Read below about knee instability, including causes, treatment options and remedies. Or get a personalized analysis of your knee instability from our A.I. health assistant. At Buoy, we build tools that help you know what’s wrong right now and how to get the right care.

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Knee Instability Symptoms

Ligaments are the tough fibrous bands that hold the bones together. If the ligaments within the knee become damaged, the knee joint will be painful, wobbly, and unstable. It may feel as though it could give way at any moment while you are walking, exercising, or even just standing.

If the muscles of the knee are damaged, they cannot contract properly, and you will experience weakness and pain. Swelling may have the same effect.

Knee injuries are usually sports injuries, though they can happen during any physical activity that leads to twisting of the knee or to a traumatic injury of the joint.


  • The sensation that the knee is popping out of place or is about to collapse under you.
  • The sensation that the structures within the knee are loose.
  • Feeling that the knee joint is locking or catching.
  • Feeling, or even hearing, a popping or clicking from the knee.
  • Finding it impossible to straighten the knee.
  • Pain that may be mild, moderate, or quite severe.
  • Swelling.

Who is most often affected by knee instability symptoms?

  • Young, fit, active athletes in their teens and twenties are the ones who most often suffer sports injuries.
  • Dancers.
  • Anyone doing hard physical labor.
  • Anyone who is overweight or obese.
  • Women may be more prone to knee problems, due to naturally having a wider pelvis. Therefore, women have a predisposition to misalignment between the top of the kneecap and the bottom of the thighbone.
  • Older people may experience gradual wearing away of the cartilage of the knee.
  • A prior injury can predispose you to another one.

When are knee instability symptoms most likely to occur?

  • Acute injury:

    • When playing sports.
    • With falling down.
    • During an automobile accident.
  • Chronic pain:

    • With mild exercise.
    • While climbing up and down stairs.

Are knee instability symptoms serious?

  • A mild strain or sprain is a common sports injury and can be healed with rest and physical therapy.
  • Damage to the cartilage can lead to arthritis. The pain and instability of an acute injury may become chronic if not treated right away.
  • A more severe injury, if neglected, can suddenly worsen if you overdo it. For example, a partial tear may become a complete tear.

Knee Instability Causes Overview

Most common knee instability cause types:

  • Sprain of the knee ligaments, which means these ligaments have had their fibers damaged due to wear and tear, sudden stress, or direct trauma.
  • Tear of the ligaments, meaning the fibers have been partially or completely torn through. This usually happens when you run and then make a sudden change of direction – the knee stays pointing one way while the rest of you twists the other way.

Less common knee instability cause types:

  • Inability of the damaged muscle to physically contract properly.
  • Fluid buildup from the injury, interfering with muscle action.

Rare and unusual knee instability cause types:

  • If you do something strenuous enough to damage the ligaments, it is likely that you will have damage to the cartilage around the knee bone as well. The patella, or kneecap, can become partially or completely dislocated. A partial dislocation is called a subluxation. Dislocation can occur if the ligaments are damaged and are not holding the kneecap firmly in place as usual.
  • The cartilage at the ends of the upper and lower leg bones, which meet under the kneecap, can become torn. This often happens along with a ligament sprain.
  • This same cartilage can gradually wear away over time, causing pain and difficulty moving since there is no longer enough cushioning material between the bones.
  • You may have been born with knee structure that makes the joint vulnerable to slipping out of place.

8 Potential Knee Instability Causes

Disclaimer: The article does not replace an evaluation by a physician. Information on this page is provided as an information resource only, and is not to be used or relied on for any diagnostic or treatment purposes.

  1. 1.Patellofemoral Pain Syndrome

    The kneecap (patella) is located directly in front of the thigh bone (femur), and should normally glide freely up and down. In this condition, called patellofemoral pain syndrome, the kneecap may rub against the thigh bone instead of gliding smoothly, causing damage and pain.

    Most people get better within weeks to months of physical therapy.

    Top Symptoms:
    knee pain, pain in one knee, knee pain that gets worse when going up stairs, dull, achy knee pain, knee pain that gets worse when squatting
    Symptoms that always occur with patellofemoral pain syndrome:
    knee pain
    Primary care doctor
  2. 2.Meniscal Injury

    A torn meniscus is one of the most common knee injuries. Any activity that causes forceful twisting of the knee, especially when putting the pressure of one's full weight on it, can lead to a torn meniscus.

    6 to 8 weeks

    Top Symptoms:
    pain in one knee, knee stiffness, knee instability, pain in the inside of the knee, swollen knee
    Primary care doctor
  3. 3.Knee Arthritis

    Arthritis is inflammation of one or more of the joints. Pain, swelling, and stiffness are the primary symptoms of arthritis. Any joint in the body may be affected by the disease, but it is particularly common in the knee.

