Weakness and instability in the knees aren’t common, but something that I have seen in runners struggle with throughout my career.
Typically, someone will report that their knee starts to feel weak and wants to buckle. Sometimes it’s painful, and sometimes it’s not. When a patient walks into the clinic with these complaints, it warrants a thorough evaluation as these symptoms can come from a few different areas or a combination of things. Here are some of the potential culprits that can contribute to the “weak knee” dilemma.
Muscle Imbalance and Fatigue
This one is usually a slam dunk. A review of the whole kinematic chain, from the hip down to the foot, shows where someone is strong and where their weaknesses might hide. Team that up with a sound running gait analysis and whammo. We can see where their compensations are in running, and how that might lead to the knee giving out. For instance, if the person is very quad dominant with weak hip stability, as they run, the quad will start to fatigue, and the knee will become unstable and weak. This happens because the brain only knows how to stabilize the knee using the quad and when that is shot, bingo, the knee gets loosey-goosey.
Internal Structures Are Not Healthy
There are certain words that people will say that set alarms off in a PT’s brain: “weak,” “locking” and “unstable” are some of the big ones. When someone is seeing us about their knee and they say those three words, we immediately need to test the structures on the inside of the knee to make sure that they are doing what they should. The medial and lateral meniscus, medial and lateral collateral ligaments, anterior cruciate ligament and the posterior cruciate ligament all need to be tested. If those structures are not the way they should be, then someone might have feelings of weakness and instability in their knee while running.
Swelling
We’ve all had our knees swell for one reason or another in our lifetime. The swelling can come from a lot of different areas, and part of our examination of the above structures can help us to wheedle that out. But swelling can cause other things to happen. Regardless of where the swelling is located, it can influence knee stability. First off, swelling is space-occupying. The knee is normally filled with fluid and when we get swelling, we add more fluid to the system. This added fluid pressure changes the mechanics of the knee, and feelings of weakness can be a symptom.
Another thing that can happen with swelling is the brain will turn off, or inhibit, the muscles around the knee. The quad is especially susceptible. Say you are out on a long run, pounding out the vert, and, as a result of the pounding, the knee joint starts to get inflamed. In reaction, the brain inhibits your quad muscle, and that lack of control starts to make your knee feel weak and unstable.
We’ve addressed potential underlying factors that can lead to your knee feeling weak and wanting to lock with running. What do we do about it? If there is nothing serious going on with the structures of your knee, then we tackle the muscle imbalances, clean up your running gait pattern and maybe take anti-inflammatory measures to keep the swelling down. Hopefully, the combination of those interventions really helps, and you can get back after it as soon as possible. If those measures aren’t helping, then we might have you see an orthopedist to delve a little deeper into the health of the internal structures and find out if there is something that needs to be addressed surgically or with medication.
See you out on the trails!
Medical disclaimer. What I write here in no way substitutes for an in-person, thorough evaluation by a licensed Physical Therapist. As with many body issues, there can be multiple factors involved with your aches and pains, and, in some cases, more serious underlying conditions that can be manifesting as physical symptoms. It is always best to have a PT that you can see when you have concerns, so that you can make sure your personal situation is being addressed appropriately and safely. This column should, in no way, serve as a substitute for seeing a licensed medical practitioner.