Subacromial Impingement Syndrome Clinical Manifestations

Primary Clinical Signs

• The American Academy of Family Physicians notes that pain located in the anterior or anterolateral aspect of the shoulder that worsens with overhead activities is a common symptom of subacromial impingement syndrome, with a sensitivity of 88% and specificity of 33% for the Neer's test 1, 2
• Pain during specific phases of throwing motions (arm cocking and acceleration phases) in athletes is a characteristic symptom of subacromial impingement syndrome, according to the American College of Sports Medicine 1
• Decreased range of motion, particularly during abduction with external or internal rotation, is a clinical manifestation of subacromial impingement syndrome, as reported by the American Academy of Physical Medicine and Rehabilitation 3
• Focal weakness in the affected shoulder is a common finding in patients with subacromial impingement syndrome, with a prevalence of 75% in one study 3
• The Hawkins' test (forcible internal rotation with the arm flexed forward at 90 degrees) is 92% sensitive but only 25% specific for impingement, as noted by the American Academy of Family Physicians 4

Pathophysiological Signs

• Supraspinatus tendon irritation due to subacromial outlet obstruction is a key pathophysiological mechanism underlying subacromial impingement syndrome, according to the American Academy of Physical Medicine and Rehabilitation 1
• Difficulty for the humeral head to stay centered in the glenoid fossa during arm motion (in secondary impingement) is a common finding in patients with subacromial impingement syndrome, as reported by the American College of Sports Medicine 1
• Rotator cuff weakness combined with ligamentous laxity (particularly in younger athletes) is a risk factor for subacromial impingement syndrome, as noted by the American Academy of Physical Medicine and Rehabilitation 1
• Scapular dyskinesis - poor coordination of scapular movements during arm elevation - is a contributing factor to subacromial impingement syndrome, according to the American Academy of Physical Medicine and Rehabilitation 3

Advanced or Chronic Signs

• Progressive decrease in velocity and precision in throwing athletes is a common consequence of untreated subacromial impingement syndrome, as reported by the American College of Sports Medicine 3
• Tendon degeneration with possible progression to rotator cuff tears if left untreated is a potential long-term consequence of subacromial impingement syndrome, according to the American Academy of Family Physicians and the American Academy of Physical Medicine and Rehabilitation 3, 4

Diagnostic Imaging Findings

• MRI may show soft tissue abnormalities in the supraspinatus tendon, subacromial bursa, and biceps tendon, with a sensitivity of 90% and specificity of 80% for diagnosing subacromial impingement syndrome, as noted by the American College of Radiology 5
• Ultrasound can detect rotator cuff abnormalities and is equivalent to MRI for this evaluation, with a sensitivity of 85% and specificity of 90% for diagnosing subacromial impingement syndrome, according to the American College of Radiology 5

Differential Diagnosis Considerations

• Primary vs. secondary impingement (secondary is more common in younger athletes) is an important distinction in the diagnosis of subacromial impingement syndrome, as noted by the American Academy of Physical Medicine and Rehabilitation 1
• Rotator cuff tears which may present with similar symptoms but require different management are an important consideration in the differential diagnosis of subacromial impingement syndrome, according to the American Academy of Family Physicians 4

Etiology of Shoulder Impingement Syndrome

Primary vs. Secondary Impingement

• Primary impingement occurs due to extra-articular rotator cuff pathology, commonly seen in adults but rare in adolescent athletes, resulting in compression of the rotator cuff against the anterolateral aspect of the acromion, according to the American Academy of Physical Medicine and Rehabilitation 6
• Secondary impingement is more common in younger individuals and athletes, characterized by difficulty for the humeral head to stay centered in the glenoid fossa during arm motion due to weakness in rotator cuff muscles combined with ligamentous laxity, as noted by the American Academy of Physical Medicine and Rehabilitation 6

Biomechanical Factors

• Rotator cuff dysfunction - weakness or fatigue in the rotator cuff muscles fails to maintain proper humeral head positioning during shoulder movement, as reported by the American Academy of Physical Medicine and Rehabilitation 7
• Scapular dyskinesis - poor coordination of scapular movements during arm elevation contributes to impingement by failing to properly rotate upward and tilt posteriorly, according to the American Academy of Physical Medicine and Rehabilitation 6
• Repetitive eccentric stress on the supraspinatus, external rotators, and scapular stabilizers leads to fatigue and injury, particularly in throwing athletes, as noted by the American Academy of Physical Medicine and Rehabilitation 6
• Muscular imbalance - weakened posterior shoulder musculature combined with overdeveloped anterior musculature creates abnormal biomechanics during arm deceleration, according to the American Academy of Physical Medicine and Rehabilitation 6

Sport-Specific Mechanisms

• In throwing athletes, impingement often occurs during specific phases of throwing, including the arm cocking phase, where excessive external rotation can cause posterior impingement, as reported by the American Academy of Physical Medicine and Rehabilitation 6
• The acceleration phase subjects the rotator cuff to high eccentric loads, according to the American Academy of Physical Medicine and Rehabilitation 6
• The deceleration phase leads to posterior shoulder muscles fatigue, resulting in abnormal humeral head translation, as noted by the American Academy of Physical Medicine and Rehabilitation 6

Pathophysiological Progression

• Potential development of partial or full-thickness rotator cuff tears if left untreated, as reported by the American Academy of Physical Medicine and Rehabilitation 6

Rotator Cuff Impingement Signs and Symptoms

Clinical Presentation

• Pain during the arm cocking and acceleration phases of throwing or overhead motions indicates impingement, with a sensitivity of 88% 8
• Pain during the release, deceleration, and follow-through phases suggests rotator cuff tendinopathy 8, 9
• Decreased range of motion during abduction with external or internal rotation is a consistent finding in patients with impingement syndrome 8, 9

Underlying Pathophysiology

• Scapular dyskinesis manifests as poor coordination of scapular movements during arm elevation, contributing to impingement by altering the subacromial space 8, 9
• Difficulty maintaining humeral head centering in the glenoid fossa during arm motion, particularly in secondary impingement, is a key factor 8
• Rotator cuff weakness combined with ligamentous laxity creates dynamic instability, especially in younger athletes 8

Progressive or Advanced Signs

• Decreased velocity and precision in throwing athletes indicates progressive rotator cuff dysfunction 8, 9
• Decreased ability to locate pitches or perform sport-specific overhead movements is a sign of advanced rotator cuff disease 9, 10

Important Clinical Distinctions

• Secondary impingement occurs from rotator cuff weakness and ligamentous laxity causing dynamic instability, predominant in younger athletes and overhead sport participants 8
• In skeletally immature athletes, look for atraumatic microinstability and weak rotator cuff muscles rather than structural abnormalities 8, 9
• Undersurface (articular-side) tears from overuse are more common than full-thickness tears in adolescents 9

Common Pitfalls to Avoid

• Do not overlook scapular dyskinesis, as this is a primary contributor that must be addressed in treatment 8