Table 3.

Definitions of revision reasons

Reason	Definition
Septic loosening	All patients treated with a two-stage reimplantation based on clinical suspicion or proven infection; patients with negative culture samples remained in the septic loosening group because the two-stage treatment was similar to the proven infection cases
Aseptic loosening	Loosening without signs of infection; polyethylene wear with emerging bone loss but no complete loosening also was included in this group
Malposition	Presence of clear malpositioning or malrotation of one or both components, causing pain or patella maltracking
Instability	Instability was defined as a clinical diagnosis with pain and instability experienced by the patient caused by a collateral ligament laxity or PCL insufficiency without any sign of component malpositioning
Stiffness	Stiffness was defined as a clinical condition with a limited ROM (< 70°) after TKA, with or without pain; even if the stiffness was caused by a component malposition or other earlier defined main diagnosis, these patients were solely analyzed in this single group, with the exception of patients with stiffness caused by septic loosening. These patients remained in the septic loosening group