Autologous Chondrocyte Implantation (ACI)

Articular Cartilage Repair

Autologous Chondrocyte Implantation is a surgical technique aimed at repairing damaged articular cartilage. It involves implanting chondrocytes (articular cartilage cells) into the damaged region. These cells subsequently form new articular cartilage.


Articular cartilage is the firm, smooth covering on the ends of bones where they contact other bones to form an articulating joint such as the knee. Together with the thick synovial fluid within the joint, articular cartilage forms a surface that allows low friction movement and assists as a shock absorbing tissue, distributing loads around the joint when walking or running.

Chondrocytes (articular cartilage cells) build articular cartilage by forming a matrix (a complex combination of proteins and water). When articular cartilage is damaged, it does not repair itself effectively like other tissues. Consequently injury can lead to increasing joint pain and reduction in joint movement and can also lead to degenerative change or osteoarthritis (slow degeneration of articular cartilage).

Autologous Chondrocyte Implantation (ACI) is a process whereby articular cartilage cells (chondrocytes) are collected, multiplied in a laboratory to increase cell number and then re-implanted (after approximately 4 weeks) with a special surgical technique into the damaged area of the knee. This would allow cell growth and cartilage repair to occur producing new, durable cartilage.

ACI is suitable for treating cartilage damage caused by direct injury (e.g. sports injuries, car accidents, falls) where the damaged area is surrounded by normal healthy cartilage. Widespread cartilage damage (osteoarthritis) or inflammatory disease ( rheumatoid arthritis) is not suitable for this treatment. Your specialist surgeon will advise you whether ACI is suitable for your condition.

ACI Surgery

This procedure is indicated for those patients who have an isolated full thickness articular cartilage defect in the knee, which is causing symptoms such as pain and clicking. This injury is generally from an acute injury, but can also occur over time, due to repeated injuries. The knee is generally swollen and pain is located over the site of the cartilage injury. It is not a suitable procedure for established osteoarthritis as yet.

The procedure involves taking a biopsy (sample) of the healthy cartilage from the knee through an arthroscopy (keyhole surgery). The size of the defect will also be assessed at this time. The cartilage biopsy is processed in a laboratory where the cartilage cells will be cultivated in a matrix and this takes approximately four to six weeks. Once the matrix or cartilage is ready, it will then be re-implanted. The re-implantation occurs through an arthrotomy where the joint is opened through a small incision to allow accurate placement of the cartilage graft.

Pre-Operative Preparation

After a thorough clinical assessment of the joint, the patient will generally have plain X-rays and an MRI scan of the knee to help accurately assess the location and size of the cartilage defect. At times, the patient may have previously had an arthroscopy. A range of motion brace will be organised prior to the surgery and this will restrict the joint movement and protect the cartilage graft.

The hospital will contact you on the day prior to your surgery to advise you of your admission time. You will also be instructed not to eat or drink anything from midnight the night before your surgery until the surgery has been completed.

First Procedure

The initial arthroscopy for the biopsy is preformed as a day surgery procedure.

Biopsy of Articular Cartilage

The first operation involves the surgeon taking a small biopsy (sample) of your articular cartilage. The operation is performed as a day case and an overnight stay is usually not necessary. The articular cartilage biopsy is then sent to Mercy Tissue Engineering for processing.

Cell Culture

The biopsy is processed, releasing the chondrocytes (articular cartilage cells) from the articular cartilage.

These cells are placed in a nutrient rich medium and incubated which promotes cell growth. The culture process continues until an optimal cell number is attained. This can vary depending upon lesion size but normally ranges between 3 and 4 weeks.

Second Procedure

The implantation surgery requires a hospital stay of two to three days.

Implantation of Cells

The second operation is performed to deliver the new cells into the damaged area. The procedure is usually performed under a general anaesthetic and supplemented with a femoral nerve block to help the post-operative pain. Dr Parker achieves this by sealing the damaged area with a waterproof cover and injecting the cells underneath the cover into this area. The cells attach to the bone and then begin the process of re-establishing the articular cartilage matrix.

The procedure takes approximately 2 hours after which the leg is placed in a knee immobiliser and rested for 24 hours, to minimise the risk of patch disruption and to enable the cells to begin cartilage matrix formation. To ensure the implanted cells are protected, it is necessary to stay in hospital for a number of days to allow progressive joint mobilisation.

Adequate pain relief will be provided using wound infiltration, nerve blocks or demand narcotics using Patient Controlled Analgesia while antibiotic cover will be continued for 48 hours intravenously.

During this time, the physiotherapist will instruct you how to go about walking with crutches wearing a straight-leg splint touching the operated foot to the ground without putting weight on the leg. The brace should be worn day and night and removed only when doing your knee curl exercises (lying on your stomach) and for showering. You will continue to do your quadriceps contraction exercises hourly, throughout waking hours, without removing the brace.

Before you leave the hospital the nursing staff will make an appointment for you to see your surgeon at approximately ten days from surgery.

Post-Operative Rehabilitation

A special rehabilitation program needs to be followed following the implantation of cells. This involves bracing of the knee and a gradual return to full weight bearing. It is vital that the rehabilitation protocol given by the surgeon is followed closely to maximise the benefit of the operation.

Post Operative Reviews

At your ten day post surgery review the wounds will be checked, and an assessment made of pain, swelling, quadriceps control and functional capacity. You will continue to use the brace and crutches. You will again be seen at three weeks from surgery at which time non-resistive cycling and swimming can be added to your program. The duration at which you can start weight-bearing on the leg and be shifted to a range of motion brace will depend on the location of the lesion in your knee.

You will be reviewed again at six weeks to check your progress. At nine weeks from surgery, you should be able to walk without the crutches and at twelve weeks, the brace can be discarded. Activities requiring standing and walking can commence however, all activities such as squatting, kneeling, stair-climbing and bent knee activity should be delayed until six months from implantation, if possible.

Return to sport is not advised within twelve months of implantation and high impact activities should be avoided for two years.

Knee brace

A knee brace will be required for a period of up to three months, depending on the exact location and size of the cartilage defect. The range of motion that will be allowed in the knee brace will also be determined by the exact location and size of the cartilage defect. Generally the patient's weight bearing is restricted for the first six weeks.


This will be commenced immediately and range of motion will also be determined by the exact size and location of the cartilage defect. Initial physiotherapy is concentrated on static quadriceps and hamstring exercises to maintain muscle bulk.

The post-operative rehabilitation regime will be coordinated through your doctor and physiotherapist.

The patient will be seen at two weeks, six weeks, three months and one year post-operatively.

Return to sport is generally at one year. Sport specific exercises however can be commenced at six months. There will be no jogging or running unsupervised until six months. Some sports, such as swimming and cycling, can be commenced at six months; however no contact or high impact sport can be played for one year.

Return to Work

Sedentary work: This can be commenced from two to six weeks after surgery.

Non-sedentary work: This can be commenced from six weeks to three months, depending on the exact nature of the employment.

Results of Autologous Chondrocyte Implantation

International studies show that with the use of cartilage culture and implantation, about 85% of patients are significantly improved, many returning to full, normal pain free activity. The results of cartilage cell implantation are substantially better than those of previous treatments.

Cost of Autologous Chondrocyte Implantation

The total cost of the operation depends upon the type of private health insurance the patient has. For the cell implant, there are no out of pocket costs to patients with private health insurance, and for approved compensable patients e.g. Workers compensation.


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