Total knee arthroplasty is one of the most commonly performed surgeries in the United States. Complications following knee arthroplasty are uncommon, especially dislocations. Knee dislocations can be associated with popliteal artery injuries, which are potentially catastrophic and limb threatening. Emergency Department (ED) physicians should be familiar with the management of knee dislocations and complications following total knee arthroplasty. A 61-year-old female presented to the ED with acute right knee pain approximately 10 weeks after undergoing a total knee replacement for tricompartmental osteoarthritis. While at her first outpatient physical therapy evaluation, the patient felt a pop while going from a seated to standing position. Subsequently, she experienced a popping sensation and was unable to bear weight or extend the knee. On exam, she was in obvious pain, her surgical scar was well healed, and her knee was flexed to about 90 degrees and could not be extended. She had a palpable dorsalis pedis pulse and brisk capillary refill. Radiography revealed a posterior dislocation of her tibial prosthesis relative to her femoral prosthesis. Under procedural sedation, the dislocation was reduced and placed in a knee immobilizer. Her neurovascular exam was intact pre and post-reduction. Several months later she experienced another episode of spontaneous dislocation during a routine office visit requiring a second ED visit for reduction under procedural sedation. She was subsequently scheduled to undergo a revision of her total knee replacement due to suspected flexion instability with an inadequate extensor mechanism.