Which of these types of joint best describes the joint between of the proximal ends of the radius and uln?
options: a) ball and socket b) hinge c) gliding d) pivot e) saddle
The correct answer and explanation is:
Correct Answer: d) pivot
Explanation (300 words):
The joint between the proximal ends of the radius and ulna is best classified as a pivot joint. This specific joint is known as the proximal radioulnar joint.
A pivot joint is a type of synovial joint that allows rotational movement around a single axis. In the case of the proximal radioulnar joint, the head of the radius rotates within a ring formed by the radial notch of the ulna and the annular ligament. This arrangement allows the radius to rotate over the ulna, enabling pronation (palm down) and supination (palm up) of the forearm.
Here’s how this fits into everyday movement: When you turn your hand from a palm-up to a palm-down position (like when turning a doorknob), it’s the pivot motion at this joint that makes it possible. The rotation does not come from the wrist itself, but rather from the radius rotating over the ulna at the elbow area.
Let’s look at why the other options are incorrect:
- a) Ball and socket joints (e.g., shoulder, hip) allow movement in almost all directions — not the case here.
- b) Hinge joints (e.g., elbow, knee) allow bending and straightening, not rotation.
- c) Gliding joints allow bones to slide past each other, as seen in some wrist bones.
- e) Saddle joints allow movement in two planes (like the thumb), not rotation around a single axis.
Thus, the pivot joint classification accurately reflects the type and range of motion found at the proximal radioulnar joint — making option d the correct answer.