Knee instability is a condition, characterized by a loose feeling in the knee, particularly while making movements. Some activities can exert more pressure on the knee joint and the structures that surround it, which can cause knee instability. While there are many causes of knee instability, injury to the knee joint is one of the commonest causes.

What Can Cause Knee Instability?

What is Knee Instability?

Knee instability can be felt when there is increased laxity of the ligaments supporting the knee joint. It can be either physiological laxity or it can be pathological laxity, in which an injury may have caused the ligament to stretch.

The knee joint is a very important structure, which bears most of the weight of the body. It is a crucial weight-bearing joint that enables one to move around with ease. Taking steps in different directions, jumping, twisting and many other movements of the knee are possible because of the supporting structures that maintain the stability of the knee joint. Injuries, sports, falls and other conditions can cause knee instability, which can affect the routine activities. The causes of knee instability must be properly understood and evaluated to manage the condition and treat the injury in time.

Sportspersons, players, dancers and people involved in other physical activities use the knee joint to its fullest potential and in various directions. Certain activities although indirectly, can cause knee instability. Activities like dance, aerobics, sports and athletics, exert a lot of stress on the knee joint and its surrounding structures. Moreover, in such activities, the person is more prone to injuries, which can commonly cause knee instability. Different movements like twisting and turning the legs, jumping, running, etc. can cause damage to the structures supporting the knee, which can cause knee instability.

What Can Cause Knee Instability?

Some of the factors that can cause knee instability include strain, injury or tear of the ligaments supporting the knee joint. In some cases, knee instability may also be caused or worsened by certain conditions or people with some disorders may be at increased risk of knee instability.

Knee Instability Caused Due to Ligament Injury

Ligament injuries are the commonest cause of knee instability. Ligaments of the knee play a very important role in stabilizing the knee and aid in various movements performed by the knee joint. The main ligaments that support the knee include

  • Anterior Cruciate Ligament (ACL) – The main role of the ACL is to enable rotational movements of the knee and prevent the leg bone from moving forwards. Injury to the ACL commonly occurs during sudden forceful landing or twisting movements and can cause knee instability. ACL injury can commonly occur in combination with other injuries and can cause knee instability.
  • Posterior Cruciate Ligament (PCL) – The main role of PCL is to prevent the forward movement of the thigh bone and also supports the knee joint. Injury to the PCL can sometimes occur during sports or other physical activities. PCL can also occur along with ACL tears or other injuries and cause knee instability.
  • Collateral Ligaments – These are medial (inner side of the knee) and lateral (outer side of the knee) collateral ligaments supporting the knee from the sides. While medial collateral ligament injuries are more common, lateral collateral ligaments may also get injured in some cases. Both injuries can affect knee function and are an important causes of knee stability.

Ligament tears and injuries that cause knee instability can be graded based on the severity of the condition. Ligament injuries of grade one, which is a minor tears but can still cause some degree of knee instability. Such minor ligament tears can heal well with prompt treatment and adequate rest. Ligament tears of moderate to severe degrees usually cause great deal of knee instability and can be more difficult to manage. The grade three ligament tear may often require surgical treatment to repair the ligament and help to regain the knee functions. Ligament tears can cause severe pain, inability to move the knee, large swelling, other signs of inflammation and cause knee instability.

Knee Instability Caused Due to Knee Sprain

A sudden forceful movement that or a fall causing overstretching of a ligament or a muscle. Even if it is not a typical ligament tear or a major strain, simple knee sprain that causes strain on the soft tissues of the knee can cause knee instability. It can lead to knee pain, difficulty in movement and can be triggered by further activities of the knee joint. Knee sprain, which is more common during sports or other similar activities, can cause knee instability that can lead to easy loss of balance when running or playing.

Meniscal Tears Can Cause Knee Instability

Knee joint is maintained in position with the help of its bone structure, the shape of its condyles and the supporting structures. While ligaments supports the knee from all sides, there are other structures called the menisci, which support the knee joint within. Each meniscus is a c-shaped cushion placed in each of the knee joint, located in between the two bones forming the joint. They provide stability to the knee, support the knee and acts as a shock absorber, thus preventing damage to the knee joint.
Meniscal injuries are also common amongst sports players, dancers or are seen during other activities, particularly those involving twisting movements. Meniscal tears are another common cause of knee instability and can affect the knee function to a great extent. Partial meniscal tears are more common and can cause knee instability that cannot cause discomfort but also cause great pain. This makes it difficult to move or turn the knee, bear weight on it or walk and cause knee instability that makes a person limp on attempting to walk.

Meniscal injuries too present with severe knee pain, either on the inner side or on the outer side of the knee, depending on which meniscus is affected.

Degenerative Changes Cause Knee Instability

As the stability of the knee is maintained due to the shape of condyles, it is important to understand that any condition affecting the condyles or the menisci that supports the joint can affect the knee joint. Knee instability can also be caused by degenerative changes in the knee joint. People suffering from arthritis often complain of knee instability; osteoarthritis, a degenerative condition of the knee is common cause of knee instability.

In osteoarthritis, due to degeneration or wear and tear, the meniscus, which acts as a cushion get eroded. This exposes the joint surfaces and lack of shock absorbing material causes the exposed bony surfaces and condyles to rub against each other, causing degeneration of the bones. This wear and tear causes knee instability and as the bones continue their friction, the bones begin to get eroded from all sides. As degeneration continues, the condition only progresses and increases knee instability.

