Knee Pain When Bending: Causes, Prevention, Treatment, and Best Exercises
Medically reviewed by orthopedic surgeon Jonathan Lee, MD, senior expert physician at Hinge Health
Your body's ability to move smoothly through life hinges (pun intended) on your knee. The knee (a hinge joint) has many parts that work seamlessly so you can bend, straighten, squat, walk, run, and jump. But age, injuries, or an uptick in your daily activity are all reasons your knee can hurt when it bends. "Knee pain can really limit so much of our day-to-day functioning. It prevents people from doing the things they love, like squatting down to pet a dog or pick up their grandchild," says Mary Kimbrough, PT, DPT, OCS, a physical therapist at Hinge Health.
Although knee pain is common, it's very treatable and preventable, often without surgery.
Here, learn more about what causes pain when you bend your knee, and how to prevent and treat it - especially with exercises from our Hinge Health physical therapists.
What Is Knee Pain?
Your knee joint has three bones: the lower thighbone (femur), the upper shin bone (tibia), and the kneecap (patella). Ligaments and tendons connect these bones and help keep them stable. Cartilage surrounds the ends of the bones, allowing them to move without rubbing against each other. The meniscus, a shock-absorbing cushion, sits between the thigh and shin bones.The synovial membrane, a lining that surrounds multiple surfaces, produces joint fluid to keep the cartilage lubricated. The quadriceps tendon connects the thigh muscle to the kneecap, while the patellar tendon connects the kneecap to the shin bone.
These interconnected parts, which stretch from hip to ankle, work together to allow the knee to bend, straighten, and rotate, explains Cody Anderson, PT, DPT, a physical therapist at Hinge Health. Any disruption to these structures can result in pain when you bend your knee.
Causes of Knee Pain When Bending
A surprising truth: Just because you feel knee pain does not mean there's a visible cause. "Studies that have found that X-rays on people experiencing pain often don't pick up an anatomical injury that explains it," says Dr. Anderson. He encourages people to worry less about "damage" to the joint and focus more on getting moving again.
In fact, your perspective is part of your treatment, so try to stay positive. "Pain is an alarm system. It's your body's way of telling the brain there is an issue that needs some help. It does not mean that the pain won't get better. If we feed the brain this idea that we're damaged or broken, we feed the alarm system, making pain worse," says Dr. Anderson.
That said, knowing what's causing your knee pain can help you and your healthcare providers determine your treatment. Here are some of the most common reasons you may experience pain while bending the knee:
Patellofemoral syndrome. Nicknamed "runner's knee," patellofemoral syndrome accounts for about 25-40% of visits to sports medicine clinics, research shows. You'll feel pain (often a dull ache) behind or around the kneecap, which gets worse by movement such as using stairs, squatting, running, jumping or sitting with flexed knees.
Overuse is a driving cause - many people report an increase in the duration or intensity of their physical activity shortly before developing patellofemoral syndrome. Other studies have found it involves weak hip muscles or a misalignment or muscle imbalance in the lower legs. After acute symptoms are treated (see below), exercise therapy can reduce pain, restore function, and enhance long-term recovery. One seven-year study found that 85% of people prescribed a home exercise regimen reported good outcomes.
Osteoarthritis (OA). As some people age, the cartilage that surrounds the bones can wear away. The loss of this cushioning causes pain, aching, and stiffness that makes everyday movements from walking to climbing stairs more difficult. One study estimated that 14 million U.S. adults have painful osteoarthritis of the knee. While risk increases with age, nearly 2 million adults under age 45 have symptoms. You also may be more at risk for knee osteoarthritis if you're overweight, have a previous knee injury, or have a family history of osteoarthritis. Other types of arthritis may also cause cartilage loss. For example, rheumatoid arthritis causes inflammation of the synovial membrane, which damages cartilage over time. In posttraumatic arthritis, fractured bones following a knee injury damage or tear cartilage, leading to pain.
Meniscus tears. Each year, approximately 1 million people tear the shock-absorbing menisci that sit between the thigh bone and shin bone. Meniscus tears are either acute (from a sports injury that involves jumping or twisting the knee) or degenerative (the meniscus degrades with age, leading to tears). A telltale sign: Your knee feels like it's catching or locking, along with pain, stiffness, swelling and reduced range of motion. Some meniscus tears feel better on their own and others might require surgery.
