What axis of rotation does ulnar and radial deviation occur about?
The correct answer and explanation is:
Ulnar and radial deviation occur about the anterior-posterior axis.
Ulnar deviation refers to the movement of the wrist toward the ulna (the inner side of the forearm), while radial deviation involves movement toward the radius (the outer side). These movements are specific types of wrist flexion and extension, but instead of involving the sagittal plane (which divides the body into left and right halves), they occur within the frontal plane (also called the coronal plane). The motion takes place around the anterior-posterior axis, which runs horizontally from the front of the body to the back.
The anterior-posterior axis is perpendicular to both the sagittal and frontal planes. When considering wrist movements like flexion and extension (which happen in the sagittal plane), the anterior-posterior axis allows for those rotational movements to occur. In contrast, the ulnar and radial deviations involve shifting the hand sideways, either toward the pinky (ulnar) or the thumb (radial). Since these motions are happening in the frontal plane, the corresponding axis of rotation that allows this side-to-side movement is the anterior-posterior axis.
A practical example would be when a person moves their wrist from a neutral position, bending it inward toward the ulna (ulnar deviation) or outward toward the radius (radial deviation). The wrist joint has limited movement in these directions, which is why these deviations are smaller in comparison to other motions like flexion or extension.
To summarize, ulnar and radial deviation occur around the anterior-posterior axis, which is perpendicular to the frontal plane and allows for the wrist to move side to side.