Internal and external rotation of the shoulder occurs around which axis?

Internal and external rotation of the shoulder occurs around the Y axis, which is aligned with the length of the humerus when the arm is in a neutral position. In anatomical terms, when the arm is in the standard anatomical position (arms at the sides, palms forward), internal rotation refers to the rotation of the shoulder that brings the arm closer to the body, while external rotation moves the arm away from the body.

Understanding the axis around which this rotation occurs is critical for comprehending various movements of the upper extremity. The Y axis serves as a vertical line through the center of the shoulder joint, allowing for rotational movement around it.

In this context, the other axes mentioned are associated with different types of movements: the X axis typically relates to flexion and extension (movement forward and backward), while the Z axis, which runs horizontally, is involved in movements like adduction and abduction (moving towards and away from the midline). The sagittal axis, being an anatomical reference, correlates mainly with forward and backward movements rather than rotational.

Thus, recognizing the significance of the Y axis in facilitating internal and external rotation enhances the understanding of shoulder biomechanics and movement assessments.