The meniscus is a semi-circular structure that is triangular in its cross section. Humans have two in each knee. One is on the inner side, the medial meniscus, and the other is on the outer side, the lateral meniscus. They absorb shock, spread the load out over a large surface area, and act also as secondary stabilizers in our knees. Designed to last a lifetime, they are subjected to stresses constantly, and can be injured with trauma, or degenerate with time. Traumatic injuries generally happen at a younger age, and are caused by high level trauma, usually in sports, and happen to otherwise normal, healthy menisci. Often, the injury is associated with ligament injuries, especially the Anterior Cruciate Ligament (ACL).
Because the meniscus is healthy, the torn meniscus may be repaired in some cases. Often, the pattern of the tear is vertical in orientation, and if the tear occurs in the outer part of the meniscus, where there is a blood supply to promote repair, the surgical options may include stitching, or suturing, the torn structure. This is done arthroscopically, but in certain circumstances may require accessory skin incisions. The healing potential is good, but not perfect. Depending on the literature one reads, successful repair defined as not having to remove the meniscus at a later date, can approach 80 to 90 percent. If the tear is in the avascular (no blood) zone, the healing rates are very much lower, and often repair is not attempted.
A second pattern of tear is degenerative, or atraumatic. Usually in an older population, which is very variable, the tears are caused by biology and degeneration and breakdown of the structure. Patients will often say But I twisted my knee, and it was perfect before the injury. However, the tear pattern is very different, and is often a horizontal tear pattern. This happens because of the degeneration and internal architecture pattern of the meniscus. Why is any of this important to the patient? This is important because the treatments are very different.
Often, the tear is internal, or in a fish mouth pattern, which is always seen on MRI’s, but may not have any free meniscal fragments that cause mechanical symptoms in the knee. These can often be treated without surgery through conservative treatment. In some instances, the degenerative meniscus will fragment, and the loose fragment will cause symptoms of catching or locking. These may require surgical treatment. However, the treatment is removal of the torn piece. Repair is not an option as in the young, traumatic injury. The degenerative tear cannot manifest the necessary biologic process for successful repair in most cases.
Common patient questions:
- If you take out the meniscus, won’t I get arthritis? This is a simple question, yet a complicated answer. Removing the piece does not increase the risk over the tear itself because the torn fragment is already nonfunctional. However, often, the arthritis already coexists, and if severe, may be a reason not to operate. Proper preoperative evaluation should include standing x-rays to look for narrowing of the joint, which is a sign of arthritis, and if a MRI is performed, it should be done in a center that does high quality imaging that will show the state of the articular cartilage preoperatively. Unfortunately, this is not always the case.
- Will stem cells or other injections make my knee heal? This type of therapy is hopefully, in the future, a reality. However, currently, it is not a proven treatment on a broad scale. It is expensive, not often covered by insurance, and now does not have enough evidenced based medicine to support its use as a front line treatment. Many modalities can make a knee feel better. And often, that is the primary goal of the patient. It is important to keep in mind that improvement in symptoms does not mean the knee is healthier, or has grown new cartilage.
- The other doctor said he repaired my meniscus and I still have problems. Be specific in your questions to the surgeon. I repaired your knee isn’t the same as I fixed your meniscus. The patient assumes one thing, but the reality is that they underwent a partial meniscal excision.
- How can I prevent a meniscal tear? You really can’t do that. You can avoid sports to avoid the traumatic tears, but this is not an option that most people would want to consider. To date, we can’t change our biology to prevent the degeneration. Maybe someday this will be a possibility.
Dr. Thomas Wickiewicz is an Orthopedic Surgeon at Hospital for Special Surgery. He specializes in sports medicine, meniscus surgery, ACL surgery, and shoulder surgery. He spent eight years as Assistant Team Physician for the New York Giants, and he now serves as the Head Team Physician for all Division 1A College sports at St. Peter’s College. Dr. Wickiewicz has published over 100 scientific papers on his extensive research on knee and shoulder surgery and given more than 200 invited presentations.