Acute Haematogenous Periprosthetic Knee Infection: DAIR or Two-Stage Revision?
A 68-year-old man had a cemented cruciate-retaining total knee arthroplasty 14 months ago. He presents with 18 days of increasing knee pain, swelling and low-grade fever; there is no sinus tract and the wound is well healed. Aspiration yields turbid fluid with a white cell count of 48,000/mm³ and 92% neutrophils; Gram stain shows Gram-positive cocci and culture grows Staphylococcus aureus at 24 hours. CRP is 78 mg/L, ESR 55, WBC 9.2. Radiographs show no loosening and the implant appears well fixed. He is a non-insulin-dependent diabetic with HbA1c 8.1%, BMI 34, and takes metformin. He asks whether he can keep the knee and avoid the big operation. The microbiology laboratory offers oral rifampicin and ciprofloxacin as options.
1. What criteria determine whether this implant can be salvaged with debridement and modular exchange, and how do they apply to this patient?
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DAIR (debridement, antibiotics and implant retention) is reasonable when all of the following hold: symptoms for less than 3-4 weeks, a well-fixed implant with no radiographic loosening, no sinus tract, an organism susceptible to biofilm-active antibiotics, and adequate soft tissues allowing thorough debridement. Modular components should be exchanged.
This patient meets most criteria: 18 days of symptoms, no sinus tract, radiographs showing a well-fixed implant, and S. aureus that is usually susceptible. However, S. aureus (particularly MRSA), diabetes with HbA1c 8.1%, obesity and immunosuppression all lower the success of DAIR, which is roughly 60-80% for staphylococcal infection. He should be counselled that a two-stage revision offers a higher chance of cure but at the cost of two operations, a spacer, a period of reduced mobility and greater bone loss. If he accepts a 20-40% failure risk, DAIR is legitimate; if he prioritises certainty, staged revision is the alternative. Informed patient preference is decisive.
2. Outline your surgical and antibiotic strategy if DAIR is chosen, including duration and the role of rifampicin and ciprofloxacin.
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Surgery: open arthrotomy through the previous incision, full synovectomy, debridement of all compartments and the posterior capsule, exchange of the polyethylene insert and any modular components, and lavage with several litres of saline. Send at least three intraoperative cultures and histology. Preoperative antibiotics are not stopped here because the organism is already known.
Antibiotics, with infectious diseases input: start IV therapy guided by susceptibilities. For susceptible S. aureus, IV flucloxacillin or cefazolin is standard, with vancomycin if MRSA is suspected. Add rifampicin 300-450 mg twice daily once the wound is dry and debridement is complete, because it penetrates biofilm; it causes hepatic enzyme induction (warfarin, DOACs, statins) and resistance emerges if it is used alone. Ciprofloxacin is useful for Gram-negative cover but should not be relied on for staphylococci, where resistance develops quickly. Duration is typically 6 weeks IV followed by oral therapy, or about 12 weeks in total in some protocols, with CRP monitoring. Optimise glycaemic control during admission.
3. If the DAIR fails, describe the staged approach, including the antibiotic holiday and criteria for reimplantation.
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Staged revision: remove the components and all cement, perform thorough debridement, obtain multiple cultures and histology, then implant an antibiotic-loaded cement spacer (for example vancomycin plus gentamicin or tobramycin in Palacos) that maintains limb length and allows some weight-bearing. Give 6 weeks of organism-directed antibiotics with infectious diseases input, then stop all antibiotics for an antibiotic-free interval of at least 2 weeks. During that interval, reaspirate the joint and check CRP and ESR; reimplant only if the aspirate is culture-negative, the soft tissues are healthy and the inflammatory markers have normalised. Reimplantation may require a revision knee prosthesis with augments or cones if bone loss is severe. Warn about spacer fracture, dislocation, renal toxicity from antibiotics, and the risk of failed eradication, which may require arthrodesis or amputation.