Unusual form of the distal bone defect of ulna with neurofibromatosis type 1

Rationale: Bone malformation occurs in 10% to 25% neurofibromatosis type 1 (NF-1) patients, and the manifestations are scoliosis, congenital arch and pseudo-joint formation, bone cyst, and pathologic fracture. However, a large segmental defect without obvious signs of bone destruction has rarely been reported. Patient concerns: A 4.5-year-old male presented with a 4-year history of shortening of the right upper limb and radial head dislocation. The X-ray indicated a lack of the distal part of the right ulna and radial head dislocation. Diagnosis: The X-ray showed obvious bone resorption at the right ulna distal, proximal stubble, and distal part of the epiphyseal residue, which was 4.3 mm shorter after 14 months. The patient was finally diagnosed with NF-1 according to the pathologic examination. Interventions: The treatment included tumor resection, ulnar osteotomy, and fixation by an Ilizarov frame. Outcomes: The Ilizarov frame was removed after 2.7 months of surgery. The radial head was successfully repositioned, and the elbow joint function was significantly improved. No recurrence of the deformity was noted until now. Lessons: Osteolysis (defect without bone destruction) is an extremely rare symptom in patients with NF1. Therefore, it is essential to make the right diagnosis by comprehensive and careful physical examination.