A parosteal osteosarcoma is a low-grade, well-differentiated fibroblastic bone-forming tumor that arises from the surface of the bone, namely the outer layer of the periosteum. Parosteal osteosarcoma is a rare form of osteosarcoma, representing only 5% of all osteosarcomas. Parosteal osteosarcoma is not associated with periosteal reaction and is associated with a low risk of metastasis. Low-grade parosteal osteosarcoma is managed surgically. This video demonstrates radical resection of parosteal osteosarcoma of the proximal tibia and prosthetic reconstruction. The video demonstrates many aspects of the procedure, including radical resection of the right proximal tibia and knee joint, reconstruction with the use of a rotating constrained knee prosthesis, mobilization of the popliteal blood vessels, neuroplasty of the tibial and peroneal nerves, and the use of a rotational gastrocnemius muscle flap.