There is a section of absent tibial shaft at the junction of the middle and distal thirds. There is angulation at this point with cupping of the tibia proximal to the absent section and sharpened narrow appearance of the bone distal to this mimicking the appearance of a joint. This appearance is known as tibial pseudoarthrosis
and is usually seen in neurofibromatosis type 1
which was true in this case. There is similar deformity of the fibular.