Where patients have a focal articular chondral (cartilage) defect which is more than 2cms2 and the surrounding cartilage is healthy in a stable knee, it may be suitable for a cartilage transplant utilising autologous chondrocytes harvested using an arthroscopic cartilage biopsy technique which are then implanted one month later through a “mini open” technique.

Articular cartilage covers the ends of the bones in the knee joint including the back of the patella (knee cap), bottom of the femur and top of the tibia and when healthy is a firm, smooth, glistening white coating that is responsible for the frictionless movement of the surfaces of joints.

Not to be confused with the meniscal fibrocartilage (SEE meniscal repair, meniscal transplant), the articular cartilage is a hyaline cartilage and does not have a blood supply, hence has a very limited capacity to regenerate. Once damaged, the articular cartilage, if only partial thickness will initially remain thinned and may experience pain and swelling with more vigorous activities, but over time is likely to progress to a focal full thickness defect or ulcer.

Full thickness chondral defects may form some fibrocartilage within the defect or remain as a local area of “bare bone”, and depending upon the location and surface area are likely to lead to persistent swelling, joint pain, aching with activity clicking, catching and eventually aching at rest. MRI Scans and/or arthroscopy will generally confirm the site and size of the lesion and whether the underlying bone is significantly affected with inflammation (subchondral oedema) and/or cyst (geode) formation.

If the patient is not morbidly obese, and the chondral defect is focal with a surface area of greater than 2 square cms with healthy surrounding articular cartilage in a stable knee with normal alignment and no history of infection or inflammatory arthritis, with such a focal defect in 1 or several locations, they may be suitable for consideration of cartilage transplant.

Cartilage transplant is not suitable for patients with generalised arthritis who are being considered for knee replacement surgery. Cartilage transplant or Autologous Chondrocyte Implantation (ACI) historically was performed with a periosteal patch cut and stitched over the underlying defect & the new cartilage cells (chondrocytes) were injected in a gelatinous medium under the patch.

Newer techniques (MACI, Arthromatrix, Orthocell) overcame the problem of the gel leakage, by implanting the cells directly onto a biocompatible collagen membrane which is then cut to the size of the defects using a series of templates and an adhesive fibrin glue. Both techniques require a two stage approach, with the initial operation being an arthroscopic biopsy of a small piece of healthy articular cartilage from the knee as a day surgery procedure.

The new cartilage is then grown in a tissue engineering lab and using the newer technique, the chondrocyte cells that have been seeded onto the collagen membrane are then implanted through a small incision (arthrotomy) on the front of the knee approximately 4 to 6 weeks later. Patients usually require a two night stay in hospital and are fitted with a protective brace and crutches.

The rehabilitation process is influenced by the location(s) of the cartilage transplant(s) and there are differences in rehabilitation for the patellofemoral and the tibiofemoral transplants, but generally requires restricted knee bending and weight bearing, increasing on a weekly basis over a 2 to 3 month period before patients are back to walking more normally full weight bearing and with a full range of motion.

This gradual increase in knee function and load helps to stimulate the chondrocytes and surrounding matrix formation. A tailored return to recreational activities and sport is determined based upon specific lesion and patient variables, but usually requires a minimum of 6 to 12 months before recommencing vigorous running and other sporting activities.