Description

• Degenerative disease of the acromioclavicular (AC) joint
  • Acute: usually due to traumatic AC separation, can lead to chronic osteoarthritis (OA) over time
  • Chronic: due to repetitive strain and degeneration over time (classic form of AC arthritis)
• Caused by mechanical friction of the articular surfaces of the distal clavicle and acromion

Epidemiology

• Acute
  • More common in adolescents and young adults
  • Due to trauma (not chronic degeneration)
  • Less common than chronic form
• Chronic
  • Typically affects middle-aged adults
  • AC joint normally degenerates over several decades. AC arthritis occurs earlier in life than glenohumeral joint arthritis or other types of OA.
  • Second most common shoulder pathology in adults >40 years (after rotator cuff pathology) (1)

Incidence

• 15/1,000 primary care patients have shoulder pain annually (1).
  • 24% of patients in PCP setting with shoulder pain have AC arthritis; 77% have >1 etiology for shoulder pain (2).
• ~20% of Americans have shoulder pain in lifetime.
  • 5% of Americans experience AC arthritis during their lifetime.
• Predominant age: 40s
• No predominant sex

Prevalence
~16% of musculoskeletal (MSK) complaints seen in PCP office are due to shoulder pain: second only to back pain (1)

Etiology and Pathophysiology

• Result of repeated movements or trauma that wears away fibrocartilaginous disk between the acromion and clavicle
• Articular disk can begin to break down by 2nd decade of life, often not symptomatic until years later.
• Prior AC separation contributes to AC joint arthritis.
• Inflammation from rotator cuff pathology can impact AC joint mechanics, contributing to arthritis.

Risk Factors

• History of trauma or contact sports, history of overhead sports (baseball, swimming, tennis), active weight lifting (bench or military press)
• Rheumatoid arthritis (RA) or other inflammatory arthritides

General Prevention

• Avoid highly repetitive motions that involve the AC joint (encourage proper technique for those who participate regularly in overhead/cross-body activities such as golf, swimming, and tennis).
• For throwing sports such as baseball, encourage pitch count in young athletes.
• For weight lifters with heavy overhead lifting, encourage use of a wider grip.

Commonly Associated Conditions

• Rotator cuff disorders (often concurrent)
• RA (consider with bilateral AC arthritis)

History

• History of trauma (prior AC separation)
• History of overhead sports such as baseball, weight lifting, tennis, and swimming (3)
• Patients may complain of popping, clicking, grinding, or catching sensation with movement of shoulder (2).
• Family or personal history of inflammatory disease or arthritis
  • Pain typically located at top of shoulder
  • Pain worse with cross-arm movements or with internal rotation (1)
  • Pain may wake patients from sleep, particularly when rolling on affected shoulder (2).

Physical Exam

• Inspection
  • Assess for enlargement or asymmetry of AC joint, muscular atrophy, or evidence of prior trauma.
  • Presence of step-off at AC joint (suggests AC separation)
• Palpation
  • Anterior/superior pain localized to AC joint
  • Tender to palpation at AC joint 96% sensitivity, 10% specificity (4)
  • Palpable osteophyte (not common)
• Active range of motion
  • Usually preserved but can have pain or hesitation with adduction/cross-body test
• Special provocative tests
  • Cross-body adduction
    • Passive motion of upper extremity into 90 degrees of forward flexion and maximal adduction, causing compression along AC joint
    • Most sensitive test with 77% sensitivity, 79% specificity, and +3.5 LR for AC joint OA (1)
  • AC resisted extension test
    • Upper extremity in 90 degrees of forward flexion; patient asked to actively extend against resistance
  • O’Brien active compression test
    • Upper extremity in 90 degrees of shoulder flexion and 10 degrees of horizontal adduction
    • Patient internally rotates shoulder and pronates forearm (thumb down); physician provides distal pressure as patient actively raises upper extremity.
    • Repeat in neutral position of shoulder/forearm (thumb up).
    • Pain/clicking of AC joint with thumb down (not up) suggests AC pathology.
    • Most specific test with 95% specificity and 83% sensitivity (2)
  • Physical exam testing less beneficial if pretest probability unequivocal; in these instances, may proceed with procedural tests to evaluate AC joint pathology (4)

Differential Diagnosis

• Rotator cuff disorders (tendinopathy, partial, and complete tear)
• Adhesive capsulitis (more common in older patients or patients with diabetes, thyroid disorders)
• Shoulder instability (history of dislocation)
• Glenohumeral arthritis (glenohumeral joint)
• Biceps tendonitis
• Referred pain (extrinsic cause such as subdiaphragmatic irritation): less likely, usually correlates with systemic symptoms

Diagnostic Tests & Interpretation

• History and physical exam provide an accurate diagnosis in most cases.
• Tender to palpation plus positive cross-body test is indicative of AC joint arthritis.
• Radiographs may be nonspecific; often have abnormal findings in asymptomatic patients due to natural joint degeneration (3)
  • Bilateral AP (comparison needed) with and without weight-bearing
  • Zanca view: AP view centered at AC joint with 10- to 15-degree cephalic tilt; allows for better AC visualization, eliminates scapula and tissue overlap on standard AP views (3)
  • May see distal clavicle lysis or elevated distal clavicle (1)[A]
  • Sclerosis of lateral head of acromion or hypertrophic spurs also common
• Magnetic resonance imaging (MRI)
  • Imaging of choice for rotator cuff tear or tendinopathy
  • Reactive bone edema more reliable predictor than degenerative changes; 82% of patients with AC joint arthritis on MRI are asymptomatic (2,3).

