Knee Pain: What Is Causing It?

Knee pain causes by location

Front of the knee

Patellofemoral pain is the most common cause of knee pain in active teens and young adults. It aches around or behind the kneecap and worsens with stairs, squatting, kneeling and sitting for long periods with bent knees ("moviegoer's sign"). Patellar tendinitis (jumper's knee) hurts just below the kneecap. In growing children, Osgood-Schlatter disease causes a tender bump below the kneecap.

Inside of the knee

A meniscus tear causes pain along the joint line, swelling over a day, and catching or locking. Medial collateral ligament sprains follow a blow to the outside of the knee. Knee osteoarthritis often starts on the inner side.

Outside of the knee

Iliotibial band syndrome causes sharp pain on the outer knee during running or cycling, typically at a predictable distance into a run.

Back of the knee

A Baker's cyst is a fluid-filled swelling behind the knee, usually from arthritis or a meniscus tear. It causes tightness, especially when bending fully. If it ruptures, fluid tracks into the calf, causing pain, swelling and bruising that can look exactly like a DVT, so it needs a scan.

Lump on the calf and knee pain in the same leg

The commonest cause is a Baker's cyst that has enlarged or leaked into the calf. Other possibilities include a DVT (warm, swollen, tender calf), a muscle tear or hematoma, a ganglion, or a fatty lump (lipoma). A firm, growing lump on the outer calf that affects walking needs imaging, because rarely it can be a nerve sheath tumor or soft tissue sarcoma, and pressure on the peroneal nerve near the outer knee can cause foot drop.

Knee pain by how it started

After a sudden injury

• ACL tear: a pop, rapid swelling and instability after pivoting or landing. See ACL injury.
• Meniscus tear: a twist with the foot planted, swelling over hours, locking.
• Kneecap dislocation: the kneecap slips out to the side, often in teens.
• Fracture: after a fall or direct blow, with inability to bear weight.

Gradual onset

• Osteoarthritis: aching with activity, morning stiffness under 30 minutes, creaking, more common after 50. See knee osteoarthritis.
• Overuse: tendinitis, IT band syndrome, patellofemoral pain.
• Inflammatory arthritis: rheumatoid arthritis and others, with morning stiffness over an hour and other joints involved.

Sudden hot, swollen knee without injury

• Gout or pseudogout: extremely painful, red and swollen over hours.
• Septic arthritis: a bacterial joint infection. An emergency that needs fluid drained from the joint.

How doctors diagnose knee pain

The doctor asks how it started, where it hurts, and whether it swells, locks or gives way. They check movement, ligament stability, joint line tenderness and the hip, which can refer pain to the knee, especially in children. X-rays show arthritis and fractures. MRI shows meniscus, ligament and cartilage injuries. Fluid drawn from the joint is tested for crystals and infection.

Home care for knee pain

• Relative rest: avoid activities that hurt, but keep the knee moving.
• Ice for 15 to 20 minutes a few times a day for swelling.
• Compression and elevation for a swollen knee.
• Pain relief: acetaminophen (paracetamol) or an anti-inflammatory such as ibuprofen, following the label dose. Topical NSAID gels are a good option for older adults. Avoid oral NSAIDs with kidney disease, stomach ulcers or blood thinners.
• Strengthen: quadriceps and hip muscle exercises help most knee conditions, especially patellofemoral pain and osteoarthritis.
• Weight loss: each pound lost removes about 4 pounds (1.8 kg) of load from the knee with each step.

Treatment options from physical therapy to injections and surgery are covered on our knee pain treatment page.

Frequently asked questions

What does pain behind the knee mean?

Pain behind the knee is often caused by a Baker's cyst, a hamstring or calf strain, or arthritis. A swollen, warm, tender calf with pain behind the knee could be a deep vein thrombosis and needs same-day assessment.

When should I worry about knee pain?

Worry if you cannot bear weight, the knee is deformed, it swells quickly after injury, it is hot and red with fever, or the calf is swollen and tender. Also see a doctor if the knee locks or gives way, or pain persists beyond a few weeks.

Why does my knee hurt going up and down stairs?

Stairs load the joint between the kneecap and thighbone, so pain on stairs typically comes from patellofemoral pain in younger people or osteoarthritis in older adults. Strengthening the thigh and hip muscles is the most effective treatment for both.

What causes inner knee pain without injury?

Common causes are early osteoarthritis, a degenerative meniscus tear and pes anserine bursitis, which causes tenderness a few inches below the inner joint line. These often follow increased activity or weight gain and improve with strengthening and activity changes.

Can knee pain come from the hip?

Yes. Hip problems such as arthritis, and in children slipped capital femoral epiphysis or Perthes disease, can cause pain felt mainly in the knee. A child who limps with knee pain should always have the hip examined.