Dysplasia, also known as epiphysealis hemimelica or Trevor disease, is a disorder that affects the bone joints. It is a rare developmental disorder in young children. It is characterized by overgrowth of the cartilage on the end of one or more of the long bones (carpal or tarsal bones) in the hand or foot. Usually only one limb is involved. Dysplasia may cause limbs that are unequal in length. Less often, the cartilage on other bones, such as those in the ankle, knee, or hip joint, can be impacted.