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Difficulty: MediumInterpreting Imaging Results

A 42-year-old woman with a history of systemic lupus erythematosus on chronic glucocorticoid therapy presents with progressive right anterior groin pain that worsens with weight-bearing. Given her high risk for osteonecrosis (avascular necrosis) of the femoral head, a series of plain radiographs is utilized over time to track the progression of her disease.

Arrange the following classic plain radiographic findings of untreated osteonecrosis of the femoral head in their typical chronological sequence of appearance, from the earliest stage to the most advanced.

  1. 1Normal femoral head contour and preserved architecture
  2. 2Patchy areas of sclerosis mixed with cystic radiolucencies
  3. 3Subchondral radiolucent line (crescent sign)
  4. 4Flattening and macroscopic collapse of the articular surface
  5. 5Joint space narrowing and acetabular osteophyte formation

Answer

The correct chronological progression of avascular necrosis on plain radiograph is: Normal contour -> Patchy sclerosis and cysts -> Crescent sign (subchondral radiolucency) -> Flattening/collapse of the femoral head -> Joint space narrowing (secondary osteoarthritis).
The natural history of osteonecrosis (avascular necrosis) of the femoral head on plain radiographs follows the Ficat and Arlet staging system. Stage I features normal radiographs (requires MRI for diagnosis). Stage II involves reactive bone remodeling, showing patchy sclerosis and cysts without structural collapse. Stage III represents mechanical failure, beginning with a subchondral fracture (the 'crescent sign') that progresses to macroscopic flattening and collapse of the femoral head. Stage IV is the end-stage result of joint incongruity, culminating in secondary osteoarthritis with definitive joint space narrowing and acetabular changes.

Step-by-Step Solution

1
Identify the underlying pathology and affected structure.
The patient has osteonecrosis (avascular necrosis) of the femoral head, driven by chronic glucocorticoid use.
Establishing the disease process dictates the expected pathophysiology, which involves sequential ischemia, remodeling, mechanical failure, and joint destruction.
2
Determine the early radiographic presentation of the disease.
The earliest plain radiographs are strictly normal. MRI is required for early detection.
Bone cell death does not immediately alter bone mineral density enough to be visible on X-ray until remodeling begins.
3
Sequence the intermediate structural changes of the femoral head prior to joint space involvement.
Patchy sclerosis/cysts occur first due to remodeling. This is followed by a subchondral fracture (crescent sign), which then rapidly progresses to macroscopic flattening and collapse.
Mechanical failure begins on a micro-level (crescent sign) before large-scale architectural collapse (flattening) occurs.
4
Identify the final stage of the disease process.
Joint space narrowing and osteophyte formation occur last.
Unlike primary osteoarthritis, the articular cartilage in osteonecrosis remains viable (nourished by synovial fluid) until the underlying collapsed bone physically destroys the congruency of the joint, leading to secondary osteoarthritis.

Key Concept

Radiographic progression of osteonecrosis (avascular necrosis) of the femoral head
Estimated Time:1m 15s
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Topics

Interpreting Imaging Results

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