Internal impingement of the shoulder

1. High-Yield Summary

Internal impingement of the shoulder represents a distinct pathoanatomic phenomenon in overhead throwing athletes characterized by repetitive, physiologic-turned-pathologic contact between the articular surface of the rotator cuff (posterior supraspinatus and anterior infraspinatus) and the posterosuperior glenoid labrum and rim.

• Core Pathoanatomy: Compression and shear failure of the articular-sided rotator cuff fibers against the posterosuperior glenoid labrum occurring in the extreme late cocking phase of throwing (90 to 110 degrees abduction and maximal external rotation).
• The Essential Driving Cascade: Typically driven by posterior-inferior capsular contracture producing Glenohumeral Internal Rotation Deficit (GIRD > 18 to 20 degrees or total arc deficit > 5 degrees), frequently coexisting with subtle anterior capsular attenuation and scapular dyskinesis (SICK scapula).
• Pathologic Lesion Spectrum: Concomitant undersurface partial-thickness rotator cuff tears (PASTA lesions), posterosuperior labral tearing, Type II superior labral anterior-to-posterior (SLAP) lesions generated by the peel-back mechanism, and posteroinferior glenoid reactive ossification (Bennett lesion).
• Diagnostic Cardinal Benchmark: Posterior shoulder pain provoked during late cocking or the Meister internal impingement test, accompanied by marked loss of internal rotation and positive relocation testing, with pain relief upon posteriorly directed humeral pressure.
• Management Algorithm: Greater than 80% to 90% of athletes achieve complete symptom resolution with targeted nonoperative kinetic chain rehabilitation (posterior capsular stretching, periscapular kinetic stabilization, core pelvic control). Operative intervention is reserved for refractory cases failing 3 to 6 months of structured physical therapy, prioritizing conservative debridement or anatomy-specific repair while avoiding anterior overtightening.

2. Anatomy

Understanding internal impingement requires precise knowledge of the static and dynamic stabilizers of the posterosuperior and posteroinferior glenohumeral capsulolabral complex, as well as adjacent neurovascular corridors.

Capsulolabral Complex and Rotator Cuff Undersurface

The posterosuperior glenoid rim is cushioned by the fibrous glenoid labrum, which deepens the shallow glenoid fossa by approximately 50%. The long head of the biceps tendon originates from the supraglenoid tubercle and superior labrum. Immediately overlying the posterosuperior labrum are the deep, non-capsular articular fibers of the junctional zone between the supraspinatus and infraspinatus tendons. The posterior band of the inferior glenohumeral ligament (PIGHL) forms a hammock-like dynamic sling that tightens during internal rotation and forward elevation. When chronically shortened or hypertrophied, the contracted PIGHL acts as a fulcrum that shifts the glenohumeral contact point posterosuperiorly during arm elevation and abduction.

Neurovascular Corridors and Danger Zones

• Axillary Nerve Corridor: Traverses the quadrilateral space accompanied by the posterior circumflex humeral artery. The nerve courses directly beneath the inferior glenohumeral capsule, lying merely 5 to 7 mm inferior to the 6 o’clock glenoid rim. During arthroscopic capsular release or low posterior portal placement, blind radiofrequency or mechanical resection at the inferior pouch poses catastrophic risk of axillary neurotmesis.
• Suprascapular Nerve Corridor: Enters the infraspinatus fossa by coursing around the lateral border of the scapular spine through the spinoglenoid notch. The nerve lies approximately 1.5 to 2.0 cm medial to the posterosuperior glenoid rim. Deep suture anchor placement, transmural glenoid drilling exceeding 14 mm, or aggressive posterior glenoidplasty medial to the labral attachment jeopardizes the motor innervation to the infraspinatus.
• Musculocutaneous Nerve: Enters the coracobrachialis muscle 3 to 5 cm distal to the coracoid process tip. Retraction during anterior exposure or anterior capsular work must respect this boundary.

