- asymmetrical femoral epiphyseal size (smaller on affected side)
- apparent increased density of the femoral head epiphysis
- widening of the medial joint space
- blurring of the physeal plate (stage 1: see staging of Legg-Calve-Perthes syndrome)
- radiolucency of the proximal metaphysis
Eventually, the femoral head begins to fragment (stage 2), with subchondral lucency (crescent sign) and redistribution of weight-bearing stresses leading to thickening of some trabeculae which become more prominent.
The typical findings of advanced burnt out (stage 4) Perthes disease are:
- femoral head deformity with widening and flattening
- proximal femoral neck deformity
Additionally, tongues of cartilage sometimes extend inferolaterally into the the femoral neck, creating lucencies, which must be distinguished from infection or neoplastic lesions. The presence of metaphyseal involvement no only increases the likelihood of femoral neck deformity, but also make early physeal closure with result leg length disparity more likely.