To this day, the cause of Perthes disease remains unclear.  A great review article available publicly on https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6429000/ summarizes prior research studies identifying potential causes and associations with Perthes disease. The article concisely summarizes previously studied associations including various exposures, genetic factors, and socioeconomic factors. There certainly is need for more research on the cause

MRI and sonography in Legg-Calvé-Perthes disease: clinical relevance of containment and influence on treatment.  Journal of Children’s Orthopaedics, 2018 October Jandl NM, Schmidt T, Schulz M, Rüther W, Stuecker MHF In a recent study, ultrasound measurements were correlated with magnetic resonance imaging (MRI) measurements to evaluate the utility in determing how contained the femoral head was in the acetabulum (hip socket).