Sudden knee pain has many causes. According to MedlinePlus, a service of the U.S. National Library of Medicine and the National Institutes of Health, knee pain can be debilitating, and it can significantly affect a person's activities of daily living. MedlinePlus states that the treatment of knee problems largely depends on the cause of the condition. Some knee pain occurs over time, from repetitive overuse. Other types of knee pain manifest suddenly, often following a traumatic sports injury or a motor vehicle accident.
ACL Tear
An anterior cruciate ligament, or ACL, tear can cause sudden knee pain. According to the Sports Injury Clinic website, the ACL is one of four principal stabilizing ligaments of the knee along with the posterior cruciate ligament, or PCL; medial collateral ligament, or MCL; and the lateral collateral ligament, or LCL. The ACL helps connect the femur, or thigh bone, with the tibia, or shin bone. It starts at the back of the knee joint and runs toward the front of the knee joint, where it attaches to the tibia's flat upper surface. ACL tears are usually caused by a rapid twisting motion of the knee. ACL tears are a relatively common injury in sports such as football, rugby and basketball. ACL tears occur more frequently in females. Common signs and symptoms associated with an ACL tear include the following: an audible pop at the time of the injury, extreme knee pain, knee swelling, the sensation of knee instability and reduced active range of motion in the knee joint.
Patella Fracture
A patella fracture can cause sudden knee pain. Cedars-Sinai Medical Center, a Los Angeles-based nonprofit hospital and academic medical center, states that the patella, or kneecap, is a triangular bone situated on the front of the knee. The patella is a common site of tendon and ligament attachment, and it helps improve muscular efficiency and dampen the stress placed on the knee by the thigh and lower leg. According to CSMC, the patella is vulnerable to fracture and can break in several different ways, including a partial fracture or a complete fracture. The patella can also fracture into many pieces or just a few pieces. Patella fractures are often accompanied by ligament sprains and tendon tears. Common signs and symptoms associated with patella fractures include the following: severe pain in and around the patella, knee swelling, reduced active range of motion in the knee joint and a kneecap that's tender to the touch.
Meniscal Tears
Meniscal tears can cause sudden knee pain. According to the American Academy of Orthopaedic Surgeons, meniscal tears are one of the most common injuries, especially among athletes who participate in contact sports. The menisci are two crescent-shaped pieces of cartilage inside the knee joint that absorb force between a person's femur and tibia and help stabilize the knee joint. Menisci possess a rubbery texture and are extremely durable. The AAOS states that meniscal tears occur in numerous ways, and that tears are described by their appearance, along with the location of the tear. Examples of meniscal tears include the parrot-beak, flap and bucket-handle tears, named after the tear's appearance. Common signs and symptoms associated with meniscal tears include the following: an audible pop at the time of injury, pain in the affected area, knee stiffness and swelling, knee catching or locking, reduced active range of motion in the knee joint, and the sensation of knee joint instability.
