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Annex A - What is ACI ?

Jun 22, 2007
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What is knee ACI – it’s the acronym for Autologous Chondrocyte Implantation. It is now considered a fairly established medical procedure to repair damaged or partially worn knee cartilages, although not many people have heard of it. Knee cartilages are avascular, meaning they have no blood vessels and they are, therefore not able to be regenerated by the body.

Autologous means using one’s own cells; chondrocytes are specialised type of cells that form the cartilage; and implantation means to patch new cultivated cells back into the knee. This is a two-stage surgery process, where healthy cells are first scraped off from non-weight bearing area of cartilage surface using a technique called arthroscopy. Two keyholes are opened up, one to insert a fibrescope lightsource & camera and the other to insert the tool for the biopsy where about 300mg or some 10,000 cells are harvested. While examining the interior of the knee compartment, any broken fragments of cartilage are removed. The damaged area, known as chondral ulcer, is cleaned up and the jagged edges are trimmed (debrided), to prepare the area for the next stage.

The harvested cells are then taken to a lab, together with a substantial amount of the patient’s blood (about 70 ml) to grow in a special nutrient rich bioreactor. Normally, within 3 to 4 weeks, the 10,000 cells would have multiplied to some 10 to 12 millions cells and ready for implantation. NUH is currently the only medical facility in this region with a cell culture lab called Therapaeutic Tissue Engineering Laboratory (TTEL) to grow these cells. Previously, they are sent to US, UK, Sweden, Japan or Australia for the culture. In my case, owing to the surgeon’s fully booked schedule, my operation was some 5 weeks later. My ulcer was found to be larger and deeper than originally estimated and I probably needed those additional millions of cells.

During the second stage of the surgery, which is an open knee surgery, 2 incisions are made. The major incision is for the main surgery – about 100mm to 150 mm long over the kneecap, to expose the damaged ulcer. In my case, it is at the end of the thighbone, a femoral chondral ulcer. The surgeon then measured and made a template in the exact shape of the ulcer. He then opened a second incision on the shinbone (tibia); about 50 to 70 mm long, to expose the periosteum, the membrane or skin that covers the bone. Using the template created earlier, he cut out a slightly larger layer of the periosteum and immediately sutured this on the ulcer. Bone glue made from one’s own blood was used to cement over the sutured area to seal the overlap. To ensure that the newly created pouch is fully watertight, pressurized sterile saline water was injected into the pouch to test for leak (something like hydrostatic test used in industries). Once no leak was detected, the saline water is drained and the prepared cultured cell is implanted

into this pouch using a syringe. The pouch acts as the formwork where the cells continued to grow and eventually hardened to form the newly created cartilage. Both the pouch and the incisions are then sutured or stitched up. The photos below showed the ulcer before the repair and the fully regrown cartilage.