When you look at your forearm, you may think of it is a single entity but in reality, underneath the covering of a skin lies not one but two bones. Another interesting thing about the forearm is when you look at the orientation of the muscles, it can be seen that almost all muscles are parallel to one another.
Although the two bones are situated at close proximity to each other, they are completely different. The Ulna, located at the posterior aspect of the proximal extremity is characterized by the olecranon, a massive bone mass. The olecranon can be easily felt at the back of the elbow. In front of the olecranon is what we call the trochlear notch which meets with the trochlea of the bone humerus at a point called the humeroulnar joint which is a synovial and hinge joint. As you travel down from the humeroulnar joint, a portion of this faces the radius or what is referred to as the radial head. This point, which is called the radial notch, contributes to form the proximal radioulnar joint which is a synovial and pivot joint.
The shaft of the ulna then narrows distally as it terminates to the head of the ulna. Another joint, called the distal radioulnar joint forms with the articulation of both bones. The type of joint produced is a pivot type, synovial joint. This joint shares an articular disc that fits between the ulnar head and lunate and trequetral bone of the wrist. This disc contributes to the radiocarpal joint or the wrist joint but the ulnar head does not. The ulnar shaft forms a movable, fibrous joint called the syndesmosis, with the shaft of the radius by means of the interosseous membrane.
When compared to the ulna, the radius is much shorter and is located laterally. The proximal end of the radius connects with the humerus and the distal end connects with the carpus. The unique thing about the radius is that the body or the shaft is thin and then it increases in size in both ends.
The radius has a small rounded head proximally that connects to the capitulum of the humerus forming the radiohumeral joint, a synovial type, pivot joint. The proximal head of the radius also connects to the radial notch of the ulna and forms the proximal radioulnar joint. The weakest point between all of the connections in the forearm is contained in the wrist or the articulation between the distal extremity and the shaft.
During movement of the hand, specifically supination and pronation, the ulna does not move.
Our hands are considered as the greatest tool that man ever encountered with. It receives its signal from nerves that traverse the forearm. It is vital to have knowledge on the compartmental anatomy regarding the forearm to better understand the complexities it presents. Because there are many connections or articulations in the forearm, it is easy for it to be injured or traumatized.