OBJECTIVE A knee fusion is associated with considerable restrictions, including the inability to sit properly, use public transportation, and climb stairs. The purpose of this study is to report and discuss our cases of spontaneous ankylosed knees which were taken down and underwent total knee arthroplasty (TKA). METHODS Six patients who experienced spontaneous ankylosis of the knee undergoing conversion to TKA between 2003-2012 were enrolled retrospectively in this study. The etiology was childhood pyogenic arthritis in 2 patients, intraarticular fractures in 2, gunshot in 1, and juvenile rheumatoid arthritis in 1. The clinical data were recorded with the use of the Hospital for Special Surgery (HSS) knee rating system, Western Ontario and McMaster Questionnaire (WOMAC), and Visual Analog Scale (VAS), preoperatively and postoperatively at final follow-up. RESULTS The average follow-up time was 86 months (range: 22-126 months). At the final follow-up, the average range of active flexion was 85° (range: 75-95°). Postoperative average HSS knee rating system was improved from 19.5 (range: 18-22) to 57.49 (range: 46-80), WOMAC was improved from 39.75 (range: 36.4-43) to 62.41 (range: 50.8-74.5). VAS was improved from 9.5 (range: 7-9) to 2.8 (range: 2-4). A pyogenic infection developed in 2 patients; 1 was managed by debridement, and 1 was managed by arthrodesis 2 years later. CONCLUSIONS The ability to walk and sit in a normal fashion is of great importance for patients. With good preoperative planning and careful handling, gratifying results are possible with TKA.