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 relevance is crucial for anyone studying anatomy, orthopedics, or related fields. This article will provide a comprehensive overview of this important anatomical structure.

Anatomy of the Capitulum

The capitulum is a part of the elbow joint, specifically the articulation with the radius. It's situated lateral to the trochlea, another articular surface on the distal humerus that articulates with the ulna. The capitulum is smooth and convex, perfectly shaped to fit the concave head of the radius. This articulation allows for the pivotal movement of the forearm, crucial for supination and pronation.

Relationship with Surrounding Structures

The capitulum is closely associated with several important anatomical structures:

Radial Head: The capitulum articulates directly with the head of the radius. This articulation is a critical component of the elbow joint's function.
Lateral Collateral Ligament: This ligament provides stability to the lateral aspect of the elbow joint, helping to prevent excessive lateral movement. It originates near the capitulum.
Annular Ligament: This ligament encircles the head of the radius, helping to maintain its articulation with the capitulum.

Function of the Capitulum

The primary function of the capitulum is to articulate with the radial head, enabling:

Radiohumeral Joint Movement: The articulation allows for flexion and extension of the elbow.
Pronation and Supination: The capitulum's shape and the annular ligament's action facilitate the rotation of the radius, enabling pronation and supination of the forearm.

Clinical Significance of the Capitulum

Injuries to the capitulum are relatively common, especially in children and young adults who are more prone to fractures.

Common Injuries:

Capitulum Fractures: These fractures can range from small, minimally displaced fractures to more complex, comminuted fractures. Mechanism of injury often involves a fall onto an outstretched hand. Treatment depends on the severity of the fracture and can range from conservative management (casting) to surgical intervention.
Capitulum Osteochondritis Dissecans (OCD): This condition involves a separation of a fragment of bone and cartilage from the capitulum. It can lead to pain, swelling, and limited range of motion. Treatment options vary from conservative measures to surgical intervention.
Lateral Epicondylitis ("Tennis Elbow"): While not directly involving the capitulum, this condition often affects the surrounding tendons and muscles, leading to pain radiating from the lateral aspect of the elbow.

Diagnosis:

Diagnosis of capitulum injuries typically involves a physical examination, followed by imaging studies such as:

X-rays: These are crucial for visualizing fractures and assessing the alignment of the bones.
MRI: Magnetic Resonance Imaging provides detailed images of soft tissues, including ligaments and cartilage, allowing for better assessment of OCD and other soft tissue injuries.
CT Scans: Computed tomography scans can provide detailed three-dimensional images of the bone, which can be helpful in evaluating complex fractures.

Conclusion

The capitulum of the humerus, though small, plays a significant role in the mechanics of the elbow joint. Understanding its anatomy, function, and potential injuries is vital for accurate diagnosis and effective treatment of elbow conditions. Further research into the biomechanics of the radiocapitellar joint continues to refine our understanding of this crucial anatomical structure and its role in upper extremity function.