
  • Most commonly in weight lifters, less commonly basketball, swimming
• Joint instability
  • Due to local elevation of contact stresses, dynamic loss of joint congruity, and alterations in range of motion

Anatomy of the Acromioclavicular Joint

• General
  • Planar diarthrodial synvoial joint
  • Formed by the junction of the anteromedial acromion and lateral clavicle
• Stabilizers
  • Static: Acromioclavicular Ligament, Coracoclavicular Ligaments
  • Dynamic: Deltoid, Trapezius, Serratus Anterior

Associated Injuries

• Rotator Cuff Disease
  • Includes: Rotator Cuff Tear, Rotator Cuff Tendonitis
  • Condition most frequently associated condition with AC joint disorders
  • Coexisting rotator cuff disease occurs in approximately 79-98% of cases
• Subacromial Impingement
  • Frequently co-exist with AC joint pain and can be difficult to distinguish clinically
• Glenoid Labral Tears
  • Superior labral anterior-posterior (SLAP) lesions and other labral tears are common
  • 45% of younger patients (under 50), 29% of older patients (oveer 50) have labral tears
• Proximal Biceps Tendon Injuries
• Glenohumeral Osteoarthritis
  • Present in 14% of patients with symptomatic AC degeneration

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Risk Factors

Traumatic Risk Factors

• Direct fall onto the lateral shoulder (most common mechanism)
• Contact sports (e.g., football, hockey, rugby)
• High-energy trauma (motor vehicle collisions, cycling accidents)
• Prior AC joint sprain or separation (predisposes to chronic pain and instability)

Repetitive / Overuse Risk Factors

• Repetitive overhead activity (throwing athletes, swimmers)
• Weightlifting (especially bench press, dips, overhead press)
• Occupational overhead labor (construction, painting, manual labor)
• Chronic microtrauma leading to distal clavicle osteolysis

Degenerative Risk Factors

• Increasing age (AC joint osteoarthritis is common after age 40)
• Prior joint injury accelerating degenerative changes
• Chronic mechanical stress across the AC joint
• Joint space narrowing and osteophyte formation

Anatomic / Biomechanical Risk Factors

• Scapular dyskinesis altering AC joint loading
• Clavicular malalignment or prior fracture
• Ligamentous laxity or instability of the AC joint
• Abnormal shoulder kinematics (poor rotator cuff or periscapular control)

Sport-Specific Risk Factors

• Contact athletes (football, rugby, wrestling)
• Overhead athletes (baseball, tennis, volleyball)
• CrossFit and heavy resistance training athletes
• Repetitive axial loading across the shoulder

Post-Surgical / Iatrogenic Risk Factors

• Prior distal clavicle resection (persistent instability or pain)
• Failed AC joint reconstruction
• Altered biomechanics following shoulder surgery

Systemic / Other Risk Factors

• Inflammatory arthritis (e.g., rheumatoid arthritis, pseudogout)
• Infection (rare, septic AC joint)
• Osteolysis related to metabolic or endocrine factors
• Tobacco Use Disorder (associated with impaired healing and degeneration)

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Differential Diagnosis

Differential Diagnosis Shoulder Pain

• Fractures
  • Proximal Humerus Fracture
  • Humeral Shaft Fracture
  • Clavicle Fracture
  • Scapula Fracture
  • First Rib Fracture (traumatic or atraumatic)
  • Floating Shoulder
• Dislocations & Separations
  • Acromioclavicular Joint Separation
  • Glenohumeral Dislocation (Acute)
  • Sternoclavicular Joint Dislocation
  • Chronic Glenohumeral Dislocation
  • Glenohumeral Instability (Chronic)
• Arthropathies
  • Glenohumeral Arthritis
  • Acromioclavicular Joint Arthritis
  • Sternoclavicular Arthritis
• Muscle & Tendon Injuries
  • Pectoralis Major Injuries
  • Pectoralis Minor Injuries
  • Proximal Biceps Tendon Injuries
  • Scapular Dyskinesis
• Rotator Cuff
  • Rotator Cuff Tear
  • Rotator Cuff Tendonitis
  • Calcific Tendinitis of the Rotator Cuff
  • Subcoracoid Impingement Syndrome
• Bursopathies
  • Subacromial Bursitis
  • Scapulothoracic Bursitis
• Ligament Injuries
  • Glenoid Labral Tears
• Neuropathies
  • Suprascapular Nerve Injury
  • Parsonage-Turner Syndrome
  • Quadrilateral Space Syndrome
  • Winged Scapula
• Other
  • Adhesive Capsulitis
  • Paget-Schroetter Syndrome
  • Shoulder Injury Related To Vaccine Administration
  • Distal Clavicle Osteolysis
• Pediatrics
  • Coracoid Avulsion Fracture
  • Humeral Head Epiphysiolysis (Little League Shoulder)

