Why Does My Knee Keep Giving Way?

What "giving way" feels like

Giving way, also called buckling, is a sudden, brief loss of support: the knee bends or shifts when you expect it to hold. It often happens when turning, pivoting, stepping down a stair or curb, or walking on uneven ground. It may or may not hurt.

Giving way is different from locking, where the knee gets stuck and won't straighten. Some people have both, and the causes overlap.

Common causes

• ACL tear. Usually starts with a pivoting or landing injury, often with a pop and swelling within hours. Afterward, the shin bone can shift forward and rotate, so the knee gives way with twisting.
• Other ligament injuries. MCL and LCL injuries cause side-to-side looseness. A PCL injury lets the shin sag backward and often feels worst going down stairs or hills.
• Meniscus tear. A torn flap of cartilage can catch in the joint and cause a momentary buckle, often with catching, swelling, or pain along the joint line.
• Kneecap instability. The kneecap slips partly (subluxation) or fully (dislocation) out of its groove, usually with a twist, and the knee collapses. It's most common in teens and young adults.
• Osteoarthritis. A sudden jolt of pain can make the thigh muscles briefly switch off, and changes in alignment can loosen the knee's supporting structures.
• Weak or inhibited thigh muscles. The quadriceps are the knee's main active stabilizer. Weakness after an injury or surgery, or swelling in the joint, which reflexively shuts the quadriceps down, can make the knee buckle even when the ligaments are intact.
• Nerve problems. Buckling without pain can come from the nerves rather than the knee, for example a femoral nerve injury, peripheral neuropathy, a pinched nerve in the lower back, multiple sclerosis, or a stroke.

Why it matters even when it doesn't hurt

In the same large study, most people who had buckled did so more than once, about 1 in 8 of them fell during an episode, and more than half had no arthritis on X-ray. Buckling was also linked to worse physical function and to fear of falling.

With a torn ACL, each episode of giving way puts extra stress on the meniscus and cartilage. That's a big part of why a knee that keeps giving way should be evaluated rather than ignored.

What helps

• Strengthening. Building the quadriceps, hamstrings, and hip muscles is the foundation of almost every plan.
• Balance and control training. Single-leg balance and controlled step-downs retrain the quick reactions that keep a knee from buckling.
• Calming swelling. A swollen knee shuts down the thigh muscles, so reducing swelling often makes the knee feel steadier.
• Changing how you move for a while. Cutting back on pivoting, twisting, and jumping gives the rest of your plan a chance to work.
• A knee brace. External support limits the side-to-side and twisting motions that make the knee give way.
• Surgery, for some people. Examples include ACL reconstruction for people who want to return to pivoting sports, repair of a displaced meniscus tear, and kneecap stabilization after repeated dislocations.

Where a knee brace fits in

A brace works immediately, doesn't wear off, and can be worn during the activities where your knee is least reliable, such as work, sports, or walking on uneven ground. It doesn't repair a ligament, and it works best alongside strengthening.

Fit decides whether a brace helps. A brace that slides down the leg stops lining up with the knee and stops supporting it. BISHOP braces are modeled from a 3D scan of your leg so they contact the leg evenly and stay in place.

When to get checked promptly

• The knee gave way during an injury, you felt a pop, and it swelled within a few hours.
• You can't put weight on the leg, or the knee looks deformed.
• The knee is locked and won't fully straighten.
• Your kneecap has dislocated.
• The knee keeps giving way, or you've fallen because of it.
• The buckling comes with numbness, tingling, back pain, or weakness elsewhere in the leg.

Common questions

Why does my knee give way going down stairs?

Going down stairs asks the quadriceps to control the knee while it bends under your full body weight. Weak thigh muscles, kneecap problems, a PCL injury, and arthritis often show up first on the way down. Use the handrail, and ask a physical therapist about controlled step-down exercises.

Can weak muscles make my knee give way?

Yes. The quadriceps are the knee's main active stabilizer, and weakness after an injury, surgery, or a period of inactivity can make a knee buckle even when the ligaments are fine. That's why strengthening is part of nearly every treatment plan.

Should I wear a knee brace if my knee keeps giving way?

A brace is a reasonable way to protect the knee during the activities that cause giving way while you strengthen it. Get evaluated as well, because the cause changes the best treatment.

Sources

• Felson DT, et al. Knee buckling: prevalence, risk factors, and associated limitations in function. Ann Intern Med. 2007;147(8):534-540
• AAOS OrthoInfo: Anterior Cruciate Ligament (ACL) Injuries
• AAOS OrthoInfo: Meniscus Tears
• AAOS OrthoInfo: Unstable Kneecap
• AAOS OrthoInfo: Arthritis of the Knee