What causes Legg-Calve-Perthes disease?

Without an adequate blood supply, part of the rounded top of the thigh bone weakens. The body later removes and rebuilds the affected bone, and the hip can change shape during this process. An ordinary bump or fall does not generally explain the underlying blood-flow interruption.

The femoral head forms the ball of the hip joint. In a growing child, its shape can be affected while damaged bone is being replaced. Stiffness, pain in the hip, groin, thigh or knee, and reduced hip movement may occur. Children with Perthes disease commonly present with limping, sometimes before they clearly describe pain.

This is not the same process as wear-related hip arthritis in an adult. The child's age, the amount of femoral-head involvement and how well the joint moves help the orthopaedic team understand the problem and plan care.

Arrange an assessment if a child has a persistent limp, hip stiffness or recurring pain around the hip, thigh or knee. The clinician may examine hip movement and walking, then decide whether imaging is needed. Keep a note of when symptoms began, whether activity makes them worse and whether the child has started avoiding play or sport.

Follow the activity guidance given by the treating team. Paediatric physiotherapy may help preserve comfortable movement and strength without placing unsuitable stress on the hip. Some children need monitoring alone, while others may be offered bracing or an operation such as osteotomy according to joint shape and stage of healing.

Seek prompt medical assessment if the child cannot put weight on the leg, has severe or rapidly worsening pain, or develops fever, marked swelling or redness around the hip. These features need evaluation for causes other than Perthes disease, including infection or an acute injury.

Book a non-emergency appointment for a limp that continues, restricted hip movement, repeated knee or thigh pain without a clear knee injury, or a noticeable change in activity. Early assessment helps identify where the symptoms originate and avoids assuming that growing pains are responsible.

Ask which part of the femoral head is affected, whether movement or weight-bearing should change, and how the team will monitor bone reshaping. It can also help to ask what exercises are appropriate, which symptoms should trigger an earlier review, and what findings would make surgery worth considering.