When a child suddenly refuses to put weight on one leg, or when an adult develops an unexplained deep ache in the hip that appeared without obvious cause, the experience is disorienting. Transient synovitis — an acute inflammation of the synovial membrane lining the hip joint — is the most common cause of acute hip pain in children between three and twelve years old, and it also affects adolescents and adults more often than most people realize.

If you or someone you care about is on corticosteroids — or has already been told that osteonecrosis has developed as a result — the information you've received has probably been frustratingly thin. The standard message is to reduce steroid dosage where possible, take calcium and vitamin D, and watch for hip pain.

Receiving a diagnosis of avascular necrosis (AVN) of the hip—also known as osteonecrosis of the femoral head—can feel like a sudden and silent betrayal by your own body. The primary bone in your hip joint, starved of blood, begins to suffer micro-fractures, initiating a cascade that can lead to joint collapse and severe osteoarthritis.