Causes of Knee Pain and Treatment Options

Why do my knees hurt? Arthritis, injuries, and more

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Knee pain is quite common and can be debilitating. A lot of things can cause pain in your knee(s), including medical conditions, trauma, and injuries from putting too much pressure on the joint.

The key to proper treatment is finding out what causes your knee pain. Then your healthcare provider can form the right treatment plan for you.

In this article, you'll learn about many causes of knee pain, how they're diagnosed, and what treatment options are available.

What causes knee pain?
Illustration by Alexandra Gordon, Verywell 

Why Do My Knees Hurt? Common Causes

Your knee is a complex structure. It includes three bones:

  • The bottom of the thighbone
  • The top of the shinbone
  • The kneecap

Strong ligaments and tendons hold these bones together. Cartilage under the kneecap cushions and stabilizes the bones.

Any damage or disease in these structures can lead to knee pain. Common causes of knee pain include:

  • Arthritis
  • Ligament injuries
  • Torn meniscus
  • Patellar tendonitis and tear
  • Patellofemoral pain syndrome
  • Baker's cyst
  • Prepatellar bursitis
  • Iliotibial band syndrome

Knee Arthritis

Several types of arthritis can affect the knee joint, causing various levels of pain, inflammation, and disability. Some common ones are:

  • Osteoarthritis (OA): Develops due to "wear and tear" on the cartilage; more common in people over 50; may start as a sharp pain when you move
  • Rheumatoid arthritis (RA): An autoimmune disease in which your immune system attacks your joints; causes pain, swelling, redness, and warmth; pain tends to improve with activity
  • Gout: High uric acid levels form sharp crystals inside the joint; affects the knee, hip, fingers, and especially the big toe; pain can be severe
  • Post-traumatic arthritis: Develops after knee injury due to left-over damage, instability, or excessive wear and tear

Knee Ligament Injuries

You have four primary ligaments in your knee:

  • Medial collateral ligament (MCL): Runs up the inside of your knee. Medial means toward the middle.
  • Lateral collateral ligament (LCL): Runs up the outside of your knee. Lateral means away from the center of the body.
  • Anterior cruciate ligament (ACL): Runs diagonally through the inside of your knee joint, in front of the PCL. Anterior means front.
  • Posterior cruciate ligament (PCL): Runs diagonally through the inside of the knee joint, behind the ACL. Posterior means behind.

They all attach your thighbone (femur) to your tibia (shin bone).

LIGAMENT INJURY CAUSES FEELS LIKE
MCL Direct blow to the outside of the knee Pain inside the knee
LCL  Blow to the inside of the knee Pain on the outside of the knee
ACL  Direct blow or sudden direction change while running The knee is giving out or "popping"
PCL  High-energy impact, like from a car accident Pain in the back of the knee plus instability

ACL injuries are the most common type of knee injury. PCL injuries are fairly uncommon.

Torn Knee Cartilage (Meniscus)

The menisci are tough, "C" shaped pieces of cartilage. Two in each knee cushion the joint. A torn meniscus is a common cause of knee pain.

When a meniscus tears, you may hear a "pop." That's followed by gradually developing symptoms such as:

  • Stiffness
  • Swelling
  • Clicking
  • Locking
  • Catching

When you're young, it's most likely a sports injury. When you're older, weakness from age makes them more prone to tears.

Patellar Tendonitis and Tear

Patellar tendonitis is inflammation of the patellar tendon. That's a large tendon connecting your kneecap to the top of your tibia.

Patellar tendonitis is most common in athletes who do a lot of running and jumping. It's often described as a constant dull pain that becomes sharp when you're active.

In some cases, a weak patellar tendon can tear. A patellar tendon tear causes:

  • Severe pain
  • Swelling over the knee
  • A tearing or popping sensation

If it's a bad tear, you might notice an indentation at the bottom of your kneecap. The knee may give out when you walk.

Patellofemoral Pain Syndrome

Patellofemoral pain syndrome is most common in adolescents and young adults. It's usually caused by vigorous activities that stress the knee, such as:

  • Running
  • Squatting
  • Climbing stairs

Abnormal knee alignment can cause it, as well. So can softened cartilage that's wearing away. This is a condition called chondromalacia patella.

Patellofemoral pain syndrome causes a dull, aching pain under the kneecap. Pain gets worse with frequent knee bending or after sitting for a long time. It may pop when you climb stairs or stand up.

