Risk of Instability After Revision Total Knee Arthroplasty for Periprosthetic Joint Infection.

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Periprosthetic joint infection (PJI) remains a major source of morbidity after total knee arthroplasty (TKA). The risk of recurrent infection has been more extensively studied than the risk of mechanical failure. We sought to define the incidence of instability after revision TKA for PJI and to compare this incidence with that for revision TKA for instability. We retrospectively reviewed patients treated by 4 arthroplasty surgeons at 1 institution. The primary outcome was a new diagnosis of clinical instability after index revision. We analyzed potential risk factors that may contribute to postoperative instability after PJI, including demographic characteristics, implant alignment, number of previous procedures, level of constraint during index revision, and type of spacer used. Patients were matched 1:1 with patients undergoing revision TKA for instability. Continuous variables were compared with Student's t test for normally distributed variables and Mann-Whitney U test for non-normal variables. Categorical variables were compared with Fisher's exact test. Thirty-seven patients who underwent revision TKA for PJI were identified. Twelve (32.4%) had clinical instability after revision, compared with only 3 (8.1%) in the matched cohort (P=.019). Use of a revision, midlevel constraint device in the PJI cohort did not correlate with a lower risk of instability (P=.445). A greater number of previous surgical procedures increased the likelihood of instability (P=.041). Revision TKA for PJI is associated with a high risk of subsequent instability. Midlevel constrained implants may not be sufficient to prevent instability. A focus on soft tissue tension and a lower threshold for increasing constraint may be prudent in this cohort. [Orthopedics. 2022;45(3):145-150.].