Comparing in vivo three-dimensional shoulder elevation kinematics between standing and supine postures

Area of Science:

• Biomechanics
• Orthopedics
• Human Movement Science

Background:

• Assumed changes in shoulder muscle activation and range of motion with body posture (standing vs. supine) lack objective assessment.
• Hypothesized that supine posture may facilitate scapular rotation and alter subacromial pressure.

Purpose of the Study:

• To evaluate the influence of body posture on shoulder kinematics during arm elevation.

Main Methods:

• Shoulder kinematics assessed in standing and supine postures using single-plane fluoroscopic images in 18 participants.
• 3D to 2D model-image registration techniques applied to measure glenohumeral translation, acromiohumeral distance, and scapular rotations.
• Effects of sex on shoulder kinematics were also evaluated.

Main Results:

• Humeral head position differed between standing and supine postures, with a significant inferior shift during elevation in the supine position.
• Acromiohumeral distance was not significantly affected by body posture during elevation.
• Scapular upward rotation and posterior tilt showed significant differences between standing and supine postures.

Conclusions:

• Body posture demonstrably affects shoulder kinematics during humeral elevation.
• Findings provide valuable insights for optimizing rehabilitation exercises and enhancing diagnostic capabilities for shoulder conditions.