Why Does Your Knee Hurt? Injuries, Overuse, and Arthritis
Original Publication Date: September 2018
Updated October 2026
When your knee hurts, almost everything can feel harder. Climbing stairs, kneeling in the garden, getting out of the car, or keeping up on a weekend hike can all start to feel like a chore. Persistent knee pain can also wear on your mood and keep you from the activities that help you feel like yourself.
Most knee pain comes from one of three places: an injury, repeated stress on the joint over time, or changes that come with age. Each affects the knee differently, and each calls for its own plan.
Thankfully, knee pain is often very manageable once the source is clear. Our team at Rocky Mountain Spine & Sport consists of physiatrists, doctors of physical medicine and rehabilitation, who focus on restoring function and supporting the body’s ability to heal. Read on to learn what can cause knee pain and when it is time to have it checked.
How Your Knee Is Built
Three bones come together at the knee. The femur sits on top of the tibia, and the patella rests in front of them.
Four ligaments hold these bones in place. Ligaments are strong bands of tissue that link one bone to another. Two of them, the MCL and LCL, run along the inside and outside of the knee and help steady it against side-to-side forces. The other two, the ACL and PCL, cross in an X at the center of the joint and guide its front-to-back movement.
Between the femur and tibia sit two C-shaped pads of rubbery cartilage called the menisci, which act as shock absorbers. A smooth layer of articular cartilage covers the ends of the bones so they glide as you move. Tendons link the quadriceps and hamstrings, the large thigh muscles, to the bones around the knee.
Injuries That Cause Knee Pain
Knee injuries are common in sports, but they also happen during everyday mishaps like a slip on winter ice or a misstep off a ladder.
ACL Injuries
An ACL tear often happens during activities with sudden stops, jumps, pivots, or quick changes in direction. Basketball, soccer, and skiing are familiar examples. Many people feel a pop, followed by swelling and a sense that the knee might be unstable.
Collateral Ligament Sprains
The MCL and LCL are usually hurt by something that pushes the knee sideways, such as a blow to the side of the leg. MCL injuries are far more common. Doctors grade these sprains from a mild stretch (grade 1) to a partial tear (grade 2) to a complete tear (grade 3) that leaves the knee unstable.
Fractures
The kneecap and the ends of the leg bones can break in a fall or a car accident. In people with bones that have been affected by osteoporosis, even a simple misstep can sometimes cause a fracture.
Meniscus Tears
A meniscus tear often happens when your foot stays planted and your knee rotates under your body weight, like when you pivot quickly during a basketball game, for example. These kinds of tears are some of the most common knee injuries. Afterward, your knee may swell and stiffen, or it may feel like it is locking partway through a bend.
Overuse and Repetitive Stress
Not every sore knee can be traced back to one bad step. Sometimes the pain shows up gradually, after weeks or months of the same motion. Running and cycling can do this, and so can sports with a lot of jumping. Jobs that keep you on your knees for long stretches, like construction or work on a farm or ranch, can also put repeated strain on the joint.
Common overuse causes include:
- Bursitis: Bursae are small sacs of fluid that act as cushions so tendons can slide smoothly over the knee. When these sacs become inflamed, the knee can become painful, swollen, and stiff.
- Iliotibial band syndrome: The IT band is a long strip of tough tissue outside of the thigh, running from the hip down past the knee. If it gets too tight, it can rub against the end of the thighbone and cause a sharp ache on the outer knee. People who run or cycle long distances are especially prone to it.
- Patellar tendinitis: This is inflammation of the tendon connecting the kneecap to the shinbone. It is common in runners, skiers, cyclists, and people who play jumping sports.
- Patellofemoral pain syndrome: This describes pain at the front of the knee, between the kneecap and thighbone. It is often seen in athletes and in young adults whose kneecap does not track smoothly in its groove.
Age and Arthritis
Over time, the tissues in the knee change. Unfortunately, this can make the joint more vulnerable to pain, even without a clear injury.
Degenerative Meniscus Tears
The meniscus becomes more prone to tearing as it ages. An older meniscus may tear from something as minor as an awkward twist while getting up from a chair.
Osteoarthritis
With osteoarthritis, the cartilage that protects the ends of the bones slowly wears thin. As that cushion breaks down, the knee may start to feel stiff or look a little swollen. Many people notice it most when they get out of bed in the morning or stand up after sitting for a while. A busy day on your feet can also leave the knee sore by evening.
Your past can play a role, too. A torn meniscus or ligament, even one that healed years ago, may raise your chances of developing arthritis later. Extra body weight is another factor, since it increases the pressure on your knees with each step you take.
Other Types of Arthritis
Rheumatoid arthritis works differently. It is an autoimmune disease, so the body’s own immune system turns on the joint, and the joint lining becomes swollen and painful. Gout and pseudogout are caused by crystals that form inside the joint and can set off painful bouts of inflammation.
When to See a Specialist
Plenty of minor knee aches settle down after a few days of rest and care at home. Others are a signal to get checked sooner Mayo Clinic recommends contacting a doctor if you notice the following:
- Fever: A fever along with a red, swollen, painful knee may point to an infection, which needs treatment right away.
- Giving way: The knee buckles, feels wobbly, or will not hold your weight.
- Heavy swelling: The joint looks clearly enlarged or feels tight.
- Pain after an injury: Severe pain started with a fall, a collision, or a sudden twist.
- Restricted movement: You cannot fully bend or straighten your leg.
- Visible deformity: The knee or leg looks misshapen or out of alignment.
Even without these signs, pain that lingers for more than a few days or disrupts your routine is worth having evaluated. Finding the cause is imperative, because the right treatment for a torn ligament is very different from the right treatment for arthritis.
Reach Out Today for Local Knee Care
Knee pain can be frustrating, especially when it keeps you from work, family, or the outdoor activities you love.
Our team can examine your knee, review your history and symptoms, and order imaging when needed to pinpoint the cause. From there, we can recommend a plan that fits your goals. Learn more about our knee pain treatment options, which include physical therapy, joint injections, and regenerative treatments.
Connect with us today to schedule a visit at our Idaho Falls or Rexburg location.