Knee Pain Overview

Medically Reviewed by Poonam Sachdev on May 14, 2023
16 min read

Knee pain is the most common musculoskeletal complaint that brings people to the doctor. It affects about 25% of U.S. adults. Several different things can lead to knee pain, and the treatments for it vary depending on what's causing it.

The knee joint's main function is to bend, straighten, and bear the weight of your body (together with your ankles and hips). The knee is more than just a simple hinged joint. It also twists and rotates. To do all of these things and support your body while doing so, the knee relies on several structures. They include bones, ligaments, tendons, and cartilage.

Bones

The knee joint involves four bones: 

  • The thighbone, or femur, makes up the top part of the joint.
  • One of the bones in the lower leg (or calf area), the tibia, is the bottom weight-bearing part of the joint.
  • The kneecap or patella rides along the front of the femur.
  • The remaining bone in the calf, the fibula, isn't involved in the weight-bearing part of the knee but provides ligament attachments to help keep it stable.

Ligaments

Ligaments are dense bands that connect bones to each other. The knee includes 4 important ligaments, all of which connect the femur to the tibia:

  • The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) provide stability for front and back (anterior and posterior) and rotation movements.
  • The medial collateral ligament (MCL) and lateral collateral ligament (LCL), found along the inner (medial) and outer (lateral) sides of the knee, give stability to the knee in those areas.

Tendons

Tendons are fiber-like bands similar to ligaments. But instead of connecting bones to other bones, they connect muscles to bones.

  • There are 2 important tendons in the knee. The quadriceps tendon connects your quadriceps muscle, on the front of your thigh, to the kneecap. The patellar tendon connects the kneecap to the tibia (it's technically a ligament since it connects two bones).
  • The quadriceps and patellar tendons are sometimes called the extensor mechanism. Together with the quadriceps muscles, they help you straighten, or extend, your leg.

Cartilage

Cartilage is a flexible connective tissue. 

  • Menisci (plural for meniscus) are structures made of cartilage that line the top of your tibia and lie between your tibia and the two knuckles at the bottom of your femur (the femoral condyles).
  • The menisci's main job is to cushion the knee joint.

Bursae

Bursae are fluid-filled sacs that also help cushion the knee. The knee has three important groups of bursae:

  • The prepatellar bursae in front of the patella
  • The pes anserine bursae in the inner side of the knee, about 2 inches below the joint
  • The infrapatellar bursae underneath the patella

Inflammation is your body's response to injury. In treating many types of knee pain, doctors try to break what's called the inflammatory cycle. That cycle starts with an injury. When you're hurt, substances in your body that cause inflammation invade your knee to help with healing. But if the injury and the inflammation it causes don't go away, the inflammation becomes long-lasting, or chronic. This leads to more inflammation and additional injury. You end up with knee pain that lasts a long time or gets worse. You can break the cycle by controlling the substances that cause inflammation and by preventing further injury to tissues in your knee.

If you have knee pain, some things you can do at home to help break the inflammatory cycle are protection, rest, ice, compression, and elevation (known as PRICE).

PROTECT the knee from further injury.

  • You can do this with knee pads or splints.
  • Keeping a pad over your kneecap, for example, helps control the symptoms of some knee injuries (like a type of bursitis sometimes called housemaid's knee) by preventing further injury to your prepatellar bursae.

REST the knee.

  • Rest reduces the strain that activities you do over and over put on the knee.
  • It not only gives your knee time to heal, but helps prevent further injury.

ICE the knee.

  • Icing your knee reduces swelling. You can use it for both short- and long-term knee injuries.
  • Most experts recommend icing the knee two or three times a day for 20-30 minutes each time.
  • You can use an ice pack or just place a bag of frozen vegetables on the sore knee.

COMPRESS the knee with a knee brace or wrap.

  • This reduces swelling.
  • In some knee injuries, you can use compression to keep your kneecap aligned and keep the joint working as it should.

ELEVATE the knee.

  • Raising your knee also helps reduce swelling.
  • Elevation works with gravity to help keep fluid from building up in your knee.
  • Prop your leg up when you're sitting, or sit back in a a recliner. Elevation works best when your knee is higher than the level of your heart.