Surgical Planes and Intervals

Operative intervention is routinely arthroscopic. In open approaches, the posterior internervous plane resides between the infraspinatus (innervated by the suprascapular nerve) and the teres minor (innervated by the axillary nerve). Anterior exposures utilize the deltopectoral interval between the deltoid (axillary nerve) and pectoralis major (medial and lateral pectoral nerves).

3. Pathogenesis

Internal impingement is a mechanical and biological disease process resulting from repetitive, high-velocity overhead athletic cycles. The modern biomechanical paradigm recognizes a triad of contributing pathomechanisms: physiologic contact, acquired soft-tissue adaptations, and kinetic chain breakdown.

Biomechanical Triad and Kinematic Cascade

• Physiologic vs. Pathologic Contact: In asymptomatic individuals, abducting the shoulder to 90 degrees and externally rotating beyond 90 degrees brings the greater tuberosity and rotator cuff footprint into proximity with the posterosuperior glenoid rim. This contact becomes pathologic when frequency, forces, or translation exceed tissue tolerance.
• Posterior-Inferior Capsular Contracture and GIRD: During repetitive throwing deceleration, massive eccentric tensile distraction loads (exceeding 750 N) are absorbed by the posterior capsule and external rotators. Over time, microtrauma triggers thick fibroblastic scar contracture and thickening of the PIGHL. The contracted posterior capsule acts as a taut tether, preventing normal inferior gliding and forcing the humeral head to translate posterosuperiorly during maximal external rotation.
• Anterior Micro-Instability (The Jobe Mechanism): Repetitive late cocking places extreme tensile stretch on the anterior capsule and anterior band of the inferior glenohumeral ligament (AIGHL). Micro-attenuation of these anterior restraints permits excessive anterior translation of the humeral head, exacerbating the hyper-external rotation envelope and intensifying posterosuperior cuff compression.
• The Peel-Back Phenomenon (The Burkhart Mechanism): As the humeral head rotates into extreme external rotation on a posterosuperiorly shifted pivot, torsional vectors transmitted through the long head of the biceps tendon generate a posterior-to-anterior twisting force. This rotational torque peels the superior labrum medialward off the glenoid margin, producing classic Type II SLAP lesions.
• Rotator Cuff Articular Tensile Undersurface Failure: The articular side of the supraspinatus and infraspinatus has significantly less vascularity and lower tensile yield strength than the bursal side. Repetitive compression against the bony glenoid rim, combined with high shear strains during deceleration, leads to progressive fraying, delamination, and PASTA lesions.

4. Natural History

Internal impingement predominantly affects young, competitive overhead athletes between 15 and 35 years of age, most notably baseball pitchers, javelin throwers, tennis players, volleyball hitters, and competitive swimmers. The clinical trajectory follows a progressive evolutionary continuum if left uncorrected:

• Early Prodromal Phase: Transient post-throwing posterior shoulder soreness, delayed muscle recovery, subtle loss of terminal pitch velocity (2 to 5 mph), and early loss of throwing command. Structural tissue damage is limited to microscopic capsular remodeling and mild labral fraying.
• Established Pathologic Phase: Chronic, focal posterior pain during the cocking phase. Progressive GIRD establishes fixed glenohumeral translation changes. Significant macroscopic partial-thickness articular cuff fraying (Ellman Grade I to II) and unstable superior labral detachment emerge. Athletes experience the “dead arm syndrome” with sharp pain inhibiting maximum throwing velocity.
• Late Chronic Degenerative Phase: High-grade delaminating PASTA lesions (> 50% tendon depth), full Type II SLAP detachments, cortical erosion or subchondral cyst formation at the posterosuperior glenoid rim, and reactive posteroinferior ossification (Bennett lesion). Athletes face complete inability to compete at their prior competitive tier. Untreated cases in older throwing cohorts can eventually progress to full-thickness rotator cuff tears and premature glenohumeral secondary chondral degeneration.

