The word 'autologous' means 'from the same body'. 'Chondrocyte' means 'a joint cartilage cell'. So the procedure of autologous chondrocyte implantation (ACI) is to do with the implantation of a person's own joint cartilage cells back into their body.
If there is a fairly substantial area of joint surface damage in the knee (usually on the end of the thigh bone - the femoral condyle or the patella - the kneecap), it is now possible to take healthy cartilage cells and send them to a laboratory for culture (where they are multiplied and make many cells), and then return them for implantation into the damaged area to grow into healthy cartilage.
This means that there are two surgical procedures - one minor procedure to harvest the tiny fragment of normal material to go to the laboratory, and a second bigger procedure some weeks later to do the next step, the implantation.
The damaged area is surgically cleaned up, and then usually a bit of fibrous material (periosteum) is taken from a superficial bone like the shin bone and sewn over the defect, then the cells from the laboratory are injected behind the fibrous restraint, where they start to grow into a sheet of normal cartilage cells.
A similar procedure, MACI®, leaves out the painful periosteum step and uses another material onto which the cartilage cells are seeded and then glued into the damaged area.
ACI is part of an armamentarium of procedures which are now available to help repair the damage of early arthritis:
Other relevant resources on this site: