Have you been told that you are “missing cartilage” in your knee?
Please read on….
Types of Cartilage:
In the human knee there are two forms of cartilage. We have the two cushions, each of which we call a meniscus. We also have cartilage on the end of the thigh bone or femur, and cartilage that covers the top of the shin bone or tibia. This cartilage is known as articular cartilage — and damage to the articular cartilage is the focus of this section. If you have been told that you are “missing cartilage in your knee” your physician is likely referring to the articular cartilage on ends of the bone, and not the meniscus.
Cartilage “Tears” vs Cartilage “Defects” :
If you have been diagnosed with a “cartilage tear” your physician was probably referring to a meniscus tear. If your physician says you have a hole or defect in your cartilage, they are likely referring to the “articular” cartilage layer which we have on the ends of the bone. Articular cartilage is typically 1/8-1/4″ thick in an adult knee. It is a firm, exceptionally smooth surface and enables your joints to glide and move without friction, grinding, catching or discomfort. The picture above shows normal appearing cartilage on the end of the femur and the top of the tibia when viewed during an arthroscopic procedure.
Meniscus tears and articular cartilage injuries or defects (holes) are completely different injuries — apples and oranges — and require different treatment plans or procedures to address them.
Injuries to articular cartilage can occur through numerous mechanisms. Many injuries occur in teenagers from track and field injuries. In those cases, a piece of cartilage is literally ripped off the end of the bone (see the image below). These are relatively uncommon and usually produce pain, swelling, locking, a feeling that something is loose within the knee.
By far the most common injury is the result of blunt trauma—a fall from a height, a car accident where your knee hits the dashboard or falls directly onto the front of the knee.
After practicing for a few years I have now seen a number of patients with identical cartilage defects in both the right and left knees. This implies, but does not absolutely mean, some form of genetic predisposition.
In certain situations, osteoarthritis will cause defects or holes in the cartilage too. Osteoarthritis, by definition means that the cartilage on the ends of the bone is becoming thin. If you lose a little cartilage, that is mild arthritis — if you loose all the cartilage you have severe arthritis. This topic deals with isolated defects or holes in the cartilage and not necessarily arthritic defects where all the cartilage in the knee is thin or lost. That said, in some cases of arthritis, the initial presentation may be a solitary defect — and that may be amenable to the various treatments we will review.
Here are two pictures obtained during an arthroscopy where a fiber-optic camera is placed in the knee to view everything. In the
upper picture you can see the cartilage literally peeling off of the bone beneath it. This is an acute or fresh defect. The picture below shows that scar tissue has tried (ineffectively) to fill a defect that has been present for months.
Cartilage injuries can be severe, because the natural history of cartilage loss is a strong association with developing osteoarthritis as the cartilage around the defect takes on more stress, degenerates, thins and eventually disappears. Cartilage defects, if large enough, are best treated as soon as they are recognized.
To aid in making the diagnosis an MRI might be necessary. It depends on the index of suspicion of your surgeon. Not all knee problems require an MRI— if you present with the symptoms I mentioned previously an MRI will be very useful for demonstrating the location, size and potential repairability of the cartilage defect.
Once the diagnosis is made, a discussion will ensue to provide you with the techniques available to “repair” the lesion or defect in the cartilage. Bear in mind… in situations where multiple surgical options exist and there is no “clear winner”, that means that the *perfect* repair has not been identified yet. This is one of those situations. We have many good procedures to help restore the cartilage, but none of them are perfect and some are more invasive then others. The typical procedures available are:
Cartilage Defects Treatment - Micro-Fracture
A Micro-fracture or “Marrow Stimulating Technique” is a technique that is arthroscopic and involves making many small holes in the cartilage hole or defect– into the bone beneath it. Bone marrow cells, stem cell and blood will come out of the holes and coat the cartilage defect. Theoretically those new cells which have entered the knee will reside or grow within the hole in the cartilage and result in a layer of fibrocartilage covering the defect. Fibrocartilage is not the same as the original hyaline articular cartilage. It has different properties and might not stand the test of time.
Cartilage Defects Treatment – Carticel
Genzyme developed a procedure known as Carticel. This involves two procedures. The first is an arthroscopic assesment of your defect and if we believe you are a good candidate for a Carticel procedure, we will take a small biopsy of normal cartilage. Genzyme will amplify, or grow the cartilage cells and send them back to us. During a second stage procedure those cells are implanted and will hopefully grow into a layer of hyaline-like cartilage that covers the defect.
Osteochondral Grafting or Cartilage Transplant (OATS):
Cartilage Grafting or Cartilage Transplant procedures may also be referred to as a Moscaicplasty in the literature you will read online. I find this to be one of the more satisfying and successful procedures in addressing large defects in the cartilage. A cartilage transplant or grafting involves taking cartilage from a cadaver (if you have a large defect or hole) or from low-weight bearing areas of the knee and transferring it to fill the defect in your knee. The advantage of a cartilage transplant, grafting, OATS or Mosaicplasty (all relatively the same) is that we are placing true articular cartilage back into the defect. The area where we take the cartilage from is filled with a plug that will encourage hyaline-like cartilage growth. Below are images from two different patients. In both instances you see the defect in the first image — and then the end-result after the defects were addressed with a large cartilage transplant of graft.