The knee is one of the largest joints in the body. It takes wear and tear from walking, running and other activities the body goes through. The Mayo Clinic recognizes the complexity of the joint and states there are many causes and symptoms of knee pain. The most common injuries are likely to happen to ligaments, tendons, bursa and cartilage. Injury to any of the structures within the joint can cause pain in the knee.
Ligament Disorders
The Mayo Clinic states there are four main ligaments of the knee, one on either side of the knee called the medial and lateral collateral ligaments, and two in the center of the knee that cross as they span from top to bottom and front to back. These ligaments are called the anterior and posterior cruciate ligaments. Damage can happen to any of these ligaments from direct trauma, a fall or a twisting or landing motion. A tear to any of these ligaments will cause pain inside the knee, along with swelling and a possible feeling of the knee giving out. Since these ligaments help stabilize the joint when running, the pain may be noticed during or after a run.
Meniscus Damage
Cartilage is a tough spongy material that helps to cushion the joints and prevent the bones in the joint from touching. Runners Rescue Online posted an article on inner knee pain and running. The article states there are two menisci within the knee that not only function as shock absorbers but also distribute the weight of the body evenly across the knee. Without this cartilage, the bones will touch, and excessive force would be placed on one area of the knee, causing further damage. The outer part of the meniscus has a small blood supply, while the inner part of the menisci have no blood supply. Damage can happen to these tissues in the same way ligaments are damaged. The poor blood supply will lead to a slow healing time or no healing at all, and running will cause further damage and pain within the knee. What part of the meniscus is damaged will help determine where in the knee the pain will be.
Tendon Tears
Tendons are usually torn partially or completely with repetitive overuse or a rapid stretch of muscle. A partial tear will take two to eight weeks to heal, depending on the grade of the tear. Tendons help connect muscle to bone. There are no tendons directly within the knee joint, but they cross and attach near the joint. Damage to the tendons can cause local pain but can also refer pain into and around the knee joint.
Bursa
Bursa are small fluid-filled sacs outside joints that help pad the tendons and ligaments and decrease friction. Damage to the knee can cause these bursa to swell and become painful. Left untreated, they can go on to irritate either the tendons or ligaments nearby.
Chondromalacia Patella
This problem is also known as runners knee, or patellofemoral pain syndrome. The knee joint is made up of the femur at the top and the tibia and fibula at the bottom. The knee cap tracks in a groove over the joint. There is cartilage on the back of this bone that helps the patella track. Ligament and tendons help hold the knee cap in place. Most of the pain of this syndrome is felt just below or behind the knee cap, which is sometimes described as inner knee pain. Dr. Pribut's Sport Pages explain many causes for developing runners knee, but most of the pain generators are from irritated, richly innervated bone in the knee cap and the retinaculum. This pain is worse when running downhill, down stairs or even sitting for long periods of time with the knee bent.
