Understanding shoulder pseudoparalysis: Part I: Definition to diagnosis

Area of Science:

• Orthopedics
• Biomechanics
• Shoulder Surgery

Background:

• Variable definitions of pseudoparalysis exist in literature.
• Recent studies advocate for grading loss of force couple balance and using specific terminology.
• Pain must be excluded as a cause of functional loss.

Purpose of the Study:

• To define and grade pseudoparalysis based on rotator cuff muscle function.
• To identify key muscle-tendon units critical for shoulder force couple balance.
• To emphasize the importance of preserving specific rotator cuff muscles to prevent pseudoparalysis.

Main Methods:

• Review of systematic reviews and biomechanical studies.
• Analysis of muscle-tendon units involved in shoulder force couple balance.
• Clinical assessment of active range of motion (forward elevation, external rotation, internal rotation).

Main Results:

• Loss of three out of five muscle-tendon units (including upper and lower subscapularis) predicts pseudoparalysis.
• The 'Shoulder equator concept' identifies pseudoparalysis with loss of all three posterior, superior, or anterior muscle-tendon units.
• Lower subscapularis and teres minor are identified as key players in maintaining force couple balance.

Conclusions:

• Precise definition and grading of pseudoparalysis are essential, focusing on force couple balance.
• Preventing tears in the subscapularis and posterior rotator cuff is vital for maintaining shoulder function.
• Clinical assessment of active motion, alongside patient factors, aids diagnosis and treatment planning for pseudoparalysis.