Internal impingement, also called posterior-superior glenoid impingement, is a condition specific to overhead throwing athletes in which the rotator cuff tendons contact the posterior-superior rim of the glenoid during the late cocking phase of throwing. The resulting friction and compression produce characteristic injury patterns to the labrum and the undersurface of the rotator cuff. Unlike standard subacromial impingement, internal impingement occurs inside the joint and affects a narrow athletic population.
What Is Internal Impingement?
When the arm is cocked back to throw, the shoulder reaches extremes of abduction and external rotation. In that position, the undersurface of the rotator cuff (particularly the supraspinatus and infraspinatus) comes into contact with the posterior-superior rim of the glenoid and the adjacent labrum. Normal shoulders tolerate this contact without injury. Repetitive throwing at high velocity, particularly when combined with acquired laxity of the anterior capsule, creates injurious contact that gradually damages the tendon undersurface, the posterior-superior labrum, and the cartilage of the posterior glenoid.
Internal impingement is a companion to two adaptive changes in throwers:
- Acquired anterior capsular laxity from repeated stretching during the cocking motion
- Glenohumeral internal rotation deficit (GIRD) from posterior capsule tightness
These adaptations allow the thrower to generate high shoulder external rotation and velocity, but they also shift the humeral head anteriorly during cocking, amplifying the posterior-superior contact and damage.
Causes and Risk Factors
- Overhead throwing sports (baseball, softball, javelin, water polo)
- Repetitive high-velocity throwing, particularly without adequate rest periods
- Posterior capsule tightness (GIRD)
- Anterior capsular laxity from chronic throwing
- Improper throwing mechanics, especially those that load the shoulder in late cocking
Symptoms
- Posterior shoulder pain, specifically during the late cocking phase of throwing
- Loss of velocity or command
- Pain reproduced at specific points in the throwing motion rather than at rest
- Dead arm sensation during throwing
- Resolution of pain during rest from throwing, with recurrence when throwing resumes
Diagnosis
Dr. Chudik’s evaluation includes the throwing history, delivery mechanics, and the specific pain pattern through the throwing motion. Physical examination documents shoulder range of motion with specific measurement of internal and external rotation to identify GIRD. Provocative tests that load the shoulder in the cocking position reproduce symptoms. MRI arthrogram is the imaging study of choice and characterizes undersurface rotator cuff fraying, posterior-superior labral tears, and posterior glenoid cartilage wear. The Westmont office has on-site high-field MRI.
Treatment
Non-surgical treatment is the first line and is successful for most throwers, particularly when addressed early. It includes:
- Rest from throwing
- A targeted physical therapy program focused on posterior capsule stretching (sleeper stretch, cross-body stretch) and periscapular strengthening
- Correction of throwing mechanics under coaching review
- Gradual throwing progression before full return to competition
Surgery is considered when non-surgical treatment fails and a significant labral or rotator cuff tear is present. Dr. Chudik performs arthroscopic debridement of the undersurface cuff fraying and labral repair when an unstable tear is identified. Posterior capsule release is occasionally added for refractory GIRD.
Recovery and Outcomes
Recovery with non-surgical treatment typically requires three to six months before full return to competitive throwing. Throwing is reintroduced through a graduated long-toss program under supervision.
Recovery after arthroscopic treatment depends on whether labral repair was performed. For debridement alone, return to competitive throwing is typically four to six months. For labral repair, recovery is longer, typically six to nine months with a graduated return-to-throw program.
Return-to-throw outcomes are less predictable than for many other shoulder conditions in throwers. Addressing the underlying laxity and mechanics is the most important predictor of durable return.
When to See Dr. Chudik
Schedule an evaluation if you are a thrower with posterior shoulder pain during the cocking phase, if velocity or command has dropped unexpectedly, or if prior treatment has not resolved symptoms. Call 630-324-0402 or request an appointment online.