by EBSCO Medical Review Board


Cartilage is a bendable tissue found in joints. Associated chondrocyte implantation (ACI) replaces damaged cartilage in the knee by taking out healthy cartilage, growing it in a lab, and placing it back in the knee.

Reasons for Procedure

Cartilage helps joints move smoothly. It can get worn down over time or may get damaged by injury. It can cause pain and limit movement.

Possible Complications

Potential problems are rare, but all procedures have some risk. Your doctor will review problems that may happen, like:

  • Excess bleeding
  • Adverse reaction to anesthesia
  • Infection
  • Blood clots
  • Sore throat
  • Surgery failure
  • The need for repeat surgery

Before your procedure, talk to your doctor about issues that may increase your risk of complications such as:

  • Smoking
  • Drinking
  • Chronic disease such as diabetes or obesity

What to Expect

Prior to Procedure

Your doctor will review test that have already been done. This may include x-rays or MRI scans.

Before surgery, you will need to:

  • Arrange for a ride home.
  • Arrange for help at home while you recover.
  • Some medicine can cause problems during the procedure or recovery. These medicines may need to be stopped up to 1 week before the procedure.
  • Talk to your doctor before the procedure about all medicine that you take. This includes over the counter medicine and supplements.
  • Do not eat or drink anything after midnight the night before the procedure.


General or regional anesthesia will be used.

You will be asleep with general anesthesia.

Regional anesthesia will numb the lower half of the body. You will be awake.

Description of Procedure

ACI is done in 2 steps that happen several weeks apart.

Arthroscopy to Remove Healthy Cells

Tiny cuts will be made in the skin along the joint. Special tools will be passed through the cuts. The tools include a small camera. It will send images to a screen in the room so the doctor can see the joint. The doctor will take healthy sample of cartilage. Your incisions will be closed, often with just tape.

The cartilage will be sent to a lab. It will be stored to help grow a large volume of cells. This process takes 6 to 8 weeks.

Open Surgery to Implant New Cells

A larger cut will be made near the joint. The damaged parts of the joint will be removed. The new cells will be implanted into the damaged area. They will be passed in a liquid through a syringe. A membrane will be sewn over the liquid. It will help to secure the cells. The cut will be closed with stitches or staples. You may need to remain in the hospital for 1 to 3 nights after this procedure.

How Long Will It Take?

Removing the healthy cells will take half an hour.

Implanting the new cells will take 1 to 3 hours.

Post-procedure Care

At the Care Center

You will rest as the anesthesia wears off. The care team may give you pain medicine.

At Home

When you return home from the arthroscopy:

  • Use crutches for 2 to 3 days to help support your leg.
  • Follow your doctor’s instructions.

When you return home from the open surgery:

  • Wear a brace as advised by your doctor. It will help keep your knee straight.
  • Use crutches as advised by your doctor. This may be for 6 to 10 weeks.
  • Participate in physical therapy as directed.
  • Maintain a healthy weight. This will reduce stress on the knee.
  • Follow your doctor’s instructions.

If you think you have an emergency, call for emergency medical services right away.

If you think you have an emergency, call for emergency medical services right away.


Family Doctor—American Academy of Family Physicians 

Ortho Info—American Academy of Orthopaedic Surgeons 


Canadian Orthopaedic Association 

Canadian Orthopaedic Foundation 


Articular cartilage restoration. Ortho Info—American Academy of Orthopaedic Surgeons website. Available at: Updated February 2009. Accessed March 29, 2018.

Autologous chondrocyte implantation (ACI). Washington University Physicians website. Available at: Accessed March 29, 2018.

Autologous chondrocyte implantation (ACI). International Cartilage Repair Society website. Available at: Accessed March 29, 2018.

Cartilage repair. UCSF Health website. Available at: Accessed March 29, 2018.

Harris JD, Siston RA, et al. Failures, re-operations, and complications after autologous chondrocyte implantation—a systematic review. Osteoarthritis Cartilage. 2011 Jul;19(7):779-791.

What is autologous chondrocyte implantation (ACI)? Cartilage Repair Center website. Available at: Accessed March 29, 2018.

Revision Information