One day you felt a click or pop in your knee. A few days later you can barely walk. You are usually between 45 and 75 years of age. After kneeling down, or squatting to pick something up you felt a pop inside your knee. You have some pain in the knee, but immediately after the pop it wasn’t terrible pain. The next day the pain is worse, and the pain on the inner part of your knee continues to worsen to the point that you can not walk. Now your knee starts to swell. Why has the pain on the inside of your knee worsened over the last few days?
Although not described as a terrible triad in the scientific literature, over my 20 years of experience I have heard this story enough to know what the list of diagnoses will be in this situation after talking with you for a few minutes. This is a very common cause of medial knee pain, or pain on the inner side of your knee in people between 45-75 years of age.
Your MRI will often show a:
- Root tear (Radial tear) of the medial meniscus
- mild or moderate knee arthritis
- bone marrow edema, or an insufficiency fracture in inner part of the knee.
Those three findings on your MRI are related to one another… one caused the next to occur and so on. This is what I refer to as the Terrible Triad of (medial) knee pain. It is often over-treated, under-recognized and poorly understood by patients I see for second opinions.
The Terrible Triad: Part I – Meniscus Root Tear
The meniscus plays a very important role as a cushion inside the knee. It distributes the stresses of walking very efficiently. A meniscus root is where the meniscus is actually attached to the bone. The meniscal root attachment degenerates (or wears out) in our knee just like many other tissues in our body. That’s why it will pop while simply squatting down or twisting while walking. That was the straw that broke the camel’s back. This post goes into more detail about root tears of the medial meniscus.
The Terrible Triad: Part II- Osteoarthritis of the knee
The degeneration of the meniscus root causes it to “tear”. When the tear occurs the function of the meniscus is lost. That loss of cushioning function causes an increase in stress on the bone. In the terrible triad you also have osteoarthritis. Osteoarthritis of the knee implies that you have lost some of the articular cartilage which covers the ends of the bones in the knee. That cartilage also cushions the knee.
The Terrible Triad: Part III- Insufficiency fracture
So… if you tear the root of the meniscus the stress in the knee increases. You already have arthritis so the cartilage cushion was thin and less protective. All of this causes an increase in the stress within the bones in the knee. In many of you that will lead to a stress fracture or an insufficiency fracture. Those insufficiency fractures of the knee cause a ton of inflammation which shows up on an MRI as bone marrow edema. It takes 1-3 days or more for the stress fracture to occur following a root tear. That’s why the pain worsens over the next few days after you felt the pop.
The bone marrow edema caused by the insufficiency fracture causes severe pain. The meniscus is not the most likely cause of pain in this situation. Bone is a confined space, it can not expand. If you have inflammation and swelling in the bone then the pressure in the bone will increase. That’s why an infected tooth hurts so much… that infection is confined to a tight space, so the pressure rises and it is the pressure that hurts so much.
The terrible triad hurts a lot. That usually leads to a visit to your doctor or an Orthopedic Surgeon. An MRI is obtained and the findings I mentioned earlier are identified.
Treatment of The Terrible Triad of Medial Knee Pain
Most of you who have all three of the findings I mentioned above will usually have very severe pain. For some of you, your Doctor will focus only on the meniscus and recommend surgery to remove the torn meniscus. That is not recommended as the best way to proceed if you have a degenerative root tear in the presence of osteoarthritis and bone marrow edema. If your doctor recommends surgery to “clean out” the knee, again the research shows that the surgery often fails to alleviate your pain, and increases your risk of needing a knee replacement.
It is often the bone marrow edema from the stress reaction or insufficiency fracture which is causing your pain. Usually time and limiting weight bearing can improve that pain. It can take 1-3 months for the pain to subside. A subchondroplasty for bone marrow edema can help a limited number of people feel better. In a knee with mild arthritis and persistent pain then a root repair (not removal of the torn piece) in combination with a subchondroplasty might be and an option to discuss with your doctor. Make sure that your Orthopedic Surgeon knows how to perform meniscus root repairs. They are not easy to perform, and most surgeons still remove these torn pieces. Focusing on meniscus preservation and repair will offer your the best chance of long term success.
If the arthritis is moderate to severe and your pain persists despite rest, and limited weight bearing, then a knee replacement might prove to be your best option.
Bottom line is that treatment recommendations need to be individualized to improve your chance of success, and minimize the risk of worsening arthritis or the risk of having an unnecessary surgery.