Scapular positioning assessment: is side-to-side comparison clinically acceptable?

Area of Science:

• Orthopedics
• Biomechanics
• Sports Medicine

Background:

• Clinicians often assume scapular symmetry between shoulders for assessing shoulder pathology.
• Scapular asymmetry is frequently considered pathological.
• The kinematic symmetry of the scapula in healthy individuals during arm elevation remains unproven.

Purpose of the Study:

• To test the hypothesis that scapular kinematics are symmetrical during arm elevation in healthy adults.
• To investigate potential differences in scapular positioning between dominant and non-dominant shoulders.

Main Methods:

• Simultaneous 3D scapular positioning measurement of dominant and non-dominant shoulders in 14 healthy young adults.
• Utilized a 6 degrees of freedom electromagnetic tracking device.
• Measurements were taken at rest, hands on hips, and 90° shoulder abduction with internal rotation.

Main Results:

• The dominant scapula demonstrated significantly greater retraction (P < 0.001) and upward rotation (P < 0.001) across all measured arm positions.
• No significant difference was found in the amount of scapular retraction or upward rotation from rest to 90° abduction between dominant and non-dominant shoulders.
• A notable difference in posterior tilting was observed, with the dominant shoulder showing greater posterior tilt (3.8° vs 0.9°).

Conclusions:

• Scapular positioning relative to the thorax is not identical between dominant and non-dominant shoulders in healthy individuals.
• Observed kinematic patterns during arm elevation may appear similar despite underlying positional differences.
• Clinicians should consider these findings when comparing symptomatic and contralateral shoulders to avoid misinterpreting natural asymmetry as pathology.