Final answer:
The most common joint used in radiographic studies to determine a child's bone age is the wrist. The radiograph reveals epiphyseal plates whose development is compared with growth charts to estimate age. The femur's epiphyseal plates also provide age estimates based on their presence and developmental stage.
Step-by-step explanation:
A radiographic study to determine the bone age of a child most commonly involves the wrist joint. The wrist contains multiple growth plates that can be assessed for skeletal maturity. Such a radiograph shows the epiphyseal plates, or growth plates, that appear as dark epiphyseal gaps near the ends of long bones like the radius, ulna, metacarpals, and phalanges. These plates are more cartilaginous and therefore less dense than bone, making them visible in contrast to the ossified areas on the radiographic image. The presence or absence of these epiphyseal plates, which appear and vanish at known ages, can be compared with standard growth charts to estimate the child's age.
The femur also has epiphyseal plates which can be observed in radiographs to estimate the age of the child. The epiphyseal plate located at the base of the lesser trochanter of the femur appears at around age 9–10 years and disappears at puberty, roughly around 11 years of age. Therefore, being able to identify these plates and their stages of development provides valuable information about a child's skeletal age.