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Clinical Features

Demonstration of Paxino's Test

Illustration of Cross Arm Test

History

• Can be difficult to distinguish from other causes of shoulder pain
• Often other pathology co-occurs including rotator cuff tears, labral injuries and biceps tendonitis
• Patient may report pain with passive and active range of motion
• Pain typically anterior shoulder but can but can be referred to anterolateral neck, anterolateral deltoid, and trapezius
• In patients with traumatic history, they should be able to describe a prior injury and treatment
• Degenerativee causes are often more insidious with no clear eetiology
• Pain descriptions may include
  • Pain exacerbated by overhead activities and cross-body adduction
  • Pain localized to the AC joint without radiation below the elbow

Physical: Physical Exam Shoulder

• Inspection: AC Joint may demonstrate swelling, deformity, or prominence
  • Observe for asymmetry, deformity, swelling, or prominence of the distal clavicle
• Tenderness to AC joint is sensitive, not specific
• In isolated injuries, range of motion is usually preserveed

Special Tests

• Crossover Test: Examiner passively flexs, adducts arm across body
• Resisted AC Joint Extension Test: Flex, internally rotatoe shoulder and abduct against resistance
• OBriens Test: Shoulder flexed to 90, flexes further against resistance
  • Crossover test most sensitive (77%), O'Briens Test is most specific (95%)
• One Finger Test: Have patient point to most painful spot with 1 finger (AC joint = positive)
• Paxinos Test: Apply pressure at the acromion and clavicle
  • Sensitivity 79%, specificity 50%
• AC Joint Line Tenderness Test: palpate the AC joint directly
  • Sensitivity 96%, specificity 10%
• Bell Van Riet Test: cross body test with resisted abduction

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Evaluation

Radiograph demonstrating AC joint OA

Ultrasound demonstrating AC joint OA

Acromioclavicular joint arthrosis classified by Shubin–Stein

Radiographs

• Standard Radiographs Shoulder
  • Initial imaging study of choice
  • OA Findings: joint space narrowing, subchondral cysts, osteophytes, and subchondral sclerosis
  • May see distal clavicle osteolysis
  • Asymptomatic AC joint OA findings are common (need citation)
• Zanca View: 10-15° cephalid tilt best visualizes joint
• Weighted vs. Non-Weighted Views
  • The utility of weighted radiographs remains controversial
  • One study showed that bilateral comparative views are necessary for accurate classification
  • Another study of 140 patients found that weighted radiographs caused no significant changes in classification

CT

• Provides superior osseous visualization
• Indications
  • Evaluating complex fracture patterns involving the distal clavicle
  • Assessing bone quality before surgical reconstruction
  • Detecting subtle osteophytes and subchondral changes

MRI

• General
  • MRI enables visualization of the capsuloligamentous structures
  • Including the integrity of the AC joint ligaments, coracoclavicular ligaments
  • Assocaited rotator cuff tears, labral pathology
• MRI Findings in Degenerative Disease
  • Bone marrow edema (observed only in symptomatic patients)
  • Inferior joint distension
  • Impression on the supraspinatus muscle

Ultrasound

• Diagnostic accuracy
  • Ultrasound can detect AC joint changes reliably
  • For acute AC injuries: Agreement with MRI is very good (correlation coefficient 0.83)
  • For AC joint arthropathy: Ultrasound has good sensitivity and high specificity
• Advantages
  • Non-invasive, accessible, and cost-effective
  • Can assess dynamic horizontal instability in real-time
  • Useful for excluding joint inflammation
  • Improves accuracy of diagnostic and therapeutic injections

Diagnostic Injection

• Diagnostic injection can help clarify etiology of shoulder pain
  • Ultrasound improves injection accuracy from 70%-75% to 90%-98%
  • Positive test: ≥50% immediate pain relief after local anesthetic injection

