Knee pain affects roughly one in five adults, and that number climbs to more than one in four for people over 55. The cause depends heavily on where exactly you feel the pain, your age, and what you were doing when it started. A dull ache at the front of your knee points to very different problems than sharp pain on the outer side or tightness behind the joint.
Pinpointing the location of your pain is the single most useful thing you can do before deciding on next steps. Here’s what each region of the knee typically signals.
Pain at the Front of the Knee
Front-of-knee pain is the most common complaint, and the most frequent culprit is patellofemoral pain syndrome, often called runner’s knee. It causes a dull, aching sensation around or behind the kneecap that gets worse when you run, climb stairs, squat, or sit for a long time with your knees bent. It happens when repeated stress irritates the underside of the kneecap, usually because of a sudden increase in activity, weak hip or thigh muscles, or movement patterns that pull the kneecap slightly off track during bending.
Other front-of-knee conditions include cartilage softening on the underside of the kneecap (which feels similar to runner’s knee but tends to produce a grinding sensation), patellar tracking problems where the kneecap doesn’t glide smoothly in its groove, and irritation of the fat pad that sits just below the kneecap. Osteoarthritis can also settle specifically in the kneecap joint, producing stiffness and a crunchy feeling when you bend.
If you kneel frequently for work (flooring, gardening, cleaning), the fluid-filled sac in front of your kneecap can become inflamed. This is called prepatellar bursitis, and it’s easy to identify: you’ll see and feel a squishy, swollen area directly over the kneecap. It may ache even at rest or only hurt when you kneel or bend. If the swollen area turns red, feels warm, or comes with fever and chills, the bursa may be infected, which needs prompt treatment.
Pain on the Inner Side of the Knee
Inner (medial) knee pain often traces back to the medial collateral ligament, which stabilizes the inside of the joint. This ligament gets overstretched from a direct blow to the outer knee or a sudden twisting motion, common in contact sports and skiing. You’ll typically feel tenderness along the inner edge of the knee and notice instability when putting weight on it.
A meniscus tear is another frequent cause of inner knee pain. The meniscus is a C-shaped piece of cartilage that cushions the space between your thighbone and shinbone. It tears when the knee is forcefully twisted or compressed, often during a pivot or deep squat. Classic signs include a pop at the moment of injury, swelling over the next day or two, a knee that feels like it might give out, and difficulty fully bending or straightening the leg. Some people also feel the knee “locking” in one position.
A less obvious source of inner knee pain is pes anserine bursitis, an inflammation of the bursa on the inner side of the shinbone just below the knee. It’s common in runners and people with osteoarthritis, and the pain is usually lower than you’d expect, sitting a few inches below the joint line.
Pain on the Outer Side of the Knee
If your knee hurts on the outside, especially during or after running, iliotibial band syndrome is the most likely explanation. The IT band is a thick strip of connective tissue that runs from your hip down the outside of your thigh to just below the knee. When it repeatedly rubs against the bony bump on the outer side of the knee, the fluid-filled sac underneath becomes inflamed and painful.
IT band syndrome is overwhelmingly an overuse injury. It shows up in runners who increase mileage too quickly, cyclists with poor bike fit, and hikers tackling long descents. The pain typically starts as a mild annoyance partway through a run, then gradually worsens until it forces you to stop. It can also cause discomfort at the outer hip, where the same band crosses another bony prominence.
Pain Behind the Knee
A feeling of tightness or fullness behind the knee often points to a Baker’s cyst, a fluid-filled sac that forms when the knee produces too much lubricating fluid. This overproduction is usually driven by an underlying problem like osteoarthritis or a cartilage tear. The excess fluid migrates to the back of the joint and collects in a bursa there, creating a visible bulge. Pain and stiffness tend to worsen with activity or when you try to fully bend or straighten the knee.
Hamstring tendon irritation and calf muscle tendon inflammation can also cause posterior knee pain, particularly in athletes. Cruciate ligament injuries, especially tears of the anterior or posterior cruciate ligament from a direct blow or awkward landing, produce pain that can radiate to the back of the knee along with significant swelling and instability.
Osteoarthritis: The Most Common Chronic Cause
For anyone over 40, osteoarthritis is the leading cause of persistent knee pain. The hallmark pattern is pain that increases with movement and improves with rest, morning stiffness lasting less than 30 minutes, and a gradual loss of range of motion over months or years. Many people notice a crunching or grinding sensation when bending the knee, and the joint may develop bony enlargements you can feel along the edges.
Osteoarthritis doesn’t always show up on X-rays, especially early on. Clinical guidelines from European and American rheumatology organizations recognize that pain with movement, brief morning stiffness, crepitus (that grinding feeling), and age over 40 are enough to identify the condition without imaging. Weight, previous injuries, and family history all influence your risk. The knee pain prevalence data shows the steepest increases in middle-aged adults between 45 and 64, largely driven by rising rates of osteoarthritis in that group.
What to Do Right After a Knee Injury
The old advice of rest, ice, compression, and elevation has been updated. Current sports medicine guidance uses a two-phase approach. In the first one to three days, the priorities are protecting the knee by limiting movement enough to prevent further damage (but not resting completely, which weakens tissue), compressing it with a bandage to control swelling, and elevating the leg above heart level to help fluid drain.
One notable shift: anti-inflammatory medications and even ice are no longer universally recommended in the acute phase. Inflammation is part of the repair process, and suppressing it with high-dose anti-inflammatories may slow healing. Ice can reduce pain in the moment, but there’s no strong evidence it improves recovery, and it may interfere with the blood flow and immune cell activity needed to rebuild tissue.
After the first few days, the focus shifts to gradually reloading the knee. Adding movement and gentle exercise as soon as pain allows promotes tissue repair and builds the strength needed to prevent reinjury. Passive treatments like ultrasound or electrical stimulation in the early phase don’t meaningfully improve outcomes compared to simply staying active. Your mindset matters too: people who approach recovery with confidence and realistic expectations consistently do better than those who catastrophize or avoid all movement out of fear.
Signs That Need Immediate Attention
Most knee pain improves with time, activity modification, and gradual strengthening. But certain symptoms signal something more serious. Seek emergency care if you notice any of the following after an injury: severe pain or bleeding, visible deformity where the knee looks out of place, exposed bone or tendon, sudden swelling or redness, inability to bear weight or bend the knee, or a clear popping sound at the moment of injury followed by instability. Knee pain paired with fever and chills can indicate an infection in the joint or bursa, which can cause permanent damage if not treated quickly.