**5. Conclusions**

This chapter concludes with the principle, classification, and management of three typical conditions, which are considered serious and unsatisfied results after TKA. Causes of stiff TKA divide into three different periods and each period needs specific management, but the most important risk factor for postoperative stiffness is the limitation of preoperative ROM. Patient education and motivation either before or after surgery are necessary to prevent further problems and meet the patient's satisfaction. An exploration of new diagnostic tests enhances the accuracy of PJI diagnosis and the latest scoring-based definition achieved more sensitivity than the previous criteria. Major criteria of two positive cultures of a similar pathogen or the presence of a sinus tract to the knee joint can diagnose PJI. If a diagnosis has not been made, the further investigation of minor criteria, including serum and synovial laboratory tests, would have been collected preoperatively. An inconclusive diagnosis from the minor criteria needs furthermore investigation from intraoperative findings. Periprosthetic fractures are principally classified from the anatomy of fracture site. The most common is a femoral supracondylar fracture and the surgical options depend on fracture location and configuration. Finally, the goal of treatment among these three conditions is return to ambulation with a well-function knee prosthesis.
