The term “the radial” in human anatomy refers not to a single structure but to a group of three distinct components located on the lateral, or thumb, side of the forearm. These structures—the radius bone, the radial artery, and the radial nerve—are intimately related, running parallel to one another from the elbow to the wrist. This anatomical grouping provides the foundation for the arm’s mechanical support, blood supply, and neurological control.
The Radius Bone: Anatomy and Joint Function
The radius is one of the two long bones that make up the forearm, extending from the elbow to the wrist on the side where the thumb is located. The radius articulates with the humerus at the elbow and with the carpal bones of the wrist, specifically the scaphoid and lunate bones, at its distal end. The proximal end features a disc-shaped head that fits into the humerus and the radial notch of the ulna, the other forearm bone. This unique articulation allows the head of the radius to rotate, which is necessary for the forearm’s rotational movements. The radius is the primary bone involved in supination, the act of turning the palm upward, and pronation, the movement that turns the palm downward. During pronation, the distal end of the radius crosses over the ulna, inverting the hand’s position.
The Radial Artery: Monitoring Circulation
The radial artery arises from the bifurcation of the brachial artery near the elbow and runs distally down the forearm, following the path of the radius bone. It is situated between the tendons of the brachioradialis and the flexor carpi radialis muscles. The artery’s course makes it important for clinical assessment because of its superficial location close to the wrist. At the wrist, it is easily palpable just lateral to the flexor carpi radialis tendon, which is the site commonly used to check the radial pulse. Checking this pulse allows assessment of a patient’s heart rate, rhythm, and blood flow. The radial artery is also a common site for medical procedures, such as the collection of arterial blood gas samples or the insertion of arterial lines.
The Radial Nerve: Signal Transmission
The radial nerve descends along the arm, traveling down the forearm near the radius bone. It is responsible for both motor control and sensory perception in the upper limb. Its motor function primarily involves controlling the muscles responsible for extension, including the triceps muscle, which extends the elbow. More distally in the forearm, the radial nerve supplies the muscles that allow a person to extend the wrist and the fingers. The sensory role of the nerve provides feeling to the skin over the back of the forearm and the lateral portion of the back of the hand, including parts of the thumb and first two fingers.
Clinical Relevance: Diagnosing Radial Injuries and Issues
A radius bone fracture, such as a Colles’ fracture, is a common injury where the distal end of the bone is displaced, typically resulting from a fall onto an outstretched hand. Damage to the radial nerve, known as radial nerve palsy, often results in a characteristic presentation called “wrist drop.” This occurs because the patient cannot actively extend their wrist or fingers due to paralysis of the extensor muscles. Circulatory problems related to the radial artery are commonly assessed by checking for the presence, rate, and regularity of the radial pulse. An absent or weak pulse may indicate compromised blood flow to the hand, requiring immediate attention.