Fishtail deformity of the distal humerus: association with osteochondritis dissecans of the capitellum

Abstract

Background: Fishtail deformity is a rare deformity of the humerus exhibiting concavity of the lateral trochlea, resulting in ulnotrochlear joint derangement. We wanted to share our experience that osteochondritis dissecans of the capitellum is a common associated complication.

Objective: To summarize imaging of fishtail deformity in children centered on complications of the radiocapitellar joint.

Materials and methods: From the radiology information system, we identified all patients <18 years with the diagnosis of fishtail deformity. We included only patients with V-shaped deformity of the distal humerus due to concavity at the lateral trochlea (fishtail deformity). Each patient's initial injury, most recent radiograph and available MRI were evaluated for radiocapitellar joint derangement.

Results: Seven patients (4 males) with a mean age of 12.9 years (range: 9.7 to 14.4 years) were identified. Radiocapitellar joint abnormalities were identified in six patients including osteoarthritis (n=5), flattened and sclerotic capitellum (n=4), osteochondritis dissecans (2 associated with loose body, n=4) and radial head subluxation (n=2). In 4 patients, MRI detected changes of osteoarthritis (n=4), osteochondritis dissecans (n=2) and loose body (n=1) not identified on radiography. Two patients with osteochondritis dissecans underwent surgery and one patient has planned surgery.

Conclusion: Radiocapitellar joint abnormalities (particularly, capitellar osteochondritis dissecans) are common in patients with fishtail deformities. MRI should be performed in these patients since some abnormalities, possibly requiring surgery, are not detected on elbow radiographs.

Keywords: Children; Fishtail deformity; Humerus fracture; Magnetic resonance imaging; Osteochondritis dissecans; Radiocapitellar joint; Radiograph.