Complex sentence: Perthes' disease is one of the most common hip disorders in young children, occurring in approximately 5.5 of 100,000 children per year-therefore the lifetime risk of a child developing the disease of about 1 per 1,200 individuals.
Split into simpler sentences: Perthes' disease is one of the most common hip disorders in young children, occurring in approximately 5.5 of 100,000 children per year. The lifetime risk of a child developing the disease is about 1 per 1,200 individuals.