Knee pain is an extremely common complaint. While unpleasant and frustrating, the upside is that knee pain is often a very treatable problem.
Diagnosing your knee pain first requires a focused medical history, one that sorts out the details of the pain, like what it feels like (e.g. aching, sharp, or burning), where it's located (e.g. front of or behind the knee), when it started (e.g., gradually or suddenly), and whether there was any recent trauma (e.g. blow to the knee).
Besides a medical history, your doctor will perform an examination of the knee joint and potentially order imaging tests to make or confirm a diagnosis.
In the end, understanding the precise cause of your knee pain is key to you and your doctor formulating an effective treatment plan—one that optimizes the knee healing process.
Your knee is a complex structure consisting of three bones—the lower part of the thighbone, the upper part of the shinbone, and the kneecap. Then, there are strong ligaments and tendons that hold these bones together, as well as cartilage beneath the kneecap and between the bones to cushion and stabilize the knee. Damage or disease that affects any of these structures may lead to pain.
If you have knee pain, some common causes include:
There are different types of arthritis that affect the knee joint, the two most common ones being osteoarthritis and rheumatoid arthritis.
Knee osteoarthritis develops as a result of "wear and tear" of the cartilage in the knee and is more common in people over the age of 50. As the cartilage deteriorates, pain develops, often gradually escalating from a sharp pain that worsens with knee movement to a constant dull, aching pain.
Rheumatoid arthritis is an autoimmune disease whereby a person's immune system attacks multiple joints in the body. In addition to pain, swelling, redness, and warmth over the kneecap may develop. Unlike osteoarthritis, knee pain from rheumatoid arthritis tends to improve with activity.
Knee Ligament Injuries
There are four ligaments in your knee—two collateral ligaments and two cruciate ligaments.
Collateral Ligament Injury
The collateral ligaments (medial collateral and lateral collateral) are found on the side of your knee and connect your thighbone (femur) to your lower leg bone. Injury to the medial collateral ligament (MCL) often results from a direct blow to the outside of the knee, which causes pain on the inside of the knee. A blow to the inside of the knee may cause a lateral collateral ligament (LCL) injury, which causes pain to the outside of the knee.
Cruciate Ligament Injury
The cruciate ligaments (anterior cruciate and posterior cruciate) cross each other inside the knee joint, with the anterior cruciate being in the front and the posterior cruciate being in the back. Anterior cruciate ligament injuries are the most common type of knee injury, often resulting from a direct blow or a sudden change in direction or speed when running. Usually, a "popping" noise is heard, along with sudden swelling, and a giving out of the knee.
Posterior cruciate ligament injuries are uncommon and are generally caused by some sort of high-energy force to the knee (for example, a bent knee colliding with the dashboard during a car accident). Besides pain at the back of the knee, knee swelling and stiffness are typical symptoms associated with this ligament injury.
Torn Knee Cartilage (Meniscus)
There are two "C" shaped, tough pieces of cartilage (called menisci) located between your thighbone and shinbone. Tearing of the meniscus is a common cause of knee pain and may occur in young people (often during sports) or older people, as the cartilage weakens with age making it more prone to tear. Besides pain, a person with a meniscus tear may initially hear a "pop" when the tear occurs. This is followed by a gradual development of knee stiffness and swelling, along with knee clicking, locking, or catching.
Patellar Tendonitis and Tear
Patellar tendonitis refers to inflammation of the patellar tendon—a large tendon that connects your kneecap to the top of our shinbone. Patellar tendonitis is most common in people who engage in sports or activities that require frequent running and jumping. Often times, people with this condition describes a constant dull pain that becomes sharp with activity.
Patellar tendonitis weakens the patellar tendon, making it more likely to tear. A patellar tendon tear causes severe pain, swelling over the knee, and a tearing or popping sensation. Depending on the degree of the tear, a person may notice an indentation at the bottom of the kneecap and experience walking difficulties due to the knee giving out.
Patellofemoral Pain Syndrome
Patellofemoral pain syndrome is most common in adolescents and young adults and is usually caused by vigorous activities that put stress on the knee, like running, squatting, or climbing stairs. This condition causes a dull, aching pain felt underneath the kneecap. Abnormal knee alignment may also cause or contribute to this condition. Besides pain, which worsens with activities that require frequent knee bending or sitting for long periods of time (for example, working at a desk), a person may note popping sounds in the knee when standing up from prolonged sitting or when climbing stairs. Knee swelling and locking are rarely seen with this syndrome.
In some people with patellofemoral pain syndrome, a condition called chondromalacia patella is present, which means that the cartilage behind the kneecap has softened and begun to wear away. It develops as a result of overuse (i.e. bending the knee too much) or from a knee injury. Symptoms include pain, either sharp or aching, located in front of, around, and/or behind the kneecap.
A Baker's cyst is swelling in the back of the knee joint and is sometimes a sign of another underlying problem such as a meniscus tear. While not all Baker's cysts cause pain, if they do, the "tightening" pain is felt in the back of the knee and is often associated with knee stiffness and a visible bulge that worsens with activity.
Your prepatellar bursa (a fluid-filled sac) is located right over the kneecap. Prepatellar bursitis—when the bursa becomes inflammed— is most commonly caused by people who frequently kneel, like gardeners or carpet layers. Less commonly, an infection, gout, rheumatoid arthritis, or a direct blow to the knee may cause bursitis. Besides a mildly aching knee pain that may only be felt with knee movement or when touching the affected area, rapid swelling over the kneecap typically occurs.
Iliotibial Band Syndrome
Iliotibial band syndrome refers to inflammation of the iliotibial band—a thick collection of fibers that runs along the outside of the thigh. Iliotibial band inflammation commonly happens as a result of overuse, especially in runners, and causes an aching, burning pain on the outside of the knee joint. Sometimes, the pain spreads up the thigh to the hip.