If you heard a 'pop' on the stairs: meniscus root tear
There is something I hear often in clinic.
“I squatted down while working in the field and felt a 'pop' behind my knee. It hurt terribly for a few days, but now it is a little better.”
I hear this especially from women in their 50s and 60s. And it is the “a little better” that worries me most. When an MRI is taken, a good many of them have a meniscus root tear.
What is the 'root' of the meniscus?
Inside the knee, between the thighbone and the shinbone, there are two crescent-shaped menisci, one on the inner side and one on the outer side. They are cushions that absorb shock and spread the load when weight is applied.
Both ends of this crescent are firmly tied to the shinbone, and this part is called the root. Think of the iron hoop around a wooden barrel. Just as the ends of the hoop must be fastened for the barrel not to spread apart, the meniscus holds up under weight without being pushed outward only if its roots are attached.
Normal: the roots at both ends are firmly tied down
Posterior root tear of the medial meniscus: the hoop has come undone and is pushed outward from its original position (dotted line)
Why does it tear with a 'pop'?
In young people, meniscus tears often come from a large force during sports. A tear of the posterior root of the medial meniscus, by contrast, often happens after middle age, in a meniscus already weakened bit by bit, during a very minor movement.
- When getting up from a squat
- When going down stairs or a downhill slope
- When sitting cross-legged, or just walking
The 'pop' sound or feeling that patients remember is this very moment. Afterward the back or inner side of the knee hurts, especially going down stairs.
Why “it's better, so it must be fine” is dangerous
The severe pain of the first few weeks usually settles. That is why many people let it pass. The problem is that changes continue inside the knee in the meantime.
A meniscus with a torn root is like a barrel whose hoop has come off. The shape remains, but it cannot bear the load and is pushed out of the joint. Biomechanical studies regard a completely torn root as a state similar to removing the whole meniscus. When bone and cartilage strike each other directly where the cushion has gone, the following can happen.
- Degenerative arthritis progresses faster than expected
- Tiny stress fractures form just under the bone surface and the pain suddenly becomes severe
- The time at which an osteotomy or knee replacement is needed comes sooner
How is it diagnosed?
The meniscus is not visible on a plain X-ray. The X-ray is used to check the joint space, the alignment of the leg and the degree of arthritis, and the root tear itself is diagnosed with MRI. On MRI you can see that the place where the root should be looks empty, or that the meniscus has been pushed out of the joint.
If back-of-the-knee pain continued after a 'pop,' I recommend being examined at least once even if the pain has eased. The time when there are the most treatment choices is right after the injury.
How is it treated?
Not every root tear is operated on. Treatment differs by age, how far the arthritis has advanced and whether the leg is bowed.
| Condition of the knee | Treatment mainly considered |
|---|---|
| Little arthritis, with fairly straight leg alignment | Meniscus root repair: the torn root is tied with sutures and pulled through a small tunnel in the bone to be fixed again |
| Arthritis is not severe, but the bowlegged alignment is clear | Osteotomy plus root repair: shifts the weight concentrated on the inner side outward to protect the repaired root |
| Arthritis is already far advanced | Conservative treatment such as pain control and exercise therapy, and if needed joint replacement (partial or total) |
| Older patients, or when surgery is difficult | Medication, injections, strengthening exercises, weight management, temporary use of crutches |
In the past, partial meniscectomy, cutting out the torn part, was often done, but studies showing that it does not stop progression of arthritis in root tears have appeared and it is rarely recommended now. For a knee in which the root can be fixed, the principle is to reattach rather than cut out.
What about after surgery?
A root repair needs time for the reattached site to heal. It differs by hospital and surgical method, but usually for a little over a month after surgery you use crutches and do not put weight on the leg. Deep knee-bending movements are also restricted for a period. I tell patients to avoid squatting and sitting cross-legged for several months or more.
Repair does not stop arthritis completely. But there are many reports that by helping the meniscus act as a cushion again it slows arthritis and helps delay knee replacement.
What you can do for your knees starting today
- Cut down on squatting and sitting cross-legged: deeply bent positions put the most strain on the back root of the meniscus. Use a low stool for fieldwork or hand-washing laundry.
- Take the elevator rather than the stairs: the load is especially great going down.
- Thigh strengthening exercises: if the muscle at the front of the thigh is strong, the shock reaching the knee is reduced.
- Weight management: studies suggest that losing 1 kg lowers the load on the knee by about 4 kg when walking.
In closing
Going through my surgical photo folders, I found far more meniscus root tear cases than I expected. A good many of them were patients who said, “it hurt at first, but it got better so I just carried on.”
If you heard a 'pop' behind your knee and going down stairs has been uncomfortable since, have it checked once even if the pain has eased. Even for the same knee, the treatment differs depending on when it is found.
This article is general medical information, and diagnosis and treatment can differ with the individual's condition. If you have symptoms, please consult an orthopedic specialist.
References
- Lee DW, Ha JK, Kim JG. Medial Meniscus Posterior Root Tear: A Comprehensive Review. Knee Surg Relat Res. 2014;26(3):125–134.
- Moon HS, Choi CH, Jung M, et al. Medial Meniscus Posterior Root Tear: How Far Have We Come and What Remains? Medicina. 2023;59(7):1181.