Degenerative changes in the knee joint that causes knee instability are usually seen in both the knees, however in some cases, it may be different. Knee joints, which have suffered from previous injuries, infections or septic arthritis, may show early degeneration than the other knee joint in the same person. In such cases, knee instability may be caused more or only in the affected knee joint, while the other knee may be normally in stability. This occurs more commonly in young people with knee instability due to early osteoarthritis, which has resulted from certain problems in that knee joint. These usually present with knee pain, swelling in the affected knee and cause knee instability.

Aging – Aging is a common cause of knee instability. As a person grows older, the muscles of the legs and the tissues around the knee joint may become weak. The overall health of the person may also be affected due to other medical conditions and some people may also experience problems in maintaining their balance. While there may be other medical problems, playing a role in this, degeneration and overuse of the knee joint due to aging too plays an important role in causing knee instability.

Other Causes of Knee Instability

Sometimes there may be other causes of knee instability, which may not be instability of the knee joint in the real sense. In some cases, people may feel that the knee is giving way or feeling instable but not have true knee instability. These may be due to minor injuries that cause knee pain, giving a feeling as if there is knee instability. Ligaments injuries causing knee instability can be detected with certain clinical tests and can be differentiated from such just feeling of knee instability.

Certain conditions of the knee, like those causing pain in the patella, chondromalacia patellae, anterior knee pain can cause knee instability. People having weak muscles, strained tissues or foot deformities can sometimes feel knee pain, which may resemble to cause knee instability.

Knee instability tests are usually performed at the clinic and usually give an idea regarding the possible cause of knee instability. However, for some cases, either those with complex injuries or other conditions causing any kind of knee instability may need appropriate investigations to find the cause of knee instability.

Risk Factors That Can Cause Knee Instability

Certain factors can increase the risk of knee instability and may be seen in some people more commonly.

  • Many people experience minor injuries to the knee joint, falls, sport injuries or other minor sprains. While wear and tear is a normal course as a person continues to use the joints, any kind of damage to the knee joint can speed up the degenerative process.
  • Usually degeneration of knee joint is commonly seen in aging population. However, the risk of knee joint degeneration as a cause of knee instability may be more in people who are obese or those who have a previously injured knee joint.
  • Certain types of infections, occurring in some people may also cause knee instability or increase the risk. People who have other forms of arthritis, rheumatoid arthritis, etc. can experience conditions that cause knee instability. People with autoimmune conditions, connective tissues disorders are at greater risk of soft tissue injuries or conditions that can cause knee instability.
  • People who have undergone surgical repairs for ligament injuries, or those with other surgical treatments of the knee joint, too are at greater risk of degeneration and knee instability. Those who have undergone previous treatment for knee problems or other causes of knee instability, are also at increased risk of recurrence of the condition and knee instability.
  • Those who have undergone treatment for causes of knee instability but without adequate or proper rehabilitation too are at greater risk. If proper rehabilitation is not done, the muscles and soft tissues of the knee joint may remain weak. This increase the risk of sprains, ligament tears or other injuries of the knee joint causing knee instability.

Diagnosis of Knee Instability

Cause of knee instability can be detected using clinical tests, in most cases of knee or ligament injuries of the knee. Clinical examination also reveals signs of inflammation, swelling, warmth and tenderness around the knee joint, any signs of injuries, bruising and cut wounds.

X-rays, CT scans and MRI can help to detect structural deformities, fractures, soft tissue injuries and degenerative changes in the knee joint that can cause knee instability. Depending on the condition of the person, additional tests may be done to rule out infections, other forms of arthritis, connective tissue disorders, etc.

Other tests to find causes of knee instability can include arthroscopy, which is used as diagnostic and treatment modality. It can help to detect the cause of knee instability, forms of arthritis, or other causes of knee inflammation or pain.

Treatment of Knee Instability

Treatment of knee instability depends on the cause. Minor cases, which do not require any intervention are usually treated with anti-inflammatory medicines, ice and rest.

Injuries or inflammatory conditions of the knee joint causing knee instability may require surgical treatment. Ligament injuries can be successfully repaired with arthroscopic procedure. The commonest ligament ACL is normally injured and the surgery performed is ligament reconstruction for major ACL tears. For meniscal tears and injuries, procedures may be required to shave of the torn parts (partial meniscectomy) that may have caused knee instability. For osteoarthritis causing knee instability, appropriate treatment needs to be planned. For severe cases, knee replacement surgery may be considered.

Physical Therapy for Knee instability

Whether surgery is required or not, physical therapy plays an important role in cases of knee instability. For minor injuries, only physical therapy too can help along with rest, ice and medications. It aims at strengthening the muscles, improving range of motion and flexibility of the knee joint, which can reduce knee instability. It helps to improve stability of knee, along with balance, ability to walk or run and prevent injuries in future.

Persons with knee injuries, osteoarthritis can benefit from physiotherapy to reduce the risk factors that can cause knee instability. Post-operative physical therapy is very important to improve knee joint function and regain the capacity to walk and move without pain or discomfort. People with knee instability may be advised to wear knee braces, particularly when walking, playing or participating in sports after recovery.

Compliance to therapeutic exercises in physical therapy is important to strengthen the knee joint. Discontinuing exercises or not following medical advice after knee conditions or injuries can cause knee instability after some period of time. Hence, it is advisable to follow medical and physical therapy instructions, in addition to taking appropriate protective measures.

Written, Edited or Reviewed By:


Last Modified On: September 27, 2016

Pain Assist Inc.

Pramod Kerkar
  Note: Information provided is not a substitute for physician, hospital or any form of medical care. Examination and Investigation is necessary for correct diagnosis.

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