Juvenile idiopathic arthritis(JIA) is chronic inflammation commonly occurs in early childhood. Recently, biological therapies are used in JIA at the early stage as same as rheumatoid arthritis, due to retain joint cartilage. However, some of young patients have painful knee problems requiring knee replacement. We experienced 4 cases of JIA treated by knee arthroplasty. The average age at surgery was 33.5 years (range, 26–38 years) with a mean follow-up of 9.5 years (range, 5–18 years). We evaluated the knee range of motion and functional outcomes by the Knee Society Score (KSS), implant selection, postoperative complication, surgery of another joint. Mean range of motion improved from 76.3° (0°–120°) at pre-operation to 110.6° (80°–130°) at post-operation (P<0.05). Mean KSS increased from 47.3 ±20.1 preoperatively to 86.9 ±11.1 (P<0.01) at last follow-up and the mean KSS function from 27.5 ±25.9 to 62.5±20.2 at last follow-up (P<0.05). All of the TKAs were cemented, 5 were cruciate-retaining implant designs, whereas 2 TKAs had constrained posterior stabilized implant designs. Patellar resurfacing was undergone in all knees. Bone graft required in 1 knee within severe knee deformity. Complication were occurred in 5 knees. Medial instability in 2 knees. Skin necrosis, MCL avulsion, recurrence of the synovitis are one in each. All cases had polyarticular type. Previous THA had undergone in 5 hips, synovectomy in 3 knees, foot surgery in 2 feet. At latest follow-up, 1 of 8 TKAs (12.5%) had been revised, and had revision of its polyethylene exchange only. Patients with JIA often have valgus alignment with a flexion contracture and poor bone quality is also frequently compromised. Prescribed immunosuppressive medication or biological agents may cause to infection. In our series there were no infection, but some of these need much more soft tissue release because of severe deformity and flexion contracture. TKA survivorship for JIA is inferior to that typically seen in younger patients with osteoarthritis or rheumatoid arthritis. The knee of conservative therapy were often caused to severe functional limitations. Timimg of TKA may be indicated no matter how young the patient is. Extending timing of TKA may leads to worse outcome and postoperative function. But it may be caution that the surgical exposure can be difficult, because of stiffness, flexion contracture, bony deformity, osteopenia.
