What is articular cartilage and
what does it do?
There are two types of cartilage in
the human knee:
- Meniscus cartilage -
This is the cartilage most commonly referred to when the term
"torn cartilage" is used. These two rubbery shock
absorbers sit between the upper bone of the thigh (femur)
and the large bone in the lower leg (tibia).
- Articular cartilage -
This cartilage is the shiny, white surface that covers the
ends of most bones. Articular cartilage protects the ends of
bones and allows the joints to glide smoothly with less
friction. It also helps to spread the loads applied to a
joint. This covering is only a few millimeters thick and it
has no blood supply to facilitate the healing process.
Therefore, if it gets damaged, there is very little capacity
What is an articular cartilage
An articular cartilage injury, or chondral
injury, may occur as a result of a pivot or twist on a bent knee,
similar to the motion that can cause a meniscus tear. Damage may
also be the result of a direct blow to the knee.
may accompany an injury to a ligament, such as the anterior
Small pieces of the articular cartilage
can actually break off and float around in the knee as loose
bodies, causing locking, catching, and/or swelling.
often, there is no clear history of a single injury. The patient's
condition may, in fact, result from a series of minor injuries
that have occurred over time. Articular cartilage also wears down
as a person ages.
Chondral damage is graded from
mild to severe, and all grades can have characteristics of
- Grade I - The cartilage
"blisters" and becomes soft in the earliest form of
- Grade II and III - As
the condition worsens, the cartilage may become fibrillated
(it has a shredded appearance). The grade of injury
depends on the size of the involved area and how much of the
cartilage thickness is worn down. Noise as the knee bends,
called crepitus, may be present.
- Grade IV - The
cartilage may wear away completely, leaving the underlying
bone exposed in small or widespread areas. When the involved
areas are large, pain usually becomes more severe, causing a
limitation in activity.
The symptoms of an articular
cartilage injury are not as obvious as those of a meniscus tear or
- Intermittent swelling -
This is often the only symptom. The loose cartilage fragments
floating in the knee can cause swelling to occur.
- Pain - Pain with
prolonged walking or climbing stairs can occur.
- Giving way - The knee
may occasionally buckle or give way when weight is placed upon
- Locking or catching -
The loose, floating pieces of cartilage may block the joint as
it bends, causing the knee to lock.
- Noise - The knee may
make noise (crepitus) during motion, especially if the
cartilage on the back of the kneecap is damaged.
It can be difficult to diagnose an
articular cartilage injury.
Physical examination may show a
swollen knee, but frequently the exam is normal.
Imaging may help the doctor make a diagnosis in some, but not all,
cases. X-rays may be normal in most cases because only bone damage
is visible on X-ray. One indication of advanced cartilage loss
is a decrease in space between two bone surfaces.
A loose bone
fragment may be detected in a condition called osteochondritis
dissecans (OCD), in which a portion of bone
detaches with the articular cartilage.
An MRI (Magnetic Resonance Image) may reveal softened
cartilage in many cases. This softening can be difficult to
detect, however, and the diagnosis may require the most sensitive
and highest quality MRI images, which may show changes in the
underlying bone. Cartilage thinning or loss is also usually
visible on MRI.
- Articular cartilage damage is
most reliably diagnosed with an arthroscopic examination of
the joint. In this procedure, a tiny fiberoptic scope is inserted
into the joint. The doctor uses this scope to visually assess the
Articular cartilage degeneration is
often treated without surgery. Some measures that the physician
may recommend are:
- weight loss.
- exercises to strengthen the
muscles around the joint.
- shock absorbent shoe inserts.
- changes in physical activity.
- glucosamine and chondroitin
supplements (not FDA regulated).
- injections of hyaluronic acid
to improve joint lubrication and reduce friction.
The doctor usually prescribes
medications to treat the symptoms and watches the patient's
Although there are medicines that can treat the
symptoms associated with articular cartilage damage, there are no
medications that can repair or encourage new growth of cartilage.
Further treatment would require a surgical procedure.
In the past 10 years, there have
been many advances in the surgical treatment of articular
cartilage defects. The most commonly used treatment involves
smoothing the rough areas of the defect with a shaving technique;
however, significant research in this area of medicine has led to
the development of several new ways to address this difficult
Factors that influence the choice of procedure include:
- the size of the defect.
- the location of the defect in
- the age and weight of the
- the patient's future goals and
- the patient's motivation and
ability to participate in postoperative rehabilitation.
- the patient's limb alignment:
Is the patient bow-legged or knock-kneed?
Shaving and Microfracture
The most commonly performed
procedures for treating chondral defects are:
- Shaving or
Debridement: This arthroscopic technique has been popular for 20 years
and has had very satisfactory results for over 75% of
patients. It is a common treatment for patients with a
cartilage defect that has not worn all the way down to the
bone, especially under the kneecap. This procedure is also
used in the more arthritic knee when other resurfacing
techniques are not appropriate. Using special arthroscopic
instruments, the physician smoothes the shredded or frayed
articular cartilage. Ideally, this treatment will decrease
friction and irritation, reducing the symptoms of swelling,
noise, and pain.
This technique encourages the growth of new cartilage into a
defect. This is a well-accepted technique that is a common
procedure for patients with damage through the full thickness
of articular cartilage, all the way down to the bone. Using an
arthroscopic procedure, the base of the damaged area is
scraped to create a bleeding bed of bone. Blood is
essential for healing. Small holes are then
"picked" into the defect with a special instrument,
allowing blood vessels and bone marrow cells to be in contact
with the exposed cartilage defect. Bone marrow then fills the
defect promoting the formation of a clot, which will
eventually mature into firm scar cartilage. Research has shown
that this tissue is a hybrid cartilage. Although this newly
grown cartilage is durable and can function for many years, it
may not have the same durability or strength as the original hyaline
cartilage that existed before the injury.
The following procedures to repair articular cartilage defects
are currently being researched and evaluated. Although these
newer techniques hold some promise, their effectiveness and
long-term outcomes have not been established and only a few
surgeons perform them. Some of these procedures can be very
- Osteochondral Autograft
Resurfacing: Ideally, defects of the
articular cartilage in the knee would be replaced with normal
hyaline cartilage. This cartilage would withstand years of use
and prevent the development of arthritis. Osteochondral
autograft resurfacing offers some hope in achieving this goal.
The advantage of this treatment is that the patient's own
cartilage is used to repair the damaged area. This procedure involves the
transfer of normal cartilage from one area of the knee to
another. Cartilage plugs are taken from areas of the knee that
do not bear the weight of the body during walking, and then
"planted" in the damaged areas with a technique that
is similar to the one used for a hair transplant. This procedure is best for
defects smaller than 15-20mm in size because there is a limit
to the number of plugs that can be harvested. It is not
recommended for osteoarthritis, in which the cartilage is
thinning around the defect. This procedure can be done
arthroscopically except when multiple plugs are required. In
the case of a larger defect, a small incision may be necessary
to position the plugs correctly.
- Autologous Chondrocyte
Implantation: This procedure is most
commonly reserved for defects over 20 mm in size or when the
damaged site is too large to be reliably treated with other
techniques. It is only recommended if there is no cartilage
wear around the defect. This treatment involves using
the patient's own cartilage cells. The patient's articular
cartilage cells are arthroscopically removed from the injured
knee and grown outside the body in tissue culture. After a
growth period of three weeks, a second surgical procedure is
performed to implant these cells into the defect. Ideally,
these cells will fill the defect with a new cartilage surface
over time. The implantation process requires a large incision
so that the cartilage cells can be properly placed on the bone
surface and begin to grow. It takes two to three years for
these new cells to mature completely.
- Osteochondral Allograft
Resurfacing: This procedure is used if
there is bone damage in combination with articular cartilage
defects. It requires the transplantation of fresh cartilage
and bone from a donor, soon after that person's death. One
large graft is implanted into the damaged area. (The tissue
banks that provide grafts carefully screen the donors for
infectious diseases, including AIDS and hepatitis.) Although
this procedure has been done for over 20 years, it has only
recently gained popularity because fresh grafts have become
more readily available.
What types of
complications may occur?
- None of the above procedures
are perfect, but each one may be helpful for patients with
painful articular cartilage defects.
- Although the results have
not been evaluated in controlled trials, these techniques have
been shown to be safe and effective with positive results in
the 70-80% range. The success rate seems to be time dependent.
