Meniscus: "Cartilage" Injury
  

 About your knee... "torn meniscus???" 

First a few words about anatomy...
The doctor has just told you  you have a "torn meniscus".  First a little background the meniscus, AKA - knee cartilage, is in its simplest sense, a cushion or shock absorber in the knee. There are two one on the inside  (medial) side of the knee and one on the outside (lateral) side of the knee. They are c-shaped structures about the size and shape of a shrimp, that serve to absorb force traveling up and down the leg, and protect the surface cartilage of the knee.

To avoid confusion, one must understand that there are two types of cartilage within the knee.  The surface or hyaline cartilage  is teflon like and is very smooth to facilitate gliding and sliding of the bone ends upon each other. Hyaline cartilage is present in all of the joints of the body and is unique in that there is no man-made cartilage that can approach its coefficient of friction.  The other type of cartilage in the knee is the meniscus cartilage.  Therefore, typically when refers to a "torn cartilage" it is the meniscus that is injured.

Now about function...
Although the basic function is shock absorption, meniscus cartilage also acts in other ways, such as providing a role in knee stability, and additional nutrition of the surface cartilage.  The knee meniscus is an invaluable and extremely important component to knee function.  Its value began to be understood, as the result of large numbers of open meniscectomies (cartilage removal) done as a standard procedure in the 1950's and 1960's for tears.  This was in the days before the advent and common use of arthroscopy.  Many of those who had meniscectomies went on to develop arthritis ("wear and tear") of the knee on a delayed basis.

Cartilage tears can occur at all ages, typically before age 35, cartilage tears occur as a result of an injury, such as sporting injuries commonly associated with twisting, or in combination with ligament tears such as a torn anterior cruciate ligament (ACL).  Later in life, tears can occur to a degenerative meniscus, cartilage that is wearing out as a result of trivial insult such as squatting down or kneeling, or even on a spontaneous basis.

Symptoms of a torn cartilage most commonly include: pain along the junction of the thigh and leg bones on the inside and outside margins of the knee, or behind the knee.  Typically, swelling is seen, next to or above the knee cap.  Swelling can be subtle or prominent.  Additional symptoms may include:  a sense of instability or giveaway, catching (loss of the smooth gliding motion), or locking (knee getting stuck). Symptoms are usually aggravated by bent loaded knee activities such as squatting and kneeling or sitting for long periods such as in a car or in a chair.  Impact activities such as running and jogging also tend to aggravate the situation.  Early symptoms may respond to rest, avoidance of aggravating activities, medications, especially anti-inflammatories, ice, etc.

If symptoms persist, usually the diagnosis is straight forward at medical evaluation, especially if seen by a knee specialist who is familiar with this common condition.  On exam, typical findings include:  knee effusion (water on the knee), pain with flexion (bending) of the knee and especially if loaded such as with squatting, tenderness along the lines of the joint of the junction between the thigh and leg bones, and pain on a special maneuver called the McMurray's test.  In general, if three or four out of these four signs are noted one can be about 95% certain that one is dealing with a meniscus tear, if x-rays do not show arthritis.

After the history is taken and the physical exam is done.  It is customary to order x-rays, to rule out the possibility of osteoarthritis, which may mimic a meniscus tear.  There are numerous other conditions that can mimic a tear and these usually can be differentiated by the subtleties of complaints and physical exam.

Ordering an MRI is a matter of clinical judgment.  In general, if the history and exam findings are highly suggestive and consistent, an MRI is not necessary to confirm the diagnosis.  This test is expensive.  However, an MRI  is highly sensitive and accurate for the diagnosis of meniscus tears.

MRI showing posterior horn tear of the medial meniscus.

Operative versus Non-Operative Management:
Conservative, non-operative care is a reasonable starting point, especially if symptoms have been present for a short period of time and are not significantly disabling.  Treatment includes:  avoidance of aggravating activities such as squatting and high impact activities, treatment with ice, knee wraps or sleeves, and medications, especially anti-inflammatories.  Cortisone injections may be helpful in selected circumstances.  In general, the knee will respond to some degree to these measures, but a cure or healing of the tear should not be expected.  The best one can usually hope for is for symptoms to settle down or dissipate.

Meniscus healing is difficult to obtain at any age, because the bulk of the cartilage has no blood supply and is therefore called "avascular".  Most healing in the body is dependent upon a blood supply to initiate healing response, and deliver the cells that contribute to the healing process.  The meniscus is 70 to 90% avascular, and tears in the avascular portion, generally remain idle with limited healing capacity.  The exception to this rule is a tear that occurs in the outer 10 to 30% of the cartilage, which has access to the blood supply trickling in from the periphery.  These tears may heal, if the environment promotes healing.

For isolated tears that are unresponsive to non-operative care, operative treatment may be indicated, should disabling symptoms continue.  Operative treatment includes:  leaving small tears alone, and repairing or removing large unstable tears.  This is a matter of surgical judgment.  The decision to repair a tear is highly dependent upon the following factors:  location of the tear, age of the tear, geometry of the tear, age of the patient, and co-existing injury, such as that to the anterior cruciate ligament.  In general, the principle is to save the meniscus whenever possible.  This means either leaving small tears alone or repairing tears if possible.  Loss of meniscus tissue can have  a poor prognosis long-term.  The likelihood of future arthritis proportional to the amount of meniscus tissue that is torn or removed.  There is a wide range of variability among orthopedic surgeons in regard to philosophy of meniscus repair and technical ability to perform this procedure.

In general, it is always a better idea to save the meniscus tissue if possible, as one can always go back to remove it at a later date.  Once it is gone however, there is no easy replacement or reconstruction available for missing meniscus.

Meniscectomy is an operative procedure, nowadays done arthroscopically, that involves  trimming or removing the unstable torn portion of the cartilage, with the goal of eliminating or minimizing symptoms.  This is done as an outpatient arthroscopic procedure, usually under local anesthesia. It is unusual to need a general anesthetic for this problem. Advantages of  local anesthesia include:  less side effects post-operatively such as nausea and vomiting, a quicker discharge and recovery, and the ability to observe the surgery.  It is typically done through several small puncture wounds called portals, that facilitate use of the arthroscope and specific instruments designed to trim and smooth out the torn cartilage segments. Additional arthroscopic procedures can be performed at the same time, if indicated and necessary.

Radial tear: unrepairable.

The success rate, if no arthritis co-exists, is very high ranging from 95 to 98% for short-term reduction and elimination of symptoms, and recovery of normal activity level.  Operative risks include, but are not limited to, infection and blood clots and the estimated incidence rate of these complications is about 0.3%.  Rehabilitation is rapid and can often be performed at home with minimal equipment. Early exercises include wiggling the toes and pumping the ankle up and down, and squeezing the thigh muscles for 6 to 8 second.  Straight leg raises are also advisable for the first several days post-operatively, while either sitting or lying down, again, holding the leg about 40 degrees elevated for about 6 to 8 seconds at a time.  At 3 to 5 days post-operatively, use of a stationery bike, Nordic Track or stair master may also be helpful, with low resistance.  At 5 to 7 days resistance is gradually increased in a progressive fashion.

Crutches are typically not necessary, nor is a splint or brace. The knee is wrapped with an ace bandage to help reduce swelling, and ice is helpful, continuously for the first 48 to 72 hours, and on an intermittent basis thereafter.  Recovery is typically fast with resumption of normal day-to-day activities in two to three days and resumption of low impact sports in 2 to 3 weeks. Full activity is usually the norm at three weeks, though it may take about 3 months for full recovery.

The unknown here is long term results.  We know that removal of all of the meniscus (total meniscectomy) often leads to osteoarthritis of the knee, especially of the involved compartment. What is not known is the long-term effects of partial meniscectomy, the typical case with arthroscopic surgery. It is generally felt that the incidence of late arthritis is proportional to the amount of tissue that is removed. Other factors such as genetics, family history of osteoarthritis, activities such as high impact (long distance running, jumping sports, labor intensive activities, etc.), and co-existing problems within the knee, all influence late arthritis. More needs to be learned and researched regarding late effects of meniscectomy.  In general, large losses of meniscus typically leads to increased loading of the surface cartilage with its wear, with subtle changes of knee alignment, increasing the forces on the cartilage further, which generally leads to premature wear and progressive destruction of the joint. This is an insidious and subtle process that may take many years or even decades.

Meniscal Repair:  A more favorable alternative to removing cartilage is retaining it, by stitching the meniscus material. This can be done by a philosophically inclined, and experienced trained surgeon also under an arthroscopic technique and often under local anesthesia as well.  There are numerous techniques available, some which can be done using the small puncture wounds, and some which require a large incision in the back corners of the knee.

In general, the procedure involves roughing up the injured surfaces of the tear in some fashion, and placing sutures or another fixation device across the tear to keep the edges opposed to facilitate healing.  General principles include:  stimulation of a healing response, usually through encouragement of vascular response, and pulling the tear surfaces together and holding them in place while a scar matures.

