 Everyone
has heard of a torn cartilage and they tend to think of that
and they tend to think of that as the much more common problem
where the shock absorber type of cartilage is damaged in
the knee. This confuses people because they don’t understand
the difference between that type of cartilage and articular
cartilage.
An anatomy lesson is required. Articular
cartilage is the "smooth Teflon lining" of the knee
joint that coats all the gliding surfaces and makes the knee
joint slippery and smooth. This articular cartilage has a coefficient
of friction that is better than any man-made product. This
remarkable structure is extremely smooth and slippery. In its
best state it functions very efficiently for the mechanics
of the knee joint. Unfortunately it can be damaged and when
this smooth articular cartilage is damaged it is usually a
much bigger problem than when the U-shaped shock absorber type
of cartilage is torn (see diagram).
History
Up until recent years the treatment of
articular cartilage defects has been remarkably poor. The most
that could be done was to shave it down with mechanical instruments
in an attempt to smooth it but we could do very little to replace
the defect in the smooth surface.
Occasionally the whole, or damaged
area, would be drilled with a wire to try and promote bleeding
which we hoped would form a fibrous clot that would smooth
over to scar tissue which would be better than having a defect
in the cartilage. This is a very poor healing technique but
it is better than nothing. The concept is that you would violate
so that you would pierce the bone plate just underneath the
cartilage and allow cell migration by bleeding into the area.
In its more modern form this is referred to as "microfracture" technique.
Improvement in daily activities can be expected in about 2/3
of patients when performed at its best.
Abrasion chondoplasty is an easy to understand
technique. A high-speed burr is used on the roughened area
particularly if hardened bone is formed. Once again this high-speed
burr is hoped to help promote the formation of scar tissues
but cannot be expected to form normal articular cartilage.
Autologous Chondrocyte Implantation
Originally developed in Sweden, this is
an advanced technique where the goal of the surgery is to actually
transplant cells into the area which can be expected to form
normal hyaline cartilage. Hyaline cartilage is the specific
type of cartilage that is usually present in normal articular
cartilage. With this technique a biopsy is taken during the
first arthroscopic surgery which is simply a small piece of
cartilage removed from a non-critical area of the knee joint.
This piece is sent to a laboratory where the tissue is cultured
to produce many more chondrocytes (cartilage cells) until there
is enough to transplant back into the knee joint.
The patient is then taken back into surgery
where a bigger operation is performed through an open incision.
A piece of tissue from one of the bones of the leg is used
to cover the defect in the joint surface and then the liquid
form of the cartilage which has been grown in the lab is placed
by syringe underneath this "patch". The patch is
then sealed over completely. And the patient remains non-weightbearing
for an extended period of time until knee is safe to weight
bear on and the cartilage transplant has taken.
This technique is usually reserved for
lesions that are at least 2 square centimeters is size and
in patients who are usually less than 50-55 years old. It is
not a good operation for lesions on the patella (kneecap) but
it is good for lesions of the femoral chondro (see diagram).
Any ligament instability of the knees has to be corrected first
and any mal-alignment deformities such as genovarigm (bow-legged)
must also be corrected first.
This operation is contraindicated in diseases
such as rheumatoid arthritis and severe osteoarthritis. If
the patient is markedly obese or has other medical contraindications
then he or she is not a good candidate. With this operation,
reports have shown up to 85% improvement at 12 months. Interestingly
with time they can get even better results because the patients
tend to improve as time goes on. It should be understood that
it’s the patient’s own cartilage cells that are
transplanted back into the knee joint, they are simply grown
and cultured in the laboratory to multiply.
Osteochrondro Autograft Transplantation
This procedure is also known as an Oates
Procedure. It is also been called mosaicplasty. This procedure
is usually used on smaller lesions between 1-2 square centimeters
Again the goal is to achieve normal articular hyaline cartilage
with this operation.
With this particular technique special
instruments are used to harvest an area of hyaline cartilage
from a non-critical area of the knee. This cartilage is immediately
transplanted into the area of the damaged cartilage without
any intervening growth period in a laboratory. This means that
the size of the transplant is limited by the amount of cartilage
that you are able to remove from the non-critical area of the
knee. This is why we can’t do it for lesions much more
than 2 square centimeters in size.
The advantage is that it is all done in
one operation and can usually be done arthroscopically. The
grafts are harvested by hollow tubes that are used to drill
over the area that we use as a donor site. And then again,
the damaged area is drilled out and the tube of bone and cartilage
is transplanted into the damaged area (see picture). This operation
has the advantage of a much shorter recovery period and it
removes the necessity for two operations.
Postoperative Course
Depending on the type of surgery the post-op
course is quite different. With the micro-fracture technique,
the patient may be required to be non-weight bearing for a
relatively brief period of time but recovers relatively quickly.
With the Oates type of procedure where
the cartilage is transplanted all in one setting, the patient
again is going to be non weight bearing for a period of about
6 weeks but afterwards recovers quick quickly.
Unfortunately, the recovery period for
the autologous chondrocyte implantation technique where the
cartilage is grown in a lab is much longer but we must remember
that it is used in much more difficult situations and bigger
lesions. It also has to be done through a relatively large
open incision when compared to the other two operations.
Summary
Articular damage to the surface of the
knee joint is one of the most difficult problems to treat in
the knee. Up until very recently there was little that could
be done. But now there are some options available to patients.
These have to be understood and the limitations of these operations
as well as the risks have to be understood. While certainly
not guaranteed, they do offer patients at least a chance at
getting more normal knee joint and participating in the activities
and work that they want to.
If you have any
questions about any of these techniques please do not hesitate
to speak with one of our orthopedic surgeons.
One of the most famous orthopedic surgeons
in the world is Dr Henry Mankin. He has done a great deal of
research into cartilage and has a famous quote in regards to
its problems. He has said:
"… it should be clear
that cartilage does not yield its secrets easily and
that inducing it to heal is not simple. The tissue is
difficult to work with, injuries to joints are a risk – whether
traumatic or degenerative – are unforgiving, and
the progression to osteoarthritis is sometimes so slow
that we delude ourselves into thinking that we are doing
better than we are. It is important, however, to keep
trying."
|
