Internal impingement of the shoulder

Area of Science:

• Orthopedics
• Sports Medicine
• Biomechanics

Background:

• Internal impingement was previously considered a cause of dead arm syndrome in athletes.
• New evidence suggests internal impingement is a normal protective mechanism against excessive shoulder rotation.

Purpose of the Study:

• To clarify the role of internal impingement in dead arm syndrome.
• To differentiate between pathologic and non-pathologic causes of dead arm syndrome.
• To guide appropriate treatment strategies for throwing athletes.

Main Methods:

• Literature review and analysis of biomechanical principles related to shoulder rotation.
• Clinical correlation of symptoms with underlying pathologies.
• Evaluation of treatment outcomes for different causes of dead arm syndrome.

Main Results:

• Internal impingement is a natural restraint, not a cause of dead arm syndrome.
• Pathologic loss of internal impingement allows excessive rotation, leading to rotator cuff failure.
• Superior labrum anterior and posterior (SLAP) lesions and SICK scapula syndrome (scapular dyskinesis) are identified as primary causes.
• SLAP lesions often require arthroscopic repair; scapular dyskinesis is treatable with rehabilitation.

Conclusions:

• Dead arm syndrome in throwing athletes is primarily caused by SLAP lesions or scapular dyskinesis.
• Loss of internal impingement function is the pathologic event, not impingement itself.
• Open anterior stabilization surgery is contraindicated for dead arm syndrome; targeted treatments are recommended.