Ulnar focal cortical indentation: a progressive, deforming variant of focal fibrocartilaginous dysplasia

Focal fibrocartilaginous dysplasia is a rare growth disturbance of bone resulting in deformity. In the ulna, focal fibrocartilaginous dysplasia is particularly rare, and the characteristic fibroligamentous tether can result in progressive deformity with progressive dislocation of the radial head. The fibroligamentous tether is similar in appearance and function to the Vickers ligament seen in Madelung deformity. The imaging features of ulnar focal fibrocartilaginous dysplasia include a unilateral angular deformity in the ulna with a radiolucent cortical defect and surrounding sclerosis, with secondary radial bowing or radial head dislocation. Focal fibrocartilaginous dysplasia of the ulna has been described using the term ulnar focal cortical indentation. To review the clinical and radiologic features of four cases of ulnar focal cortical indentation occurring in pediatric patients. We retrospectively reviewed picture archiving and communication system and electronic medical record imaging findings with surgical correlation of ulnar focal cortical indentation at two large specialty pediatric hospitals. Ulnar focal cortical indentation lesions typically arise in the ulnar metaphysis and result in angular forearm deformities with progressive radial deformity including radial head dislocation. Early surgical intervention prevents progression of the deformity and retains range of motion. Ulnar focal cortical indentation, although rare, is likely a progressive form of focal fibrocartilaginous dysplasia resulting in significant deformity and disability. Early recognition of the characteristic imaging features is important for early surgical intervention to preserve range of motion and prevent radial head dislocation.