Knee Instability

The knee consists of four bones: femur(thigh), tibia (leg), fibula (leg), and patella (kneecap), and four major ligaments: ACL, PCL, MCL and LCL. The two ligaments in the middle of the knee cross each other and are therefore known as the cruciates. On the inner, or medial side is the Medial Collateral Ligament (MCL) and on the outer, or lateral side, the Lateral Collateral Ligament (LCL). Between the femur and tibia are the meniscal cartilages, medial meniscus on the inner side, and lateral meniscus on the outer side. The quadriceps muscle, in front, attaches, by the quadriceps tendon, to the patella, which, in turn attaches by the patella tendon, to the tibia. When working properly, the quadriceps mechanism can straighten the knee and provide kicking power. The hamstring muscles attach to the fibula and the back of the tibia to help to power bending the knee.

Knee instability is most commonly the direct result of injuries or complications with the ligaments in the knee joint. Instability of the knee is most commonly related to the sensation of the knee “giving out” or buckling under pressure. Issues regarding the ligaments can lead to bones not being held tightly enough in position, thus making for a wobbly sensation when attempting to bear weight on the knee(s). ACL, MCL, and PCL tears are all commonly related to knee instability.

The root cause of knee instability is usually a result of damage, tearing, or other problematic occurrences regarding the ligaments of the knee. This may include tears of the ACL, MCL, or PCL. Arthritis is another known contributor to knee instability, as it commonly wears down and depletes the cartilage found on the ends of the bones that come together in the knee joint.

There are many risk factors to consider regarding knee instability as some groups are more susceptible to it than others. These groups are more common to experience knee instability than others due to strenuous activity:

• Athletes
• Dancers
• Those with occupations that require physical labor
• Those who are overweight or obese
• Women
• The elderly
• Those with a prior injury

The most common symptom of knee instability is the sensation of buckling of the knee when attempting to bear weight on it. Symptoms are most likely to occur if there is an acute injury or chronic pain of the knee. The severity of knee instability can vary depending on the root cause and underlying factors. The most common characteristics of knee instability include:

• The knee feeling out of place
• Looseness of the knee
• Locking of the knee
• Popping of the knee
• Difficulty straightening the knee
• Decreased range of motion
• Pain
• Swelling
• Bruising

During the physical exam, a physician will test the reflexes of the knee and ask if there is any pain, discomfort, or lack or range of motion associated with the reaction of the hinge joint. More often than not, a doctor will recommend imaging tests to determine the underlying cause of the symptoms. XRays, MRIs, CT scans, and ultrasounds will reveal the status of the soft tissue, cartilage, and bones of the knee. This will help the doctor  determine whether the root cause is arthritis, a tear or rupture, sprain, muscle damage or deterioration of any tissue.