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Why does my knee feel weak all of the sudden?

My right knee feels very weak. Like it wants to bend backward or something. Could I have damaged my knee or knee ligaments without knowing it?
The knee is a complex joint because even though it is intended to only move in one plane--unlike, for example, the shoulder joint which has much greater flexibility--restricting the mobility of the knee is important for a stable and steady gait. As you are experiencing, when the knee becomes unstable it can make walking or running very uncomfortable. The knee is, in fact, supported by multiple ligaments and tendons which help provide the stability required for walking. Weakness in the joint can sometimes be a symptom of an underlying problem with one of these ligaments. However, it is also very unusual for this to happen without some kind of inciting event or trauma, whether that be a skiing or soccer injury or a car accident. Overall, it sounds like you have had a recent change in the stability of your knee, so the best thing for you to do is see your primary care physician. He or she can ask you about any recent events that might have led to an injury as well as examine your knee for evidence of inflammation, swelling, or joint instability. Physical exam can help identify whether there is weakness or instability in the various ligaments and tendons of the knee. Depending upon the results of this exam, your physician may send you for imaging studies (such as MRI) and a consultation with an orthopedic surgeon.
This answer is for general informational purposes only and is not a substitute for professional medical advice.
If you think you may have a medical emergency, call your doctor or (in the United States) 911 immediately. Always seek the advice of your doctor before starting or changing treatment. Medical professionals who provide responses to health-related questions are intended third party beneficiaries with certain rights under ZocDoc’s Terms of Service.
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Answers are written by doctors from top institutions:
  • Cleveland Clinic
  • Boston Children's Hospital
  • NYU Langone Medical Center
  • Brigham and Women's Hospital
  • Johns Hopkins Hospital
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  • Beth Israel Medical Center
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