What is the appropriate treatment for a loosened acetabular cup after total hip arthroplasty?

Treatment of Loosened Acetabular Cup After Total Hip Arthroplasty

A loosened acetabular cup after total hip arthroplasty requires revision surgery with the specific approach determined by the extent of bone defect, cup stability, and infection status—with two-stage exchange for infected cases and single-stage revision with impaction bone grafting or cementless reconstruction for aseptic loosening.

Initial Diagnostic Workup

Before determining treatment, you must definitively rule out infection, as this fundamentally changes management:

• Obtain joint aspiration with culture and cell count analysis
• If infection is suspected but aspiration is negative, consider In-111-labeled leukocyte/Tc-99m-labeled sulfur colloid marrow scanning (96% sensitivity, 87% specificity for periprosthetic infection) 1
• Never treat based on superficial wound swabs alone—these are misleading and promote unnecessarily broad antimicrobial treatment 2

Treatment Algorithm Based on Infection Status

If Infection is Present (Septic Loosening)

Perform two-stage exchange revision 2:

1. First stage: Remove prosthesis, thorough debridement, insert antibiotic-impregnated cement spacer
2. Administer 6 weeks of pathogen-specific intravenous antibiotics
3. Second stage: Re-implant new prosthesis after infection clearance (typically 6+ weeks later)

Critical pitfall: Do not attempt debridement with implant retention (DAIR) for a loosened cup—this is reserved only for acute infections with stable, well-fixed components 2.

If Infection is Excluded (Aseptic Loosening)

Your surgical approach depends on the severity of acetabular bone defect (use AAOS classification):

For Paprosky Type 3A Defects (Contained or Medial Defects)

Use impaction bone grafting with cemented cup 3, 4:

• Morsellized cancellous bone allograft compacted into defect
• Medial metallic mesh if needed for medial wall deficiency
• Cemented polyethylene cup
• Survival rate: 83% at 15 years 4
• This approach successfully restores hip center of rotation in 66% mediolaterally 3

For Paprosky Type 3B Defects (Lateral/Rim Segmental Defects)

Avoid lateral mesh—use alternative reconstruction 4:

• Do not use lateral metallic mesh (hazard ratio 2.942 for loosening, only 54% survival at 15 years with bilateral mesh) 4
• Consider cementless hemispherical cup with superior augments
• May require structural allograft or custom triflange components for severe cases
• Survival rate with appropriate technique: 73% at 15 years 4

For Stable, Well-Positioned Cups with Isolated Osteolysis

Consider isolated liner exchange 5:

• Only if cup demonstrates intraoperative stability
• Patient must be asymptomatic
• No progressive osteolysis in weight-bearing areas
• No implant defects or massive polyethylene wear
• Can fill osteolytic lesions through screw holes, though long-term benefit remains unclear 5

Surgical Technique Considerations

For impaction grafting reconstructions 3, 6:

1. Transform segmental defects into cavitary defects through graft compaction
2. Achieve primary cup stability through press-fit
3. Restore anatomic hip center of rotation
4. Use shaped metallic mesh for uncontained defects (medial only)
5. Allow early weight-bearing—the stress promotes faster graft incorporation 6

For severe bone loss requiring double-cup technique 7:

• Outer trabecular metal cup fills defect
• Inner cup provides bearing surface
• Good press-fit eliminates need for screw fixation
• Restores anatomic rotation center

Monitoring vs. Intervention Decision Points

Proceed with revision surgery if any of the following 5:

• Radiographic cup loosening or migration
• Cup malposition
• Osteolysis in weight-bearing areas
• Imminent or present periprosthetic fracture
• Rapid progressive osteolysis
• Implant defects or massive liner wear
• Symptomatic patient with progressive pain

Continue monitoring if 5:

• Cup well-fixed and well-positioned
• Asymptomatic patient
• Stable, non-progressive osteolysis
• No implant defects
• No high-grade polyethylene wear
• No infection signs

Key Clinical Pitfalls to Avoid

1. Never attempt antimicrobial therapy alone without surgery for a loose cup—this has higher failure rates and is only for patients who cannot tolerate surgery 2

2. Do not use lateral metallic mesh for rim defects—this nearly triples the risk of re-loosening 4

3. Do not rely on plain radiographs alone for early loosening—consider dynamic radiography to detect gross cup mobility when standard imaging is inconclusive 8

4. Do not perform isolated liner exchange without confirming intraoperative cup stability—preoperative imaging can be misleading 5

5. Avoid one-stage exchange in chronic infections—two-stage procedures have superior infection eradication rates 2