What are the causes of pain in internal rotation of the arm?

Causes of Pain with Internal Rotation of the Arm

Pain with internal rotation of the arm most commonly indicates subscapularis tendon pathology, posterior capsular contracture, or internal impingement syndrome, with the specific cause determined by patient age, activity level, and associated movement restrictions.

Primary Pathologic Mechanisms

Rotator Cuff Pathology (Most Common)

• Pain with internal rotation and extension (arm behind back) specifically implicates the subscapularis tendon and posterior rotator cuff structures, which control and stabilize these movements 1
• Rotator cuff injuries result from repetitive eccentric stress on the supraspinatus, external rotators, and scapular stabilizers, leading to undersurface tears from overuse 1
• Focal weakness with decreased range of motion during abduction with external or internal rotation is the hallmark physical examination finding 2
• The mechanism involves repetitive eccentric loading during the deceleration phase of overhead activities, causing progressive tendon degeneration 2

Internal Impingement Syndrome

• Internal impingement occurs when the supraspinatus tendon contacts the posterior-superior glenoid rim with the shoulder in 90 degrees of abduction and maximum external rotation 3, 4
• This pathologic contact leads to articular-sided rotator cuff tears and posterosuperior labral lesions, particularly in overhead athletes 4
• The condition is characterized by excessive or repetitive contact of the greater tuberosity with the posterosuperior glenoid during abduction and external rotation, causing pain during internal rotation as the damaged structures are compressed 4
• Internal impingement can occur in a wide spectrum of shoulder disease, not limited to throwing athletes, with 85% of patients demonstrating contact at an average of 95 degrees of abduction and 74 degrees of external rotation 3

Posterior Capsular Contracture

• Posterior capsular contracture presents with restricted internal rotation and reproduction of pain during internal rotation movements 5
• The condition causes increased anterosuperior translation of the humeral head with forward flexion, mimicking impingement syndrome but distinguished by restricted range of motion 5
• In throwing athletes, repetitive forces on the posteroinferior capsule cause posteroinferior capsular hypertrophy and limited internal rotation, potentially leading to superior labrum anteroposterior (SLAP) lesions and rotator cuff tears 5

Age-Specific Considerations

Skeletally Immature Athletes (Under 18 Years)

• In adolescent athletes, the opposing forces of excessive external rotation moment of the distal humerus and increased internal rotation torque of the proximal humerus can lead to proximal humeral physis injury 2
• The epiphyseal plates remain open until late teens (proximal humerus: 17-18 years; glenoid: 16-18 years) and are weaker than surrounding joint capsules and ligaments 2, 6
• Maximum velocity of shoulder internal rotation can approach 7000° per second during throwing, creating shear forces that lead to physeal or labral injury 2
• Proximal humeral epiphysiolysis (Little League shoulder) results from repetitive stress compromising the physis in skeletally immature pitchers 2

Adults Over 35-40 Years

• Rotator cuff disease and degenerative changes predominate as the primary causes of pain with internal rotation 1
• Impingement of the rotator cuff muscles becomes more common with overuse in mature athletes 2

Secondary Impingement Syndrome

• Secondary impingement occurs when weakness in the rotator cuff muscles combined with ligamentous laxity prevents the humeral head from staying centered in the glenoid fossa during arm motion 2, 6, 7
• Pain is located in the anterior or anterolateral aspect of the shoulder and worsens with overhead activities 2, 7
• This condition is more common in younger throwers and results from rotator cuff weakness rather than structural anatomic abnormalities 2, 6
• Weakened posterior shoulder musculature combined with overdeveloped anterior musculature creates pathologic biomechanics during arm deceleration 2, 6

Underlying Biomechanical Factors

Scapular Dyskinesis

• Poor coordination of scapular movements during arm elevation is a primary contributor to shoulder pathology, with the scapula failing to properly rotate upward and tilt posteriorly during overhead movements 6, 7
• Scapular dyskinesis contributes significantly to rotator cuff injury and must be assessed, as poor scapular coordination may be both cause and effect of underlying pathology 1

Glenohumeral Instability

• Chronic anterior instability can cause impingement of the rotator cuff, particularly in athletes engaged in overhead motion with abduction/external rotation 8
• Varying degrees of glenohumeral instability, posterior capsular contracture, and scapular dyskinesis play a role in developing symptomatic internal impingement 4
• In 90% of athletes with chronic anterior or multidirectional instability causing impingement syndrome, the athlete is unaware of the underlying instability 8

Critical Diagnostic Distinctions

Physical Examination Findings

• Hawkins' test (92% sensitive, 25% specific) and Neer's test (88% sensitive, 33% specific) help identify impingement pathology 1, 7
• Assessment for scapular dyskinesis during active arm elevation and evaluation of rotator cuff strength, particularly external rotation compared to contralateral side, are essential 6
• Restricted passive internal rotation with pain reproduction suggests posterior capsular contracture rather than pure rotator cuff pathology 5

Imaging Recommendations

• Plain radiographs (AP, Grashey, axillary, scapular Y projections) are the initial imaging modality to exclude fractures and bony abnormalities 1
• MRI without contrast is the preferred imaging for rotator cuff disorders in patients over 35 years with suspected tendinopathy or tears, with 90% sensitivity and 80% specificity 1, 6
• Ultrasound with appropriate expertise is equivalent to MRI for rotator cuff evaluation (85% sensitivity, 90% specificity) and allows dynamic assessment during arm movement 1, 6

Common Pitfalls to Avoid

• Do not overlook scapular dyskinesis, as this primary contributor must be addressed in treatment 7
• Do not assume absence of instability in athletes with impingement symptoms, as 90% are unaware of underlying instability 8
• In throwing athletes, do not miss posterior capsular contracture, which may be the initial pathologic event leading to SLAP lesions and rotator cuff tears 5
• In adolescents, do not attribute all shoulder pain to soft tissue injury without considering physeal injury, particularly with high pitch counts (>75 pitches doubles injury risk) 2