WHAT IS THE ROLE OF CARTILAGE TRANSPLANTATION IN THE KNEE?
Evolution in biotechnology gives us the ability to harvest chondrocytes from the knee and stimulate them to reproduce in the lab. They can then be inserted back into the articular defect with the aim of laying down a hyaline articular matrix. This is known as Autologous Chondrocyte Implantation (ACI). We are now using the third generation of this technology in which the cells are grown onto a Type III collagen membrane which is then “glued” into place with fibrin glue, which is called Matrix Autologous Chondrocyte Implantation (MACI) .
Knee articular hyaline cartilage is an avascular tissue and if it is damaged, is unable to repair itself. In the past, no method to restore hyaline cartilage existed and often a damaged joint surface has signalled the end of an athlete’s career. Typically, patients damage the joint surface through a combination of compression and sheer forces, such as during an anterior cruciate rupture or a patella dislocation.
MACI Graft Undergoing Preparation
Before and after MACI Graft Insertion
Currently ACI or MACI is indicated for traumatic lesions greater than two centimetres in size where the matching articular surface is in good condition and the patient is less than 55 years or age. Patellofermoal defects do more poorly than tibio-femoral defects.
At this stage osteoarthritis is a contraindication as the graft will not survive in an arthritic joint, but improve techniques may change this. Trials are currently underway in some osteoarthritic OA defects, if the original cause for the OA can be reserved. It is important that the patient has a neutrally aligned limb, else the graft will fail. At times, a simultaneous osteotomy maybe necessary to correct the limb alignment prior to the MACI.
Other treatments for chondral defects are available such as marrow stimulation or Moscaiplasty, but have they disadvantages, particularly with large defects.
The most exciting area of Autologous Chondrocyte Implantation is that it offers a pathway in the future to move away from Knee Replacement toward chondral resurfacing in the arthritic knee. Knee replacement is inherently problematic as the metal alloy and polyethylene bearing surfaces continually wear, limiting the joints survival. New alloys and other materials wear less slowly helping the problem , but the best solution is to replace the knee with new chondral surfaces. Future advances will enable the production of the chondrocytes in a hyaline-like gel that can be directly implanted into the knee.