Hyperextension of the knee occurs when your knee is straightened beyond the joint's normal range. Essentially, the joint bends backwards potentially leading to bruising, swelling, pain and soft tissue damage. The ligaments of your knee -- the cruciate and collateral ligaments -- work to hold the joint in place and can sustain damage during hyperextension. Though you might injure any of these tendons, the anterior cruciate ligament, or ACL, is the most likely candidate to tear or rupture.
Knee Anatomy
As the largest joint in your body, your knee is responsible for maintaining your bipedal motion. The joint is composed of four bones and a variety of ligaments, tendons and muscles as well as two pads of cartilage that provide cushioning. The anterior and posterior cruciate ligaments as well as the medial and lateral collateral ligaments hold your bones in place. Your quadriceps muscle and tendon as well as the patellar tendon are mainly responsible for straightening your leg while your hamstring muscles provide a counter-force to prevent hyperextension.
Hyperextension
Absorbing a strong force while your knee is straight can lead to hyperextension. Sports like basketball, gymnastics and soccer -- where you jump frequently or change directions quickly -- can lead to knee injuries. Knee hyperextension injuries during sports are not always serious, according to the MayoClinic website; however, you can damage ligaments, cartilage and tendons in your knee. You can also dislocate your knee, which may tear or stretch soft tissues. Symptoms often include bruising, swelling and pain when you straighten your joint.
Cruciate Ligament Tears
The cruciate ligaments hold your thigh and shin bones together, crossing over each other within the knee joint. This "X" shape brings stability to your joint. The ACL works to limit the rotation and forward movement of your shinbone, or tibia. Conversely, the PCL or posterior cruciate ligament's role is to prevent backward movement of the tibia. Because hyperextension involves your shinbone moving forward, your ACL is more prone to injury during this motion. Symptoms of a torn cruciate ligament include a "popping" sound or you may feel your knee buckling or giving out, causing you to stumble or fall. Pain and joint swelling accompany a tear, which affects your leg muscle strength and inhibits bending or straightening your leg.
Other Types of Damage
Though your knee is also held together by the lateral and medial collateral ligaments, neither ligament is typically torn during hyperextension. These ligaments hold the sides of the joint together and often sustain injury from side-moving impacts. You can, however, damage knee cartilage -- the cushioning surrounding your bones -- during hyperextension from a forceful impact. Tearing your ACL or PCL increases your likelihood of damaging cartilage. A high-impact hyperextension can also affect the medial and lateral menisci that sit in between bones to provide cushioning. ears to either of these pads leads to pain, swelling and immobility.
