Knees are a hinge-like joints that make jumping, crouching, walking, and running possible. All joints are comprised of tendons, cartilage, bone, ligaments, and muscle. Inflammation of or injuries to any of these components in the knee can ultimately cause knee problems, which are a very common ailment and affect people of all ages. There are several different types of diseases and injuries that can cause knee problems.
Patellar Tendinitis
The Mayo Clinic reports that the patellar tendon is a thick cord that attaches the muscles of the thigh to the lower leg bone, the tibia. A person with knee problems may have patellar tendinitis, a condition in which the patellar tendon becomes inflamed. People who often run, ski, and bicycle are particularly prone to this type of tendinitis due to the strain these activities place on the patellar tendon. The specific symptoms of patellar tendinitis are pain, especially pain that worsens when jumping, running, or otherwise putting strain on the knee; swelling in the front of or just below the knee; and being unable to straighten the leg.
Arthritis
According to the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), there are 100 different types of arthritis and arthritis-related conditions, such as rheumatic diseases. One very common type of arthritis that affects the knees is osteoarthritis, which involves the gradual disintegration of the cartilage between the thighbone and the lower leg bone. Without padding from the cartilage, the bones of the joint gradually disintegrate. Osteoarthritis can be caused by joint injury or being overweight, and is more common as people age.
Another common type of arthritis is an autoimmune disease called rheumatoid arthritis. In this disease, the immune system attacks the membrane that lines the joint, called the synovium. Other rheumatic diseases can also cause knee problems: gout, lupus, ankylosing spondylitis, and psoriatic arthritis. Though the causes of these conditions are distinct, these rheumatic diseases ultimately cause inflammation in the knee joint. The symptoms of arthritis and arthritis-related diseases include pain and stiffness and may include swelling. The Mayo Clinic adds that the stiffness is especially acute immediately after long periods of rest, such as sleeping at night.
Chondromalacia
This condition, as described by NIAMS, is characterized by softening of the cartilage in the kneecap and is caused by injury, abnormal alignment of the patella, or weakness of the thigh muscles. In chondromalacia, the kneecap rubs against the top of the thighbone rather than gliding smoothly across it, causing pain. Early in the disease, damage may affect only the cartilage itself; if left untreated, the top of the thighbone can eventually wear away. The symptoms of this condition include dull pain underneath the kneecap, which often becomes more severe when you walk down hills or stairs.
Meniscus Injury
The Mayo Clinic describes the meniscus as the C-shaped piece of cartilage within the knee joint. Injury to the knee may cause the meniscus to tear, which causes pain, mild to moderate swelling, and trouble straightening the knee.