Over-the-counter pain medicine

Commonly used pain relievers, such as nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen and naproxen, also play a role in treating knee pain.

  • These drugs directly control pain. And at higher doses, they act as anti-inflammatory agents, helping to break the cycle of inflammation. Like all medications, however, they have side effects.
  • Don't use NSAIDs if you have a problem with bleeding or stomach ulcers or some types of kidney disease.
  • Acetaminophen can help control knee pain, but it doesn't have anti-inflammatory properties like NSAIDs. Still, it can help with many types of knee pain, such as that caused by osteoarthritis.

There's a good rule of thumb for most long-term knee pain (as well as short-term pain that isn't disabling): If your symptoms don't go away after a week of PRICE therapy and over-the-counter anti-inflammatory pain meds, make an appointment. You might see your doctor, a physical therapist, or a sports medicine orthopedic (bone and muscle) specialist.  

Remember, though, that this is just a general guideline.  If you're concerned about the pain, call your doctor.

If you can't put weight on your knee, feel sick, have a fever, or if your knee is red and hot, consider going to the ER. You might have a fracture or infection:

  • For many fractures, you need to be immobilized to prevent movement of the bone or joint.  You might even need surgery.
  • Infections can be managed but need attention right away. 
  • Putting off seeing a doctor may hinder healing.

Other symptoms for which you should get medical help right away:

  • Unbearable pain
  • Pain that doesn't get better with rest
  • Pain that wakes you 
  • Drainage of pus or fluid
  • Large wounds
  • Puncture wounds
  • Swelling, if you're on a blood thinner (warfarin or Coumadin) or have a bleeding disorder (like hemophilia)

History: Even in today's world of technology, doctors rely on a detailed medical history and physical exam more than any single test.

The doctor will usually want to know the exact nature of the pain:

  • Where in the knee is your pain?
  • What does it feel like?
  • How long have you had the pain?
  • Has it happened before?
  • Describe any injuries to the knee.
  • What makes it better or worse?
  • Does the knee pain wake you up at night?
  • Does the knee feel unstable?
  • Have you been limping?

The doctor will also want to know a bit about you:

  • Do you have any major medical problems?
  • How active is your lifestyle?
  • What are the names of the medications you are taking?

The doctor will want to know about any related symptoms:

  • Do you still have normal sensation in your foot and lower leg?
  • Have you been having fevers?

Physical exam

  • The doctor will likely have you undress to completely expose the knee. If possible, wear shorts to your appointment.
  • The doctor will then inspect your knee and press around it to see exactly where it's tender.
  • They may also do movements to stress the ligaments, tendons, and menisci of your knee so they can evaluate how well these are working.

X-rays, CT scans, and other tests

  • Depending on your medical history and exam, the doctor may suggest X-rays of the knee. X-rays show fractures (broken bones) and dislocations of bones as well as arthritis and abnormally large or small joint spaces.
  • Rarely, the doctor may order a CT scan (a 3D X-ray) of the knee to give them more information about a fracture or deformity.
  •  X-rays and CT scans work well for diagnosing fractures. But neither is good at assessing soft tissue structures of the knee, like ligaments, tendons, and menisci.

MRI

  • Magnetic resonance imaging (MRI) uses large magnets to create a 3D image of the knee.
  • In contrast to CT scans, these aren't used to get images of bones and fractures. But they can help your doctor evaluate your ligaments and tendons.

Fluid removal

  • The knee and all its bursae are filled with fluid. If your symptoms suggest infection or crystalline arthritis, such as gout, your doctor may use a needle to remove fluid from your knee. They'll analyze this fluid to help them get a diagnosis.
  • Crystals, which can be a sign of crystalline arthritis, often can be seen under the microscope. Doctors may also see signs of infection like bacteria and pus.
  • Your doctor may also do blood tests to look for signs of infection or diseases such as rheumatoid arthritis, lupus, and diabetes.

Arthroscopy

  • If you have chronic knee pain, an orthopedic surgeon may do an arthroscopy. The surgeon inserts a camera, called an arthroscope, into your knee joint. It's attached to a camera that relays real-time images to a video monitor.
  • They may be able to see small particles in your knee or look more closely at damaged menisci or cartilage.
  • At the same time, they may also be able to treat damage by shaving down torn cartilage or removing particles from your knee.

