Some (including the OP) were asking for links stating that Legg Perthes was not proven to be genetics, like as with Luxating Patella's, it could be also be caused from injury.
Legg-Perthes SiriusDog.com - LEGG CALVÉ PERTHES DISEASE http://www.angelfire.com/fl/atjournal/lp.html
Just a couple stating it is not confirmed to be genetic, that injury and trauma may also be a cause