When it comes to joints, pain and swelling often go hand in hand. The conditions that produce swelling are generally painful, and the added pressure of the swelling itself compounds the pain. The knee is a particularly common victim; being neither very mobile nor very stable, it often is prone to injury. The causes of painful knee swelling are many.
Patellofemoral Pain Syndrome (PFPS)
Despite its more familiar name, "runner's knee," PFPS is the most frequent cause of knee pain. This condition is caused when the patella, or kneecap, grinds against the femur, or thigh bone, rather than gliding smoothly. That irritative friction can lead to swelling. The pain occurs in the front of the knee and is typically sharp when walking downstairs or achy during prolonged sitting. While PFPS most often develops over time from abnormal mechanics, it can result from direct trauma. Treatment is almost always conservative and may include medications, bracing, shoe modification and physical therapy.
Osteoarthritis (OA)
The more official term for "wear and tear" arthritis, osteoarthritis is a condition of degraded cartilage within the joint, and the knee is the most frequently affected joint. Although OA is far more common in older people, it is not limited to older people, nor is it a normal part of aging. Arthritic joints can be intermittently painful and even swollen at rest, but increased activity of the joint often incites acute episodes. The pain tends to be dull and achy, and the joint may feel unusually warm. Treatment ranges from conservative to aggressive, depending on the severity of the condition's impact on the patient.
Internal Injury
In cases of significant trauma, pain and swelling tend to begin immediately, causing the joint to balloon rapidly with fluid. There is often internal bleeding from torn structures such as ligaments and menisci. There may be associated bruising or discoloration around the joint as well. In such circumstances, do not attempt to work through the pain as the risk of further injury is high.
Medical Causes
Although often overlooked, there are several non-mechanical causes of knee pain and swelling, at least one of which should be considered an emergency. Septic arthritis, an active infection within the joint, typically results from bacteria being transferred into the joint--for example, via a needle or piercing trauma--or it can be from an infection in the blood that seeds the joint. The pain will usually be exquisite, worse with motion and progressive. Often the joint will become red and hot, and a fever may develop. Rhis condition requires immediate medical attention.
A more common, less emergent medical cause of painful knee swelling is gout, which is the deposit of uric acid crystals in a joint. These crystals cause inflammation and severe pain, similar in presentation to a septic joint. The underlying problem is due to faulty metabolism, so the main treatments involve medication and diet modification.
