Prosthetic Loosening on Bone Scan

Understanding Prosthetic Loosening on Bone Scan

Joint replacement surgery (arthroplasty) is one of the most successful orthopedic procedures, providing pain relief and improved function for millions of patients. However, prostheses can loosen over time, causing pain and requiring revision surgery. Bone scintigraphy is a valuable tool for evaluating painful joint replacements to determine the cause of symptoms.

Prosthetic loosening occurs when the bond between the prosthesis and bone fails, allowing movement at the interface. This can result from:

• Aseptic loosening: Mechanical failure due to wear, stress, or bone resorption (most common)
• Infection: Bacterial colonization of the prosthesis (serious complication)
• Osteolysis: Bone loss from particle disease (polyethylene or cement debris)

Why Bone Scan Is Valuable

Bone scintigraphy offers several advantages:

• Functional assessment: Shows bone turnover around prosthesis before X-ray changes appear
• Whole-bone evaluation: Can see activity around entire prosthesis, including stem tip
• Differentiation: Helps distinguish loosening from infection using blood flow patterns
• Multiple prostheses: Can evaluate both lower extremities simultaneously

Imaging Patterns

Normal Postoperative Evolution

After joint replacement, bone scan shows characteristic evolution:

• First 6 months: Moderate to marked diffuse uptake (normal healing)
• 6-12 months: Gradual decrease in uptake intensity
• 12+ months: Minimal to mild uptake around prosthesis

Aseptic Loosening Pattern

Aseptic loosening typically shows:

• Focal uptake at bone-prosthesis interface
• Common locations: Stem tip (for femoral components), cup periphery (for acetabular components)
• Increased intensity: Greater than normal postoperative pattern for that time period
• Normal blood flow: Blood flow phase typically normal (unlike infection)

Infection Pattern

Prosthetic infection typically shows:

• Diffuse uptake around entire prosthesis
• Increased blood flow: All three phases positive
• Soft tissue uptake: May indicate abscess formation
• Persistently abnormal: Unlike normal healing which decreases over time

Clinical Applications

Evaluating Painful Prosthesis

When a joint replacement becomes painful:

• Confirm loosening: Identify components that have failed
• Distinguish aseptic vs septic: Critical for treatment planning
• Assess extent: Determine if one or both components involved
• Guide surgery: Help plan revision approach

Preoperative Planning

For revision surgery planning:

• Confirm loose components: Avoid revising well-fixed components
• Identify bone loss: Areas of osteolysis may need bone grafting
• Rule out infection: Prevents inappropriate revision in infected cases
• Document baseline: Establishes postoperative comparison

Treatment Implications

Aseptic Loosening Treatment

Revision surgery considerations:

• Single-stage revision: Remove loose component, implant new prosthesis
• Bone grafting: May be needed for significant bone loss
• Component selection: May choose more constrained designs
• Recovery: 6-12 weeks protected weight bearing

Infection Treatment

Prosthetic infection requires different approach:

• Two-stage revision: Remove infected prosthesis, place spacer, later reimplant
• Long-term antibiotics: 6+ weeks of targeted therapy
• Multiple surgeries: Higher morbidity than aseptic revision

Evidence-Based Outcomes

Preparing for Your Scan

• Hydration: Drink plenty of water before and after
• Medications: Take usual medications
• Surgical history: Provide date of original surgery, complications
• X-rays: Bring recent X-rays for correlation

Understanding Your Results

Frequently Asked Questions

Does increased uptake always mean loosening?

No, mild diffuse uptake can be normal for up to 12 months after surgery. Focal intense uptake at the bone-prosthesis interface, especially beyond the normal postoperative period, suggests loosening.

Can bone scan distinguish between loosening and infection?

Bone scan can suggest infection (diffuse uptake with increased blood flow) versus loosening (focal uptake without increased flow), but specificity is limited. Joint aspiration and blood tests (ESR, CRP) are often needed for definitive diagnosis.

Will I need revision surgery?

Not necessarily. If symptoms are mild and function is good, observation may be appropriate. Revision surgery is typically reserved for significant pain, functional limitation, or documented component loosening.

References

1. American Academy of Orthopaedic Surgeons. AAOS Guidelines for Revision Joint Arthroplasty. 2024.
2. Society of Nuclear Medicine and Molecular Imaging. SNMMI Procedure Guidelines for Musculoskeletal Imaging. 2023.

Medical Disclaimer: This information is educational only. Always discuss findings with your healthcare provider for personalized medical advice.