Scapulohumeral Rhythm: The coordinated movement of the scapula across the thoracic cage (scapulothoracic movement) and the movement of the humerus to the glenoid cavity (glenohumeral movement).
Necessary for full upper limb elevation.
Movements
Scapular Superior Rotation: Tilts the glenoid fossa upwards, accentuating glenohumeral joint movement.
Predictable coordination is crucial; disturbances indicate muscular or joint dysfunction.
Abduction Process
Initial 30° of Abduction:
Scapula remains stationary against the rib cage.
Movement occurs only at the glenohumeral joint.
Beyond 30° of Abduction:
Inferior angle of the scapula shifts outward, undergoing superior rotation.
Movement Ratios
2:1 Ratio: Typically 2 degrees of glenohumeral movement for every 1 degree of scapulothoracic movement.
Up to 90° Abduction:
Glenohumeral Joint: 70°
Scapulothoracic Joint: 20°
Up to 150° Abduction:
Glenohumeral Joint: 110°
Scapulothoracic Joint: 40°
Variability
The ratio varies across different portions of the arc and between individuals.
Importance of comparing the involved side with the uninvolved side.
Muscles Involved
Scapulothoracic Stability and Motion:
Serratus Anterior
Rhomboids
Levator Scapulae
Trapezius
Assessment
Conducted with the patient standing and abducting the upper extremity in the scapular plane (approximately 30° forward from the coronal plane).
Examiner observes the motion of the glenohumeral and scapulothoracic joints, checking for smooth, coordinated movement and comparing to the uninvolved side.