All the parts of the bones involved in articulation within the knee joint, are covered with articular cartilage. This is a shiny smooth continuous layer that allows for a friction free movement in the knee. It is this articular cartilage that is worn away, leading to osteoarthritis.
Articular cartilage can be damaged acutely in an injury (which has the potential to heal) or become chronic when it fails to heal. When there is a general loss of articular cartilage this is termed osteoarthritis.
When a lesion fails to heal, there are many methods to try and regrow cartilage, none of which are perfect. One of the most used and successful techniques is micro fracture, which was popularised by Professor Steadman from Vale, Colorado.
This is a biological form of trying to regrow cartilage from stem cells. It is done via arthroscopic day surgery.
WHAT IS DONE AT THE TIME OF OPERATION?
The articular cartilage is stabilised and all loose bits of cartilage are removed. This leaves a solid rim of supporting cartilage around the lesion. The top layer of bone is then removed. Small holes are then made in the bone by using a small pick. Care is then taken to ensure that the bone bleeds, and specifically from the newly made holes. The knee is then washed out and the operation is finished.
HOW IS CARTILAGE FORMED?
Blood and the stem cells leak out from the holes made in the bone. The blood and stem cells forms a clot in the hole left where the cartilage used to be. This then needs to change and form cartilage. Studies done on stem cells show that when they are exposed to shear stresses or movement, they form into cartilage cells and produce cartilage. For the next 6 weeks, the rehabilitation is very important. The patient is non weight bearing and needs to stimulate the stem cells with movement. This is best done in the form of continuous passive motion (CPM), done via a CPM machine or physiotherapist. The more movement and CPM one can do, the better the success. It is best to exercise the knee everyday and as many times a day as possible.
THE PROCESS AFTER THE FIRST 6 WEEKS
At 6 weeks, the clot in the lesion has started to form cartilage and is basically a gel like substance. One can now begin to weight bear on the leg and start doing more strenuous exercise. This gel then forms to immature cartilage and matures over the coming months to year.
The cartilage will hopefully start to strengthen and allow the patient to regain their pre-injury exercise level. It must be stated though, that even with a successful outcome, the best exercises are going to be cycling and swimming as these are the least weight bearing exercises. Patients can however get back to more robust and contact sports.
Other options for articular cartilage lesions are:
- Cartilage scaffold (as in a Maioregen). This is an “off the shelf” scaffold which is placed into the defect and allows for the body to lay down chondrocytes into the scaffold and form new articular cartilage. The early results of these are extremely encouraging.
- Osteochondral plugs. Cartilage along with bone is taken from another area of knee and put into the defect. Good results but does carry morbidity at the donor site.
- Metal resurfacing (Hemicap). This is a non biological option where the damaged area is replaced with a small metal cap.