The more medial of the two long bones of the forearm is called the ulna. It is an important site for muscle attachment, and can be palpated along the entire posterior aspect of the forearm.
The olecranon is a curved projection on the proximal aspect of the ulna that forms what we know as the “elbow.” It serves as the insertion of the triceps brachii muscle, a muscle responsible for forearm extension.
The coronoid process is a projection of the proximal ulna (near the elbow) on the anterior side. It is the attachment site for the brachialis muscle.
The distal humerus meets the proximal ulna at a bony landmark called the trochlear notch. It is uniquely shaped to exactly fit the trochlea of the distal humerus, which contributes to the stability of the humeroulnar joint.
The radial notch refers to an indentation on the lateral surface of the ulna. This is the location where the radial head meets the proximal ulna, creating the proximal radioulnar joint. This unique ellipsoid joint is responsible for the ability to pronate and supinate the forearm.
On the distal aspect of the ulna (near the wrist) there is a small bony projection called the ulnar styloid process. It can be palpated at the medial aspect of the wrist. It is an attachment site for the ulnar collateral ligament, which plays an important role in the stabilization of the wrist joint.
The head of the ulna is located distally on the bone, and is a rounded, articulating surface. The ulnar head is recieved by the ulnar notch of the radius, helping to form the radioulnar joint.
The more lateral of the two long bones of the forearm is called the radius. It is able to rotate around the ulna due to their unique attachments at the proximal and distal radioulnar joints. The radius serves as an attachment site for many muscles that act on the forearm and hand.
The head of the radius is a round structure that articulates with both the proximal ulna and the capitulum of the distal humerus. Collectively, the three joints between the humerus, ulna, and radius comprise the elbow joint.
The neck of the radius refers to the narrow area just distal to the head. The annular ligament originates and inserts on the coronoid process of the ulna, encircling the head of the radius as it narrows to the neck. This acts to prevent dislocation of the proximal radioulnar joint after a forceful upward pull, a condition common in children known as nursemaid’s elbow.
The radial tuberosity is a rough area on the proximal radius that serves as the insertion point for the biceps brachii muscle. This attachment site is important for understanding the muscle’s action. The biceps brachii is a much stronger arm/forearm flexor when the forearm is supinated due to its attachment on the radius.
The radial styloid process is a bony projection on the distal aspect of the radius. It can be palpated at the lateral wrist, just proximal to the anatomic snuff box.
At the distal end of the radius there is an indentation known as the ulnar notch. Laying on the medial aspect of the radius, it accommodates the ulnar head, producing the distal radioulnar joint. While the proximal radioulnar joint’s function is to allow spinning of the radial head in place, the distal radioulnar joint allows the entire radius to rotate around the ulna.
On the dorsal aspect of the distal radius, there is a small, yet important, projection called Lister’s Tubercle. This bony landmark serves as a pulley around which the tendon of the extensor pollicis longus wraps. This pulley system increases the strength of this muscle, producing extension of the thumb.
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