McClure and colleagues tracked the scapula directly through bone pins to describe its 3‑dimensional motion during active shoulder movements.
In vivo bone‑pin study of 8 healthy volunteers aged 27 to 37 (left shoulder in 7).
Methods
Model
8 healthy volunteers (5 men, 3 women)
Mean age 32.6 years
Two 1.6‑mm pins in the scapular spine carrying a 3D motion sensor
Sensor taped over T3
Humeral sensor on a custom cuff
Loading
Active scapular plane elevation and lowering
Flexion
Internal‑to‑external rotation at 90° abduction, elbow at 90°
Outcome measures
Scapular upward rotation
Posterior tilt
External rotation
Glenohumeral to scapulothoracic (GH/ST) motion ratio
Key Findings
Raising the arm in the scapular plane moved the scapula about 3 axes: a mean 50° of upward rotation (SD 4.8°), 30° of posterior tilt (SD 13.0°) and 24° of external rotation (SD 12.8°).
Posterior tilt and external rotation were nonlinear, and most of each took place only after the arm passed 90° of elevation.
Upward rotation was roughly linear in mid‑range, but the scapula moved very little in the first 30° of elevation and rotated faster at end range.
Pooled across subjects, the GH/ST motion ratio was 1.7:1 for scapular plane elevation and 2.0:1 for flexion.
With the arm at 90° abduction, the scapula moved little during humeral rotation until end‑range external rotation, when it tilted posteriorly, rotated upward and externally rotated.
Board pearl
Normal elevation is not just upward rotation: the scapula also tilts posteriorly, a motion that may help clear the humeral head and cuff tendons under the anterior acromion.
Authors' conclusion
Normal scapular motion consists of substantial rotations around 3 axes, not simply upward rotation. Understanding normal scapular motion may assist in the identification of abnormal motion associated with various shoulder disorders.
McClure and colleagues tracked the scapula directly through bone pins to describe its 3‑dimensional motion during active shoulder movements.
In vivo bone‑pin study of 8 healthy volunteers aged 27 to 37 (left shoulder in 7).
Methods
Model
8 healthy volunteers (5 men, 3 women)
Mean age 32.6 years
Two 1.6‑mm pins in the scapular spine carrying a 3D motion sensor
Sensor taped over T3
Humeral sensor on a custom cuff
Loading
Active scapular plane elevation and lowering
Flexion
Internal‑to‑external rotation at 90° abduction, elbow at 90°
Outcome measures
Scapular upward rotation
Posterior tilt
External rotation
Glenohumeral to scapulothoracic (GH/ST) motion ratio
Key Findings
Raising the arm in the scapular plane moved the scapula about 3 axes: a mean 50° of upward rotation (SD 4.8°), 30° of posterior tilt (SD 13.0°) and 24° of external rotation (SD 12.8°).
Posterior tilt and external rotation were nonlinear, and most of each took place only after the arm passed 90° of elevation.
Upward rotation was roughly linear in mid‑range, but the scapula moved very little in the first 30° of elevation and rotated faster at end range.
Pooled across subjects, the GH/ST motion ratio was 1.7:1 for scapular plane elevation and 2.0:1 for flexion.
With the arm at 90° abduction, the scapula moved little during humeral rotation until end‑range external rotation, when it tilted posteriorly, rotated upward and externally rotated.
Board pearl
Normal elevation is not just upward rotation: the scapula also tilts posteriorly, a motion that may help clear the humeral head and cuff tendons under the anterior acromion.
Authors' conclusion
Normal scapular motion consists of substantial rotations around 3 axes, not simply upward rotation. Understanding normal scapular motion may assist in the identification of abnormal motion associated with various shoulder disorders.