The distal end of the humerus in newborns is composed of cartilage. As they grow older, ossification centers gradually appear, separated from the metaphysis by the epiphyseal cartilage plate, which is structurally weak. Therefore, young children may occasionally experience epiphyseal separation due to trauma. Its clinical characteristics are similar to those of humerus supracondylar fracture, representing a special type of supracondylar fracture that occurs during early childhood development and is relatively uncommon. According to statistics from Beijing Jishuitan Hospital, its incidence accounts for 0.16% of all fractures. Since the epiphyses in young children's elbows are often not yet ossified, the fracture line cannot be directly visualized on X-rays, leading to a very high misdiagnosis rate.

bubble_chart Pathogenesis

Complete epiphyseal separation is commonly seen as the extension-ulnar deviation type. It is caused by indirect external force. Most cases occur when the affected arm is extended to support the body during a fall. At the same time, the trunk rotates toward the affected side, the elbow joint hyperextends, and the body's center of gravity falls on the affected arm, resulting in the elbow being subjected to a strong internal rotation (actually external rotation of the upper arm), varus, and hyperextension stress. In children, the strength of the epiphyseal plate is weaker than that of the joint capsule and ligaments, making complete epiphyseal separation more likely to occur than elbow dislocation.

The flexion-type complete epiphyseal separation is relatively rare. It is caused by an external force impacting the olecranon in a flexed elbow position, which is then transmitted to the condyle. This type of injury mostly occurs in older children, possibly due to changes in the direction of the epiphyseal plate (increased inclination).

The clinical presentation is similar to that of a humerus supracondylar fracture.

bubble_chart Diagnosis

Its typical manifestation is the separation of the distal humerus along with the ulna and radius, which are displaced posteriorly and medially, while the lateral hip bone epiphysis and the proximal radius maintain a good alignment. If the lateral hip bone epiphysis of the humerus has not yet ossified, it can easily be confused with an elbow dislocation. For grade I displacement, a contralateral X-ray should be taken for comparison. After the ossification of the lateral hip bone, its X-ray image serves as the diagnostic basis, with the following radiographic features:

(1) The humeroradial joint is normal, and both the anteroposterior and lateral views of the elbow joint show that the longitudinal axis of the radius passes through the capitulum of the humerus.

(2) The ulnoradial relationship remains unchanged, meaning the superior ulnoradial relationship is normal.

(3) The alignment between the humerus and the ulna/radius is disrupted, often with the ulna and radius carrying a metaphyseal fracture fragment or the lateral condyle of the humerus displaced posteriorly and superiorly.

bubble_chart Treatment Measures

The treatment method is essentially the same as for humerus supracondylar fractures. Closed reduction and external fixation are commonly performed. Under manual traction, the lateral displacement is corrected first, followed by the anterior-posterior displacement. The elbow is fixed in a flexed position of 60-90 degrees for three weeks. External fixation alone is often insufficient to prevent fracture redisplacement and subsequent cubitus varus. Therefore, some advocate switching to an extended position early. Local small splintage combined with traction therapy yields better results. Others prefer closed reduction followed by fixation with thin steel pins inserted through the skin. For open fractures, debridement is performed first, followed by fixation with thin steel pins. Old fractures generally do not require special treatment; for those with secondary deformities, osteotomy and correction are performed after skeletal maturity.

1. If the lateral condyle of the humerus is not ossified, it is difficult to distinguish the X-ray findings from complete epiphyseal separation. The age of onset and the direction of displacement can serve as references. The elbow joint is commonly dislocated laterally, while the distal segment in complete epiphyseal separation often shifts medially. The "tactile sensation" during reduction can aid in differential diagnosis. Once the lateral condyle of the humerus has ossified, its X-ray image can serve as a diagnostic basis.

2. Separation of the lateral condylar epiphysis of the humerus (or lateral condylar fracture). Tenderness is localized to the lateral side of the joint, and abnormal movement of the lateral condyle can sometimes be palpated. X-ray films show normal alignment between the humeral shaft and the ulna-radius, but the lateral condyle of the humerus is displaced laterally.

3. Lateral condylar fracture combined with elbow dislocation. This is extremely rare and occasionally seen in school-aged children. The clinical presentation combines features of both lateral condylar fracture and elbow dislocation. If the lateral condyle of the humerus aligns with the proximal end of the radius, it is more likely to be complete epiphyseal separation.