Why Does My Knee Hurt? Common Causes and When to See a Surgeon
Knee pain is one of the most common reasons people see an orthopedic surgeon — and the location of your pain is often the biggest clue to its cause. Inner-knee pain points toward arthritis or a meniscus tear; kneecap pain flares on stairs; pain behind the knee is often a Baker’s cyst. Some causes settle with therapy and time, others deserve an evaluation. Here’s how to read your knee pain — and when to have it looked at.
Key takeaways
- The location of knee pain is the biggest diagnostic clue: inner knee (arthritis, meniscus), outer knee (IT band, lateral arthritis), kneecap (patellofemoral pain, stairs), behind the knee (Baker’s cyst).
- Knee osteoarthritis is the most common cause of knee pain in adults over 50 — pain with walking, stiffness, swelling, and trouble with stairs, developing slowly over years.
- Persistent night pain often suggests more advanced arthritis — but night pain alone doesn’t mean surgery.
- Weight-bearing X-rays often tell us more about arthritis than an MRI.
- See a surgeon for pain lasting more than a few weeks, recurring swelling, instability, locking, or pain that limits daily life — early evaluation means more options.
- Red flags needing urgent care: can’t bear weight after injury, deformity, fever with a swollen knee, or rapid swelling after trauma.
Knee pain is one of the most common reasons people visit an orthopedic surgeon. Whether it started suddenly after an injury or has crept up over months or years, identifying the underlying cause is the first step toward the right treatment. Some causes settle with rest, physical therapy, or medication; others eventually deserve surgical consideration. Understanding what's driving your symptoms helps you act before the problem becomes more severe.
Where does your knee hurt?
Pain on the inside of the knee
Pain along the inner (medial) side is most often caused by osteoarthritis, a medial meniscus tear, an MCL injury, or pes anserine bursitis. This is the most common location for arthritis, because the inner compartment bears the greatest load during walking.
Pain on the outside of the knee
Outer (lateral) knee pain may come from iliotibial (IT) band syndrome, a lateral meniscus tear, lateral-compartment arthritis, or an LCL injury. It's common in runners and active people — but arthritis can live here too.
Pain at or behind the kneecap
Front-of-knee pain usually involves the patellofemoral joint: patellofemoral pain syndrome, cartilage wear beneath the kneecap (chondromalacia), patellar tendonitis, or quadriceps tendonitis. Patients typically notice it on stairs, with squatting, or standing up after sitting a while.
Pain behind the knee
Pain in the back of the knee is often a Baker's cyst — which usually develops because arthritis or a meniscus tear is producing extra joint fluid. Hamstring tendon irritation, arthritis with swelling, and (less commonly) vascular conditions can also cause it.
The most common causes of knee pain
Knee osteoarthritis
The most common cause of knee pain in adults over 50 is osteoarthritis. As cartilage wears away, the bones begin rubbing against one another — often with bone spurs forming along the joint edges. Symptoms build slowly over years:
- Pain with walking and after prolonged standing
- Stiffness, especially in the morning
- Swelling
- Difficulty with stairs
- Loss of motion
When the cartilage is gone entirely, that's bone-on-bone arthritis — advanced, but even then, surgery isn't automatic.
Meniscus tear
The meniscus is the knee's shock absorber. It can tear during sports, with a twisting injury — or simply with age. Typical symptoms: sharp pain, catching, locking, swelling, and pain with twisting. Many degenerative tears occur alongside arthritis, which is why telling a meniscus tear from arthritis matters so much for choosing treatment.
Ligament injuries
Sudden twisting, pivoting, or direct impact can injure the ACL, PCL, MCL, or LCL — typically with immediate swelling, instability, and difficulty walking after the trauma.
Tendonitis
Overuse can inflame the tendons around the knee — patellar tendonitis (“jumper's knee”) and quadriceps tendonitis are the common ones. Pain worsens with activity and eases with rest.
Bursitis
Small fluid-filled sacs (bursae) reduce friction around the knee. When one becomes inflamed, you get localized swelling, tenderness, warmth, and pain with kneeling.
Patellofemoral pain syndrome
Common in younger, active people: pain behind the kneecap on stairs, with squatting, and after prolonged sitting. Physical therapy often provides significant improvement.
Why does knee pain get worse at night?
Many patients notice the knee hurts more once they lie down. The usual reasons: arthritis-related inflammation, stiffness after inactivity, swelling that accumulated during the day, and simply having fewer distractions from the pain.
What night pain means
Night pain alone does not mean you need surgery. But persistent nighttime pain often suggests more advanced arthritis — and it's one of the symptoms I weigh most heavily when a patient and I discuss whether it's time to consider next steps.