Other common causes of knee pain when bending include:
Patellar tendon tear or patellar tendinitis. The patellar tendon attaches the kneecap to the top of the shin bone. It's essential for straightening your leg. If the patellar tendon becomes inflamed (patellar tendinitis), small tears may develop and cause discomfort. If the patellar tendon ruptures (usually because of a fall), you'll likely feel a popping sensation followed by severe pain. Your kneecap may "float" out of alignment, and your knee may not be able to bear weight. Your doctor will usually recommend surgery followed by physical therapy.
Iliotibial (IT band) syndrome. If your pain is on the outside of your knee, you may have an inflamed iliotibial tract, or IT band. The IT band is fibrous tissue that connects the hip to the outside of the knee. When you repetitively bend and straighten your knee, the IT band can get strained, leading to pain. You may also feel a popping or clicking sensation on the outside of the knee. This is common in people who cycle, run, ski, and row.
Prepatellar bursitis. The front of the kneecap contains a small, fluid filled sac called a bursa that provides cushioning. When you put too much force on the bursa (say, through extended kneeling) it can produce too much fluid and swell. Occupations that require constant kneeling (plumbers, roofers, gardeners) are more prone to this condition, as are people who have rheumatoid arthritis or gout.
Baker's cyst. When the knee joint produces excess fluid, a cyst (fluid-filled lump), may form at the back of the knee, causing irritation and discomfort. Baker's cysts usually form alongside another issue irritating the knee joint, such as osteoarthritis or a meniscus tear.
Anterior cruciate ligament (ACL) injury. The ACL is one of four major ligaments (along with the PCL, MCL, and LCL, see below) that connects the bones of the knee and helps control side-to-side motion. The ACL runs diagonally in the center of the knee and helps control the knee's ability to twist and rotate. When the ACL absorbs too much force (from a rapid change in direction or landing a jump, for instance), the ligament can have a complete or partial tear, leading to severe pain, tenderness, loss of motion, instability, and difficulty walking.
Other ligament injuries. The medial collateral ligament (MCL) and the lateral collateral ligament (LCL) run down the sides of the knee, providing stability and helping control side-to-side motion. A direct blow that pushes the knee sideways may cause a sprain, partial tear, or complete tear. You'll feel an MCL injury on the inside of the knee; an LCL injury is on the outside of the knee. The posterior cruciate ligament (PCL), located just behind the ACL, requires severe force to be injured (like a bent knee hitting the dashboard during a car accident).
Osgood-Schlatter disease. This knee pain condition is common in adolescents experiencing growth spurts. The patellar tendon - just below the kneecap - becomes irritated and tender, in part because of the bony growth plates in the area.
Bone fracture or dislocation. A serious fall or motor vehicle accident could fracture the kneecap or the end of the thigh or shin bone where it meets the knee. It could also force the bones out of alignment.
When to See a Doctor
If the pain doesn't improve after a few days with at-home measures like relative rest, ice, over-the-counter pain relievers and gentle exercise, see a doctor to get evaluated. The doctor can help you figure out what's irritating the knee and whether there is a structural problem that needs treatment. If your knee pain was brought on by trauma (like a blow to the knee) or you're struggling to do normal movements like bending or walking, see a doctor for an evaluation as soon as possible. See a doctor if you notice any of the following:
A high level of pain or very sharp pain
Difficulty bearing weight through the leg
Feeling unsafe or unstable standing or moving on your leg
Swelling around the knee
Hearing a popping noise at the time of injury
Limping or inability to walk normally
Difficulty bending the knee immediately after injury
The simplest way to prevent knee pain is to adjust your lifestyle and physical activity to avoid irritation and strengthen the muscles and structures that support the knee. "Motion is lotion," says Dr. Kimbrough.
The golden rule: exercise! A good general rule of thumb is to stay active as part of your day-to-day routine, because exercise is so important to joint health," says Dr. Kimbrough. Try a walking program or resistance training. The American College of Sports Medicine recommends 150 minutes of moderate aerobic activity a week and muscle-strengthening exercises at least twice a week.
Reduce or avoid activities that aggravate your knee, or switch to lower-impact modifications. A physical therapist can help you develop an individualized plan and goals. You can see a physical therapist in person or use a program like Hinge Health to access a PT via telehealth/video visit.
Warm up before physical activity. A dynamic warm-up preps your body for more intense movement and has been shown to reduce injury. Try butt kicks, side shuffles, high knees, and squats - doing each for 20-30 seconds.
Stretch your quads and hamstrings. These are the main muscle groups that support the knee, as well as your calves and hips, suggests Dr. Kimbrough.