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Classification

Acromioclavicular joint arthrosis classified by Shubin–Stein

• Grade I
  • No capsular distension
  • No joint space narrowing
  • No evidence of osteophyte formation
• Grade II
  • Capsular distension
  • Occasional mild joint space narrowing
• Grade III
  • Capsular distension
  • Joint space narrowing
  • Subacromial fat effacement
  • Marginal osteophyte formation
• Grade IV
  • Everything in grade I, II and III
  • Marked joint space irregularity and narrowing with large osteophytes

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Management

Shoulder Sling

Nonoperative

• First line therapy in most patients
• Activity Modification
  • Avoid: aggravating activities such as cross-body, pushing, weight lifting, throwing, overhead work
• Physical Therapy
  • Can help with range of motion, flexibility, and strength
• Immobilization
  • Temporary immobilization with Shoulder Sling in the setting of acute exacerbation
• Medications including NSAIDS, Acetaminophen
• Acromioclavicular Joint Injection

Operative

• Indications
  • Failure of non-operative therapy, typically a minimum of 6 months
• Technique
  • Arthroscopic clavicle resection
  • Open clavicle resection (Mumford procedure)

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Rehab and Return to Play

Scapular clocks are effective closed-chain exercises that allow recruitment of the periscapular musculature, while limiting AC joint stress by unweighting the arm

Early mobility phase

Phase 3 involves periscapular and rotator cuff strengthening. Top, rowing exercises with resistance tubing at various level of forward elevation are helpful, but the patient needs to focus on scapular retraction rather than compensation with shoulder extension. Middle, kinetic chain exercises including lawn mower and disco exercises help re-build functional strength. Bottom, Blackburn exercises, also called “T’s and “Y’s” are advanced strengthening exercises, recruiting high levels of middle and lower trapezius, at the expense of high stress placed at the AC joint. These are generally reserved for later in the rehabilitation process.

Intermediate strengthening phase

In those with apprehension, closed chain exercises including table slides (top), roller exercises (middle), and wall slides (bottom) unweight the arm, allowing the patient to isolate and focus on periscapular muscle activation. With the arm in a fixed position, asynchronies between the trunk, scapula, and arm are minimized.

Advanced strengthening phase

Rehabilitation

• General rehab objectives
  • Pain control and restoration of range of motion (ROM)
  • Scapular stabilization and rotator cuff strengthening
  • Sport-specific conditioning and gradual return to activity
• Dictated in part by concomitant procedures
• Distal clavicle excision
  • Immobilized in shoulder sling, allowed to perform pendulums
  • 2 weeks: begin passive, active range of motion
  • 4 weeks: discontinue immobilization, full range of motion permitted
• Note: If significant deltoid dissection, flexion and abduction restricted up to 6 weeks

Phase 1: Acute/Protection Phase (Weeks 0-2)

• Goals: Pain and inflammation control, tissue protection, maintain elbow/wrist/hand mobility
• Immobilization
  • Broad-arm sling for comfort (typically 2-4 weeks depending on injury severity)
  • Remove sling 4 times daily for gentle exercises
• Pain Management
  • Ice application: 15-20 minutes every 2-3 hours
  • Oral NSAIDs or analgesics as prescribed
  • Activity modification: Avoid overhead activities, cross-body movements, and heavy lifting
• Exercises
  • Pendulum exercises (Codman's): Gentle circular motions using gravity, 2-3 minutes, 4x daily
  • Elbow, wrist, and hand range of motion exercises
  • Cervical spine gentle range of motion
  • Scapular squeezes (gentle isometric retraction in neutral position)
• Criteria to Progress: Pain at rest 3/10, able to tolerate passive range of motion

Phase 2: Early Mobility Phase (Weeks 2-4)

• Goals: Restore passive and active-assisted range of motion, begin gentle strengthening
• Range of Motion:
  • Passive and active-assisted forward flexion (supine, using opposite arm or wand)
  • Passive external rotation with arm at side
  • Active-assisted abduction in scapular plane
  • Avoid cross-body adduction and end-range overhead positions
• Early Strengthening:
  • Isometric exercises in neutral position:
  • Shoulder flexion, extension, abduction (submaximal, pain-free)
  • External and internal rotation isometrics
  • Scapular clock exercises (gentle protraction/retraction)
• Scapular Stabilization (Early Stage):
  • Low row exercise (activates serratus anterior and lower trapezius at moderate levels)
  • Inferior glide exercise
  • Wall slides (limited range)
• Frequency: 2-3 sets of 10-15 repetitions, 2x daily
• Criteria to Progress: Near-full passive range of motion, minimal pain with active motion

