The Joint EBJIS-MSIS 2026 Conference

Management of early periprosthetic joint infection (PJI) after total knee arthroplasty complicated by soft-tissue defects remains challenging — particularly the role of flap coverage after debridement. While a gastrocnemius flap may improve soft-tissue healing and offer blood supply to the periosteal bone, increasing the chance to get rid of infection, its influence on infection eradication and its potential to mask persistent infection, are not well established.

CASE PRESENTATION

• 66-year-old female with rheumatoid arthritis (RA), treated with hydroxychloroquine (Plaquenil®), sulfasalazine (Salazopyrin®) and methotrexate (MTX)

• Primary TKA with a full-constrained (LCCK) prosthesis, indicated for a severe AORI III_B tibial bone defect in a genu varus Ahlbäck V knee osteoarthritis (secondary to RA)

• 6 weeks post-op: sinus tract with purulent discharge at the left knee, elevated inflammatory markers CRP, fibrinogen and ESR, w. normal WBC

• Symptom onset approximately 2 weeks prior to admission

DIAGNOSIS

Early periprosthetic joint infection (PJI) of a fully constrained (LCCK) primary TKA, in a host with rheumatoid arthritis (RA) on immunosuppressive therapy.

CLINICAL CONTEXT

Rheumatoid arthritis (RA) and long-term immunosuppressive therapy are established risk factors for periprosthetic infection and can impair infection clearance — a relevant background factor throughout this case, particularly around the timing of hydroxychloroquine and sulfasalazine reinitiation (stopped MTX due to side effects).

IMPLANT RATIONALE

A full-constrained (LCCK) design was indicated for the severe tibial bone defect AORI III, providing constrained stability where bone loss precludes a primary condylar-constrained or posterior-stabilized implant — but such constrained constructs also carry a recognized higher infection burden in the literature.

CASE TIMLINE

03.09.2025 - Index Surgery

late oct. 2025 - Sinus tract, purulent discharge, elevated CRP/fibrinogen/ESR → DAIR + gastrocnemius flap; MRSA isolated

Jan. 2026 - Sinus tract recurrence after hydroxychloroquine reinitiation at 2 weeks post → persistent infection suspected

March 2026 - Prosthesis removal, antibiotic cement spacer, external fixator; recurrent MRSA isolated — antibiogram identical to Oct 2025, confirming persistence of the same strain

Apr. 2026 - Gradual clinical and biochemical normalization; discharged home in good condition on suppressive rifampicin + co-trimoxazole (≥6 months)

SURGICAL MANAGEMENT - DAIR 1st

• DAIR (Debridement, Antibiotics, and Implant Retention) performed in an attempt to preserve the prosthesis

• Complete excision of the sinus tract, replacement of mobile prosthetic parts - inlay

• Medial gastrocnemius flap with split-thickness skin graft (STSG) for soft-tissue reconstruction

PATHOGENS IDENTIFIED

Methicillin-resistant Staphylococcus aureus (MRSA) at both the initial DAIR (Oct 2025) and the March 2026 revision — identical antibiogram at both timepoints (Fig. 7), and a molecular panel (Sepsis Flow Chip) at revision confirmed S. aureus + mecA only, negative for other pathogens.

POST-DISCHARGE

Oral suppressive therapy (rifampicin + co-trimoxazole) — reinstituted after the March 2026 revision and planned for a minimum of 6 months.

REVISION SURGERY - prosthetic explantation 2nd

• Prosthesis removal with extensive debridement

• Antibiotic-loaded cement spacer implanted — insufficient stability due to deficient bone stock after debridement

• External fixator applied to ensure limb stability

• Recurrent MRSA isolated — antibiogram identical to the initial DAIR culture (Fig. 7), confirming persistence of the same strain; molecular panel negative for other pathogens

OUTCOME

Gradual clinical and biochemical normalization through April 2026 (see Fig. 6). Discharged home in good general condition on suppressive rifampicin + co-trimoxazole, planned for a minimum of 6 months.

DISCUSSIONS

• Gastrocnemius flap may improve soft-tissue healing, but its effect on infection eradication is not well established

• Soft-tissue reconstruction may delay recognition of, or mask, persistent infection beneath healed coverage

• DAIR success is debatable in a complex host: rheumatoid arthritis, immunosuppressive therapy, fully constrained implant, and major bone defect

• Reinitiation of hydroxychloroquine preceded clinical recurrence — a possible contributing factor, not stated in literature

• Prolonged retained hardware (spacer, fixator) may not guarantee eradication of a resistant organism — the identical antibiogram at relapse raises the question of when eradication is achievable versus chronic suppression

Learning pearls:

1. Flap coverage can heal the wound while infection persists beneath it.

2. Immunosuppression timing should be closely coordinated with infection surveillance.

3. An identical antibiogram months apart indicates relapse of the same organism, not reinfection — arguing for long-term suppression once eradication has failed

twice.

CONCLUSION:

This case underscores the diagnostic and therapeutic dilemma of DAIR for PJI complicated by a soft-tissue defect requiring flap coverage, in an immunocompromised host. Flap coverage may obscure clinical signs of persistent infection, and — as this patient's course shows — apparent control can be followed months later by relapse of the very same MRSA strain, confirmed by an identical antibiogram. This supports vigilant, prolonged surveillance and a pragmatic shift toward long-term suppressive therapy once repeated eradication attempts fail.

REFERENCES:

1. Schenk HM et al. Risk factors for treatment failure in late acute PJI in RA patients treated with debridement. J Bone Joint Infect. 2025.

2. Wiberg R et al. Outcome following soft tissue coverage with a medial gastrocnemius flap of an exposed/infected TKA. Acta Orthop. 2023.

3. Grassa D. et al. The role of the gastrocnemius flap in implant retention strategies for acute PJI following TKA: Asystematic review. Arch Orthop Trauma Surg 2025.

4. Auw Yang KG et al. Gastrocnemius muscle flaps for soft tissue coverage in periprosthetic knee joint infection. J Arthroplasty. 2020.

5. Munoz-Gallego i. et al. Microbiological and molecular features associated with persistent and relapsing S. aureus prosthetic joint infection. Antibiotics. 2022.

6. Lo CH, Tang YHB. Outcomes of primary and revision TKA with constrained condylar knee prosthesis - A retrospective Review. J Orthopaedics, Trauma and rehabilitation 2025.

7. Westberg et al. Infection after constrained condylar knee arthroplasty: incidence and microbiological findings in 100 consecutive TKAs. J Bone Jt Infect. 2018.

8. Pramhas D et al. Mid-term results of the LCCK constrained total knee arthroplasty. Bone & Joint (Orthop Proc). 2016.

9. Greenberg a. et al. Survivorship and complications in revision TKA with a constrained condylar knee implant: minimum 10-year follow-up. J Arthroplasty. 2025.

10. Chalmers B.P. et al. External fixator arthrodesis antibiotic spacer in two-stage revision TKA for eradication of PJI. Arthroplasty Today. 2019.

11. Harrabi H. et al. Suppressive antibiotic therapy in prosthetic joint infections: a contemporary overview. Antibiotics. 2025.

12. Shao H. et al. Which serum markers predict the success of reimplantation after periprosthetic joint infection? J Orthop and Traumatology 2022.

13. Zhao D. et al . The role of fibrinogen in predicting reinfection after DAIR for periprosthetic joint infections. BMC Musculoskelet. Disord2021.

The Joint EBJIS-MSIS 2026 Conference

Debatable DAIR in PJI associated to a primary complex TKR in a patient with known PRA - Discussions

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