Wear the right shoes for your sport or activity. "I've seen people hike in flip flops!" says Dr. Kimbrough. You can try arch supports, which might make you more comfortable.
Increase your exercise routine gradually. The body works best when it has time to gradually adapt to increased stress. Think about how a marathon runner builds up to the big race, says Dr. Kimbrough.
Prioritize a healthy lifestyle. The habits that maintain overall good health and prevent problems like heart disease and diabetes - not smoking, maintaining a healthy weight, getting enough sleep, and managing stress - also help the body heal optimally, says Dr. Kimbrough.
Treatment for Knee Pain
Having some pain when bending your knee doesn't have to mean a lifetime of limited movement. Many of the most common knee issues (such as patellofemoral syndrome, osteoarthritis, and IT band syndrome) can be treated with conservative remedies like exercise and physical therapy. More serious injuries, such as ligament tears, might require surgery, followed by rehabilitative exercises to restore strength and movement.
The following tips from our Hinge Health physical therapists and medical doctors can provide relief for mild to moderate knee pain.
RICE: Relative Rest, Ice, Compression, Elevation. This healing routine helps by reducing swelling. "The 'rest part' of RICE should not last for longer than a couple of days or until you're out of a high level of pain. Then you should do normal movement as much as possible," says Dr. Anderson. Apply ice (cold packs) every 20 minutes throughout the day. To compress, lightly wrap the area using a soft ace bandage. Elevate the leg above your heart while relaxing.
Over-the-counter (OTC) medication. Pain relievers, such as ibuprofen (Advil, Motrin), naproxen (Aleve), and acetaminophen (Tylenol), can be helpful for knee pain. It's important to make sure that you are safely able to take these medications, based on your medical history.
Braces or knee sleeves. You can use these for additional compression and stability.
Steroid injections. If over-the-counter medication does not offer sufficient pain relief, your doctor may suggest cortisone steroid injections to help counter pain and inflammation. Shots containing an anti-inflammatory steroid go into the knee and help with pain and inflammation. The effects of an injection vary and can last from a few weeks to a few months.
If you have persistent pain, swelling, and evidence of structural damage, you may need surgery on your knee. Your doctor will likely order a variety of imaging tests such as X-rays or MRIs.
Exercise for Knee Pain: Movement Is Medicine
Once acute pain has improved with rest, ice, and OTC medications, one of the best remedies for knee pain is to move the joint as much as you safely can. "People think pain means they have to avoid that motion, but that's not true," says Dr. Anderson. "We want to make sure there is not a structure that is truly damaged, but if it's just pain, bending the knee is actually good for it."
It's important to find a movement sweet spot as you recover. You should move enough to help your knee joint structures and surrounding muscles gain strength and flexibility, but not so much that you experience a lingering uptick in pain. A physical therapist can help you discover your sweet spot, says Dr. Kimbrough. Though results vary, it takes about six weeks to increase your strength and flexibility.
Healthcare providers will often send knee pain patients to physical therapy first, resorting to surgery only if they don't respond. Even those who need surgery (say, to repair an ACL tear) benefit from physical therapy beforehand so they go into the procedure as strong as possible. After surgery, physical therapy is again recommended to regain normal function.
Exercises for Bent Knee Pain
Here are a few gentle exercises from Hinge Health that are commonly used to prevent and treat knee pain. To be safe, ask your healthcare provider if these moves are right for you and your stage of healing.
Sit to Stand
This move uses all the muscles from your hips to ankles and helps the knee be able to bear more weight.This is a good exercise to help you build up to doing squats again. Bonus: Because this engages the hip muscles, it also builds support for a sore lower back.
Standing Hamstring Curl
Hamstring curls strengthen the hamstring muscles (along the back of your thighs) that support the knee and help get the knee moving.
Seated Knee Extension
This exercise is particularly good to strengthen the quadricep muscles (along the front of your thighs) that support the knee. Bend the knee back as far as you comfortably can (so that your leg goes under the chair if possible) to fully engage the muscles and increase the range of motion.
These also work the quadriceps and hips, building support for the lower back as well as the knee.
PT Tip: No Hands!
"I always tell people not to use their hands when they sit down or stand up from their couch. Removing that help means you use the knee joint and surrounding muscles to their full extent, and this helps keep them strong as you age," says Dr. Anderson.
Learn More About Hinge Health for Knee Pain Relief
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This article and its contents are provided for educational and informational purposes only and do not constitute medical advice or professional services specific to you or your medical condition.
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