A high quality repair is a technically demanding process.   If well selected tears are chosen, a healing rate of 80 to 90% should be expected.  No bridges are burned with this procedure, and if repair is unsuccessful, a re-repair is possible or worse case scenario, partial meniscectomy. Similar complications do occur to those of meniscectomy and these include, but are not limited to, infection and blood clots, and nerve and blood vessel injuries are also possible, though quite unlikely (less than 1 in 500).

Peripheral meniscal tear in the "red" (vascularized) zone, repairable.

Rehabilitation is often different from meniscectomy.  A "laissez-faire" approach similar to meniscectomy, is not recommended.  A proper healing environment for the repaired meniscus is essential, and this includes restricting activities, a short period of crutch use, and avoidance of forceful bent knee activities such as squatting and vigorous bent leg weight lifting such as leg curls.

It is difficult to tell from a clinical exam or an MRI, which tears are candidates for repair. In general, a repair can be considered pre-operatively, and this option should be discussed with the patient if an operation is planned. The patient must be prepared for the possibility as it is always preferential to repair the cartilage rather than remove it.

Long-term outlook after repair is generally good. An asymptomatic repaired cartilage typically will lead to improved knee joint function and reduce the risks of late problems such as arthritis.

Return to activities after meniscus repair is usually delayed, relative to meniscectomy. Return to high impact and turning and twisting sports generally takes 3 to 4 months at a minimum.  It is wise to avoid loaded bent knee activities and squatting for about 4 to 6 months post-operatively.

Meniscus Transplants:  For the patient who has lost the bulk of their meniscus cartilage, either as a result of a devastating tear or meniscectomy, another alternative is meniscal transplant. Although in this day and age a reconstruction or replacement using tissues from ones own body has not yet been developed, and as there is no synthetic substitute, the only alternative is to transplant a cadaveric (donor) cartilage which has been matched and sized to the patient. This is a technically very demanding procedure, the long-term results of which are unknown and unproved. The basic problem here is, although we don't know the long-term result of a transplanted cartilage, we know that loss of the major portion of the meniscus, especially at a young age, has a potentially devastating long-term effect on the knee. Many will opt for a transplant given the poor prognosis of subtotal or total meniscectomy.

While most of these procedures have been done at a few large centers throughout the country, the procedure is now available and able to be performed by a well trained, specialized, arthroscopic knee surgeon with experience in meniscus repair.

Meniscus transplant can be thought of as the "ultimate meniscus repair" wherein the donor meniscus is inserted into the prepared knee and stitched in place in the same fashion a torn cartilage would be repaired.  Although healing rates are high in the 80 to 90% range, it is unknown whether or not a transplanted meniscus will function as a shock absorber long-term, and defer or inhibit progressive degenerative change within the knee. Apart from the risk mentioned above for meniscectomy or meniscus repair, one must also be cognizant of transplanting allografts (non-self) tissue. Although donor tissue is tested exhaustively for infectious disease such as hepatitis and HIV/AIDS, a risk of this transmission is not 0. The risk of HIV transmission with allograft tissue is estimated to be one in eight-hundred thousand, about the risk of a lightening strike to the average american. Other unforeseen adverse effects cannot be excluded.

The present consensus is that meniscus transplant may offer significant benefit for a person who has lost their meniscus. No other alternatives for reconstruction or replacement are available, and a transplant may offer both short-term and long-term benefits. We have learned that performing a transplant in a knee that is already developing arthritis, has a significantly reduced success rate.  Therefore, it is best to do this procedure early, before arthritis begins to develop.

Non-isolated Tears:  Although a meniscus tear can occur all by itself, without other injury within the knee, it is also possible to have concomitant injuries to other structures such as the surface cartilage (hyaline) and ligaments. The most common association is with  a torn ACL (anterior cruciate ligament), meniscus tears occur in at least 50% of injuries that produce a torn ACL.  Once again, the philosophy is to save the meniscus if possible, and this can be done simultaneous with the ACL injury, if this management option is selected.

The same discussion applies.

Important points concerning combined injuries include the following:  (1) the healing rate of meniscus repair done in tandem with ACL reconstruction is higher than meniscus repairs done without ACL reconstruction; (2) the rehab of meniscus repair does not complicate the rehab of an ACL tear; (3) one of the main reasons to fix or reconstruct the anterior cruciate ligament is to prevent further damage to the cartilage. An ACL deficient knee carries a substantial risk of further and future damage to knee menisci. Persistent give way experienced by a person without an ACL, can lead to tearing of the meniscus cartilage and later damage to the surface cartilage as a secondary result. For further information about the knee meniscus see the ACL section.
 

For more photos of meniscus surgery, click here.


 

 Dan Wnorowski, M.D.

 

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