The nerves that provide sensation to your knee come from your lower back. They're also responsible for the sensations you feel in your hips, leg, and ankle sensation. Pain from a deeper injury (called referred pain) can be passed along this nerve and felt on the surface. That means knee pain could arise from the knee itself or happen because of issues with your hip, ankle, or lower back. All of the  sources of knee pain discussed below arise from the knee joint itself.

In general, knee pain is either immediate (acute) or long-term (chronic). Acute knee pain can happen because of infection or a sudden injury. Chronic knee pain is often from injuries or inflammation (such as arthritis). But infection can cause it, too. 

Sudden knee pain has a number of causes.

Sprained and torn cruciate ligaments

  • Description: An anterior cruciate ligament (ACL) injury is a common sports injury. It's usually caused by a hard stop or a violent twisting of the knee. The posterior cruciate ligament (PCL) is stronger than the ACL and much less likely to be torn. A PCL injury may happen when your knee takes a serious blow, like when it hits the dashboard in a car accident. That's why a PCL injury often happens along with other ligament and bone injuries.
  • Symptoms: If you tear your ACL, you may hear a pop. You'll also notice your knee give way or become unstable. And it will hurt enough that you might feel like vomiting. Almost always, this will be followed by serious swelling over the next couple of hours. That happens because the ACL bleeds briskly when it's torn.
  • Treatment: Doctors often recommend surgery for high-level athletes who need the best outcomes. Conservative treatment and knee braces may be enough for people who don't demand quite so much from their knees.

Tendon ruptures

  • Description: Both the quadriceps and patellar tendons can tear (rupture), either partly or completely. A quadriceps tendon rupture most often happens to recreational athletes over 40. A patellar tendon rupture usually affects younger people who've had tendinitis or steroid injections to the knee.
  • Symptoms: Rupture of either a quadriceps or patellar tendon causes pain (especially when you try to kick or straighten your knee). If you have a complete rupture, you can't straighten your knee. Your kneecap is also often out of place. It may be too high (with a patellar tendon rupture) or too low (with a quadriceps tendon rupture).
  • Treatment: You need medical care right away and will likely need surgery for a tendon rupture. Your doctor might treat a partial rupture with splinting alone.

Meniscal injuries

  • Description: These are usually due to sudden injuries to your menisci, but overuse can also cause them. Often, a piece of the meniscus will tear off and float in the knee joint.
  • Symptoms: Meniscal injuries may cause your knee to lock in a certain position, or to click or grind through its range of motion. They may also cause your knee to give way. You'll usually have swelling along with these symptoms, but not as much as you'd have with an ACL injury.
  • Treatment: These injuries often require arthroscopic surgery.

Knee dislocation

  • Description: You need medical help right away for a knee dislocation, which is caused by a powerful blow to the knee. A dislocation puts your lower leg out of place in relation to your upper leg. This stretches-- and often tears -- not only the ligaments of your knee but also your arteries and/or nerves. An artery injury could leave your lower leg without a blood supply. If circulation isn't restored, you may need amputation.  With nerve injuries,  on the other hand, your lower leg may lack strength or sensation.
  • Symptoms: Knee dislocations are very painful and make your knee look deformed. Many dislocations go back into alignment on their own (this is called reduction). When this happen, you might feel a dull clunk.
  • Treatment: If the knee dislocation hasn't gone back into place by itself, a doctor will immediately reduce the dislocation. But medical treatment doesn't stop here. Whether the dislocation reduces on its own or is put back into place in the hospital, you need further evaluation and care. The doctor may observe you in the hospital and do tests to make sure you don't have any artery or nerve injury. If you do, it needs to be repaired right away in the operating room.