    Knee arthritis is a chronic problem once it develops.

    Top Symptoms:
    pain in both knees, knee stiffness, knee instability, swollen knee, morning joint stiffness
    Symptoms that always occur with knee arthritis:
    pain in both knees
    Primary care doctor
  4. 4.Dislocated Kneecap

    The kneecap connects the muscles in the front of the thigh to the shinbone (tibia). When the kneecap slips out of the groove, problems and pain often result.

    Resolves upon reduction of dislocation.

    Top Symptoms:
    pain in one knee, knee pain from an injury, knee injury, swollen knee, knee instability
    Symptoms that always occur with dislocated kneecap:
    kneecap sliding out to the side, knee pain from an injury
    In-person visit

    Knee Instability Checker

    Take a quiz to find out why you’re having knee instability.

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  5. 5.Acl Injury

    The ACL (anterior cruciate ligament) is a super-important tendon that connects the femur (thigh bone) to the tibia (shin), keeping the tibia from flying forward every time a step is taken. Tearing happens in a lot of accidents and sports, unfortunately.

    Full recovery may take months of physical therapy.

    Top Symptoms:
    knee pain, pain in one knee, knee instability, swollen knee, knee pain from an injury
    Symptoms that always occur with acl injury:
    knee pain
    Symptoms that never occur with acl injury:
    mild knee pain
    Hospital emergency room
  6. 6.Baker's Cyst (Popliteal Cyst)

    A Baker's cyst, also called as Popliteal cyst, is a fluid-filled mass that causes a bulge and a feeling of tightness behind the knee. The pain can get worse when the knee is fully flexed or extended.

    Recovery with nonsurgical treatment varies

    Top Symptoms:
    calf pain, swollen knee, knee pain that gets worse when squatting, knee instability, dull, achy knee pain
    Symptoms that always occur with baker's cyst (popliteal cyst):
    lump on the back of the knee, constant knee lump
    Primary care doctor
  7. 7.Osteochondritis Dissecans

    At joints where bones meet, bones are covered with a layer of cartilage which provides shock absorbance and lubrication. Osteochondritis dissecans is a condition where a piece of cartilage with a thin layer of bone detach from the larger bone, causing pain.

    Conservative treatment should resolve the problem in 3-6 months.

    Top Symptoms:
    pain in one knee, knee stiffness, knee instability, knee pain that gets worse during a run, pop in the knee
    Primary care doctor
  8. 8.Pigmented Villonodular Synovitis

    The synovium is a thin layer of tissue that surrounds joints, providing a small amount of fluid to lubricate the joint and aid in movement. In pigmented villonodular synovitis (PVNS), the synovium thickens and overgrows. This mass typically only affects one joint, is not cancerous, and does not spread to other parts of the body.

    Recovery from arthroscopic (minimally invasive surgery) is quick and can take a few weeks to a month.

    Top Symptoms:
    joint pain, pain in the outside of the hip, pain in one knee, groin pain, deep, throbbing hip pain
    Symptoms that never occur with pigmented villonodular synovitis:
    knee instability
    Primary care doctor

Knee Instability Treatments and Relief

Seek immediate knee instability treatment in the emergency room or call 911 if:

  • You have severe and sudden pain following an injury, especially if you are unable to move the knee or bear weight on it.

Schedule an appointment for:

  • Physical therapy.
  • A program of proper stretching and exercise to help strengthen the ligaments, muscles, and tendons of the knee.
  • Possible fitting of braces and supports.
  • Surgery to repair damaged cartilage and ligaments.

Knee instability remedies that you can try at home:

  • Rest. Do not try to continue playing or exercising if you have sudden pain in and around the knee.
  • Take over-the-counter NSAIDs You may choose ibuprofen, to treat minor pain.

Questions Your Doctor May Ask About Knee Instability

  • Q.What is your body mass?
  • Q.Which of the following describes your physical fitness:
  • Q.Do you often feel your knees buckling?
  • Q.Is the knee pain affecting one or both knees?

If you've answered yes to one or more of these questions, try our knee instability symptom checker to find out more.

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Knee Instability Symptom Checker Statistics

  • People who have experienced knee instability have also experienced:

    • 23% Knee Pain
    • 8% Knee That Clicks During Movement
    • 7% Swollen Knee
  • People who have experienced knee instability were most often matched with:

    • 55% Patellofemoral Pain Syndrome
    • 43% Meniscal Injury
    • 1% Knee Arthritis
  • Source: Aggregated and anonymized results from visits to the Buoy AI health assistant (check it out by clicking on “Take Quiz”).

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