Some doctors would say your knee is unstable. The true definition of instability is when the kneecap called the patella dislocates or shifts too far to one side.

Symptoms of buckling, collapsing, or giving way are more often caused by weakness. The quadriceps muscle along the front of the thigh helps hold the knee straight. Flexion or bending the knee without warning is a sign of quadriceps insufficiency.

Such giving way or insufficiency occurs as a result of pain, deconditioning, or swelling inside the joint. When the doctor examines you he or she will try and decide if your symptoms are coming from outside or inside the joint. If the problem is outside the knee joint then is it caused by the patella or something else?

A complete diagnosis may require exam, X-rays, and even arthroscopic surgery.