I never know quite whether to tell strangers I meet at parties what I do. It doesn’t take some long to get a blow-by-blow account of their knee problem. It often starts with “I have damaged my cartilage and had keyhole surgery etc etc.” There seems to be some confusion as to what exactly “cartilage “ means. So I thought I would explain…
Inside the knee there are two types of cartilage.
1) Articular cartilage. This is the cartilage that coats the end of the thigh bone (femur) and shin bone (tibia), there is also articular cartilage on the knee cap. Articular cartilage is the same stuff that forms the knuckle on a chicken bone. Articular cartilage is a few millimetres thick and provides the slippery joint surfaces.
Articular cartilage does not have a blood supply but gains it’s nutrition from fluid that is produced by the lining of the knee. This joint fluid wets the surface and both lubricates the surfaces, and provides nutrition. For tissues to repair damage quickly and effectively they need a good blood supply. As articular cartilage doesn’t have any blood supply it cannot repair itself when it becomes damaged. It is this limited ability to repair that can lead to it wearing away. This is called osteoarthritis of the knee.
2) Meniscus cartilage. The second type of cartilage in the knee is known as the meniscus. There are two meniscii, one on the inner side of the knee (the medial meniscus) and one on the outer side of the knee (the lateral meniscus). They sit between the end of the thigh bone and the shin.
The meniscus does 3 things.
- Firstly it helps spread load and hence is sometimes referred to as a shock absorber.
- Secondly as the knee moves the meniscus wipes nutrient containing joint fluid back and forth over the articular cartilage.
- Thirdly they improve the stability of the knee.
The meniscus gets its nutrition from both the joint fluid and from a blood supply that penetrates the outer edge. The meniscus can only repair itself in the part that has blood flow to it. Hence the outer 1/3 is called the “red zone” and the part that gets its nutrition from the joint fluid is called the “white zone”
Tears of the meniscus that occur in the white zone cannot easily heal. The meniscus can be easily torn. Meniscus tears usually occur in the white zone. Attempting to repair white zone tears by stitching them will work for a while but because there is no additional healing by the body the stitched meniscus eventually comes apart again. This would mean a second operation to go in to the trim the meniscus and remove the failed stitches.
Tears occasionally occur either in the red zone or at the junction between the red and white zone. Sometimes it’s worth attempting to repair these. Repairing the meniscus is quite a specialised operation. It is generally the only carried out by specialist knee surgeons with a lot of experience of meniscus tears.
What is the surgeon thinking when treating the meniscus?
After carrying out many thousands of arthroscopies I’m comfortable deciding who gets a repair and who doesn’t. If the meniscus is to be trimmed I use a tool that is a bit like a ticket punch to remove the torn part. It’s a bit like trimming a ragged edge off a torn fingernail. I often leave 80% of the meniscus untouched as it is usually only the back part that is torn. If I think it can be repaired I will then decide if I can repair it keyhole or whether it needs a separate incision. The next step is to rough up the part with blood flow in it with a diamond tipped rasp. This makes it bleed so it will have a better chance of healing. Finally I stitch the meniscus back into place. As I choose which tears to repair with care there is an 80 to 90% chance it will heal. If the tear occurs in the red/white zone the chance of successful repair is probably closer to 70 to 80%. If there is blood in the knee at the time of repair then I know that tears are more likely to heal. Sometimes I create some additional bleeding by pricking the bone. If I am already reconstructing the anterior cruciate ligament the bleeding from this procedure will be enough on its own to encourage a better chance of healing. These days we can even sew in an artificial meniscus into the gap created. This allows a new meniscus to be formed. It is not yet widely carried out.
If the meniscus is just trimmed you usually don’t need crutches and can be back at work in a few days. After repairing the meniscus a little time is required for the body to make scar tissue within the tear. For this reason people who have had meniscal repair may be put on crutches for a week or two. This protects the repaired meniscus while it makes new scar tissue. I tend to restrict the amount of bending in the knee. I do this because most repairable tears occur at the back of the knee and as the knee bends the thigh bone (femur) rolls back onto the repair and could disturb it.
The meniscus is one of two types of cartilage in the knee. When torn, the meniscus cartilage is generally trimmed by a keyhole procedure called athroscopy. Tears can occur in either the inner or outer meniscus. The procedure is usually done as a day case procedure under general anaesthetic. Those tears that are identified as having the potential to heal can be repaired using stitches if the surgeon has the skill to do this. If repair is carried out accurately the success rate can be in the region of 80 to 90%.
So as we can see “I’ve damaged my cartilage” can mean one of many things. Most of the time I think people use that phrase when they have had a meniscus tear treated but there is quite a difference between a worn out knee and a simple meniscal tear!
If you are interested in learning more about meniscus surgery get in touch: [email protected] or 0208 944 0665.