Perthes disease affecting the entire right femoral head; this child had early disease onset at age 3 and exhibits overgrowth and deformity of the femoral head as well as premature growth arrest of the upper femoral epiphysis. Image source: L. Davidson

Legg-Calve-Perthes disease (often simply called "Perthes") is a hip disorder that affects young children (common age range 4-8, however exceptions at either end of range occur). The disorder is rarely bilateral and is not felt to be genetic in origin.

Children generally present with a painless limp and radiographic evidence of avascular necrosis of the femoral head. The exact etiology is unknown however the disorder is more common in boys and in children with a prior diagnosis of Attention Deficit Disorder. Rarely, children present with acute pain that resolves over a few days. Xrays are normal at this stage but become diagnostic over the following weeks to months as the painless, Trendelenburg limp develops.

The outcome of Perthes disease depends on the shape of the femoral head at disease healing. All treatment attempts aim to maintain a congruent hip joint (i.e. one where the ball fits the socket) by maintaining range of motion with physio and (in older children) surgically redirecting either the femoral head or the acetabulum to maintain "coverage". This is analagous to using a muffin pan to form batter as it cooks: in this case the femoral head is the soft "muffin" and the acetabulum the pan.

Young children (<6) with Perthes tend to do well into mid-adulthood regardless of treatment. Older children (>8) have a less favourable prognosis and a higher incidence of symptomatic osteoarthritis.