The traverse sclerotic bands in this case are indicative of growth resumption lines, due to periods of slowed or arrested growth from chronic illness, which in this case included multiple surgeries and periods of nutritional rickets. Historically these lines were refereed to as growth arrest lines, but this is inaccurate as the increased mineralization in times of resumed growth at the provisional zone of calcification (PZoC) are what lead to the increased density, not the temporary cessation of growth. 

An important diagnostic consideration for the knees alone is lead poisoning, where the increased density of the provisional zone of calcification is characteristic. 

Bisphosphonate therapy for osteogenesis imperfecta can give a similar appearance, which is known as the zebra stripe sign. 

Case courtesy of Dr. Deborah Forrester.