Orthopedics Hip & Knee Why You Feel Your Knee Giving Out Instability of the Knee By Jonathan Cluett, MD Jonathan Cluett, MD LinkedIn Twitter Jonathan Cluett, MD, is a board-certified orthopedic surgeon with subspecialty training in sports medicine and arthroscopic surgery. Learn about our editorial process Updated on September 07, 2021 Medically reviewed by Stuart Hershman, MD Medically reviewed by Stuart Hershman, MD on November 08, 2020 LinkedIn Stuart Hershman, MD, is a board-certified spine surgeon. He specializes in spinal deformity and complex spinal reconstruction. Learn about our Medical Review Board Print Table of Contents View All Table of Contents Symptoms Ligament Injuries Non-Ligament Causes Treatment The symptom of a knee giving out is most often due to a ligament injury. The knee is held together by ligaments, structures that connect two bones. There are four major and many secondary ones. The sensation of instability—the feeling of your knee giving out—is often due to an injury to at least one of them, which leads to the bones not being held tightly enough in position. Verywell / Brianna Gilmartin Knee Instability Symptoms Symptoms of knee instability are usually noticed with twisting or side-to-side movements. This may occur in sports activities or may occur with simple tasks, such as twisting your knee to get in and out of a car. When Your Knee Gives Out Knee Ligament Injuries Ligament injuries generally occur as the result of a sudden injury where the knee buckles or is forced awkwardly into the wrong position. When a ligament is injured, it may be either partially or completely torn. Healthcare providers often use the description of "grading" a ligament injury, although the truth is that ligaments can be injured in an endless number of ways. Injuries range from microscopic tearing within the ligament to complete tears of the ligament that may not heal without surgery. As you might expect, more minor tears generally heal with some simple steps, where more major injuries often require more invasive treatments. Knee ligament injuries can cause the knee to feel unstable and the sensation that the knee joint will give out. Anterior Cruciate Ligament (ACL) Tears The ACL is central within the knee and critical to supporting the joint with cutting and pivoting maneuvers. The ACL is most often injured with sudden shifts in direction in non-contact injury situations. People with an ACL tear often complain that their knee buckles or wants to give out when they suddenly shift direction. Most ACL tears require surgery. What to Expect With an ACL Tear Medial Collateral Ligament (MCL) Tears The MCL is on the inner side of the knee joint and prevents the knee from opening up too much on the inside. MCL tears most often occur when the knee is struck from the outside, pushing the inner side of the knee open. Most MCL tears heal with nonsurgical treatment. What to Expect With an MCL Tear Posterior Cruciate Ligament (PCL) Tears The PCL crosses over the ACL and prevents forward shifting of the shin bone. The PCL is typically injured by falling and landing directly on the front of the knee joint. PCL tears can often be treated with nonsurgical treatment when sustained as an isolated injury, but are more commonly treated surgically when combined with other injuries. What to Expect With a PCL Tear Non-Ligament Causes It is also possible for people to experience instability symptoms with injuries that cause knee pain. Often the body protects itself from pain with involuntary movements. This may feel as though the knee wants to give out, causing a sensation of instability, but it is not due to a ligament injury as described above. The best way to tell the difference between instability caused by a ligament injury, versus a sensation of instability, is by having your knee examined by a skilled healthcare provider. There are tests used to determine the function of each ligament. For example, the Lachman's test is used to test the anterior cruciate ligament. Treatment There are both surgical and non-surgical treatments for knee instability. These can include physical therapy to strengthen the muscles around the knee joint and knee braces to better support the knee joint. Surgical treatments generally involve repairing or reconstructing the damaged ligament to restore the normal structure of the knee joint. The most common type of ligament reconstruction is for ACL tears. A Word From Verywell Knee instability usually feels uncomfortable. The sooner you address it, the better you'll feel. If you're tempted to "just deal with it" because you're worried about invasive treatments, remember that nothing will be forced on you. Have a discussion with your healthcare provider about the best treatment option for you and choose one that makes the most sense. Frequently Asked Questions What can cause knee instability or giving out? The reason for a knee giving out is usually due to a ligament injury, such as a torn ACL. Knee instability can also be caused by Plica syndrome, a condition in which the inner lining of the knee joint becomes inflamed, or arthritis. If you experience knee instability or feel your leg giving out, see a healthcare provider. A knee injury has the best chance of recovery if treated as soon as possible. Learn More: When Your Knee Gives Out What does it mean to hyperextend your knee? Hyperextension of the knee is when the knee joint has extended further than normal. This can cause stress on the ligaments located inside the joint. Learn More: Understanding Knee Hyperextension If I suffer a knee injury, what should I do? If you have suffered a knee injury, immediately stop doing anything that could cause it further harm. Depending on the severity of the injury, call your healthcare provider or visit the ER to have your knee examined as soon as possible. How is a knee injury diagnosed? To diagnose a knee injury, a healthcare provider will likely start by examining the knee and asking about your symptoms and medical history. The next step may be imaging tests such as an X-ray, MRI, or arthroscopy. These tests can help identify damaged bones or tissues within the knee. Learn More: Ligament Injuries to the Knee Was this page helpful? Thanks for your feedback! Dealing with joint pain can cause major disruptions to your day. Sign up and learn how to better take care of your body. Click below and just hit send! Sign Up You're in! Thank you, {{form.email}}, for signing up. There was an error. Please try again. What are your concerns? Other Inaccurate Hard to Understand Submit Article Sources Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy. Spindler KP, Wright RW. Anterior cruciate ligament tear. N Engl J Med. 2008;359(20):2135-42. doi:10.1056/NEJMcp0804745 Andrews K, Lu A, Mckean L, Ebraheim N. Review: Medial collateral ligament injuries. J Orthop. 2017;14(4):550-554. doi:10.1016/j.jor.2017.07.017 Kiapour AM, Murray MM. Basic science of anterior cruciate ligament injury and repair. Bone Joint Res. 2014;3(2):20-31. doi:10.1302/2046-3758.32.2000241 Encinas-ullán CA, Rodríguez-merchán EC. Isolated medial collateral ligament tears: An update on management. EFORT Open Rev. 2018;3(7):398-407. doi:10.1302/2058-5241.3.170035 Vaquero-picado A, Rodríguez-merchán EC. Isolated posterior cruciate ligament tears: an update of management. EFORT Open Rev. 2017;2(4):89-96. doi:10.1302/2058-5241.2.160009 Additional Reading DʼLima DD1, Colwell CW. "Intraoperative Measurements and Tools to Assess Stability" J Am Acad Orthop Surg. 2017 Feb;25 Suppl 1:S29-S32.