My regular orthopedic surgeon sent me to a specialist who does cartilage implants. They can use my own cartilage cells to make more and then fill in the hole in my knee joint. But when I went to the specialist, I was told I also need another surgery to realign my knee joint. How do I know this new guy isn’t just trying to drum up more business by saying I need two surgeries instead of one?

Autologous chondrocyte implantation (ACI) involves the use of normal, healthy cartilage cells to fill in a hole (defect or lesion) in the joint surface of the knee. The defect goes clear down to the bone below the cartilage. It’s called a full-thickness cartilage and osteochondral lesion. Osteochondral refers to bone (osteo) and cartilage (chondral).

Autologous chondrocyte implantation is done in two separate steps. First, the surgeon removes the harvested cartilage cells from an area of the knee that doesn’t bear weight. They are taken to a lab where the cells are multiplied until they have enough to fill in and cover over the defect.

A second surgery is done to implant the new healthy cells. If there are any alignment problems or other soft tissue injuries, surgery is done before implantation to correct them. The corrective surgery is a necessary step in order to protect the implanted area. If there are uneven forces within the joint, the load imbalance can reinjure the same spot all over again.

Usually, the realignment process involves rebalancing the muscles around the knee joint so they don’t pull unevenly, reconstruction of the anterior cruciate ligament, or an oosteotomy. The osteotomy involves removing a wedge- or pie-shaped piece of bone from one side of the joint. The effect of an osteotomy is to reduce the uneven forces in a knock-kneed or bow-legged knee.

If you have any doubts about the procedure and what’s needed, ask your regular orthopedic surgeon for his or her thoughts as well as a recommendation for a second opinion.