There are a number of medical conditions linked to front knee pain. Generally, they are caused by damage from a fall or a sports injury, from overusing the knee during exercise, or from getting older.
Patellofemoral pain syndrome (PFPS) means pain related to the kneecap (the patella) and the thigh bone (the femur). Doctors sometimes call this ‘patella maltracking’ or ‘runner’s knee’. When you bend and straighten your leg, your kneecap slides up and down a groove at the end of your thigh bone. Damage or swelling where the kneecap and thigh bone meet stops the kneecap sliding smoothly and causes pain. The kneecap may also be unstable.
Patella tendinopathy means wearing away of the tendons around the kneecap due to overuse and stress over time. Small tears in the tendon can cause inflammation (tendonitis). These tears are usually due to sudden injury. These conditions are sometimes called ‘jumper’s knee’ and are most common in athletes. Quadriceps tendonitis is a similar condition, but less common. It causes pain and tenderness where the tendon from the thigh muscle attaches to the kneecap.
Infrapatellar fat pad syndrome is a condition where the fat pad behind the kneecap gets pinched between the kneecap and the thigh bone. It is most often caused by over-straightening the leg repeatedly, for example in weight lifting.
Anterior cruciate ligament injury is overstretching or tearing this ligament, which runs across the knee from the thigh to the shin bone, either completely or partly. It is a sudden injury, caused by twisting or overextending the knee, and is nearly always associated with sports.
Osteoarthritis of the knee is a common cause of knee pain. The smooth, shiny cartilage that lines the knee joint becomes worn and rough. This causes pain and increasing damage to the knee over time. It mostly affects people over 50. The older you are, the more likely you are to get it.
Less common conditions causing front knee pain
Bursitis is inflammation of the fluid sac that acts as a cushion behind the kneecap. It can be caused by kneeling a lot and is sometimes called housemaid’s knee or vicar’s knee. More commonly these days, it’s caused by overuse, a sudden increase in sports training, by being overweight, or by another condition such as rheumatoid arthritis, gout or infection.
Chondromalacia of the patella is a condition where the smooth tissue under the kneecap (the cartilage) can soften and break down. It is most often seen in teenage girls.
Recurrent partial dislocation (subluxation) of the patella is an uncommon condition that runs in families. It is most often seen in girls who tend towards being ‘knock-kneed’ – ie when the knees are together, the ankles are apart. This affects the tracking of the kneecap.
Osgood–Schlatter disease and Sinding-Larsen–Johansson disease are conditions seen mostly in teenagers who take part in a lot of sports. They both cause pain and tenderness just below the kneecap, at the top of the shin bone (the tibia).