We report a rare case of triplane the distal humeral epiphysis, which has been reported in only one case previously in the literature. In our case, ultrasonography was useful for making a diagnosis and for confirming intraoperative reduction.

Patient: A boy, aged 5 years and 11 months.

Chief complaint: Left elbow pain and deformity.

Medical history: None.

Current medical history

The patient fell from a height of approximately 1.5 m and injured the left hand. The event was unwitnessed, and the details were unknown. His mother noticed prominent left elbow pain and deformity and requested emergency treatment.

Symptoms on admission

The left elbow had significant swelling and deformity. of the left elbow. No motor or sensory abnormalities of the radial, medial, or ulnar nerves existed. The radial and ulnar arteries were both palpable.

Image findings on admission

Radiography demonstrated a fracture of the metaphysis of the lateral humerus. The forearm axis was dislocated posteromedially to the humeral axis, but the ossification center of the capitellum was correctly located on the radial axis. Similarly, Computed tomography (CT) similarly showed at the ossification center of the capitellum was correctly located on the radial axis (Fig. 1). Based on the currently available imaging findings, the differential diagnoses included distal humeral epiphysiolysis and fracture of the lateral humeral condyle with dislocation of the elbow. Arthrography or magnetic resonance imaging (MRI) is necessary for a definitive diagnosis. Preoperative arthrography was performed under general anesthesia.

Surgery

Ultrasonography was performed under general anesthesia. The long- and short-axis images of the fractured segments were evaluated. The trochlea and capitellum were dislocated from the forearm to the dorsal side; therefore, distal humeral epiphysiolysis was diagnosed. The relationship between the trochlear capitellum and the ulnar radius was normal. Part of the cartilage on the anteromedial side of the trochlea remained on the distal humerus, which suggested that this fracture crossed the articular surface, epiphysis, physis, and metaphysis (Fig. 2).

Arthrography was subsequently performed. The trochlea and capitellum were dislocated from the forearm to the dorsal side, confirming distal humeral epiphysiolysis (Fig. 2). We could not observe the part of the cartilage on the anteromedial side of the trochlea that remained on the distal humerus, as observed with ultrasonography. Manual reduction was possible; therefore, we attempted a closed reduction and percutaneous pinning.

Surgery was performed with the patient in the supine position. The fracture was reduced by pushing the distal fragment from the posterolateral side and placing the elbow joint in a flexed position (Fig. 3). We inserted a 1.8-mm Kirschner wire from the lateral side. Under fluoroscopy, the reduction appeared adequate. However, when the elbow joint was flexed, we felt a click.

Ultrasonography revealed a gap in the fractured part of the trochlea, and a slight dislocation remaining on the medial side (Fig. 3). We attempted percutaneous pinning several times under manual reduction; however, maintaining the correct reduction position was difficult. Therefore, we decided to perform open reduction and fixation.

The anterior elbow joint was exposed, using a lateral approach, and the fractured part of the trochlea was directly observed. We confirmed that the distal epiphysis was separated from the metaphysis, and part of the cartilage on the anteromedial side of the trochlea remained on the metaphysis, as observed on ultrasonography. Therefore, we reconfirmed the diagnosis of a triplane fracture (Fig. 4). The reduction position was obtained by pushing the distal bone fragment from the posterolateral side. Two 1.8-mm Kirschner wires were percutaneously inserted rom the lateral side. The reduction position was maintained in the elbow joint flexion position; therefore, a plaster splint was placed in the flexion position after surgery. The immediate postoperative radiographic findings were also favorable (Fig. 5).

Postoperative course

Radiographs revealed concentric reduction and callus formation in the distal humerus. The Kirschner wires were removed after 4 weeks (Fig. 6). In addition, ultrasonography confirmed that the reduction position of the trochlea was maintained (Fig. 6). We followed up the patient regularly. At 1.5 years after the surgery, we confirmed a slight cubitus varus deformity (Fig. 7), no ectopic ossification (Fig. 8), and no difference in the range of motion between the right and left elbows (Fig. 7). The ultrasound findings at the last examination are shown in Fig. 8. The cartilage fragment on the ulnar side can be observed as a highly echogenic areas, and the fracture line of the trochlear cartilage remains identifiable.

Distal humeral epiphysiolysis is a rare condition. To the best of our knowledge, only one case of distal humeral triplane fracture was reported by Peterson HA et al. ^[1] in 1983.

Distal humeral epiphysiolysis should be suspected, based on radiographic examination findings. The forearm axis is dislocated posteromedially or posterolaterally to the humeral axis. However, the ossification center of the capitellum is correctly located on the extension of the radial axis, thereby maintaining a normal positional relationship between the radius and ulna [2-4]. This patient also exhibited the typical radiographic characteristics; therefore, epiphysiolysis was suspected.

The usefulness of MRI ^[5] and arthrography [6,7] has generally been reported for making a definitive diagnosis of distal humeral epiphysiolysis. However, the usefulness of ultrasonography has recently been demonstrated [3,8,9]. Based on a report by Supakul N et al. ^[2] in 2015, distal humeral epiphysiolysis was diagnosed in all 12 patients by using ultrasonography when radiography suggested distal humeral epiphysiolysis. Based on these results, Supakul N et al. emphasized the usefulness of ultrasonography for making a definitive diagnosis of distal humeral epiphysiolysis. In our patient, we performed arthrography and diagnosed distal humeral epiphysiolysis. Arthrography did not reveal a cartilage trochlear fragment on the metaphysis; therefore, we could not diagnose the triplane fracture by using arthrography.

Ultrasonography can be used to observe the cartilage in detail, and it may be possible to detect special fracture types, as in our patient. Ultrasonography requires considerable experience and skill; however, it is a simple and minimally invasive procedure. Performing arthrography before surgery is very useful for improving diagnostic accuracy. It is also useful for confirming intraoperative reduction because it can be repeated.

As mentioned previously, only one previous report ^[1] has described a distal humeral triplane fracture. Distal humeral epiphysiolysis is difficult to diagnose with radiography or CT; therefore, we can infer that many triplane fractures were missed and misdiagnosed as lateral humeral condyle fractures or Salter-Harris type II epiphysiolysis. For triplane fractures, reducing the articular surface accurately is necessary. When it is misdiagnosed as Salter-Harris type II, clinicians may overlook the dislocation of the cartilage, and a postoperative range of motion limitation may persist. In addition, a triplane fracture case requires differential diagnosis to distinguish it from distal humeral epiphysiolysis, and lateral humeral condyle fracture with dislocation due to a large dislocation. However, differentiating it from a lateral humeral condyle fracture is particularly difficult when the dislocation is small ^[10].  When clinicians diagnose a distal humeral epiphysiolysis or lateral humeral condyle fracture, they should suspect the possibility of a triplane fracture, evaluate the epiphysis, and confirm the presence of the fracture by using ultrasonography or MRI.

Distal humeral epiphysiolysis is often overlooked or misdiagnosed and can result in severe growth disturbances. Ultrasonography, MRI and arthrography are useful for detailed observation of the fractured part. We were able to diagnose a distal humeral triplane fracture by using ultrasonography, which has been previously reported in only one case.

A large number of cases of distal humeral epiphysiolysis or lateral humeral condyle fracture may include cases of triplane fracture. Determining a more accurate diagnosis by using ultrasonography or MRI would be beneficial for appropriately planning a patient’s treatment strategy. Raising awareness of this issue is of great importance.