Are the outcomes of revision knee arthroplasty for flexion instability the same as for other major failure mechanisms?

Abstract Background Aseptic loosening, infection and flexion instability have emerged as the leading etiologies for revision after total knee arthroplasty (TKA). Although studies have reported improved outcomes after revision TKA, the relative functional and clinical outcomes of patients revised for flexion instability and other failure etiologies have not been extensively reported. The aim of the study was to compare the functional and patient reported outcomes of revision TKA for the common failure etiologies. Methods We retrospectively reviewed records of 228 consecutive cases of revision TKA from 2008 to 2014. Revisions performed for aseptic loosening (n=53), septic revisions (n=48) and isolated flexion instability (n=45) with a minimum of 18 months follow-up were included for analysis. Revision for all other etiologies (n=82) were excluded. The Modified Knee Society Score (MKSS), Knee Society Score Function (KSS- Function) and Western Ontario and Macmaster University Osteoarthritis Index were recorded for all cases. A seven-point Leikert scale was used to record patient’s perception of outcomes after revision surgery and analysed based on etiology. Results Although all groups showed improvement in outcome after revision TKR, the changes in MKSS and KSS-Function score varied according to the etiology of failure of the primary procedure with the smallest improvement being reported by the flexion instability group. Conclusions Patients undergoing revision for isolated flexion instability have less improvement in functional outcome as compared to other etiologies. We hypothesize this is due to a higher baseline preoperative knee function in the flexion instability group.