5. Clinical Presentation

Patient History and Cardinal Symptoms

Athletes present with insidious onset of deep posterior shoulder pain localized to the posterosuperior joint line. Symptoms characteristically occur during the late cocking and early acceleration phases of overhead mechanics. Patients frequently report a distinct sensation of heaviness or deadness in the extremity, sudden loss of control, decreased ball velocity, or inability to achieve full follow-through. Unlike external subacromial impingement, pain is absent with arms held at the side and does not typically awaken the patient at night.

Physical Examination & Diagnostic Accuracy

A meticulous clinical examination must evaluate bilateral glenohumeral rotational arcs, provocative impingement maneuvers, capsular laxity, and scapular kinematics.

6. Imaging and Diagnostic Studies

Plain Radiography

A standardized radiographic shoulder trauma and instability series is mandatory, comprising true AP (Grashey view in internal and external rotation), axillary lateral, Stryker notch, and West Point modified axillary views. Key findings include:

• Bennett Lesion: A pathognomonic crescent-shaped extra-articular ossification along the posteroinferior glenoid rim, visualized on Stryker notch or West Point projections, reflecting traction mineralization at the PIGHL attachment.
• Posterosuperior Glenoid Remodeling: Rounding, osteophytic lipping, or focal subchondral sclerosis at the posterosuperior glenoid margin.
• Greater Tuberosity Sclerosis: Reactive subcortical cysts or sclerosis at the posterosuperior aspect of the greater tuberosity footprint.

Magnetic Resonance Imaging (MRI) and MR Arthrography

Magnetic resonance arthrography (MRA) with gadolinium injection represents the definitive diagnostic imaging standard. MRA delivers 90% to 95% sensitivity for subtle capsulolabral and undersurface tendon pathology:

• Articular-Sided Cuff Tears (PASTA): High fluid-signal contrast undermining the deep footprint fibers of the supraspinatus and anterior infraspinatus on T2-weighted fat-suppressed coronal oblique and sagittal images, with intact bursal tissue.
• Posterosuperior Labral Pathology: High-signal linear contrast tracking under the superior and posterior labral attachment from the 11 o’clock to 2 o’clock positions, differentiating true Type II SLAP tears from physiologic sublabral sulci.
• ABER Sequence (Abduction and External Rotation): Placing the patient’s arm overhead in 90 degrees abduction and external rotation during scanning directly visualizes posterosuperior impingement, demonstrating mechanical pinching of the undersurface cuff between the greater tuberosity and posterior glenoid labrum.
• Subchondral Bone Bruising: T2 hyperintensity and T1 hypointensity indicative of microtrabecular edema at the posterosuperior glenoid margin and adjacent greater tuberosity.

7. Classification

Multiple validated staging systems categorize internal impingement based on clinical instability spectrum, arthroscopic tissue lesions, and partial-thickness cuff involvement.

Jobe Classification of Shoulder Impingement in Overhead Athletes

Walch Classification of Posterosuperior Internal Impingement

8. Treatment

Medical & Nonoperative Management (First-Line Protocol)

Nonoperative therapy is the gold standard and primary management line for all throwing athletes presenting with internal impingement, achieving complete symptom resolution in 80% to 90% of cases. Management follows a phased, criterion-based rehabilitation framework:

