capitulum of the humerus

2 min read 14-03-2025

The capitulum of the humerus is a small, rounded articular surface located on the lateral aspect of the distal humerus. Understanding its anatomy, function, and clinical significance is crucial for healthcare professionals and students of anatomy. This article will delve into a detailed exploration of this important anatomical structure.

Anatomy of the Capitulum

The capitulum is a smooth, convex articular surface. It's part of the elbow joint, specifically articulating with the head of the radius. This articulation allows for pronation and supination of the forearm. It's situated lateral to the trochlea, another articular surface on the distal humerus that articulates with the ulna. The capitulum and trochlea are separated by a shallow groove. The size and shape of the capitulum can vary slightly between individuals.

Relationship with Surrounding Structures

The capitulum is surrounded by several important anatomical structures. The radial collateral ligament originates near the capitulum, providing stability to the elbow joint. The annular ligament of the radius encircles the head of the radius, further securing the articulation with the capitulum. The common extensor tendon also inserts in the region of the capitulum.

Function of the Capitulum

The primary function of the capitulum is to facilitate the articulation between the humerus and the radius. This allows for the rotational movements of the forearm, pronation and supination. Without a smoothly functioning capitulum, these essential movements would be severely impaired or impossible. Its smooth, rounded surface minimizes friction during movement.

Clinical Significance of the Capitulum

Several clinical conditions can affect the capitulum, often resulting in pain, reduced range of motion, and functional impairment.

Fractures

Capitulum fractures are relatively common, particularly in children and adolescents. These fractures often result from falls or direct trauma to the elbow. Treatment typically involves immobilization with a cast or splint. More severe fractures may require surgical intervention.

Osteochondritis Dissecans (OCD)

Osteochondritis dissecans of the capitulum is a condition where a segment of bone and cartilage separates from the underlying bone. This can lead to pain, swelling, and locking of the elbow. Treatment options range from conservative management (rest, physical therapy) to surgical intervention.

Arthritis

Degenerative arthritis, such as osteoarthritis, can affect the capitulum. This can lead to pain, stiffness, and decreased range of motion. Treatment options include pain management, physical therapy, and potentially joint replacement surgery.

Radial Head Subluxation (Nursemaid's Elbow)

While not directly involving the capitulum itself, radial head subluxation is a common injury in young children. It often occurs when a child is pulled or lifted by the arm, causing the annular ligament to slip over the radial head. This typically reduces spontaneously or with simple manipulation.

Imaging Techniques

Several imaging techniques are used to diagnose conditions affecting the capitulum. These include:

X-rays: Provide excellent visualization of bone and can detect fractures and other bony abnormalities.
MRI: Offers detailed images of both bone and soft tissues, allowing for the assessment of cartilage damage, ligamentous injuries, and other soft tissue pathologies.
CT scans: Provide high-resolution images of bone, aiding in the assessment of complex fractures.

Conclusion

The capitulum of the humerus plays a vital role in elbow joint function, enabling the essential movements of pronation and supination. Understanding its anatomy, function, and the various clinical conditions that can affect it is crucial for accurate diagnosis and effective treatment. Further research continues to improve our understanding of this important anatomical structure and its role in the overall health of the upper extremity.