A quantitative system for staging avascular necrosis.

Much of the current confusion and contradiction on the treatment of avascular necrosis of the femoral head is caused by the lack of an agreed efficient, quantitative system for evaluation and staging. We have used a new system to evaluate over 1000 hips with avascular necrosis during a period of 12 years; it has proved to be very valuable. The system is based on the sequence of pathological events known to take place. It allows accurate quantification in both early and later stages, does not use older, invasive diagnostic procedures, and incorporates the newer techniques of bone scanning and MRI. Clinical records of pain and reduced function are not a specific part of the system, although they help to determine treatment and outcome. Hips are first placed into one of seven stages from 0 to VI, based upon the type of radiological change. The extent of involvement is then measured. This allows more accurate evaluation of progression or resolution and better comparison of different methods of management. The system also helps to provide a prognosis and to decide on the best available method of treatment.