Infected knee replacements: the risks a pre-operative clinic can actually change

Design

Systematic review and meta-analysis of 25 observational studies, 24 pooled quantitatively; PROSPERO-registered

Population

Adults undergoing total knee arthroplasty

Primary outcome

Periprosthetic joint infection after total knee arthroplasty

Effect

Obesity odds ratio 5.72 (95% CI 2.65-12.36), coexisting lung disease 5.54 (1.93-15.96), postoperative urinary tract infection 3.59 (1.15-11.21), ASA score 3 or more 2.73 (1.02-7.32), rheumatoid arthritis 2.64 (1.38-5.02), transfusion 2.27 (1.59-3.25), drain 24 hours or longer 2.23 (1.50-3.32), diabetes 2.09 (1.45-3.01), anaemia 1.82 (1.67-1.99), smoking 1.65 (1.34-2.04), male sex 1.39 (1.27-1.51)

Periprosthetic joint infection after knee replacement is uncommon, catastrophic when it happens, and largely managed by the infection service afterwards. This meta-analysis pooled 25 observational studies to ask which factors are associated with it, with the explicit aim of supporting perioperative risk stratification.

Several of the associations are things the patient cannot change: male sex (odds ratio 1.39), an American Society of Anesthesiologists score of 3 or more (2.73), rheumatoid arthritis (2.64), coexisting lung disease (5.54). The interesting ones are the others. Obesity carried the largest single association (5.72), type 2 diabetes 2.09, smoking 1.65, and preoperative anaemia 1.82 — all addressable, some of them over weeks rather than months. So are three intraoperative and postoperative factors: blood transfusion (2.27), intraoperative blood loss over 200 mL (1.51), and a drain left in place for 24 hours or longer (2.23). A postoperative urinary tract infection carried an odds ratio of 3.59.

That last cluster is where this changes practice, because it is nobody's specific job. Correcting anaemia before the list reduces transfusion, which is itself associated with infection. Removing the drain inside 24 hours is a decision made on a ward round. Treating a postoperative urinary tract infection promptly is routine care that becomes urgent when framed as prosthesis protection.

• Screen for and correct preoperative anaemia — it travels with transfusion, which carries its own association
• Set an explicit plan for drain removal within 24 hours rather than leaving it to output
• Treat postoperative urinary tract infection promptly and document it
• Use the weeks before an elective list for smoking cessation and glycaemic control
• Flag coexisting lung disease and an ASA score of 3 or more at the pre-assessment clinic, since these cannot be modified but should change surveillance

Why it matters

The modifiable risks here sit between specialties, which is why they are the ones most often left unowned.

Don't overread it

Observational and heterogeneous — optimising these factors is sensible on general grounds, but this analysis cannot show that doing so reduces infection.

The statistics, in plain English

These are pooled unadjusted associations from observational studies, and several confidence intervals are very wide — obesity spans 2.65 to 12.36, postoperative urinary tract infection 1.15 to 11.21, coexisting lung disease 1.93 to 15.96. A wide interval means the direction is more reliable than the magnitude. The factors also travel together: obesity, diabetes, anaemia and longer operations occur in the same patients, so pooling each separately overstates how independent any one of them is. The authors say plainly that these are associations, not causes.

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