Phase 3: Intermediate Strengthening Phase (Weeks 4-8)

• Goals: Restore full active range of motion, progressive strengthening, improve scapular control
• Active Range of Motion:
  • Full active forward flexion and abduction
  • External rotation at 0° and progressing to 45° abduction
  • Begin gentle cross-body stretching if tolerated
• Strengthening (Resistance Bands/Light Weights):
  • External rotation in side-lying position (excellent scapular muscle balance)
  • Internal rotation with resistance band
  • Prone horizontal abduction with external rotation (optimal scapular neuromuscular control)
  • Prone extension
  • Biceps curls, triceps extensions
• Scapular Stabilization (Progressive):
  • Lawnmower exercise (activates serratus anterior and lower trapezius)
  • Robbery exercise
  • Wall push-up plus (serratus anterior activation)
  • Scapular retraction with resistance band
  • Prone Y, T, W exercises
• Frequency: 3 sets of 10-15 repetitions, daily
• Criteria to Progress: Full pain-free active range of motion, 4/5 strength in all planes

Phase 4: Advanced Strengthening Phase (Weeks 8-12)

• Goals: Restore full strength, begin sport/activity-specific training
• Progressive Resistance Training:
  • Shoulder press (avoid extreme overhead positions initially)
  • Rows (seated, bent-over)
  • Lat pulldowns
  • Push-ups (floor progression)
  • Dumbbell exercises in functional patterns
• Scapular Stabilization (Advanced):
  • Push-up plus on unstable surface
  • Quadruped exercises with arm lifts
  • Plank variations with shoulder taps
  • Serratus punches
• Proprioception and Neuromuscular Control:
  • Rhythmic stabilization exercises
  • Ball tosses against wall
  • Perturbation training
  • Closed kinetic chain exercises (weight bearing through upper extremity)
• Frequency: 3-4 sets of 8-12 repetitions, 3-4x weekly
• Criteria to Progress: Strength equal to contralateral side, no pain with resistance exercises

AC Joint Pain Rehab Exercises PDF

• AC Joint Injury Rehabilitation PDF
• AC Joint Sprain Rehab Exercises PDF
• Mild acromioclavicular AC Joint Injury Rehab PDF
• Osteoarthritis of the Acromioclavicular Joint PDF

Return to Play

Return to play infographic

• Goals: Full return to work, sport, and recreational activities
• Criteria for Return to Activity:
  • Normal shoulder motion compared to contralateral side
  • Strength equal to contralateral extremity (≥90%)
  • Shoulder is asymptomatic with sport-specific movements
  • No pain with provocative maneuvers (cross-body adduction)
  • Successful completion of sport-specific drills
• Sport-Specific Progression:
  • Gradual return to sport-specific movements
  • Contact sports: Progress from non-contact drills to controlled contact to full participation
  • Overhead athletes: Interval throwing/serving programs
  • Consider protective padding for contact sports during initial return
• Average time lost
  • Low-grade, atraumatic conditions, the average time lost to sport is 10–18 days
  • Most athletes experience significant improvement with appropriate treatment within 4-6 weeks

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Prognosis and Complications

Subacromial Impingement Syndrome

Prognosis

• General
  • Most patients have favorable long term prognosis with appropriate treatment
  • High likelihood of return to previous activity levels and minimal long-term disability
  • Return to baseline function is expected in weeks to a few months for mild cases.
• Surgical outcomes
  • Distal clavicle excision provides high rates of relief and patient satisfcation

Complications

• Chronic pain
• Inability to return to sport
• AC Joint Osteoarthritis
• Subacromial Impingement Syndrome
• Rotator Cuff Tendinopathy
• Scapular Dyskinesis
• Distal Clavicle Osteolysis
• Surgical
  • AC Joint instability due to excessive clavicle resection
  • Persistent pain due to incomplete resection
  • Heterotopic Ossification
  • Deltoid dehiscence

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See Also

Internal

• Physical Exam Shoulder
• Shoulder Anatomy (Main)
• Shoulder Pain (Main)

External

• Sports Medicine Review Shoulder Pain: https://www.sportsmedreview.com/by-joint/shoulder/

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