The human skeletal system is basically made up of bones, cartilages, tendons and ligaments. It makes the framework of the human body, hence maintains the body shape and provides sites to attach muscles in the body. More than 90 % of the skeletal system is made up of bones. There are 206 bones in the human skeleton. Radius and ulna are two major bones in the lower arm and responsible to connect elbow and wrist. These two bones run parallel to each other, and are articulate with the humerus at the proximal ends while, connect with the wrist bones at the distal ends. The entire length of both bones is connected along by the interosseus membrane.
Radius
Radius is the lateral bone of the forearm when considering the anatomical position. It is wide at its distal, and narrow at its proximal end. The disc shaped proximal end of radius or the head of radius articulates with capitulum of humerus, whereas the distal end articulates with the wrist bones. Next to head is known as neck of the radius. Distal to the neck is the radial tuberosity where the muscles attach in order to permit flexion of the forearm. The long section of the radius is called the shaft. Ulna articulates to the radius at the ulnar notch, which is an expanded portion of the radius. Anchoring sites of the radius at the lateral margin is called styloid process.
Ulna
If we consider the anatomical position, ulna is medial to radius in forearm. Ulna forms the elbow joint with humerus at its proximal end with its olecranon process. The concave depression on the anterior side of ulna is known as the trochlea notch, where the trochlea of the humerus articulates at the elbow joint. Coronoid process at the inferior end of the depression cavity joins with the trochlea of the humerus during extreme flexion. The ulna tuberosity is the attaching point of muscles, and radial point serves as the point where the head of radius articulates. Articular cartilage separates the head of ulna from wrist bones.
Radius vs Ulna
• Ulna is slightly larger than the radius.
• Radius is narrow at its proximal end and wide at its distal end, whereas ulna has the opposite shape of radius.
• In anatomical position, radius is the lateral bone of the forearm, and ulna is medial to radius.
• Disc shaped head of ulna is present at the distal end, whereas that of radius is present at the proximal end.