Professor R.P. Ficat and professor J. Arlet in the late 70s devised a staging system for idiopathic bone necrosis of femoral head based on two fundamental concepts:

1. a standard radiograph shows only the shadow of the mineralized portion of the bone.
2. bone necrosis is the end result of severe and prolonged ischemia.

Staging

Stage 0

• pre clinical and pre radiographic
• suspected in one hip when other hip has definite disease (high incidence of bilateral involvement)

Stage I

• earliest clinical manifestation of syndrome
• sudden groin pain
• progressive, radiation to thigh, often worse at night
• pain may be aggravated by coughing
• limited hip movement
• standard AP and lateral radiographs
  • usually normal, or
  • show minor changes – subtle loss of clarity with poor definition or blurring of trabecular pattern; some slight patchy osteoporosis may be seen

Stage II

• extends over several months
• clinical signs persist or worsen
• changes in trabecular pattern of femoral head
• sclerosis – diffuse, localized or in a linear arc which is concave superiorly
• decalcification may be generalized or in the form of small cysts in the head, usually at some distance from the joint space
• mixed form – sclerosis and cysts may be seen

Transition phase

• crescentic line due to a subchondral fracture
• segmental flattening of femoral head resulting in ‘out of round’ appearance

Stage III

• increasing, more constant pain
• limitation of movement in all directions
• progressive functional incapacity – limp requiring use of a stick
• pathognomic appearance of sequestrum in radiograph
• break in articular margin followed by collapse of sequestrated area into femoral head
• paradoxical preserved or increased joint space in view of limited sequestrum size

Stage IV

• terminal phase of necrotic process
• progressive loss of articular cartilage
• development of acetabular osteophytes
• osteoarthritis imposed on a deformed femoral head

Two variations identified

1. Ischaemic coxopathy
   • narrowing of joint space in early stages of disease – generalized or confined to superomedial quadrant
   • mis diagnosed as primary osteoarthritis in early stages
   • seen in 6th decade
   • sudden onset with pain in night
   • morphologically normal as well as dysplastic hips
2. Bilateral involvement
   • 50% cases of idiopathic bone necrosis
   • 80% of steroid associated bone necrosis
   • frequently asymmetrical involvement

Read more

Ficat, R. P. “Idiopathic bone necrosis of the femoral head. Early diagnosis and treatment.”Bone & Joint Journal 67.1 (1985): 3-9.