Results of treatment of septic knee arthritis: a retrospective series of 40 cases.

We studied a consecutive series of 40 patients presenting a septic knee arthritis, with a mean age of 49 +/- 20 (range 19-81) years. The aetiologies were: 18 postoperative arthritis, 12 haematogenous infections, 7 arthritis following aspiration or infiltration, and 3 articular wounds. The most common organisms were Staphylococcus aureus and epidermidis (23 cases). Surgical procedures consisted in 20 arthroscopic debridements, 6 open debridements, 14 synovectomies. According to Gächter's classification, there were 8 stage I, 18 stage II, 11 stage III and 3 stage IV cases. Fifteen patients had to be reoperated after the index procedure at our institution: one open debridement, six open synovectomies, one open arthrolysis, one arthrodesis and six total knee arthroplasties (TKA). Final examination was performed after 22 +/- 26 (range 12-96) months. All cases were considered free of infection. Good functional result was present by 19/33 cases (excluding arthrodesis and TKA). The delay between the onset of symptoms and surgery was the major prognostic factor of success (P=0.023). This delay was correlated with Gächter's staging of the intra-articular lesions. The diagnosis of septic knee arthritis must be suspected at the early stage of the disease, and diagnostic joint aspiration must be immediately performed when the diagnosis is suspected. We suggest that the treatment should be more aggressive than generally advocated. Needle aspiration should be only performed at the very early stages. Arthroscopic debridement should be the routine treatment. Synovectomy should be considered even as a primary procedure when significant synovial hypertrophy is present (Gächter stage III and IV) or when a more conservative treatment did not lead to a fast improvement.