Scapular and clavicular kinematics during humeral elevation: a study with cadavers

Area of Science:

• Orthopedics
• Biomechanics
• Anatomy

Background:

• Understanding shoulder kinematics is crucial for diagnosing and treating shoulder pathologies.
• The interplay between glenohumeral and scapulothoracic motion is complex and varies with arm elevation.
• Previous studies have provided insights, but a comprehensive kinematic analysis across different elevation planes is needed.

Purpose of the Study:

• To characterize shoulder kinematics during simulated passive clinical range-of-motion examination.
• To compare shoulder kinematics across coronal, scapular, and sagittal elevation planes.
• To analyze the glenohumeral to scapulothoracic motion ratio throughout the range of elevation.

Main Methods:

• Utilized a combination of kinematic testing and graphic reconstruction of cadaveric shoulders.
• Kinematically tracked the scapula, clavicle, and humerus during passive elevation in three planes.
• Created animated graphic models from computed tomography (CT) data to visualize experimental motions.

Main Results:

• Shoulder kinematics demonstrated significant variation depending on the plane of elevation.
• Scapular and clavicular rotations were minimal until approximately 90 degrees of humeral elevation.
• Coronal plane elevation at low angles showed significantly greater clavicular and scapular rotations compared to other planes.
• The glenohumeral to scapulothoracic ratio was consistently around 2, but markedly higher during early versus late elevation.

Conclusions:

• Shoulder kinematics are plane-dependent, influencing scapular and clavicular contributions to arm elevation.
• The glenohumeral to scapulothoracic ratio is not constant throughout the range of motion, particularly varying with initial elevation.
• These findings enhance our understanding of normal shoulder biomechanics, informing clinical assessments and surgical interventions.