Functional Improvement and Expectations Are Diminished in Total Knee Arthroplasty Patients Revised for Flexion Instability Compared to Aseptic Loosening and Infection.

BACKGROUND:Instability has emerged as the most common noninfectious cause necessitating early revision after total knee arthroplasty (TKA). Although studies have documented improvement in outcomes with revision for flexion instability, it remains unknown how the outcomes compare to patients revised for other failure etiologies. The study purpose was to compare outcomes after revision TKA based on failure etiology.METHODS:A retrospective review of our prospectively collected revision TKA database was performed on patients who underwent revision TKA from October 1, 2010 to November 19, 2014. Demographic data; minimum 1-year Knee Society Scores; and University of California, Los Angeles activity level scores were obtained.RESULTS:One hundred seventy-seven consecutive revision TKAs were evaluated. After exclusion of revisions with confounding variables and diagnosis groups with small numbers, 92 patients with a revision diagnosis of flexion instability, infection, or loosening/osteolysis were compared. There were no group differences in Knee Society objective (P ≥ .460) and satisfaction (P ≥ .112) scores or UCLA activity level scores at final follow-up (P ≥ .118). Preoperative Knee Society function scores were significantly higher in patients with flexion instability (P = .019), but the amount of improvement in function relative to baseline was equivalent in the 3 groups (P = .170). Patients revised for flexion instability were significantly more likely than patients in the other 2 groups to report that their expectations were not met (P = .028).CONCLUSION:Patients and surgeons can expect that revision for isolated flexion instability may only obtain modest improvement compared with other diagnoses, potentially in part due to a higher preoperative functional level in patients with instability.