When your knee gives out after a car crash

An orthopedic knee surgeon and a physical therapist on ACL injuries

For survivors and families3 min read

Leg and foot injuriesACL tearsKnee injuriesSprains and ligament tearsPhysical therapy

The anterior cruciate ligament, or ACL, helps hold the knee steady when your leg twists or changes direction. In a crash, a direct blow or a sudden twist can hurt it. Some people feel a pop. The knee may swell or give way. [1]

Other parts may be hurt as well, such as the meniscus, the cartilage and other ligaments. The first step is to learn the full extent of the injury. Whether the ACL is torn is only part of it. [1]

Find out what else the knee needs

Tell your doctor when the knee buckles, locks or won’t straighten. Ask what the exam found and whether X rays ruled out a broken bone. An MRI can confirm an ACL injury and show other damage that came with it. If your knee looked out of place at the scene of the crash, say so. A true knee dislocation needs its own check of the blood vessels and nerves. [1, 2]

Pick treatment based on stability and your daily life

Some people handle an ACL tear with rehab and changes in activity. Others choose reconstruction, which is surgery to rebuild the ligament. For them, an unstable knee gets in the way of work, sports or daily tasks. Ask how your other injuries and your goals affect the choice. [1]

A therapist can help bring down swelling, get motion back and build strength. If you’re having surgery, ask what should get better before the operation. Also ask what rehab will require of you afterward. [1]

Repeated buckling needs attention

Contact your knee team if the joint keeps buckling or locking, or if it stays very swollen. Get urgent care if your foot turns cold or pale or you have new major numbness. The same goes for severe pain that keeps building after a knee injury. Do not twist on an unstable knee to test it. [1, 2]

What to ask your knee team

  1. Which ligaments, meniscus and cartilage were hurt?
  2. What activities are safe while my knee is unstable?
  3. What would make surgery more helpful than rehab alone?

List what makes the knee buckle

Before your next checkup, write down the activities that make your knee give way. [1]

Sources and further reading

  1. 1American Academy of Orthopaedic Surgeons ACL plain language summary
  2. 2Orthopaedic Trauma Association knee dislocation

General information from the fields of orthopedic knee surgery and physical therapy. A knee that is swollen and unstable may have more than one injury. Your treatment will depend on the full exam, any other damage and the activities you need to get back to.

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A parent kneels beside a young child at the curb next to the family car.