What is shoulder impingement?

Shoulder Impingement

Shoulder impingement syndrome is a subacromial outlet obstruction resulting in irritation of the supraspinatus tendon, which can be categorized into primary and secondary types depending on the underlying mechanism. 1, 2

Types of Shoulder Impingement

• Primary Impingement: Results from extra-articular rotator cuff pathology due to compression of the rotator cuff tendons beneath the acromion. This is common in adult athletes but rare in adolescent athletes. 1, 3

• Secondary Impingement: More common in younger individuals, caused by weakness in the rotator cuff muscles combined with ligamentous laxity, making it difficult for the humeral head to stay centered in the glenoid fossa during arm motion. 1

• Subcategories: Modern classification further divides impingement into subacromial, internal, and subcoracoid types, each with specific anatomical considerations. 2

Clinical Presentation

• Pain Location: Typically in the anterior or anterolateral aspect of the shoulder. 1

• Pain Timing: Pain occurs during specific movements, particularly overhead activities. In throwers, pain is often experienced during arm cocking and acceleration phases. 1

• Painful Arc: Characteristic pain between 70-120 degrees of abduction, which may be reduced to 50-70 degrees in severe cases. 4

• Associated Symptoms: Decreased velocity and precision in throwing athletes, weakness, and limited range of motion. 1

Physical Examination Findings

• Weakness: Focal weakness with decreased range of motion during abduction with external or internal rotation. 1

• Range of Motion: Reduced passive shoulder abduction and external rotation of the glenohumeral joint. 1

• Special Tests: Positive Neer impingement sign (shoulder pain with passive abduction of the internally rotated arm) and tenderness to palpation over the biceps tendon and supraspinatus. 1

• Scapular Assessment: Evaluation for scapular dyskinesis, as poor coordination of scapular movements (normally upward rotation and posterior tilting during arm elevation) may contribute to impingement. 1, 5

Diagnostic Imaging

• Initial Imaging: Radiographs are the preferred initial study, including anteroposterior views in internal and external rotation, and an axillary or scapula-Y view. 6

• Advanced Imaging: MRI or ultrasound may be useful for evaluating soft tissue structures:

  • Ultrasound is highly rated for suspected bursitis or rotator cuff evaluation
  • MRI helps evaluate rotator cuff quality, fatty degeneration, and muscle atrophy 6

Pathophysiology

• Mechanical Factors: Traditionally viewed as compression of the rotator cuff tendons beneath the acromion, but now understood as a complex condition involving both intrinsic and extrinsic factors. 7

• Movement Patterns: Altered scapulothoracic motions and positions resulting from coupled interactions between sternoclavicular and acromioclavicular joints contribute to impingement. 5

• Injury Mechanism: In throwers, repetitive eccentric stress on the supraspinatus, external rotators, and scapular stabilizers leads to fatigue and injury. 1

• Predisposing Factors: Weakened posterior shoulder musculature combined with overdeveloped anterior musculature can lead to injury, especially in throwing athletes. 1

Treatment Approach

Conservative Management (First-Line)

• Rest: Avoid activities that worsen pain while preventing complete immobilization to avoid muscular atrophy. 6

• Physical Therapy:

  • Rotator cuff and scapular stabilizer strengthening
  • Gentle stretching and mobilization techniques focusing on external rotation and abduction
  • Gradual increase in active range of motion exercises 1, 6

• Medications:

  • Acetaminophen as a safer first-line option
  • NSAIDs for both pain relief and anti-inflammatory effects (unless contraindicated)
  • Consider topical NSAIDs for fewer systemic side effects 6

• Ice Therapy: Apply ice through a wet towel for 10-minute periods to reduce pain and swelling. 6

Interventional Management

• Injections: Intra-articular corticosteroid injections can be used for significant pain. 6

Surgical Management

• Indications: Consider surgical referral if conservative management fails after 3-6 months. 6

• Options: Arthroscopic subacromial decompression for impingement, rotator cuff repair, or shoulder arthroplasty for advanced cases. 6

Prognosis

• Recovery Rate: Approximately 80% of patients recover completely within 3-6 months with appropriate conservative treatment. 6

• Risk Factors for Poor Outcomes: Older age, left hemiplegia (in stroke patients), early complaints of pain, and reduced proprioception. 1

Special Considerations

• Age-Related Factors: Patients over 50 have higher rates of full-thickness rotator cuff tears, which can impact outcomes. 6

• Post-Stroke: In hemiplegic patients, shoulder pain is multifactorial and associated with shoulder tissue injury, abnormal joint mechanics, and central nociceptive hypersensitivity. 1

• Cancer Patients: Breast cancer patients are at increased risk for both shoulder impingement and frozen shoulder due to treatment-related shoulder morbidity. 6