Jeevan K Karuppannan

Perthes disease, also known as Legg-Calvé-Perthes disease, refers to idiopathic osteonecrosis of the femoral epiphysis seen in children. It should not be confused with Perthes lesion of the shoulder. It is a diagnosis of exclusion and other causes of osteonecrosis (including sickle cell disease, leukemia, corticosteroid administration, Gaucher disease) must be ruled out 8. Perthes disease is relatively uncommon and in Western populations has an incidence approaching 5 to 15:100,000.

Kager triangle is a sharply marginated radiolucent triangle seen posteriorly on lateral radiographs of the ankle. It represents the Kager fat pad, although often the latter term is used as a synonym for Kager triangle, even though they are not strictly the same. It is bordered anteriorly by the flexor hallucis longus (FHL) muscle and tendon, posteriorly by the Achilles tendon, and inferiorly by the calcaneus.

Dose length product (DLP) measured in mGy*cm is a measure of CT tube radiation output/exposure. It is related to volume CT dose index (CTDIvol), but CTDIvol represents the dose through a slice of an appropriate phantom. DLP accounts for the length of radiation output along the z-axis (the long axis of the patient). DLP = (CTDIvol ) * (length of scan, cm) [units: mGy*cm] DLP does not take the size of the patient into account and is not a measure of absorbed dose.