Knee Pain Causes and Their Symptoms

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On April 18, 2025

Injuries, caused by sports, overuse, or accidents, can affect different parts of the knee, leading to pain and various symptoms depending on which area of the knee is affected.

ACL Injury

An ACL injury occurs when you tear your anterior cruciate ligament (ACL), which is one of the four ligaments that connect your shinbone to your thighbone. It’s a common injury among people who play sports like basketball and soccer, which require sudden changes in direction. You may hear a loud pop or feel a popping sensation in your knee, along with pain, swelling, buckling, and loss of range of motion.

Sprains

Ligament sprains of the knee are usually caused by a blow to the knee or a sudden twist of the knee.

Common symptoms include pain, swelling, and difficulty walking.

Torn Cartilage

Torn cartilage, which can occur with injuries of the knee or with osteoarthritis, is another common cause of knee pain. Trauma (or generalized wear and tear) to the knee can tear the menisci, which are cushioning pads of connective tissue that also absorb shock located within the knee joint.

Knee buckling, swelling, and pain on the inside, outside, or back of the knee may indicate torn cartilage. You may be unable to fully extend or bend your knee or your knee joint may catch or lock. It may be difficult to put weight on it and walk.

Fractures

A knee fracture can occur if the knee bones, including the kneecap (patella), break during incidents like falls or auto accidents. It can also be caused by something as slight as stepping the wrong way if your bones are weakened due to osteoporosis.

Signs of fracture include sudden pain around the kneecap or in the knee itself, possibly with swelling; inability to bend or straighten the knee or to hold the leg out straight; deformed appearance of the knee; or bone protruding from the skin of the knee.

Knee Bursitis

If you notice that your knee pain is accompanied by sudden swelling, redness, or a warm feeling in the affected area, this could mean that the bursa — a fluid-filled sac in the knee that helps lubricate the joint — might be inflamed.

Repetitive motions, injury, trauma to the area, or infection can cause bursitis. As can inflammatory arthritis such as rheumatoid arthritis (RA).

If you think you have bursitis, it’s best to limit your activity until the knee is evaluated by a physician. Most bursitis in the knee can be treated with at-home remedies such as ice and anti-inflammatories (like ibuprofen). But if it’s due to infection — and you also have fever, achiness, and chills — seek immediate attention from a healthcare provider.

Tendonitis

Tendonitis, or inflammation of the tendons, is another common cause of knee pain.

Tendonitis of the patellar (knee) tendon, known as jumper’s knee, frequently occurs in sports like basketball, where the force of hitting the ground after a jump can strain the tendon.

Symptoms of tendonitis typically include range of motion pain, local tenderness, and pain-related weakness of the knee.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome, which is sometimes called runner’s knee, refers to pain between the kneecap and the thighbone. This condition is common in athletes and young adults, and can develop in older adults due to arthritis.