The radial head, though small, plays a significant part in the complex mechanics of the elbow joint. Understanding its specific placement is fundamental to grasping how it contributes to arm movement and why certain conditions can affect its function. Its involvement in both elbow stability and forearm rotation highlights its considerable contribution to overall upper limb mobility.
Locating the Radial Head
The radial head is the rounded, disc-shaped end of the radius, one of the two bones in your forearm. It is located at the elbow, articulating with the capitellum of the humerus (upper arm bone) and the radial notch of the ulna (the other forearm bone).
You can feel the radial head on the outer side of your elbow, just below the prominent bony knob of the humerus known as the lateral epicondyle. Its cylindrical shape allows it to rotate within a ring-like ligament called the annular ligament, which holds it firmly against the ulna. This precise anatomical arrangement is crucial for the joint’s stability and its ability to perform rotational movements.
Its Role in Elbow and Forearm Movement
The radial head is central to two primary types of elbow and forearm movements: flexion/extension and pronation/supination. Its concave, cup-shaped surface articulates with the spherical capitellum of the humerus, enabling the elbow to bend and straighten. This articulation allows the radial head to glide over the capitellum during these hinge-like motions.
Beyond simple bending and straightening, the radial head’s unique form is essential for forearm rotation. It pivots within the annular ligament and against the radial notch of the ulna, facilitating pronation (turning the palm downward) and supination (turning the palm upward). This rotational capability is achieved as the radial head spins on its own axis. The stability provided by the annular ligament is important for this rotational movement, ensuring the radial head remains properly aligned.
Common Conditions Affecting the Radial Head
The radial head’s position and role in movement make it susceptible to injuries and conditions. Radial head fractures are common, often resulting from a fall onto an outstretched hand, where force travels up the arm to the elbow. These fractures can range from small cracks to more severe breaks with multiple fragments. Symptoms include pain, swelling on the outside of the elbow, and difficulty bending or rotating the forearm.
Another condition, particularly common in young children, is Nursemaid’s elbow, also known as radial head subluxation. This occurs when the radial head partially slips out from under the annular ligament, usually due to a sudden pull on the child’s arm. It causes immediate pain and a reluctance to use the affected arm. Additionally, the radial head can be affected by arthritis, particularly post-traumatic arthritis following a previous injury. This condition involves the wearing away of cartilage, leading to pain, stiffness, and reduced movement, especially during forearm rotation.