Dislocated kneecap (patella)

  • Description: A common injury caused by a blow or by straightening your leg hard, this could happen when you serve in volleyball or tennis. It's more common in women, people with obesity, people with knock knees, and those with high-riding kneecaps.
  • Symptoms: You'll notice the kneecap is out of place and may have trouble bending or straightening your leg.
  • Treatment: The doctor will move your kneecap back into place (reduce the dislocation). Even if the kneecap reduces by itself, it needs to be X-rayed for a fracture. The doctor will treat the injury with a splint that allows the soft tissues around your kneecap to heal, followed by strengthening exercises to keep it in line. Dislocation often damages to the cartilage on the back of your kneecap.

Arthritis: Arthritis of the knee is an inflammatory condition of your knee joint that's often painful. There are several types of arthritis.

Knee osteoarthritis

  • Description: Osteoarthritis (OA) is caused by the breakdown of cartilage in your knee (the meniscus). In its most serious form, the meniscus is completely worn away and the femur rubs  bone-on-bone on your tibia.
  • Symptoms: Osteoarthritis causes constant knee pain that often feels worse when you move around.
  • Treatment: Treatment is aimed at controlling pain. Anti-inflammatory medications, either over-the-counter or by prescription, can help. Hyaluronic acid, a lubricating gel that is injected into the knee over 3-6 weeks, can provide relief for a year or more. Doctors can treat serious OA with narcotic pain medicines or a knee replacement, in which a human-made joint replaces your knee. Physical therapy can also help you manage OA pain and improve knee function.

Rheumatoid arthritis of the knee

  • Description: Rheumatoid arthritis (RA) is a connective tissue disease of your whole body that affects many joints. 
  • Symptoms: In addition to knee pain, RA may cause morning stiffness and pain in other joints.
  • Treatment: Treatment includes pain medications, anti-inflammatory medications, and prescription drugs aimed at slowing the disease's progress.

Crystalline arthritis(gout and pseudogout)

  • Description: These intensely painful forms of arthritis are caused by sharp crystals that develop in your knee and other joints. They form due to problems with the way your body absorbs or metabolizes various natural bodily substances, like uric acid (which leads to gout) and calcium pyrophosphate (pseudogout).
  • Treatment: Treatment is aimed at controlling inflammation (using anti-inflammatory medications), and aiding your body's metabolism of the chemicals that lead to crystal formation.

Bursitis

  • Description: Because of injury, infection, or crystalline deposits, bursae in your knee can get inflamed.
  • Symptoms: Sudden or long-term trauma leads to inflammation of the bursae that causes a painful, often swollen knee. A common type is prepatellar bursitis, which happens in people who work on their knees. (It's sometimes called housemaid's knee or carpet layer's knee.) Another type is anserine bursitis. The anserine bursa is found about 2 inches below the knee along the inner side, and anserine bursitis causes pain in that area. It often gets worse when you bend the knee or at night when you try to sleep. This type of bursitis tends to be more common in women and people who carry extra weight.  
  • Treatment: Treatment usually involves home care with PRICE therapy and NSAIDs. Your doctor can treat serious forms with steroid injections.

Infection (or infectious arthritis)

  • Description: Many organisms can infect your knee. They include gonorrhea, a sexually transmitted disease, as well as common organisms found normally on your skin.
  • Symptoms: Infection causes painful knee swelling. People with a knee infection usually have fevers and chills, though less serious infections may not cause fevers.
  • Treatment: Get any new swelling or pain in your knee checked for infection by a doctor. Treatment usually involves taking antibiotics. You may also need to have the infection drained by a doctor.

Patellofemoral syndrome and chondromalacia patella (runner's knee)

  • Description: Both conditions are caused by mistracking of your kneecap, or patella.
  • Symptoms: The conditions most often affect young women, athletes of all genders, and older people. In patellofemoral syndrome, the kneecap rubs against your inner or outer femur rather than moving straight down the middle. The patellofemoral joint on the inner or outer side gets inflamed. This causes pain that gets worse when you either sit for a long time or move around. As the condition progresses, the cartilage under your kneecap gets damaged, leading to chondromalacia patella. (You might hear this called runner's knee.)
  • Treatment: Home care with PRICE therapy, NSAIDs, and exercises (such as straight leg raises) that balance the muscles around the kneecap work for most people. You might need physical therapy , evaluation and exercises; bracing or taping of the kneecap; and/or arch or orthotic foot supports to correct your foot mechanics. For serious cases, you could need surgery.

