bubble_chart Overview

The capitulum of the humerus is located on the anterolateral side of the lower end of the humerus. It is the intra-articular part of the lateral condyle of the humerus, forming a round and smooth protrusion. Its anterior lower part is an articular surface, but it does not extend posteriorly. Its lateral border connects with the lateral condyle of the humerus. During elbow flexion, the head of the radius rotates on its anterior articular surface. In extreme flexion, the edge of the radial head fits into the radial fossa above the capitulum. When the elbow is extended, the radial head rotates on the lower articular surface of the capitulum. The entire capitulum is located within the joint. Fractures of the capitulum occur in the coronal plane and are distinct from fractures of the lateral condyle of the humerus, being relatively rare, accounting for approximately 0.5-1% of elbow injuries. They are more common in adolescents.

bubble_chart Pathogenesis

Injury Mechanism and Types: It is caused by shear stress. That is, when the elbow is extended and falls in a valgus position with the hand landing on the ground, the external force is transmitted along the radius to the elbow, and the radial head pushes the capitulum of the humerus downward. At the same time, valgus stress can cause injury to the medial soft tissues. According to the extent of the injury and the range of the fracture, it is divided into the following three types.

1. Complete fracture (Hahn-Steinthal fracture): This is a coronal plane fracture at the base of the capitulum of the humerus. The fracture fragment includes the entire capitulum and the lateral one-third or one-half of the trochlea. However, sometimes it is limited to the capitulum itself.

2. Partial fracture (Kocher-Lorenz fracture): The fracture fragment only includes the capitulum, articular cartilage, and a small amount of bone beneath it.

3. Contusion of the articular cartilage of the capitulum: The injuring force is not sufficient to cause a fracture, only resulting in a contusion of the articular cartilage of the capitulum. It cannot be displayed on X-rays and is difficult to diagnose. Cartilage injury can only be discovered during advanced stage surgery, such as radial head resection.

bubble_chart Clinical Manifestations

Swelling at the back of the elbow joint is not obvious because it is inside the joint. However, there is significant limitation of movement and tenderness at the head of the humerus. In cases with combined medial ligament injury, there is tenderness and increased valgus movement.

X-ray anteroposterior and lateral views can confirm the diagnosis, with the lateral view being the most obvious. Taking only an anteroposterior view can easily lead to a misdiagnosis of fistula disease.

bubble_chart Treatment Measures

1. Closed Reduction The principle is to relax the anterior joint capsule of the elbow joint, increase the anterolateral space of the elbow joint to facilitate reduction. For some large fracture fragments without rotational displacement, closed reduction can be performed. During reduction, the elbow should be flexed to grade I to release the restraint of the anterior joint capsule on the fracture fragment. However, excessive flexion can cause the radial head to hinder reduction. Passive varus of the elbow is used to increase the lateral joint space, and the fracture fragment is pushed distally with fingers. After reduction, the elbow is fixed in a flexed position, and the fracture fragment is stable due to the blocking effect of the radial head. Active movement begins after 4 weeks of fixation with a gypsum splint.

2. Open Reduction For complete fractures where closed reduction is unsuccessful, open reduction should be performed. A lateral incision of the elbow joint is made. After reduction, due to the rough and extensive contact surface of the fracture, the fracture is quite stable in a flexed elbow position. Most cases do not require internal fixation and are fixed with gypsum in a flexed elbow position for 4 weeks postoperatively. In individual cases where the fracture fragment is unstable and tends to displace after reduction, fine Kirschner wires can be used for cross fixation from anterolateral to posteromedial. However, elbow flexion activities should not be performed postoperatively. Joint function exercises can only be started after 3-4 weeks of fixation. After reduction of the fracture fragment, cancellous bone screws can also be used for fixation from the dorsal side of the lateral condyle of the humerus, but the tip of the screw must stop below the cartilage. Due to the firm fixation, flexion and extension activities can be started 3-5 days postoperatively.

3. Fragment Excision For some smaller fracture fragments, timely excision is beneficial for elbow joint function exercises. Otherwise, they will become loose bodies in the joint, leading to osteoarthritis.

4. Management of Old Fractures After a capitellar fracture, if not treated promptly, it can lead to elbow joint dysfunction. The capitellum heals with the distal humerus in a displaced position. The joint surface often shows degenerative changes. Open reduction is no longer possible. Consideration can be given to excising the fracture fragment or radial head that obstructs joint movement, along with elbow joint release surgery. The function of the elbow joint can be improved to varying degrees.