There are many possible causes of bilateral knee pain or pain in both knees. According to the Sports Injury Clinic website, knee pain can be caused by overuse injuries, trauma or sports injuries. Bilateral knee pain can also be caused by joint inflammatory disorders. Knee pain ranges from mild to severe, and in some cases, it can even be debilitating, affecting a person's ability to perform her activities of daily living.
Rheumatoid Arthritis
Rheumatoid arthritis can cause bilateral knee pain. According to the American Academy of Orthopaedic Surgeons, rheumatoid arthritis is an inflammatory type of arthritis that may destroy joint cartilage, can occur at any age and typically affects both knees. The Johns Hopkins Arthritis Center, or JHAC, states that, along with joint cartilage destruction, rheumatoid arthritis can cause joint deformity and the loss of joint function. The typical case of knee rheumatoid arthritis is insidious—it manifests for no apparent reason. While signs and symptoms of knee rheumatoid arthritis appear gradually over a period of weeks to months, a person may first notice stiffness in his knee joints, which is often accompanied by pain when moving the joint and tenderness within the joint. The JHAC notes that morning stiffness is characteristic of rheumatoid arthritis, and that its duration is a useful gauge of the disease's inflammatory activity.
Patellar Tendinitis
Patellar tendinitis can cause bilateral knee pain. Patellar tendinitis is irritation and inflammation in the patellar tendon—a thick, fibrous cord that links the bulky quadriceps muscles of the thigh to the tibia or the larger of the two lower leg bones. Bilateral knee pain caused by patellar tendinitis will usually be accompanied by swelling in the front of the knees or just below the kneecap, increased pain with jumping, running, squatting or stair climbing, and difficulty extending or straightening the knees. The Sports Injury Clinic states that athletes who place a significant amount of stress on the patellar tendon—for example runners, skiers and cyclists—are at an increased risk of developing patellar tendinitis. Athletes who participate in sports that involve directional changes and jumping movements are also prone to patellar tendinitis.
Osteoarthritis
Osteoarthritis, also known as degenerative joint disease, can cause bilateral knee pain. According to Arthritis Research UK, when the knee joint develops osteoarthritis, the joint's surfaces become damaged, and the joint may not move as smoothly as it should. The cartilage coating the ends of the bones that compose the knee joint—the femur and the tibia—roughen over time and eventually wear down. The bone that lies directly underneath the cartilage responds to these new stresses by growing thicker, which may cause bone spurring or osteophyte formation. Other osteoarthritis symptoms that accompany the structural changes in the knee include swelling of the synovium, a thin joint membrane that secretes fluid, and a thickening and contracting of the knee joint's capsule and surrounding ligaments. Although osteoarthritis can cause bilateral knee pain, a person with degenerative knee changes may experience no pain at all, or she may experience pain in one knee but not the other.
