Articular cartilage damage

Traumatic damage to the lining surface of the joint is quite common.

As can be seen here on this arthroscopic picture, the smooth white articular cartilage has been damaged and a piece knocked of to expose the underlying bone. Some blood clots can also be seen, indicating this to be an acute injury. The underlying meniscus cartilage is normal.

This can occur either from acute trauma which is common with injuries such as cruciate ligament injury, patella dislocation or direct impact injuries.  It can also occur as a result of a pre-existing condition in the knee called osteochondritis dissecans (OCD).

Osteochondritis dissecans is a condition which usually develops in children and adolescents.  It may not present until adulthood, but commonly will present in the childhood age group.  It is caused by an abnormality to an area of bone underneath the cartilage to which it is thought there is a problem with the blood supply.  The underlying bone fails to function and mature properly with the end result that the overlying articular cartilage does not get any nutrition and therefore 'dies'.  The articular cartilage piece can come loose and actually fall off into the knee joint and cause a number of problems.  When it falls off, it leaves a bare bed of bone which in itself can also lead to mechanical symptoms.

Occasionally articular cartilage defects are found coincidentally, either on an MRI scan or an arthroscopy for some other reason and were, prior to discovery, asymptomatic.

There is debate as to the treatment for asymptomatic lesions, but certainly if they are small in size, there is some literature to suggest that they should be left alone.

The treatment options for isolated articular cartilage lesions include:-

1. Hyaluronic Acid injections.

2. Debridement. 

* This would include the removal of any loose flaps of articular cartilage that may be present.  This is usually done arthroscopically.  The size, depth and location of the lesion are recorded.  If the lesion is small and less than 1 cm in diameter, this may be all that is required.  If the overlying articular cartilage flap is loose in the joint, then this is removed.  In acute osteochondral fractures, where the articular cartilage piece has come off with a sizeable chunk of bone, the piece can be reattached and fixed with a screw, but unless the bony piece is sizeable, the overlying cartilage will usually not heal and it may therefore be better to remove the piece.  In osteochondritis dissecans, as the underlying problem is with the bone, there is really no point in trying to fix these pieces back on if they are loose, as the cartilage will not heal.  Similarly, if the piece that has been knocked off is essentially all cartilage, this should be removed, as reattaching it will serve no function as it cannot heal. If the overlying articular cartilage is loose but is attached, then one option that has been suggested is to drill through the cartilage in order to try and get the underlying bone to provide nutrition to the overlying cartilage and try and get it to heal.

3. Microfracture.

* Once the underlying bone is exposed, the aim of the treatment is either to fill the defect with scar tissue or to try and transplant viable cartilage cells into it.  Full thickness articular cartilage defect does not heal on its own to form normal hyaline articular cartilage in humans. The aim of microfracture is to make holes in the exposed bone using a bone awl. The hole will penetrate the subchondral plate and cause bleeding in to the defect. The blood will then go on to form a clot and trap fibrous tissue producing cells in the clot. Thes cells then can produce fibrous tissue (scar tissue) to fill or partially fill the defect. The filled defect is not normal articular cartilage, but will cover some or all of the exposed bone.

Diagram to show microfracture being performed

4. Abrasion chondroplasty / drilling

* The above microfracture principles can be performed using a high-speed burr or a drill to make the holes in the bone. However, these techniques result in the production of heat which is detrimental to cells. It is therefore believed that the fibrous (scar) tissue produced by these two methods is inferior in quality and less in volume than with microfracture.

Diagram of abrasion (burr) chondroplasty.

5. Mosaicplasty.

* This technique involves taking a "plug(s)" of bone and overlying cartilage from one part of the knee and implanting the plug(s) into the cartilage defect. This does have some limitations for both the donor and graft sites and really is "robbing peter to pay paul". It is going out of favour.

Diagram of mosaicplasty. Plugs are taken, the defect is drilled to form sockets and the plugs are impacted into these sockets.

6. Articular Cartilage Transplantation.

* This procedure is a state of the art technique that is being performed by selected surgeons, of whom the kneedoc is one. It involves taking a small sample of healthy cartilage from the knee arthroscopically and sending it to a lab to culture the cartilage cells. The cells are then returned back and implanted into the knee defect at a second operation. The early to medium term results are very promising.

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