Knee swelling and locking are rare in this syndrome.

Other Common Causes

Other common causes of knee pain include:

  • Baker's cyst: Swelling in the back of the knee joint. May be due to a meniscus tear. Can cause a "tightening" pain, stiffness, and a visible bulge that gets worse with activity.
  • Prepatellar bursitis: Swelling of the prepatellar bursa (fluid-filled sac over the kneecap). May cause a mild ache. Can result from kneeling a lot (e.g., gardening, laying carpet).
  • Iliotibial band (ITB) syndrome: Swelling of the ITB (thick fibers on the outside of the thigh). Often caused by overuse. Causes aching and burning pain on the outside of the knee joint.

Less Common Causes of Knee Pain

Less-common causes of significant knee pain include conditions and injuries. Injuries include:

  • Dislocated kneecap: Causes are sharp blows to the knee or twisting. Severe pain in the front of the knee plus buckling, slipping, or catching during movement.
  • Kneecap fracture: Causes are a direct blow or falling onto the knee. Pain, difficulty straightening the leg, bruising, and swelling can occur. Sometimes there's visible deformity.

Conditions include:

  • Plica syndrome: Irritation of the synovium (joint lining). Pain is in the middle and front of the knee. Worsens with inactivity or squatting, running, or kneeling. The knee may pop when bent.
  • Osgood-Schlatter disease: Strikes after growth spurts in kids between 9 and 14. Pain is in the front of the knee. It improves with rest and worsens with activities like running and jumping.
  • Osteochondritis dissecans: In children, lack of blood supply weakens the bone and cartilage. The knee may separate from the underlying bone. Causes pain with activity.
  • Knee joint infection: Causes significant pain, swelling, warmth, painful movements, and fever. It may result from a bacterial infection in the bloodstream.
  • Bone tumor: Very rarely the source of knee pain. Symptoms include fever, unintentional weight loss, and pain that's worse at night.

When to See a Healthcare Provider

Not all knee pain needs medical treatment, but delaying care when it's needed can lead to more pain and disability. Symptoms to watch for are:

  • Pain lasting more than 48 hours
  • Inflammation lasting more than 48 hours
  • Reduced range of motion
  • Instability
  • Signs of infection (fever, redness and warmth around the joint)

Your knee injury may need immediate care if:

  • The joint looks deformed.
  • The injury caused a popping or grinding noise.
  • You can't put weight on it.
  • Pain is intense.
  • You have sudden inflammation or swelling.

Diagnosis

Some knee conditions can be diagnosed based on a physical examination alone. Your provider may use additional tests to confirm a diagnosis and determine the best treatments.

Medical History

Your healthcare provider will likely ask you a lot of questions about your pain. Be prepared to tell them:

  • Location: Is the pain on one side, the front, or the back of the knee?
  • Timing: What time of day is your pain worst? What activities hurt? How long does the pain last?
  • Other symptoms: Do you have swelling, fever or chills (a sign of infection), aches in other areas, fatigue, or unexplained weight loss?

Physical Examination

A thorough physical exam is important for finding the cause of knee pain. Your provider will check for:

  • Swelling: Whether there's swelling and, if so, when it began.
  • Range of motion: How well you use your knee, including straightening, bending, and standing.
  • Stability: Damage to ligaments can make your knee feel like it's giving out.
  • Locking: Locking is when you can't bend or straighten your knee. That can be due to something physically blocking the motion or by pain that keeps you from moving it normally.
  • Noises: Painful popping, snapping, grinding, or crunching sounds are all clues as to the cause.

Chondromalacia can cause a crunching sensation when you place your hand over the kneecap and bend your knee. Knee arthritis may cause a similar grinding sensation.

Imaging

Your healthcare provider may order imaging studies. Those let them see what's happening inside.

They usually start with an X-ray. That shows the bones plus signs of soft tissue injury, arthritis, or alignment problems. They may also order an ultrasound or an MRI to help evaluate soft tissue injuries.

Differential Diagnoses

Not all knee pain points to a problem in the knee itself. Sometimes it's caused by a problem in the:

This is called referred pain. Your healthcare provider may be able to identify referred pain based on your physical exam. 

For example, if it's referred pain, your knee won't hurt when it's pressed on. You also won't have swelling or impaired range of motion.

Treatments

Treatment depends on what's causing your pain. It may include a combination of options to help relieve pain and, if possible, cure the underlying problem.

