With worldwide aging population, knee osteoarthritis (OAK) cases are rising. Joint replacement isn’t ideal for younger patients due to prosthesis lifespan. High tibial osteotomy (HTO), combined with cell sheet transplants, shows promise for long-term cartilage regeneration. Autologous chondrocyte sheets, which are derived from the patient’s own cartilage, have shown improved clinical outcomes in eight patients with no serious adverse events. However, they require preoperative tissue harvesting and have variable quality. Approved in 2019 as an advanced medical care, it can treat larger defects but has a limitation of 8.4 cm2 or less. Allogeneic chondrocyte sheets, which come from polydactyly surgery waste, tested in 10 patients had no restrictions on the size of cartilage defects and were approved as a Phase II trial due to its success in cartilage regeneration and improved clinical outcomes, and a Phase III trial has been initiated as a corporate clinical trial. Future challenges include mass production, cryopreservation, and a user-friendly design for wider use.