You may be referring to a procedure called autologous chondrocyte implantation (ACI). First the surgeon débrides (removes dead cells) the damaged area. This creates a hole that is covered with a thin piece of bone.
Normal, healthy cartilage cells are removed before closing up the hole. These are called chondrocytes. They are sent to a special lab where scientists use them to grow more chondrocytes. Up to 10 million new cells can be made this way.
When the cells are ready, the surgeon injects them underneath the bone flap right into the defect. As they grow and mature, the hole fills in with smooth cartilage once again.
Although the cost can be as high as $25,000, this may be worth it. High-level performance athletes who need to get back into sports play may find the overall costs savings well worth it. The shortened duration of painful symptoms with less time on the bench or in rehab offset the expense.
Likewise, anyone trying to keep a job, supporting self and/or a family may find the cost of restoring the joint surface acceptable.