What Causes Weakness in the Knee? Symptoms & Treatment

Medically Reviewed on 11/30/2021
What Causes Weakness in the Knee
Knee weakness can be caused by a wide range of factors, from injuries to illnesses. The most common cause is damage to the ligaments

Knee weakness can be caused by a wide range of factors, from injuries to illnesses. The most common cause of an unstable knee is damage to one of the four ligaments that hold the joint together and allow it to function normally:

  1. Anterior cruciate
  2. Medial collateral
  3. Posterior cruciate
  4. Lateral collateral

All four ligaments carry out specific tasks that allow a normal range of motion in a highly complex, load-bearing joint. They are most often injured during athletic activity, although simple daily activities can result in overuse or sprain. The extent to which they are damaged determines how urgent it is to seek medical attention.

Common causes

Serious causes

  • Osteoarthritis
  • Arthritis affecting the spine
  • Tendinitis
  • Herniated disc impinging on the nerves that supply the lower limb
  • Spinal cord injuryabscess, or tumor
  • Nerve disorders
  • Spinal degeneration (degenerative disc disease, also called spondylosis)
  • Spinal stenosis (narrowing of the spinal canal, creating pressure on the spinal cord or nerves)
  • Bone fractures
  • Stroke (a potentially life-threatening condition in which part of the brain is deprived of oxygen)
  • Multiple sclerosis (a condition that causes the immune system to attack the protective covering of the nerves)
  • Plica syndrome (caused by inflammation of the medial plica, which is a fold in the middle of the membrane that covers the knee joint).
  • Iliotibial band syndrome (overuse injury of the knee and thigh)

Toxins and drugs

What are symptoms of a weak knee?

Although symptoms of knee weakness depend on the underlying cause, signs may include:

  • Swelling and stiffness
  • Redness
  • Burning sensation
  • Instability
  • Popping noises when the joint is bent
  • Inability to straighten the knee
  • Difficulty transitioning from a sitting to a standing position

What exercises can help strengthen weak knees?

Strengthening the hips and glutes keeps the knees in proper alignment, which can relieve pressure on the joints. Exercise can also help improve the health of cartilage tissue and keep the leg muscles strong.

Exercise that can help weak knees include:

  • Quad, hamstring and glute squeeze: 
    • Sit up straight, with a pillow between the knees. 
    • Squeeze the pillow while engaging the front and back of the thighs, buttocks, and abs at the same time. 
    • Repeat 25 times.
  • Seated leg extension: 
    • Sit up straight and place the right hand on the inside of the right knee. 
    • Straighten the leg forward while engaging the muscles around the knee, especially the ones directly under the hand. 
    • Before switching legs, repeat 15-25 times.
  • Sit to stand: 
    • Try this exercise only after mastering the first two exercises. 
    • Begin by sitting and placing the feet hip-width apart. 
    • The knees should be parallel to the toes in the middle. 
    • Slowly stand while engaging the core, butt, and thigh muscles. 
    • Then slowly sit back down, muscles still engaged. 
    • Begin with 5 repetitions and increase to 10 as you get stronger.

Seek the advice of a physiotherapist or a professional trainer to make sure you are performing the exercises correctly and safely.


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How is weakness in the knees treated?

Treating knee instability and buckling involves treating the underlying cause of the symptoms. The overall goal is to treat pain while restoring joint strength and function. Treatment may include:

  • RICE (rest, ice, compression and elevation) and nonsteroidal anti-inflammatory medications for pain
  • Knee surgery for conditions such as torn ligaments
  • Physical therapy and knee rehabilitation exercises
  • Knee braces or immobilizers
  • Consuming calcium-rich foods, such as flaxseeds, sesame seeds, and walnuts
  • Consuming vitamin C-rich fruits and vegetables (these contain anti-inflammatory properties that can aid in the relief of arthritis and other types of pain)

Knee buckling or weakness can be a minor annoyance or a serious health risk. Work with your doctor to determine what is causing weakness in the knee so they can help create an effective treatment plan.

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Medically Reviewed on 11/30/2021
Image Source: iStock Images

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University of Michigan Health. Knee Problems and Injuries. https://www.uofmhealth.org/health-library/kneep

Anderson WA. Knee neuropathies. American Academy of Physical Medicine and Rehabilitation. https://now.aapmr.org/knee-neuropathies/

Luna. How PT Can Treat Weak Knees. https://blog.getluna.com/how-pt-can-treat-weak-knees

BetterHealth. Knee injuries. https://www.betterhealth.vic.gov.au/health/conditionsandtreatments/knee-injuries