• Phase 1: Acute Protection and Capsular Normalization (Weeks 0 to 4): Complete cessation of throwing and aggressive overhead ballistic activity. Judicious short-term oral nonsteroidal anti-inflammatory therapy (NSAIDs) or diagnostic fluoroscopy-guided glenohumeral corticosteroid injection. Immediate institution of isolated posterior capsular stretching:
  The Sleeper Stretch: Side-lying on the affected shoulder with 90 degrees shoulder and elbow flexion; passive internal rotation applied by contralateral hand with scapula locked against rib cage.
  Cross-Body Horizontal Adduction: Supine cross-body adduction with manual scapular stabilization. Goal is reducing GIRD to less than 15 degrees difference.
• Phase 2: Dynamic Periscapular and Rotator Cuff Strengthening (Weeks 4 to 8): Progressive resistance training emphasizing the dynamic posterior stabilizers (infraspinatus, teres minor) and scapular retractors/upward rotators (serratus anterior, lower trapezius, rhomboids). Neuromuscular rhythmic stabilization exercises in the 90/90 position. Kinetic chain integration focusing on lumbopelvic stability, hip mobility, and thoracic spine rotational extension.
• Phase 3: Plyometric Training and Interval Throwing Program (Weeks 8 to 16): High-velocity plyometric ball deceleration training. Initiation of a structured interval throwing program (e.g., graduated distance from 45 feet to 60, 90, 120, and 180 feet on flat ground) once pain-free, symmetric total rotational arc is achieved, and scapular dyskinesis is resolved.

Operative Management

Surgical intervention is indicated exclusively after failure of 3 to 6 months of disciplined, structured kinetic chain rehabilitation. The primary objectives are decompression of mechanical impingement, restoration of capsulolabral stability, and anatomical preservation of the rotator cuff footprint without inducing motion-limiting stiffness.

• Arthroscopic Diagnostic Evaluation and Debridement: Complete diagnostic arthroscopy from standard posterior and anterior portals. Dynamic visualization of internal impingement in 90 degrees abduction and maximal external rotation. Frayed labral edges and undersurface cuff tears involving less than 50% tendon depth are addressed with mechanical shaver debridement alone, which avoids footprint scarring and preserves terminal throwing external rotation.
• Type II SLAP Repair: Indicated when unstable superior labral detachment is confirmed by positive peel-back maneuver. Suture anchors are placed on the superior glenoid tubercle adjacent to the articular margin. Anchors must be situated strictly posterior to the 12 o’clock position to avoid tethering the anterior superior labrum, which causes devastating loss of throwing velocity.
• High-Grade Partial Cuff Tear (PASTA) Management: Tears exceeding 50% tendon depth require individualized decision-making. In recreational athletes, transtendinous repair or completion and anatomical repair with knotless anchors is standard. In high-level baseball pitchers, aggressive debridement is favored over formal suture repair whenever possible due to high rates of persistent postoperative stiffness and inability to regain pre-injury throwing velocity.
• Posterior-Inferior Capsulotomy / Release: Reserved for athletes with recalcitrant posterior capsular contracture and severe persistent GIRD (> 25 to 30 degrees) failing prolonged physical therapy. A radiofrequency or arthroscopic scissors release of the PIGHL is performed 5 mm off the posterior glenoid rim from 7 to 9 o’clock, with strict vigilance to avoid the axillary nerve at the 6 o’clock margin.
• Arthroscopic Posterior Glenoidplasty (Lévigne Procedure): Indicated for severe posterosuperior glenoid osteophyte formation or excessive posterior rim prominence causing refractory mechanical impingement. A motorized burr is used to resect 2 to 4 mm of the prominent posterosuperior bony glenoid rim, preserving the labral attachment and staying within 10 mm of the rim to prevent injury to the suprascapular nerve.
• Anterior Capsular Plication: Highly controversial. Should only be performed if unambiguous anterior pathologic laxity is documented. Aggressive anterior plication or thermal capsulorrhaphy is strictly contraindicated in overhead throwers, as loss of just 5 degrees of external rotation terminates competitive pitching mechanics.

Explicit Indications and Contraindications

• Surgical Indications: Documented structural pathology on MRA (unstable Type II SLAP, PASTA tear > 50%, or Bennett lesion); failure of >= 3 to 6 months of supervised rehabilitation; persistent posterior pain during cocking phase preventing athletic performance; refractory GIRD with capsular contracture unresponsive to manual therapy.
• Contraindications: Uncorrected scapular dyskinesis without prior kinetic chain rehabilitation; asymptomatic posterosuperior labral fraying or asymptomatic Bennett lesion (radiographic incidental finding); active glenohumeral infection; lack of athlete compliance with prolonged postoperative rehabilitation.

