What is the Meniscus?
The meniscus, commonly called the “cartilage” in layman’s terms, is a very important shock absorber for the knee. There are 2 menisci, both on the inside (medial) and outside (lateral) of the knee. In addition to being important shock absorbers, the menisci are also important as a backup to ensuring one’s knee remains stable during twisting, turning and pivoting activities. Therefore, when one tears the meniscus with a cruciate ligament, or other ligament tear of the knee, one should have the meniscus tear repaired to make sure that the cruciate ligament graft does not stretch out or become loose over time.
The medial meniscus is located on the inside of the knee. It has 2 attachments, which are called the “root” attachments. It is especially important as a shock absorber in the back of the knee, and this is where most meniscus tears occur. When one does lose their medial meniscus, they are at a high risk for developing arthritis. This is because the medial meniscus absorbs about 50% of one’s shock on the inside of the knee when performing most daily activities. The attachments to bone, or root attachments, are especially important anchors for the meniscus. When a root is torn, the meniscus can slip out of the joint, called extrusion, and basically be nonfunctional. Meniscus root tears are now felt to be a very common cause of why younger patients need knee replacement surgery. Therefore, it is important to address and treat these properly with a repair in most cases.
The lateral meniscus, located on the outside of the knee, covers a much larger portion of the joint surface than the medial meniscus. Thus, it absorbs about 70% of the shock applied to the outside of the knee. Therefore, people who lose their lateral meniscus are at a very high risk for the development of arthritis. Therefore, lateral meniscus tears should be repaired in all circumstances when possible to prevent the development of osteoarthritis.
Pathology of Meniscus Tear
When on does tear their meniscus, sometimes a portion will flip in the joint and prevent one from having full motion, either in straightening or flexing the knee. When these are small pieces, they usually cannot be repaired and have to be trimmed out. However, when the whole meniscus flips on itself and becomes locked in the front of the knee, called a “bucket handle tear” of the meniscus, these need to be repaired in almost all patients, especially if they have just recently happened. This is especially important because taking out a bucket handle tear essentially removes most of the meniscus and predisposes one to a significant risk to develop arthritis. Other signs of a meniscus tear include swelling, pain right along the joint line, or significant pain while squatting down or while kicking something, like a soccer ball or pushing a chair in. Meniscus tears are not known to cause a lot of pain on the front of the knee, so pain on the front of the knee may be somewhat due to a meniscus tear but it may also be due to kneecap joint problems.
How to Diagnose a Meniscus Tear
Diagnosing a meniscus tear depends upon both a good physical exam, x-rays, and an MRI scan. The physical exam should look for any decreases in joint motion, pain along the joint line, and any associated ligament injuries, which can be common with a meniscus tear. Standing x-rays show be obtained, in almost all circumstances, when one is suspicious for a meniscus tear. This is especially important for skiing where sometimes one can have a small fracture which can mimic a meniscus tear. In addition, it may show significant arthritis to the point where even if there is a meniscus tear, one has to treat the underlying arthritis as the main problem going forward. An MRI ultimately is the best way to diagnose a meniscus tear. While most MRI scans can pick up meniscus tears, it is recommended to obtain a high field, high strength, MRI, on a 3T scanner because this will provide the most information to a surgeon about the extent of the tear, the type of tear it is, and whether it is reparable or not.
When one does have a meniscus tear which requires surgery, it is important to be prepared for that type of surgery so that one can best plan their postoperative rehabilitation course. The meniscus itself has a triangle-type shape, with it being thicker towards the edge of the joint and very thin in the middle of the joint. Small meniscus tears, which involve the thin inner portion of the meniscus, usually are not reparable and need to be trimmed. In addition, degenerative meniscus tears with large flaps or portions that cannot be sewn together also usually need to be trimmed, and these are usually in older patients where the consequences of removing a meniscus tear are not as severe as in a younger patient.
