Chronic Pseudoparalysis Needs to Be Distinguished From Pseudoparesis: A Structural and Biomechanical Analysis

Area of Science:

• Orthopedic Surgery
• Musculoskeletal Imaging
• Biomechanics

Background:

• Chronic pseudoparalysis is defined by limited arm elevation (<90°) with normal passive motion and no neurological deficits.
• The current definition of chronic pseudoparalysis may require refinement based on underlying structural and biomechanical factors.

Purpose of the Study:

• To investigate structural and biomechanical differences between patients with chronic pseudoparalysis and chronic pseudoparesis.
• To determine if specific rotator cuff tear characteristics correlate with pseudoparalysis versus pseudoparesis.

Main Methods:

• Retrospective case-control study of 50 patients with massive rotator cuff tears (mRCTs).
• Patients were grouped into pseudoparalysis (<45° abduction) and pseudoparesis (>45° and <90° abduction).
• Evaluated radiographic parameters, MRI findings (fatty infiltration, tear extension), and utilized a musculoskeletal model for biomechanical analysis.

Main Results:

• No radiographic differences were found between the pseudoparalysis and pseudoparesis groups.
• MRI revealed significant differences in subscapularis and infraspinatus fatty infiltration and rotator cuff tear extension between groups.
• Over 50% subscapularis tear involvement was strongly associated with pseudoparalysis (OR 5 for abduction <45°).

Conclusions:

• Chronic pseudoparalysis and pseudoparesis are associated with distinct structural rotator cuff lesions.
• Significant subscapularis involvement (>50%) and Stage 3 fatty infiltration correlate with pseudoparalysis.
• The subscapularis muscle plays a critical role in active arm abduction, as confirmed by biomechanical modeling.