An algorithm to allow humerus translation in the indeterminate problem of shoulder abduction

Area of Science:

• Biomechanics
• Orthopedic Surgery
• Human Movement Science

Background:

• The shoulder joint's complexity arises from its extensive range of motion and active muscular stabilization.
• Existing biomechanical models often simplify the shoulder as a ball-socket joint, neglecting natural humerus translation.
• This simplification limits the accuracy of indeterminate biomechanical models.

Purpose of the Study:

• To develop and validate a novel algorithm for solving indeterminate shoulder biomechanical models.
• To incorporate feedback control of muscle activation for natural humerus translation.
• To analyze shoulder abduction in the scapular plane, including deltoid and rotator cuff muscles.

Main Methods:

• Developed a new algorithm using feedback control of muscle activation to address model indeterminacy.
• Restricted the model to two dimensions for validation against a known algebraic solution.
• Included three parts of the deltoid and rotator cuff muscles in the analysis of scapular plane abduction.

Main Results:

• The numerical algorithm achieved a relative error below 0.1% when compared to an algebraic solution.
• Calculated joint reaction forces were comparable to those found in other established shoulder models.
• Simulated humerus translation aligned with findings from in vivo and in vitro studies.

Conclusions:

• The developed algorithm accurately simulates shoulder biomechanics, including natural humerus translation.
• This approach offers a more realistic representation of shoulder joint function compared to simplified models.
• The validated algorithm has potential applications in understanding shoulder pathologies and guiding treatment strategies.