How to Save the Meniscus
It has become a slogan at most major medical meetings to “save the meniscus” whenever possible. This involves identifying the tear in surgery, either anchoring the meniscus back to bone or sewing it to the joint lining, and augmenting it with biologics to improve its healing potential when necessary. For many years, we knew that meniscus repairs performed along with an ACL reconstruction had a much higher rate of healing. It was not well-known why this happened. More recently, it has been shown that the tunnels that are reamed for an ACL reconstruction release important growth factors and cytokines which improve the healing potential of the meniscus repair. Therefore, it is recommended to perform biologic augmentation with meniscus repairs that are not performed with ligament reconstruction. We have published on this and noted that a technique of placing holes in the bone within the middle of the knee, in the intercondylar notch, called a marrow venting procedure, significantly improved the rate of meniscus repair healing. In fact, in our published series, the rates of meniscus repair healing were very similar to the meniscus repair healing rates with an ACL reconstruction. Therefore, our group strongly advocates the use of a marrow venting procedure to increase the chance of a meniscus repair healing.
Gold Standard Meniscus Repair: Inside-Out Sutures
Most meniscus tears are torn away from the joint lining and can be sutured back to it. The gold standard is to use inside-out sutures because more can be used and can pull the meniscus back into position. While some physicians use “all-inside” devices, these do have a higher rate of retear and also create larger holes in the meniscus substance itself, which means there can be fewer sutures placed. Thus, for much bigger repairs, all-inside devices are not as efficient at repairing the meniscus. For meniscus tears in which the anchor is torn, called a root tear, one should sew the meniscus back to bone to restore its function. My group has performed the largest amount of research in this area in the world and have shown that repairing it back to bone with 2 tunnels, to better flatten the meniscus down to the prepared bony bed, have excellent outcomes and that one’s age is not important. If one has too much arthritis, then the surgery may not be beneficial, but for patients who have mild or no arthritis, there is no upper age limit on performing a meniscus root repair. The other type of complex meniscus tear, which is quite common in skiing, is where the meniscus is sliced in half, called a radial tear. We have also performed extensive research to document that radial tears should be repaired, have good outcomes, and ideally should be repaired back to bone with tunnels and then sewn in place. Using the technique developed in our lab in Vail, we have found that repairing radial tears have a similar outcome to other meniscus repairs with this new technique.
Recovery Following Meniscus Surgery
The other important portion of treating meniscus tears is to ensure a proper rehabilitation program. Usually, the surgeon can find out in surgery what a “safe zone” amount of knee motion that can be performed on postoperative day one without significant tension on the meniscus repair. This is usually at least 90 degrees of knee flexion. It is common to limit our patients’ knee motion for the first 2 weeks postoperatively to this safe zone amount of knee motion. The amount of weightbearing is also important. Meniscus radial and root repairs are kept nonweightbearing for 6 weeks and there is good objective information in the peer-reviewed literature to support this. For isolated meniscus repairs, we also keep patients nonweightbearing for 6 weeks because our published outcomes are much better than those studies which have allowed for early weightbearing after meniscus repair. When one does have a peripheral meniscus repair with an ACL reconstruction, it is generally felt that it is safe to follow the ACL reconstruction protocol after surgery. It usually takes a minimum of 4-6 months, depending upon the type of meniscus tear treated, to be able to return back to full activities when it is performed without any other ligament reconstructions. When it is performed with a ligament reconstruction, one normally has to allow the ligaments to heal after surgery and this will determine the ultimate time return back to activities.
A meniscus tear can have devastating consequences on one’s ultimate joint health. Therefore, one needs to obtain a proper diagnosis and also undergo the best attempt at a meniscus repair. While for a variety of reasons all meniscus repairs may not heal, most do heal and it has been shown that these patients do much better over the long term compared to those who have had their meniscus taken out. Therefore, if you do tear your meniscus, you should strongly consider having it repaired to ensure that you can have the best knee function over the long term.