Diagnosis of Perthes Disease(Legg-Calve) 
In most children with Legg-Calvé-Perthes disease, the first sign is a limp with or without pain in the hip, knee, thigh, or groin. Ordinary x-rays (radiograms) are almost always diagnostic. The diagnosis may be confirmed by a thorough clinical evaluation, a detailed patient history, and/or a variety of specialized tests, such as magnetic resonance imaging (MRI), arthrography, scintigraphy, and/or sonography.

During MRI, a magnetic field and radio waves are used to create cross-sectional images of the upper end of the thigh bone (capital femoral epiphysis) and may demonstrate abnormal development of the epiphyses. Arthrography, in which an opaque substance is injected into a joint before X-rays are taken, is especially helpful in showing the cartilage surface of the bone and its shape. The X-rays may help to determine the shape of the end of the bone where it joins (articulates) with the hip. Viability of the bone may be evaluated using a specialized technique known as bone scan. During a bone scan, the individual ingests a radioactive substance that will accumulate in the target area (e.g., bones). A specialized camera is then used to detect the levels of radioactivity present in these structures, producing an image of the targeted structure. In sonography, reflected sound waves create an image of certain tissues and body structures and may detect characteristic changes in the hip and femur, such as Caffey sign.