Increased Risk of Infection in Unicompartmental Knee Arthroplasty Conversions Compared to Revision Primary Total Knee Arthroplasty in the Aseptic Setting: Answering the International Consensus Meeting Call for Database Research.

BACKGROUND

The risk of periprosthetic joint infection (PJI) following conversion of unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) remains unknown. Literature is limited to high-volume centers, prompting the International Consensus Meeting on Infection to call for database research. This study compared PJI incidence between UKA-to-TKA conversions and TKA-to-TKA revisions. The secondary objectives included identifying independent PJI risk factors and evaluating trends in UKA utilization and conversion over time.

METHODS

Using a national insurance claims database, patients undergoing ipsilateral UKA-to-TKA conversion were propensity matched 10:1 to revision TKAs (TKA-TKA). Patients who had an International Classification of Diseases code for PJI (ICD-10-D-T84.53/4) preoperatively or within 10 days of surgery were excluded to minimize inclusion of preoperative infections identified only after intraoperative cultures were obtained. Postoperative PJI was assessed at intervals up to five years. Kaplan-Meier survival analysis compared infection-free survival, and multivariable logistic regression identified independent risk factors. Of the 76,312 side-specific UKAs, 2,101 (2.8%) underwent UKA-to-TKA conversion (UKA-TKA).

RESULTS

The PJI incidence was higher in the UKA-TKA group at all intervals, from 30 days (5.4 versus 1.5%, P < 0.001) to five years (11.0 versus 6.5%, P < 0.001), while infection-free survival was consistently lower (30-days: 94 versus 98%, P < 0.001; 5 years: 86 versus 91%, P < 0.001). Men (odds ratio (OR): 2.89), tobacco use (OR: 1.40), and anemia (OR: 2.15) were independently associated with increased PJI odds. The proportion of UKAs subsequently converted to TKA decreased from 4.3% in 2016 to 1.2% in 2022.

CONCLUSIONS

In a large United States cohort, UKA-TKA was associated with higher rates of PJI than TKA-TKA across all follow-up intervals. Results support infection prophylaxis strategies akin to revision TKA, with heightened vigilance in men, tobacco users, and those who have anemia. Future studies incorporating operative and implant-specific variables are warranted to refine risk stratification.