Avascular necrosis or AVN is a condition where the microvascular blood supply of a section of bone is compromised to such a degree that the bone cells die and therefore regeneration of the structural component of the bone no longer takes place. This “bone death” results in gradual painful micro-fracture collapse of the weight-bearing section of the bone. It may often take months before any changes are visible on standard X-ray imaging. MRI scan will show changes much earlier than X-ray. As the bone collapse progresses, the involved joint becomes incongruous and this mal-articulation results in arthritis. Hip AVN may be caused by trauma (hip dislocation) or various atraumatic conditions (alcohol, steroids, sickle cell disease, decompression sickness etc.) – most often there is no discoverable cause. Knee AVN is called spontaneous osteonecrosis of the knee (SONK) and usually occurs in elderly female patients with no predisposing factors.
Treatment of Avascular necrosis depends on the age of the patient, the amount of collapse and the presence / absence of established arthritis. A specific type of Avascular necrosis in children (Perthes disease) may resolve spontaneously. In adults a surgical solution is required. Treatment with bone core decompression +/- vascularised strut grafting may be considered in the early stages. In cases with advanced collapse and arthritis, a total hip replacement or total knee replacement operation becomes inevitable.
