Shoulder Posterior Impingement Syndrome

Posterior shoulder impingement syndrome is a common yet often misunderstood cause of shoulder pain in overhead athletes—especially baseball pitchers. Unlike subacromial impingement, which occurs in the front of the shoulder, posterior impingement arises from the shoulder joint caspule and/or rotator cuff tendon pinching in-between the ball and socket of the shouldr joint, during the late arm-cocking/layback phase of throwing. Early recognition, targeted rehab, and biomechanical optimization are key to recovery and long-term shoulder health.

What Is Posterior Shoulder Impingement?

Posterior shoulder impingement occurs when the undersurface of the rotator cuff (particularly the supraspinatus and infraspinatus tendons) is pinched between the greater tuberosity of the humerus and the posterior-superior glenoid rim during the late cocking phase of throwing.

Contributing mechanical factors include:

• Excessive external rotation
• Anterior shoulder laxity
• Posterior capsule tightness
• Scapular dyskinesis
• Poor kinetic chain control

Over time, these stresses can lead to partial-thickness rotator cuff tears, posterior labral fraying, and persistent pain with high-velocity throwing.

Signs and Symptoms

Key clinical signs include:

• Posterior/back of the shoulder or deep shoulder pain during or after throwing
• Pain localized to the late cocking or early acceleration phase
• Loss of velocity or “dead arm” symptoms
• Discomfort with external rotation stretching
• Possible clicking, catching, or posterior tightness
• Tenderness with posterior joint line palpation

Importantly, range of motion may appear full, but there is often asymmetrical internal rotation loss (GIRD) and altered scapular control.

Frequency and Risk in Baseball

Posterior impingement accounts for a significant portion of shoulder pain in overhead athletes, particularly in collegiate and professional pitchers. Studies suggest that:

• Up to 40% of high-level throwers will experience posterior shoulder symptoms during their career (Jobe et al., 1989).
• Athletes with GIRD (glenohumeral internal rotation deficit) are at higher risk of developing internal impingement (Wilk et al., 2011).
• The condition often presents alongside rotator cuff undersurface fraying or labral wear on imaging.

It's considered a "functional impingement", meaning it's due to mechanical stresses unique to throwing, rather than a "structural impingement" like a bone spur.

Diagnosis and Imaging

Diagnosis is clinical but often confirmed with imaging:

• Posterior impingement test: Pain elicited in abduction and maximal external rotation
• Assessment of GIRD and total shoulder rotation
• Scapular motion evaluation for dyskinesis (e.g., SICK scapula)
• MRI may show posterior labral fraying, undersurface cuff tears, or joint space narrowing

Dynamic ultrasound is less commonly used but can assist in assessing infraspinatus and teres minor involvement.

Treatment Options

Non-Surgical Management Is First-Line:

Phase 1: Pain Reduction & Motion Restoration (0–2 Weeks)

• Cessation of throwing
• Modalities for pain and inflammation
• Initiate posterior capsule stretching (e.g., sleeper stretch, cross-body stretch)
• Emphasize pain-free ROM
  

Phase 2: Addressing Mobility and Strength Deficits (2–6 Weeks)

• Posterior shoulder and thoracic mobility focus
• Restore glenohumeral internal rotation
• Begin rotator cuff isometrics and closed-chain scapular stability
• Emphasize scapular upward rotation and posterior tilt control
  

Phase 3: Dynamic Control and Kinetic Chain Integration (6–10 Weeks)

• Advance to eccentric cuff and scapular strengthening
  
• Integrate core and hip stability to improve force transmission
  
• Incorporate medicine ball rotational drills
  

Phase 4: Return-to-Throwing Progression (10–16+ Weeks)

• Interval throwing program, progressing intensity and distance
  
• Focus on mechanical refinement (avoid excessive layback, early trunk rotation)
  
• Continue pre-throw mobility and scapular activation routine

Return to Sport Timelines

• Mild to moderate cases (no labral involvement): 8–12 weeks
  With partial cuff or labral fraying: 12–16+ weeks
  
• Surgical cases (rare): 6–9 months

A 2010 study by Meister et al. reported that 85–90% of pitchers returned to prior performance levels with conservative treatment and structured rehab.

Surgical intervention (e.g., posterior labral repair or rotator cuff débridement) is reserved for refractory cases that fail rehab after 3–4 months.

Risk of Recurrence and Prevention

Reinjury risk is higher in throwers who:

• Fail to address GIRD and posterior tightness
• Do not correct scapular mechanics or trunk rotation timing
• Resume throwing without a full interval throwing program
• Long-term monitoring and offseason maintenance are crucial.

Prevention Strategies

• Daily posterior capsule mobility drills
  
• Regular sleeper and cross-body stretches
  
• Emphasize posterior cuff and scapular endurance
  
• Maintain thoracic spine and hip mobility
  
• Preseason and in-season throwing screens to catch early deficits
  
• Integrate scapular control and trunk rotation drills into warm-ups

Summary

Posterior shoulder impingement is a common yet manageable source of pain in throwers. With proper evaluation, targeted rehab, and smart workload management, athletes can recover fully and return to high-performance throwing.

Key to success: "Don’t just treat the shoulder—train the entire system that controls it."

References
1. Jobe FW, et al. (1989). Posterior superior glenoid impingement: A mechanical explanation for posterior shoulder pain in throwing athletes. The American Journal of Sports Medicine, 17(4): 552–558.
2. Wilk KE, et al. (2011). Glenohumeral internal rotation deficits and its relationship to shoulder injuries in the overhead athlete. Journal of Orthopaedic & Sports Physical Therapy, 41(8): 590–598.
3. Meister K, et al. (2010). Rotator cuff and posterior-superior glenoid injuries associated with posterior impingement in baseball players. The American Journal of Sports Medicine, 38(7): 1431–1437.
4. Burkhart SS, Morgan CD, Kibler WB. (2003). The disabled throwing shoulder: Spectrum of pathology Part I: Pathoanatomy and biomechanics. Arthroscopy, 19(4): 404–420.
5. Reinold MM, et al. (2008). Current concepts in the scientific and clinical rationale behind exercises for glenohumeral and scapulothoracic musculature. Journal of Orthopaedic & Sports Physical Therapy, 38(2): 105–117.