Slipped femoral capital epiphyses in irradiated children: dose, volume and age relationships

Between 1960 and 1979, 50 patients under 15 years of age received radiotherapy to the pelvis including the non-fused capital femoral epiphyseal plate. A total of 83 epiphyseal plates were at risk. Eight epiphyseal plates (9.6%) in five patients were abnormal: symptomatic capital femoral epiphyseal slippage--4, asymptomatic slippage--1, severe epiphyseal abnormalities of radiographs--3. No complication occurred below doses of 2,500 rad (25 Gy). Children under the age of 4 at time of irradiation were at a higher risk (7/15-47%) than those over 4 years of age (1/21-4.7%). Most slippages occurred at ages between 8 and 10 years. No dose response curve was obtained--higher doses above the threshold dose of 2,500 rad did not increase the incidence of slippage. A mechanism of action is postulated. This is a preventable complication; judicious use of primary or secondary blocking systems can eliminate or limit the dose to the non-fused epiphyseal plate and prevent later morbid complications