Legg-Perthes is genetic in Yorkies. Did you get a health guarantee from your puppy's breeder? Hopefully she will work with you to get him the surgery he needs.
As MyFairLacy said, you need to let her know the diagnosis so she can stop breeding his parents.
Legg-Perthes Disease (Avascular Necrosis of the Femoral Head) in Dogs http://www.yorkietalk.com/forums/sic...-m-scared.html Legg-Calve-Perthes disease