Jumper's knee

  • Description: You can get inflammation of your quadriceps tendon (tendinitis) where it inserts at the top of your kneecap. You can also get tendinitis of the patellar tendon -- either at the bottom of the kneecap or where the tendon inserts onto the tibia below your knee. Either way, this condition is called jumper's knee. That's because it usually affects basketball players, volleyball players, and others who do sports that involve jumping.
  • Symptoms: Jumper's knee causes knee pain that gets worse with activity. It usually hurts more as you jump up than when you land.
  • Treatment: You'll start with the PRICE regimen, along with anti-inflammatory (NSAID) drugs. Especially important are rest, ice, and NSAIDs, which not only ease pain but help break the cycle of inflammation. Once the pain is under control, slowly start an exercise regimen to strengthen your quadriceps, hamstrings, hips, and calf muscles before resuming your sport of choice a few weeks down the line. A knee brace may help take stress off the tendons.

Osgood-Schlatter Disease

  • Description: Osgood-Schlatter disease usually affects teen athletes. Repeatedly straightening the knee injures and inflames the tibial tubercle. That's the bony knob at the top of your shin, just below the kneecap.
  • Symptoms: Children with this condition have pain at the tibial tubercle that usually gets worse when they straighten the leg. Over time, the tibial tubercle starts to stick out more as chronic inflammation spurs bone there to grow.
  • Treatment: Osgood-Schlatter disease usually gets better on its own as the tibial tubercle stops growing (usually at about ages 15-17). Treatment includes PRICE and NSAID therapy to ease pain. You may also need physical therapy to reduce stress to the tibial tubercle, which often includes strength training for the hips and core. In serious cases, you may wear a splint on the knee for a few weeks.

Iliotibial (IT) band syndrome

  • Description: A ligament called the iliotibial (IT) band runs from the outside of your pelvic bone to the outside of your tibia. When this band is tight, it can rub against the bottom outer part of the femur.
  • Symptoms: This condition most often affects distance runners. It causes pain on the outside of the knee that often starts 10-15 minutes into a run and gets better with rest.
  • Treatment: The most important thing is to figure out why your IT band is tight. A physical therapist can evaluate your movement and prescribe treatments, which may include stretching. Here's one IT band stretch: Stand with your left side about 2-3 feet from a wall. Place your right leg behind the left one. Then lean toward your left and hold it for 20-30 seconds, using the wall to help you support yourself. In addition to stretching, PRICE therapy and NSAIDs may  help.

Knee pain has a host of causes. Many types of pain are difficult to prevent, but you can do some things to reduce your changes of getting a knee injury.

Avoid excess weight

  • Avoiding weight gain or losing extra pounds reduces the force placed on your knee during both athletics and everyday walking. According to some medical research, it may also reduce osteoarthritis.
  • Keeping your weight down may also reduce ligament and tendon injuries for similar reasons.

Keep limber, keep fit

  • Many knee problems are caused by tight or imbalanced muscles. For that reason, stretching and strengthening also help to prevent knee pain.
  • Stretching keeps your knee joint from being too tight and helps prevent both patellofemoral syndrome and iliotibial band syndrome.
  • Strengthening exercises, especially those for your quadriceps like straight leg raises and leg extensions, can help prevent knee injury. They can also help with arthritis and its complications.

Exercise wisely

  • If you have chronic knee pain, consider swimming or water exercises. The water helps support your weight and takes the burden off your knees.
  • If you don't have access to a pool or don't enjoy water activities, at least try to limit hard pounding and twisting activities like basketball, tennis, or jogging. You may find that your aching knees act up if you play basketball or tennis every day, but not if you limit pounding sports to twice a week.
  • Whatever activity you do, listen to your body. If it hurts, change what you're doing.
  • If you're fatigued, consider stopping. Many injuries happen when people are tired.

Protect your knees

  • Wearing the right protection for the activity you're doing helps you avoid knee injuries.
  • When playing volleyball or laying carpet, use kneepads.
  • When driving, knee protection is one of many reasons to wear a seatbelt. It helps you avoid knee-versus-dashboard injuries as well as injuries to other parts of your body.