As hyperextension of the knee can occur to varying levels of severity, the symptoms of the injury will be contingent upon the individual athlete’s body, the method of hyperextension, and the overall strength of the knee joint.

Common Symptoms and Signs of Knee Hyperextension

Common symptoms of knee hyperextension include:

  • Instability of the knee. In cases of minor hyperextension, an athlete may notice that the affected knee is less stable or sturdy than the healthy one. The knee will have a feeling of giving out or buckling.
  • Pain after the injury. Following hyperextension of the knee joint, feeling localized pain in the knee is common. Depending on whether or not one of the four primary ligaments in the joint was damaged, the pain may be concentrated to one area.
  • Limited mobility. Hyperextension of the knee is likely to cause limited mobility in athletes. This will manifest as a reduced range of motion due to weakness in the joint, swelling, and pain.
  • Water on the knee. Fluid accumulation within the knee joint is common after hyperextension of the knee. This will reduce knee mobility and is sometimes called “water on the knee.”
  • Bruising. If hyperextension of the knee has been traumatic enough to cause damage to ligaments, cartilage, or other interior soft tissues, bruising may appear on the skin.

    See ACL Tear Symptoms


In the event that a knee hyperextension has caused serious damage to the structures and ligaments, the presence of sharp, severe pain will be nearly immediate. Whether the injury leading to the hyperextension was traumatic or minor, individuals experiencing these symptoms may benefit from seeking medical attention.

See Treating Acute Sports and Exercise Injuries in the First 24 to 72 Hours

Dr. Sean Colio is a sports medicine physician specializing in the treatment and prevention of sports and musculoskeletal injuries. He serves as a Clinical Assistant Professor in the Department of Orthopaedic Surgery at Stanford University. Dr. Colio co-founded the Sports Concussion Clinic at Swedish Spine, Sports & Musculoskeletal Medicine.