Self-Care Strategies

Many initial therapies for knee pain are simple, straightforward, and can be done at home.

  • Rest: The first treatment for most common causes of knee pain is temporary rest. This allows inflammation to subside. Sometimes, this is all that's needed to relieve knee pain.
  • Ice: Using a cold gel pack or bag of ice can help lessen knee pain. Don't put ice or a gel pack directly against your skin. Ice for only 15 to 20-minutes at a time, several times a day.
  • Support: Supports such as taping, braces, splints, wraps, straps, or casts may help, depending on your diagnosis.

Physical Therapy

Physical therapy is extremely important for almost all orthopedic conditions. A physical therapist will do an evaluation and prescribe exercises to:

  • Increase strength
  • Improve mobility
  • Get you back to your pre-injury activity level

Medications

Medications are often used to alleviate pain. Sometimes, they can treat the underlying problem, too.

  • NSAIDs: Nonsteroidal anti-inflammatory medications are commonly used for knee pain from arthritis, bursitis, and tendonitis.
  • Injections: For ongoing pain and swelling despite self-care, you may be given injections of cortisone—a powerful anti-inflammatory. It's especially effective against knee OA.
  • Other medications: Other medications may help with certain diagnoses. These include disease-modifying anti-rheumatic drugs for RA, antibiotics for infections, or steroids for gout.

Complementary and Alternative Therapies

A number of mind-body therapies may be used to treat knee pain. These include:

  • Acupuncture
  • Yoga
  • Tai chi

These are especially common for knee osteoarthritis.

The once-popular supplements glucosamine and chondroitin have fallen out of favor for knee osteoarthritis due to a lack of scientific proof. Always talk to your healthcare provider before taking any supplements or medications.

Surgery

Surgery is generally reserved for specific diagnoses, such as:

  • Certain ligament injuries or knee dislocations
  • Certain knee fractures
  • Infected knee joints that require surgical drainage
  • Some advanced cases of knee osteoarthritis
  • Joint replacement due to RA or other degenerative diseases

Prevention

You can do several things to prevent knee injuries or stop pain from getting worse. These include:

  • Reaching and/or maintaining a healthy weight
  • Strengthening and stretching your quadriceps and hamstrings muscles
  • Low-impact aerobic exercises that strengthen muscles without putting stress on your knee (e.g., swimming, cycling)
  • Wearing knee pads if you kneel a lot at work

Seeing a healthcare provider soon after knee pain starts can keep it from becoming a bigger problem.

Once you've had a knee injury, you're more likely to have another one, so prevention becomes more important. Ask your provider(s) what else you can do to protect your knee.

Summary

Many medical conditions and injuries can cause knee pain. Common causes include arthritis, ligament and meniscus tears, tendonitis, and patellofemoral pain syndrome. Dislocations, fractures, and bone tumors are less common.

Knee pain is diagnosed based on a description of symptoms and triggers, physical exam, and possibly imaging studies.

Treatment depends on the cause. It may include self-care, medications, physical therapy, surgery, and mind-body treatments.

You can prevent knee pain by staying active, maintaining a healthy weight, and protecting your joints from overuse.

A Word From Verywell

Your knees are important for mobility. You may even depend on them to do your job or take part in activities you enjoy.

Don't ignore knee pain when it starts. Getting a quick diagnosis and treatment can make a big difference in how long it takes to heal.

Frequently Asked Questions

  • Why does my knee hurt when I straighten it?

    Pain when you straighten your knee can come from overuse, a meniscus tear, or arthritis. Your healthcare provider should check your range of motion and look at other symptoms to find the cause of the pain.

  • How can I relieve knee pain at night?

    Pain can keep you awake. To relieve nighttime pain and sleep better:

    • Ice before going to sleep.
    • Use a knee brace to keep pressure off the joint.
    • Take over-the-counter anti-inflammatories to lower swelling and pain.
    • Try supporting your knee with pillows.
  • Do you need to have surgery to repair a meniscus tear?

    Not always. Some people are able to recover without it. Deciding factors for surgery include the size and location of the tear, your age, how active you are, your overall health, and the severity of your symptoms.

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Additional Reading

By Jonathan Cluett, MD
Jonathan Cluett, MD, is board-certified in orthopedic surgery. He served as assistant team physician to Chivas USA (Major League Soccer) and the United States men's and women's national soccer teams.