What is the appropriate evaluation and management for an 86‑year‑old who underwent hip arthroplasty two weeks ago and now presents with night sweats and weight loss?

Periprosthetic Joint Infection Workup Required

This 86-year-old patient presenting with night sweats and weight loss two weeks after hip arthroplasty has a periprosthetic joint infection (PJI) until proven otherwise and requires immediate diagnostic evaluation starting with hip radiographs followed by image-guided joint aspiration with synovial fluid analysis.

Initial Diagnostic Approach

The combination of constitutional symptoms (night sweats, weight loss) in the early postoperative period is highly concerning for infection. Begin with:

1. Plain Radiographs

• Obtain AP and lateral hip radiographs first 1
• Look for: joint distension, periosteal reaction, component loosening, or soft tissue gas
• Note: Radiographs may be normal in early infection but are essential baseline imaging

2. Image-Guided Joint Aspiration (Gold Standard)

Joint aspiration with synovial fluid analysis remains the most useful test for confirming or excluding infection and identifying the causative organism 1. This should be performed urgently given the clinical presentation.

• Sensitivity: 68.6%, Specificity: 96.4% 1
• Can be performed under fluoroscopic, ultrasound, or CT guidance 1
• Send fluid for:
  • Cell count with differential
  • Gram stain and culture (aerobic, anaerobic, fungal)
  • Alpha-defensin and leukocyte esterase testing 1

3. Complementary Advanced Imaging

If aspiration is non-diagnostic or cannot be performed immediately, the following are appropriate complementary studies 1:

MRI Hip (Without IV Contrast)

• Highly accurate for detecting infection features 1
• Look for: soft tissue edema (sensitivity 86.7%, specificity >73.3%), lymphadenopathy (80% sensitivity, 86.7% specificity), fluid collections, periosteal reaction 1
• IV contrast generally not necessary for diagnosis 1

WBC Scan with Sulfur Colloid

• High specificity (88-100%) but variable sensitivity (33-100%) 1
• Useful when aspiration inconclusive

Critical Differential Considerations

While infection is the primary concern, be aware of rare mimics:

• Adverse reaction to metal debris (ARMD): Can present with constitutional symptoms and groin mass 2. However, this typically occurs with metal-on-metal prostheses and later in the postoperative course
• Pyoderma gangrenosum: Rare neutrophilic disorder that mimics infection 3, but typically presents with characteristic skin lesions

Laboratory Workup

Obtain simultaneously with imaging:

• ESR and CRP (elevated in infection but non-specific)
• Complete blood count
• Blood cultures if febrile

Common Pitfalls to Avoid

1. Do not delay aspiration waiting for inflammatory markers—they are non-specific and the clinical picture demands definitive diagnosis
2. Do not rely on bone scan alone—sensitivity/specificity too variable (29-88%/50-92%) 1
3. Do not assume negative cultures exclude infection—consider atypical organisms (Group G streptococcus 4, Parvimonas micra 5, Candida 6)
4. Do not dismiss constitutional symptoms as unrelated—they indicate systemic involvement requiring urgent evaluation

Timeline Considerations

At 2 weeks post-surgery, this falls within the acute postoperative infection window. The incidence of PJI within 2 years after THA is 1.63% 1, but constitutional symptoms significantly elevate suspicion. Prosthesis infection can present as late as day 77 postoperatively 7, making early aggressive workup essential.

Management Algorithm

1. Immediate: Hip radiographs + laboratory workup
2. Within 24-48 hours: Image-guided joint aspiration
3. If aspiration delayed/non-diagnostic: MRI without contrast OR WBC/sulfur colloid scan
4. If positive: Urgent orthopedic surgery consultation for potential debridement/revision

The age of this patient (86 years) and timing (2 weeks postoperative) place them at higher risk for complications and mortality 8, making rapid diagnosis and treatment imperative for preserving both function and life.