Autologous cell techniques, such as autologous cell implantation (ACI) and matrix-induced autologous chondrocyte implantation (MACI) are therapeutic treatments consisting of two surgeries. During the first procedure, healthy hyaline cartilage cells are harvested from the knee. These cells are allowed to expand in-vitro in a specialised laboratorium and are thereafter implanted back into the damaged area during a second surgery. This technique is still considered somewhat experimental, is expensive and requires long rehabilitation.