collagen matrix), is indicated for healthy patients 18–55 with medium to large sized damage to their cartilage. It is not applicable to osteoarthritis patients. The patient's chondrocytes are removed arthroscopically from a non load-bearing area from either the intercondylar notch or the superior ridge of the medial or lateral femoral condyles. 10,000 cells are harvested and grown in vitro for approximately six weeks until the population reaches 10-12 million cells. Then these cells are seeded onto a film that is implanted into the area of cartilage damage and absorbed back into the tissue into the patient. The implanted chondrocytes then divide and integrate with surrounding tissue and potentially generate hyaline-like cartilage. Another ACI technique, using "chondospheres", uses only chondrocytes and no matrix material. The cells grow in self-organized spheroid matrices which are implanted via injected fluid or inserted tissue matrix. Techniques such as the EELS-TALC to enhance ACI and MACI with enabling chondrocytes to be tissue engineered with long term native knee cartilage phenotype maintenance in vitro and in vivo, with the engineered tissue construct containing stem cell progenitors along with those expressing pluripotency markers and with added advantage of enriched hyaluronic acid (HA) expression by the cells have been reported which will contribute to improvised regenerative therapies for cartilage damage. Autologous mesenchymal stem cell transplantation Because mesenchymal stem cells may regenerate cartilage, cartilage growth in human knees using autologous cultured mesenchymal stem cells is under research and preliminary clinical use, and appears to be safe as of 2016. An advantage to this approach is that a person's own stem cells are used, avoiding tissue rejection by the immune system. Stem cells enable surgeons to grow replacement cartilage, which gives the new tissue greater growth potential. While there are few long-term studies as of 2018, a history of knee problems and body weight are factors for how well the procedure will work. Microdrilling augmented with peripheral blood stem cells A 2011 study reported histologically confirmed hyaline cartilage regrowth in the knee. The successful protocol involved arthroscopic microdrilling/ microfracture surgery followed by postoperative injections of autologous peripheral blood progenitor cells (PBPCs) and hyaluronic acid. The procedure creates a blood clot scaffold on which injected PBPCs can be recruited and enhance chondrogenesis at the site of the contained lesion. See also Meniscal cartilage replacement therapy Meniscus transplant Spheroids of human autologous matrix-associated chondrocytes References External links Minimally Invasive Total Knee Replacement. American