Anatomy of the Meniscus Root
The meniscus is the all-important shock absorber of the knee. An injury to the meniscus can make or break one’s knee-joint health over the long term. Therefore, obtaining a proper diagnosis of a meniscus tear is very important to being able to continue activities as one ages. There is a special type of meniscus tear called a “root tear”, which is particularly important in preserving joint health. The meniscus root is the part of the meniscus that anchors it to bone. A meniscus that is not anchored to bone is particularly vulnerable to the development of osteoarthritis. This is because the meniscus can squirt out of the joint and no longer act as a shock absorber to joint loads. Therefore, this is a particularly important type of meniscus tear to diagnose and understand. Overall, we have not as a profession recognized meniscus root tears well until the last 7-10 years. Over the last decade, many biomechanical, MRI, and clinical outcomes studies have been performed which have demonstrated the great importance of the meniscus root attachment. In fact, a large majority of this research was performed here in Vail at the Steadman Philippon Research Institute. The importance of our research is highlighted by the fact that has won 3 major international research awards.
Pathology of Meniscus Root Tear
A meniscus root tear is usually caused by bending one’s knee back when it is loaded. This can happen in skiers so it is a common injury in patients in their 20s who fall backwards while skiing as well as in patients in their 50s and older that may be kneeling down to do housework, gardening, or working on carpets. About half the time, these people will feel a “pop”, which is associated with a meniscus root tear. Most people with meniscus root tears do not have a lot of joint line pain, like regular meniscus tears often do, and have pain when they try to squat down in the back of their knee.
How to Diagnose a Meniscus Root Tear
The diagnosis of a meniscus root tear is dependent upon both one’s physical exam and also by x-rays and an MRI scan. In thin patients, the clinician can often feel the meniscus squirting out of the joint (meniscus extrusion). Also, the patient may have pain when one’s knee is flexed all the way back. This can be particularly bothersome when the patient is asked to stand and squat down. Meniscus root tears that are associated with an ACL tear are more difficult to determine. Our biomechanical research has demonstrated that a lateral meniscus root tear that happens with an ACL tear causes the knee to be looser. Thus, it is important to diagnose this particular type of tear and fix it at the same time as an ACL reconstruction or there is a higher risk that an ACL reconstruction graft will stretch out and fail.
It is important to obtain x-rays on patients who may have meniscus root tears. This is because some patients have a small bony piece that will tear off the bone with a meniscus root tear. It is important to diagnose these. In addition, if patients have a lot of arthritis, surgery for the root tear may not be indicated in all circumstances.
The gold standard for diagnosing a meniscus root tear is to obtain an MRI. It will show the meniscus root is no longer attached to bone and often is squirted out of the joint (extruded). In some patients, they may have a stress fracture forming, called an insufficiency fracture, which is because their joint really needs the meniscus and is getting overloaded. In the past, this was called spontaneous osteonecrosis of the knee (SONK), which we now know is caused by meniscus root tears. Medial meniscus root tears are much easier to diagnose on MRI scans than lateral meniscus root tears, and it may take an experienced clinician time to recognize the presence of a lateral meniscus root tear in patients. In particular, lateral meniscus root tears are almost always associated with an ACL tear.
When to Have a Meniscus Root Repair
The treatment of meniscus root tears is based upon the amount of arthritis in one’s knee rather than a patient’s age. This is definitely becoming the standard of care thinking among experts at meetings. If one has minimal to no arthritis, then one’s age does not matter because the risk of developing osteoarthritis is quite high if one does not treat a meniscus root tear.
The most common means to fix a meniscus root tear is to place sutures in it, prepare a bony bed on the back of the tibia, and then pull the sutures down through small bone tunnels and tie them over a button on the front of the tibia. This technique, called the transtibial technique, was mainly developed in our lab in Vail and has been shown in published studies to have excellent outcomes.
Meniscus root repairs also depend upon a well-guided physical therapy regimen. Almost every center in the world requires that a patient be nonweightbearing for 6 weeks, on crutches, to maximize the chance of the root repair healing. This is because our Korean colleagues found on second-look arthroscopy that patients who walked on meniscus root repairs prior to 6 weeks after surgery had a much higher rate of retear. Thus, our lab is investigating further ways to accelerate the healing process to maximize the chance of a more accelerated early weight-bearing program after surgery.
All in all, meniscus root tears have been called “the silent epidemic” because they really were not recognized well until the last 10 years. Other teaching centers have taught us that more than 50% of patients require a total knee replacement within 5 years of having a meniscus root tear that is either not repaired or is simply trimmed, and that almost 80% of patients that are less than 60 years old who needed a total knee replacement had a meniscus root tear as the cause of their arthritis. Therefore, one should err on “saving the meniscus” and repairing a root tear at all costs to minimize or slow down the risk of one developing significant arthritis.