9. Outcome

Clinical success in internal impingement is measured by validated patient-reported outcome measures (PROMs) including the American Shoulder and Elbow Surgeons (ASES) score, the Kerlan-Jobe Orthopaedic Clinic (KJOC) overhead athlete shoulder and elbow score, and rate of return to prior competitive level.

• Nonoperative Treatment Success: Multiple long-term cohort series demonstrate that 80% to 92% of overhead throwing athletes with internal impingement and GIRD successfully return to competition following targeted posterior capsular stretching and kinetic chain correction without requiring surgery.
• Operative Outcomes and Return-to-Play: Contemporary systematic reviews indicate an overall return-to-sport rate of 78.4% across competitive overhead athletes undergoing arthroscopic intervention. However, only 63.2% return to their exact pre-injury competitive performance tier.
• Debridement vs. Suture Repair in Elite Throwers: Elite pitchers undergoing isolated arthroscopic debridement of partial-thickness cuff tears achieve higher return-to-play rates (75% to 82%) compared to those undergoing formal anchor repair (45% to 55%), due to loss of terminal external rotation compliance following suture tendon fixation.
• Postoperative Timeline: Athletes undergoing isolated debridement begin throwing at 8 to 12 weeks with full competitive return at 4 to 6 months. Patients undergoing Type II SLAP repair or partial cuff repair require 6 to 9 months before initiation of full-velocity throwing, with peak recovery taking 9 to 12 months.

10. Complications

Surgical management of internal impingement carries significant risks of neurovascular damage and athletic performance loss, categorized chronologically:

11. Pearls and Pitfalls

Mastery of internal impingement demands precise diagnostic acumen and conservative surgical restraint to safeguard athletic careers.

• Pearl 1: Total Arc of Motion Principle: Never evaluate internal rotation in isolation. An overhead throwing shoulder typically exhibits an acquired external rotation gain (ERG) of 10 to 15 degrees due to humeral retroversion. As long as total rotational arc (ER + IR) is symmetric within 5 degrees of the contralateral shoulder, isolated IR loss is physiologic. Only when total arc is deficient > 5 degrees is true pathologic GIRD present.
• Pearl 2: Scapular Dyskinesis is the Common Denominator: Almost all throwers with internal impingement display protracted, anteriorly tilted scapulae (SICK scapula). Restoring serratus anterior and lower trapezius force couples opens the posterosuperior clearance, preventing cuff-labrum entrapment.
• Pearl 3: The 12 O’Clock Anchor Boundary: When repairing a Type II SLAP lesion in an overhead thrower, never place a suture anchor anterior to the 12 o’clock position (biceps tendon). Anchoring the anterior labrum eliminates physiologic external rotation compliance and predictably causes severe loss of throwing velocity.
• Pitfall 1: Subacromial Decompression Misadventure: Performing an acromioplasty or subacromial bursectomy for internal impingement is a catastrophic diagnostic error. The pathology is intra-articular; cutting the coracoacromial ligament induces anterior instability and accelerates glenohumeral decompensation.
• Pitfall 2: Overtightening the Anterior Capsule: Interpreting physiological throwing laxity as pathological anterior instability and performing aggressive capsular plication or thermal shrinkage permanently ends competitive throwing careers by obliterating external rotation.
• Pitfall 3: Indiscriminate Cuff Suture Repair: Suture repair of partial undersurface cuff tears (< 50%) in high-velocity pitchers creates a stiff, inelastic collagen footprint scar. Conservative debridement of loose flaps yields far superior return-to-sport rates.

