CARTILAGE
TRANSPLANT
 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."
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