Knee pain has dozens of possible causes, but most cases trace back to a handful of common culprits: wear-and-tear arthritis, overuse injuries, muscle imbalances, or damage to the cartilage and ligaments inside the joint. Your age, activity level, and where exactly the pain shows up are the biggest clues to what’s going on.
Where the Pain Is Matters
The knee is the largest joint in the body, and pain in different zones points to different problems. Pain across the front of the knee, especially around or behind the kneecap, is most often patellofemoral pain syndrome. Pain along the inner or outer edges of the joint suggests a ligament issue or bursitis. Deep, diffuse aching that’s hard to pinpoint is more typical of arthritis or referred pain from the hip or lower back.
Paying attention to what triggers the pain is just as useful. Pain that flares when you go downstairs or stand up after sitting for a while points toward the kneecap. Pain that spikes with twisting or pivoting suggests a meniscus or ligament problem. Pain that builds gradually through the day and feels worst by evening is a hallmark of osteoarthritis.
Osteoarthritis: The Most Common Cause Over 50
If you’re over 50, the single most likely explanation for chronic knee pain is osteoarthritis. The protective cartilage that cushions the ends of the bones slowly wears down over years, leaving less of a buffer between surfaces. You’ll typically notice stiffness when you first get moving, a gritty or crunchy sensation during bending, and pain that worsens with weight-bearing activities. The pain tends to creep in gradually rather than starting with a single event.
Body weight plays a significant role. Every pound of body weight translates to roughly three pounds of pressure on your knees during walking. That math works in reverse too: losing even 10 pounds takes about 30 pounds of stress off the joint with every step. This is one of the reasons weight management shows up consistently as a first-line recommendation for knee osteoarthritis.
Runner’s Knee and Overuse Injuries
Patellofemoral pain syndrome, often called runner’s knee, is the most common cause of front-of-knee pain in younger, active people. It’s not a single injury but a pattern: the kneecap doesn’t track smoothly in its groove when you bend and straighten the leg. Contributing factors include weak thigh and hip muscles, tight hamstrings, flat feet, and sudden jumps in training volume.
The signature complaint is pain that gets worse with loading a bent knee. Squatting, running, climbing stairs, and sitting for long stretches with your knees bent (sometimes called “theater sign”) all aggravate it. The pain is usually a dull ache rather than a sharp stab, and it often affects both knees.
A related overuse problem is patellar tendinopathy, or jumper’s knee, which causes pain just below the kneecap where the tendon connects. It’s especially common in sports with repetitive jumping or sprinting. Pes anserine bursitis, another overuse condition, produces a tender spot on the inner side of the knee a few inches below the joint line.
Meniscus Tears and Ligament Injuries
The meniscus is a C-shaped piece of rubbery cartilage that acts as a shock absorber between your thighbone and shinbone. Tears typically happen during a cutting or twisting motion while bearing weight. The classic signs are swelling that develops over 24 to 48 hours, a feeling that the knee might give out, and sometimes a locking sensation where you can’t fully straighten the leg. Meniscus tears are especially common in men over 40, when the cartilage has become more brittle.
ACL tears feel different. They usually happen during a sudden pivot or landing, often with an audible pop followed by rapid swelling within one to two hours. The knee feels unstable, like it could buckle, but it doesn’t typically lock. That distinction, locking versus instability, is one of the easiest ways to tell a meniscus tear from a ligament tear before any imaging is done.
Pain That Starts Somewhere Else
Sometimes the knee itself is perfectly healthy, but the pain feels real because the signals are coming from somewhere else. Hip arthritis is a well-documented source of referred knee pain. The femoral nerve, which supplies sensation to both the hip joint and the front and inner side of the knee, can carry pain signals from a deteriorating hip straight to the knee. The obturator nerve does something similar along the inner thigh and knee.
Lower back problems, particularly a pinched nerve in the lumbar spine, can also produce pain that radiates down into the knee area. If your knee pain doesn’t change when you press on the joint itself, or if it comes with numbness, tingling, or back pain, the true source may be higher up.
Signs That Need Prompt Attention
Most knee pain is manageable and not dangerous, but a few scenarios call for urgency. A knee that’s hot, red, and swollen without any injury could signal an infection inside the joint or a gout flare. Gout in the knee causes intense, sudden pain, sometimes with fever, and tends to affect people over 60. A septic (infected) joint is a medical emergency because the infection can destroy cartilage quickly.
After a traumatic injury, there are well-established criteria for when an X-ray is needed: you’re 55 or older, you have isolated tenderness over the kneecap or the top of the smaller lower leg bone (the fibula), you can’t bend the knee to 90 degrees, or you can’t take four steps bearing weight. If any of these apply, imaging is warranted to rule out a fracture.
Sudden calf swelling with warmth, pain, and skin discoloration could indicate a blood clot rather than a knee problem, especially if you’ve been immobile recently, are on hormonal medications, or have had recent surgery.
What Imaging Can and Can’t Tell You
Standard X-rays are the recommended first step for chronic knee pain. They’re good at showing bone alignment, joint space narrowing from arthritis, loose bone fragments, and fractures. If X-rays look normal but pain persists, MRI is the usual next step because it reveals soft tissue that X-rays miss: torn meniscus, ligament damage, and cartilage defects.
One important nuance: if X-rays already show clear osteoarthritis, an MRI typically won’t add useful information unless your symptoms don’t match the findings. Many people over 50 have MRI abnormalities in their knees that cause no symptoms at all, so imaging results always need to be interpreted alongside what you’re actually feeling.
Strengthening the Muscles That Protect Your Knee
The knee is fundamentally a hinge caught between two long lever arms, your thighbone and shinbone. It depends heavily on the muscles around it for stability. Weakness in five key muscle groups contributes to most non-traumatic knee pain: the quadriceps (front of the thigh), hamstrings (back of the thigh), inner and outer thigh muscles, and the gluteal muscles in the buttocks. The gluteus medius, a muscle on the outer hip that controls side-to-side stability, is particularly important because weakness there lets the knee collapse inward during walking and running.
A structured strengthening program done two to three days a week can meaningfully reduce knee pain within four to six weeks. Effective exercises don’t need to be complicated. Calf raises, standing quadriceps stretches, and hip abduction exercises target the right areas. Stretching the calf and hamstring muscles on most days of the week helps maintain the flexibility that keeps the kneecap tracking properly. The key is consistency over intensity, especially in the early weeks when the joint is still irritable.
Managing a New Knee Injury
The old advice of rest, ice, compression, and elevation has evolved. Sports medicine now uses a framework called PEACE and LOVE, which better reflects what we know about tissue healing. In the first one to three days, protect the knee by limiting movement, elevate the leg above heart level, apply compression with a bandage, and avoid anti-inflammatory medications. That last point surprises many people, but inflammation is part of the repair process, and suppressing it early with medication may slow long-term healing.
After those initial days, the approach shifts. Gradually loading the knee with gentle movement, starting pain-free aerobic exercise to increase blood flow, and progressing into strengthening exercises all support recovery. Staying completely still for too long tends to make outcomes worse, not better. Early, controlled movement helps restore strength and joint awareness while reducing the risk of reinjury.