12. Controversy

Contemporary sports medicine debates surrounding internal impingement center on three pivotal dilemmas:

• Primary Instability vs. Primary Capsular Contracture: Jobe’s school of thought posited that primary anterior micro-laxity allows excessive anterior humeral translation, driving secondary internal impingement. Conversely, Burkhart’s school proved that posteroinferior capsular contracture shifts the glenohumeral pivot posterosuperiorly, generating peel-back forces and internal impingement independent of anterior laxity. Current consensus recognizes both phenotypes, with capsular contracture being significantly more prevalent in baseball pitchers.
• Management of Type II SLAP Lesions in Elite Throwers: Suture anchor repair of SLAP tears in professional pitchers yields poor return-to-prior-performance rates (often less than 50%). Consequently, surgeons increasingly debate isolated biceps tenodesis versus simple labral debridement, with tenodesis gaining traction in older throwers (> 25 years old) to eliminate the peel-back lever arm while preserving capsular compliance.
• Threshold for PASTA Repair: While traditional guidelines recommend repair for partial tears exceeding 50% tendon depth, in elite throwing athletes, repairing high-grade partial tears frequently leads to career termination due to loss of terminal external rotation. A growing contingent of shoulder specialists advocates for thorough debridement alone even in 50% to 70% partial tears, reserving formal repair as a salvage procedure.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Challoumas D, Loh C, Ibekwe N et al. Surgical management of internal impingement in overhead athletes: a systematic review. Clin Shoulder Elb. 2026. doi:10.5397/cise.2025.01123 [Level I: Systematic Review / Meta-Analysis]
• Walch G, Boileau P, Noel E, Donell ST. Impingement of the deep surface of the supraspinatus tendon on the posterosuperior glenoid rim: An arthroscopic study. J Shoulder Elbow Surg. 1992. doi:10.1016/s1058-2746(09)80065-7 [Level IV: Seminal Diagnostic & Arthroscopic Cohort Study]
• Burkhart SS, Morgan CD, Kibler WB. The disabled throwing shoulder: spectrum of pathology Part I: pathoanatomy and biomechanics. Arthroscopy. 2003. doi:10.1053/jars.2003.50128 [Level V: Seminal Biomechanical & Pathoanatomic Investigation]
• Corpus KT, Camp CL, Dines DM et al. Evaluation and treatment of internal impingement of the shoulder in overhead athletes. World J Orthop. 2016. doi:10.5312/wjo.v7.i12.776 [Level IV: Clinical Review & Treatment Algorithm]
• Lévigne C, Garret J, Grosclaude S et al. Surgical technique arthroscopic posterior glenoidplasty for posterosuperior glenoid impingement in throwing athletes. Clin Orthop Relat Res. 2012. doi:10.1007/s11999-012-2294-7 [Level IV: Prospective Clinical Case Series]

15. Master Class Pro-Tip

When evaluating an overhead throwing athlete presenting with posterosuperior shoulder pain, resist the reflex to operate on MRI findings of partial cuff fraying or labral cleavage. The key to preserving a throwing career lies in objective measurement of the Total Arc of Motion and rigorous rehabilitation of the kinetic chain. Ensure the patient performs daily dedicated sleeper stretches and cross-body adduction with strict manual scapular stabilization to eradicate Glenohumeral Internal Rotation Deficit (GIRD). If diagnostic arthroscopy becomes unavoidable after exhaustive nonoperative failure, adopt a minimalist surgical philosophy: debride the unstable articular cuff flaps smoothly without penetrating the intact bursal footprint, place no more than one or two knotless anchors for a Type II SLAP tear strictly posterior to the biceps anchor, and never perform anterior capsular plication or subacromial acromioplasty. Preserving capsular compliance and terminal external rotation is paramount: in throwing athletes, an extra millimeter of stability gained at the expense of motion is the end of the career.

Master Class Surgical Pearl: Managing Internal Impingement in Overhead Athletes