Knee weakness and instability may begin suddenly or develop slowly over time. It may be the only symptom you have, or your knee may also hurt, pop, bruise, or swell.
This article explores six possible reasons why your knees are giving out, symptoms of knee weakness, how these problems are diagnosed, and the treatment options that are available to you.
How Does the Knee Work?
The knee is a hinge joint that connects the large thigh bone to the lower leg bones. Connective tissues called ligaments connect bones to bones and help stabilize the joint.
There are several ligaments in the knee, but the four major ones are:
Collateral ligaments (MCL and LCL): These are located on either side of the knee and limit sideways bending. The medial collateral ligament (MCL) is on the inner side of your knee. The lateral collateral ligament (LCL) is on the outer side of your knee. Anterior cruciate ligament (ACL): This runs through the middle of the knee and connects the shinbone and the thighbone. It limits rotation and the forward motion of the shinbone. Posterior cruciate ligament (PCL): This connects the top and rear of the shinbone to the thighbone and limits the backward motion of the shinbone.
The cartilage pads, known as menisci, are the shock absorbers of the knee and help stabilize it. There are two per knee—one on the inside and one on the outside.
What Are the Signs and Symptoms of Knee Weakness?
With some conditions, you may only experience the symptom of having unstable knees.
However, with others, you may also have:
Popping Clicking Locking, or feeling like the knee joint is stuck Pain Joint stiffness Reduced range of motion (how far you can move the joint)
Complications of Knee Buckling
Complications of weak knees may include:
Recurrent fallsLack of confidence with balanceFeeling scared or nervous about future fallsInjuries because of falls
You should see your healthcare provider if you are experiencing the sensation of your knee giving out.
What Causes My Knee to Suddenly Give Out?
There are multiple reasons why your knee may feel weak or go out, each of which are detailed below:
Tears, including to a ligament or meniscusOther injuriesMedical conditions
Ligament Tears
Partial or complete tears to one or more of the ligaments in the knee can cause knee instability. Types of ligament tears include:
ACL tear: An ACL tear usually occurs with sudden movement, such as a change in direction during sports. Individuals may hear a “pop” while pivoting or landing after a fall. It may also occur with a car accident. The giving out sensation is often followed by pain and swelling. PCL tear: PCL tears may occur during a fall where an individual lands directly on the front of the knee. These may also occur if the shin is forcefully hit from the front, like during a car accident. This type of tear tends to occur along with other injuries, rather than on its own. MCL tear: MCL tears usually occur when the outer side of the knee gets hit. If knee instability is present, it usually implies that a significant MCL tear has occurred. Pain, swelling, and difficulty with movement are common symptoms. LCL tear: An LCL tear usually causes pain on the outer part of the knee. Like a PCL, this type of tear typically occurs along with other injuries. Feeling like your knee will give out often implies a significant injury.
Meniscal Tear
A meniscus tear may occur with activities such as twisting, turning, and pivoting. A meniscal tear is more common in people ages 30 and older, as the menisci start to weaken around this time.
Symptoms may include:
StiffnessSwellingPainPopping or locking feelingDifficulty with movement
Patellar Dislocation or Subluxation
The kneecap, or patella, normally glides through a groove. A direct blow to the kneecap, usually from an accident or sports injury, can dislocate it from this groove. This is called patellar instability.
Two types of patellar instability include:
Patellar dislocation: The kneecap is totally moved outside of its groove. Subluxation: The kneecap is only partially out of its groove.
Plica Syndrome
Plica syndrome is a condition that is caused by inflammation of the inner lining of the knee joint. It may occur suddenly with movements, such as bending, or more gradually.
Symptoms include:
Knee painClickingPopping feeling, especially when squattingDifficulty with movement
Arthritis
Arthritis, an inflammatory condition, can lead to knee instability. There are many types of arthritis that can impact the knee. These include osteoarthritis, rheumatoid arthritis, and inflammatory arthritis.
In general, symptoms of knee arthritis may include:
PainStiffnessSwellingDifficulty with movement, including walking
Nerve Damage
The femoral nerve is located in the pelvis and goes down the thigh and the shinbone. Femoral nerve damage can make it feel like your knee could give out or is giving out.
It can also cause a tingling or burning pain around the knee.
Femoral nerve damage can happen if:
An individual is injuredThe nerve experiences a lot of pressureAn individual has a condition associated with nerve damage, such as diabetes
Who Is at Risk for Injuries Related to Knee Instability?
Risk factors for injuries related to knee weakness include:
Engaging in sports, especially football, lacrosse, basketball, or skiingIgnoring knee pain: Pain is your body’s sign something is wrong. If you let it persist unchecked, you could be allowing its cause to worsen. History of torn ligament surgeryArthritisA prior knee replacement
How Is Knee Instability Diagnosed?
To diagnose knee instability your doctor will first take a detailed medical history. You may also get a physical exam, as well as imaging tests done.
Physical Exam
An examination of the knee first looks for general findings, such as:
Bruising Tenderness Crepitus, which is a crunchy sound when pushing on or moving the kneecap Any deformity Range of motion abnormalities
Special tests may also be done during this example. For example, to examine for meniscal tears and to evaluate the ligaments, a healthcare provider may perform the:
McMurray’s test, which involves rotating the knee to find tears Ege’s test, which involves squatting while the doctor feels for a click Lachman test, when a doctor bends the knee while you are lying down
Imaging Studies
The type of imaging test done depends on the suspected problem.
For example, X-rays may be helpful for evaluating a dislocation, but magnetic resonance imaging (MRI) may be used to identify ligament and cartilage injuries.
How Do You Treat Weak Knees?
Treatment for knee instability will vary depending on the specific cause. Treatments may include rest, ice, compression, and elevation, better known as the RICE method, as well as nonsteroidal anti-inflammatory medications for pain.
Conditions such as a torn ACL or arthritis may require knee surgery, but other conditions may benefit more from physical therapy and knee rehab exercises.
A knee brace may also be used in some cases.
How Do You Prevent Knee Instability?
See your healthcare provider if you are experiencing any knee-related symptoms so a knee condition, if present, can be treated as early as possible. In some cases, this may help you avoid knee instability.
Other preventative measures include:
Doing exercises like toe raises and squats to strengthen the ACL, which is especially important for athletesWearing a knee braceAvoiding overuse injuries, which are when knee trauma repeatedly occursWearing a seat belt to reduce your risk of a dashboard-related knee injury
Summary
Knees may buckle due to tears, dislocation, certain conditions, as well as nerve damage. Your knees giving out may be the only symptom, or you may also experience symptoms such as popping, pain, stiffness, and reduced movement.
To diagnose knee instability your doctor will take a detailed medical history, give you a physical exam, and may also have you get an imaging test. Depending on your diagnosis, treatment may include the RICE method, medication, and possibly surgery.
To help prevent knee instability, be sure to see your doctor as soon as possible if you start to have knee related symptoms. You can also try knee strengthening exercises and avoid overusing your knee.
