Avascular Necrosis of the Hip on MRI

What You'll See on Your MRI

Before understanding what avascular necrosis (AVN) looks like on an MRI, let's review some important context about this potentially devastating hip condition.

Think of your femoral head (the ball of your hip ball-and-socket joint) as living bone that needs a constant blood supply. When that blood supply is disrupted, the bone begins to die. This is avascular necrosis, also called osteonecrosis. Without early treatment, the dead bone can collapse, leading to severe arthritis and the need for hip replacement.

Here are the key statistics about MRI accuracy for hip AVN:

Understanding Avascular Necrosis

AVN occurs when blood flow to the femoral head is disrupted, causing bone cell death. Without intervention, the dead bone cannot maintain structural integrity and may collapse.

Causes of Blood Flow Disruption:

• Trauma: Hip fracture or dislocation damages blood vessels
• Corticosteroids: High-dose or long-term use (most common non-traumatic cause)
• Alcohol abuse: Direct toxic effect on bone cells and fat cell accumulation
• Sickle cell disease: Sickled cells block blood vessels
• Other conditions: Lupus, HIV, organ transplantation, diving disorders

Stages of AVN (Ficat and ARCO Classification):

• Stage 0: Normal X-ray, abnormal MRI (earliest detection)
• Stage I: Normal X-ray, MRI changes present
• Stage II: X-ray shows sclerosis or cysts, no collapse
• Stage III: Subchondral collapse or crescent sign
• Stage IV: Flattening of femoral head, joint space narrowing
• Stage V: Advanced arthritis

Symptoms:

• Groin or buttock pain
• Pain worse with weight bearing
• Pain that may radiate down the thigh
• Limping
• Limited range of motion
• Eventually, pain even at rest

How It Appears on Imaging

Let's compare what a normal hip looks like versus what AVN looks like on an MRI:

Key Findings Pattern

When interpreting an MRI for hip AVN, radiologists assess specific features that guide treatment:

When Your Doctor Orders This Test

Here's a typical clinical scenario where an MRI is ordered for suspected hip AVN:

Your doctor might order an MRI for suspected hip AVN if you have:

| Symptom | Why It Matters | |---------|----------------| | Persistent hip pain with normal X-ray | MRI detects AVN months before X-ray | | Risk factors (steroids, alcohol) | High risk for developing AVN | | Pain in groin or buttock | Classic referred pain pattern from hip | | Pain worse with weight bearing | Suggests mechanical problem in hip joint | | Limited range of motion | Indicates hip joint pathology |

What Else Could It Be?

Not every hip pain with bone marrow edema is AVN. Here's what else could be causing similar findings:

How Accurate Is This Test?

The evidence for MRI in hip AVN diagnosis shows excellent performance:

What Happens Next?

If your MRI confirms hip AVN, here's what to expect:

Prognosis and Treatment Outcomes

Early AVN (Stages I-II, no collapse):

• Core decompression success: 60-80%
• Best results when ＜ 15% of femoral head involved
• Combined with bone grafting: improved outcomes
• Without treatment: ＞ 80% progress to collapse

Advanced AVN (Stages III-IV, collapse present):

• Core decompression less effective
• Usually requires total hip replacement
• THR outcomes: excellent pain relief, 95% patient satisfaction
• Prosthesis longevity: 15-20+ years in most patients

Bilateral Disease:

• Present in 50% at diagnosis
• Need for eventual bilateral surgery in 30-40%
• Sequential rather than simultaneous surgery typically

Risk Factors for Progression:

• Larger necrotic area (＞ 30% of femoral head)
• Involvement of weight-bearing region
• Continued corticosteroid use
• Alcohol use
• Advanced stage at diagnosis

Frequently Asked Questions

Can AVN heal without surgery?

In very early stages (Stage 0-I), some cases may stabilize with conservative treatment (medication, protected weight bearing), but most progress. Core decompression in early stages provides the best chance of preventing collapse and avoiding hip replacement.

Will I need a hip replacement?

Not necessarily. If AVN is detected early (before collapse), hip-preserving procedures like core decompression may prevent the need for replacement. However, once collapse occurs, hip replacement is usually the most reliable treatment.

How long does it take for AVN to progress?

From early AVN to collapse typically takes 6 months to 2 years, but this varies. Some progress rapidly (months), others slowly (years). Regular MRI monitoring helps track progression.

Can AVN be prevented?

If you have risk factors (especially corticosteroids), some preventive measures may help: limit steroid dose and duration, avoid alcohol, treat underlying conditions, consider bisphosphonates (controversial), and maintain bone health with calcium/vitamin D.

What is core decompression?

Core decompression is a minimally invasive surgery where one or more holes are drilled into the femoral head. This relieves pressure inside the bone, improves blood flow, and creates channels for new blood vessels to form. Combined with bone grafting in some cases.

References

Medical Disclaimer: This information is for educational purposes. Always discuss your imaging results with your orthopedic surgeon or healthcare provider for personalized medical advice.