Some patients may have relief from symptoms for a short time,
but find that symptoms gradually reoccur. Long-term results
are still not available for some of the procedures. Joint
stiffness, infection, and continued pain may sometimes follow
surgery, as can happen with any major knee operation.
- The decision to choose any
of these procedures should be made only after the patient and
physician have carefully discussed all the options. Adequate
training and experience in the use of any of these techniques
is important to the success of the chosen procedure.
recovery process and rehabilitation requirements vary significantly
among the different operative procedures used to repair articular
cartilage damage. The patient's commitment level to the
rehabilitation process is an important factor in determining which
treatment may be the best choice.
- Crutch use is minimal.
- Rehabilitation is started
immediately after surgery.
- Regular activities are often resumed
within 4 - 6 weeks.
This procedure involves the growth and
remodeling of cartilage and a restrictive period of rehabilitation and
crutch use for 6-8 weeks, with only touch-down weight bearing of
approximately 30 pounds permitted. Continuous passive motion (CPM) is
suggested by some physicians. Recovery to full activity that is pain
free may require 6 months or longer.
Following is an example of a
recommended rehabilitation program. Programs may vary from doctor to
- A CPM machine is used for 6 - 8
hours in a 24 hour period (usually at night) for 6-8 weeks. Crutches
are required for 6 - 8 weeks following surgery.
- The patient must put no more than
30 pounds of weight on the injured leg for 6 - 8 weeks, depending on
the physician's recommendation (some physicians may recommend no
weight at all).
- Pool exercises can be started as
soon as the incisions have healed, usually two weeks after surgery.
- Full activity resumes in 3 - 6
months, depending on the size of the cartilage damage.
long-term effects on the harvested area are still unknown, as is the
long-term performance of the transplanted cartilage.
- Crutch use is required for 4 - 6
weeks after surgery.
- Pool therapy and bicycling are
usually started within 2 weeks.
- Recovery to full activity generally
takes 4 - 6 months.
- Return to running and impact sports
depends on the number of grafts taken.
is a very lengthy process with this treatment.
- Crutches and touch-down weight
bearing on the operative leg for 6 weeks, with increasing weight
bearing to full weight bearing at 12 weeks.
- Pool therapy and bicycling can be
started within 6 weeks.
- Weight can be put on the leg
starting about 6 weeks after surgery. The patient's exact
rehabilitation time frame set by the physician may vary as the time
to full weight bearing is dependent on the size of the area
resurfaced. Progressive strengthening continues as the patient's
range of motion and muscle strength permits.
- Return to sports often takes 6 - 12
- Crutches and limited weight bearing
for two weeks on the operative leg, followed by full weight bearing
in a long leg cast brace for one year.
- Pool therapy and bicycling are
usually started within 2 weeks.
- Recovery to full activity usually
occurs when the cast brace is discontinued.
- Return to running and impact sports
depends on the number of grafts used.
What are the most important things a
person can do to limit chondral or cartilage damage in the knee?
While there is not one specific thing that
can prevent cartilage damage in the knee, there are a few measures that
can be taken to delay the process.
- Since excess weight can cause damaged
cartilage to wear down more quickly, losing extra pounds may be
- A person with cartilage damage should
avoid high impact activities, such as prolonged running or jumping
sports. These are very hard on the knee and can speed the progression
of cartilage damage.
- Even those with significant joint
damage will benefit from mild to moderate activities, such as walking,
bicycling, or running in water.
My doctor has told me that I have
arthritis and will need an artificial knee in the next few years. Would I
be a candidate for growing my own cartilage so I won't need an artificial
The newer techniques involving cartilage
growth will not work if a patient is very bowlegged, knock-kneed, or has
bone rubbing on bone.
The newly grown cartilage would be quickly rubbed
away by the worn surfaces.
At some point in the progression of arthritis,
only a total knee replacement can offer pain relief.
Will glucosamine and chondroitin make new
Most studies of the effects of glucosamine
and chondroitin have been done in animals, and most of the reported
effects are based on hearsay rather than scientific evidence.
studies are currently underway and reported results do show some promise
that these substances can relieve the inflammation caused by arthritis in
60-70% of patients. It is doubtful, however, that they can cause new
cartilage to grow.
Diabetics and individuals taking blood thinners should
not use these medications without a doctor's approval.