Difficult primary total knee arthroplasty requiring a varus-valgus constrained implant is at higher risk of periprosthetic infection.

The goal of this study was to compare the risk of periprosthetic infection of a consecutive cohort of primary varus-valgus constrained (VVC) total knee arthroplasties (TKAs), with a matched 1:1 cohort of primary posterior-stabilized (PS) TKAs. 74 primary VVC TKAs performed in 66 patients were identified and matched 1:1 with a cohort of 74 primary PS TKAs performed in 73 patients. At last follow up, patients were clinically evaluated using the Knee Society Score (KSS). Kaplan-Meier survival curves were generated to analyze survivorship using as endpoints revision for any reason, revision for periprosthetic infection and revision for mechanical failure after excluding periprosthetic infection. A multivariate logistic regression analysis was constructed to determine whether revision surgery for periprosthetic infection was influenced by patients' gender, age, surgical time and reasons for TKA (primary vs secondary osteoarthritis). Demographic data were not significantly different between the two groups as regard patients' age, gender, body mass index, Charlson Comorbidity Index, reasons for replacement, and length of follow-up. Surgical time was greater in the VVC group (95.7 ± 22.5 min vs 88.6 ± 17.1 min, respectively, p = 0.032). Postoperative KSS, range of motion and radiographic data did not differ significantly between the two groups. Overall revision rate and revision rate for mechanical failure after 5 years of follow-up was not statistically different between the two groups. Considering only the revision rate due to periprosthetic infection, the risk was higher in patients with primary VVC implants (p = 0.013). The surgical time was the only factor that significantly affected the risk of revision for periprosthetic infection (OR 1.0636, CI 95% 1.0209-1.1081, p = 0.0032), whereas patients' gender, age and reason for TKA had no influence. Patients and surgeons should be aware of the higher risk of periprosthetic knee infection using a VVC prosthesis. However, the present study supports the use of VVC implants in cases of difficult knee replacements, since comparable clinical outcomes and overall revision rate was found after at least 5 years of follow up. Retrospective cohort study, Level III.