Follow-Up Tests & Special Considerations
N/A (See “Treatment” below.)

Diagnostic Procedures/Other
AC joint injection with lidocaine: diagnostic and therapeutic, used to isolate AC joint arthritis

• AC joint injection more accurate with ultrasound (US) guidance (3,5)
• 96% accuracy under US guidance versus 57% accuracy with palpation alone (5)[B]

Medication

First Line

• Acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs); few trials comparing two classes
• Ibuprofen
  • Do not exceed 2,400 mg PO daily (800 mg TID).
  • Caution in geriatric patients, history of gastrointestinal (GI) bleed or ulcer, or if renal dysfunction
• Acetaminophen
  • Do not exceed 3,000 mg PO daily (1,000 mg TID).
  • Caution in patients with liver dysfunction, heavy ethanol use, other drug use
• Topical NSAID use: insufficient data to reliably compare individual topical NSAIDs to same oral NSAID with chronic use

Second Line

• Corticosteroid injection
  • Provides acute pain relief; useful if symptoms do not improve with conservative therapy
  • Good evidence for short-term pain relief at 6-month follow-up (5)[B]; long-term outcomes not significantly different
  • AC joint space small and difficult to inject: blind technique 57% accuracy with palpation alone versus 96% accuracy under US guidance (5)[B]
  • 25-gauge needle, 1-mL steroid or less, 1-mL lidocaine. Needle advances ~1 cm under skin unless patient is very muscular or obese.
• Acute adverse effects of injections (rare): infection, vagal response, anaphylaxis, and high blood sugar levels
• Chronic adverse effects: not typical in AC injection; typically included chronic weakening or destruction of soft tissue structures surrounding the joint with repeated injections
• Opiates are typically not necessary for chronic management of AC arthritis.
  • Often given with acute pain in setting of AC separation (6)[C]

Issues For Referral

If patient fails to improve, does not regain adequate shoulder function, or has poorly controlled pain with conservative therapy, consider surgical evaluation.

Additional Therapies

• Acupuncture: limited evidence for long-term effectiveness
• US physiotherapy: not effective
• Glucosamine and chondroitin: mixed evidence

Surgery/Other Procedures

Indicated only if no improvement with conservative measures after minimum of 3 months

• Subacromial decompression with distal clavicular resection
• Arthroscopic distal clavicle resection associated with better pain relief at 3 months, lower infection risk, and faster return to activity (2)[B]
• Recommended all patients undergo shoulder arthroscopy at time of AC surgery due to high degree of concomitant shoulder pathology (rotator cuff tears, labral tears, biceps tendon abnormality, glenohumeral degeneration) at time of surgery (2)[B]
• AC joint fills with scar tissue, allowing for more normal movement.

Prognosis

• Chronic degenerative condition that is likely to progress over time
• Activity modification is the best way to slow progression.
• Surgery may be definitive treatment.

ICD-10

• M06.011 Rheumatoid arthritis w/o rheumatoid factor, right shoulder
• M06.012 Rheumatoid arthritis w/o rheumatoid factor, left shoulder
• M06.019 Rheumatoid arthritis w/o rheumatoid factor, unsp shoulder
• M12.511 Traumatic arthropathy, right shoulder
• M12.512 Traumatic arthropathy, left shoulder
• M12.519 Traumatic arthropathy, unspecified shoulder
• M13.811 Other specified arthritis, right shoulder
• M13.812 Other specified arthritis, left shoulder
• M13.819 Other specified arthritis, unspecified shoulder
• M19.011 Primary osteoarthritis, right shoulder
• M19.012 Primary osteoarthritis, left shoulder
• M19.019 Primary osteoarthritis, unspecified shoulder
• M19.211 Secondary osteoarthritis, right shoulder
• M19.212 Secondary osteoarthritis, left shoulder
• M19.219 Secondary osteoarthritis, unspecified shoulder

ICD-9

• 714.0 Rheumatoid arthritis
• 715.31 Osteoarthrosis, localized, not specified whether primary or secondary, shoulder region
• 716.11 Traumatic arthropathy, shoulder region
• 716.61 Unspecified monoarthritis, shoulder region
• 716.81 Other specified arthropathy, shoulder region
• 716.91 Arthropathy, unspecified, shoulder region

SNOMED

• 201849003 Localized, secondary osteoarthritis of the shoulder region (disorder)
• 201943001 Traumatic arthropathy of acromioclavicular joint (disorder)
• 239865003 Osteoarthritis of acromioclavicular joint (disorder)
• 429459001 Arthritis of acromioclavicular joint (disorder)
• 432733005 Acute degenerative joint disease of shoulder region (disorder)
• 43829003 Chronic osteoarthritis (disorder)