Cartilage Repair

If you suffer from knee pain, you're not alone. Each year, more than 12 million people visit their doctors because of knee pain — half of them with damage to cartilage, called articular cartilage.

Articular cartilage is a firm, rubbery material that covers the ends of bones in the knee joint. It reduces friction in the joint and acts as a "shock absorber." When cartilage becomes damaged or deteriorates, it limits the knee's normal movement and can cause significant pain. If damaged cartilage is not treated, it can worsen and eventually require knee replacement surgery.

Who Is a Candidate

Cartilage repair and regeneration is treatment for an otherwise healthy knee, but not for knees affected by osteoarthritis, a condition that causes natural cartilage deterioration from aging.

The treatment is recommended for patients with knee cartilage damage or deterioration caused by:

  • Injury or trauma, including sports injuries
  • Repetitive use of the joint
  • Congenital abnormalities, meaning those that a person is born with, affecting normal joint structure
  • Hormonal disorders that affect bone and joint development, such as osteochondritis dessicans (OCD)


Before your doctor decides which cartilage repair approach is best for you, you will have a magnetic resonance imaging (MRI) test to determine the severity, size and location of your cartilage injuries. Our Cartilage Repair and Regeneration Center is a leader in using MRI to evaluate cartilage injuries. We also use MRI in your follow-up care to determine the success of your treatment.

Most knee procedures are performed arthroscopically. During arthroscopy, your surgeon makes three small, puncture incisions around your joint using an arthroscope, a small device with a camera that provides a clear view of the inside of the knee. With improvements to arthroscopes and higher resolution cameras, the procedure has become extremely effective for both the diagnosis and treatment of knee problems.

Some procedures require larger, open incisions so the surgeon can have more direct access to the area or treat multiple problems in the joint.

In general, recovery from an arthroscopic procedure is quicker and less painful compared to traditional surgery.

We offer the following cartilage repair and regeneration procedures.

Autologous Chondrocyte Transplantation (ACI): This is a two-step procedure that takes several weeks to complete. First, healthy cartilage cells are arthroscopically removed from a non-weight bearing area of the knee. The cells are then grown in the laboratory for around six to eight weeks.

An open surgical procedure, called an arthrotomy, is then done to implant the newly grown cells. A layer of tissue that covers the outer surface of bone, called periosteum, is sewn over the area and sealed with fibrin glue. The newly grown cells are injected into the defect under the periosteum.

ACI is most often recommended for younger patients who have single defects larger than 2 cm in diameter. ACI uses a patient's own cells, so there is no danger of a patient rejecting the tissue.

Cell-based Cartilage Resurfacing: There are multiple experimental treatments that use a patient's own cells to grow new, healthy cartilage. We are one of the six centers nationwide testing a new implant technology called NeoCart. Patients have access to this treatment by participating in the study, called a clinical trial.

First, surgeons biopsy, or surgically remove, cartilage cells from non-weight bearing areas of your knee joint. Cartilage cells are then grown in a lab before being implanted into a special 3-dimensional scaffold that functions as a type of house where cells live and continue to grow. Once a big enough piece of cartilage is grown, it is implanted back into your knee. A new bioadhesive, which makes implantation quick and easy, is used, taking about an hour to complete. Within months, the cartilage matures and integrates with existing cartilage.

Meniscus Transplant: This procedure is recommended for patients who have lost most of their meniscus or have had it removed. The meniscus provides cushioning and stability to the knee. A meniscus transplant involves transplanting the meniscus from a cadaver donor to restore the shock-absorbing capability of the knee.

The procedure is usually performed through a small incision with the assistance of arthroscopy. Stitches are used to sew the cadaver meniscus to the patients knee.

Microfracture: This procedure is performed arthroscopically. During microfracture, small holes are created in the knee bone. The surface layer of the bone, called the subchondral bone, is hard and lacks good blood flow. Creating holes in the bone allows bleeding. Blood contains bone marrow cells that stimulate cartilage growth and form fibrocartilage, which covers the injured area.

Osteochondral Allograft: If a cartilage defect is too large to be treated by an autograft, an osteochondral allograft may be required. Performed through an open incision, this procedure is similar to mosaicplasty, but the graft is taken from a cadaver donor, or a donor who has died. The graft is carefully sterilized and prepared before implantation and must match the anatomy of the patient. It is then shaped to fit the exact contour of a patient's defect.

Osteochondral Autograft Transplantation (Mosaicplasty): This procedure is typically performed through an open incision. In some cases, it is performed arthroscopically. Osteochondral autograft transplantation involves transferring healthy cartilage tissue, called a graft, from one part of the knee to the damaged area. The graft is taken as a "plug" of cartilage and underlying bone.

A single plug of cartilage may be transferred or multiple plugs may be transferred in a procedure called mosaicplasty. Each plug is a few millimeters in diameter. When multiple plugs are moved to the damaged area, it creates a mosaic appearance.

Follow-up Care

After cartilage repair, you will be on crutches for six to eight weeks. It takes several months to make a full recovery. Some patients require a continuous passive motion machine (CPM), a device that is used to gently flex and extend the knee, after surgery.

We will closely monitor how well your new cartilage is developing and integrating with existing cartilage using advanced quantitative MRI imaging, developed at UCSF. This advanced MRI imaging is the most effective and non-invasive way of charting your progress. You may be a candidate for an evaluation study on cartilage resurfacing procedures using advanced MRI scans.


Reviewed by health care specialists at UCSF Medical Center.

Related Information

UCSF Clinics & Centers

Cartilage Repair & Regeneration Center
1500 Owens St.
San Francisco, CA 94158
Phone: (415) 353–7566

Condition Information

Our Experts

Hubert Kim
Dr. Hubert Kim,
orthopedic surgeon
C. Benjamin Ma
Dr. C. Benjamin Ma,
orthopedic surgeon