When should you see an orthopedic surgeon?
Get an evaluation if you have:
- Pain lasting more than a few weeks
- Swelling that keeps coming back
- Difficulty walking
- Instability — the knee gives way
- Locking or catching
- Pain limiting everyday activities
- Pain that persists despite rest and conservative treatment
Early evaluation means more treatment options — not a faster path to surgery.
When knee pain is an emergency
Seek immediate care for: inability to bear weight after an injury, visible deformity, fever with a swollen knee, rapid swelling after trauma, or a red, warm, severely painful knee. These need same-day attention.
How knee pain is diagnosed
Diagnosis starts with your history, a physical exam, and weight-bearing X-rays. In select situations — usually when a ligament or meniscus injury is suspected — an MRI is added.
Many patients are surprised to hear that for evaluating arthritis, weight-bearing X-rays often provide more useful information than an MRI — the standing X-ray shows exactly how much joint space remains under real load.
Treatment options
Treatment depends entirely on the cause. Many patients improve with:
- Activity modification
- Anti-inflammatory medications
- Physical therapy
- Weight loss
- Knee injections
- Bracing
For arthritis specifically, the usual sequence runs through nonsurgical treatment first — including cortisone injections and other options — before surgery ever enters the conversation.
When to consider knee replacement
If knee pain has progressed to the point where it limits walking, interferes with sleep, or keeps you from daily activities despite conservative treatment, it's reasonable to discuss whether knee replacement is appropriate. Modern knee replacement lets most patients walk the day of surgery, return home the same day, and resume many normal activities within weeks — see the recovery timeline and how long a replacement lasts.
Schedule an evaluation with Dr. Harb to get an answer for your knee pain.
Frequently asked questions
Why does my knee hurt when I walk?
Pain with walking most commonly comes from arthritis, a meniscus tear, tendonitis, or a ligament injury. The pattern matters: arthritis pain builds gradually and worsens with prolonged standing, while a meniscus tear often causes sharp, catching pain with twisting. Weight-bearing X-rays usually identify the cause.
Why does my knee hurt when climbing stairs?
Stair pain usually involves the kneecap (patellofemoral) joint — patellofemoral pain syndrome, cartilage wear behind the kneecap, tendonitis, or arthritis. Stairs load the kneecap with several times your body weight, which is why this is often the first place knee problems show up.
Why does my knee hurt at night?
Night pain usually reflects arthritis-related inflammation, stiffness after inactivity, swelling that accumulated during the day, or simply fewer distractions from the pain. Night pain alone doesn’t mean you need surgery — but persistent nighttime pain often suggests more advanced arthritis and is worth an evaluation.
Can knee pain go away on its own?
Often, yes — minor strains, mild tendonitis, and small irritations frequently improve with rest, activity modification, and time. Pain that persists beyond a few weeks, keeps recurring, or comes with swelling, locking, or instability should be evaluated to identify the underlying cause.
When is knee pain an emergency?
Seek immediate care if you can’t bear weight after an injury, the knee looks deformed, you develop a fever with a swollen knee (possible infection), swelling comes on rapidly after trauma, or the knee is red, warm, and severely painful. Those signs need same-day attention, not a routine appointment.
When should I see an orthopedic surgeon for knee pain?
If pain has lasted more than a few weeks, swelling keeps returning, the knee locks, catches, or feels unstable, or the pain is limiting your daily activities despite rest and over-the-counter treatment — it’s time for an evaluation. Seeing someone early usually means more treatment options, not fewer.
References
This article is for general education and is not a substitute for personalized medical advice. Recovery timelines vary by patient, procedure, medical history, and surgeon-specific protocol. Please consult Matthew Harb, M.D. about your specific condition.
What patients say
“He shared so much about my knee and gave me a plan moving forward — I feel like I know exactly what to do.”
“Dr. Harb has kept my arthritic knee going for over a year and given me a high quality of life. When the time comes for replacement, I trust him.”
“He took the time to listen, thoroughly explained my options, and answered every question with patience and clarity.”
5.0 rating based on 524 verified patient reviews
Read reviews on Google: Washington, D.C.Germantown
Keep learning
Bone on Bone Arthritis: Do You Need Knee Replacement Surgery?
If you’ve been told you have “bone-on-bone” arthritis, the first question is usually whether you need a knee replacement. The answer may surprise you: not necessarily. A severe X-ray is only part of the picture — what matters far more is how the arthritis is affecting your life. We treat patients, not X-rays.
Read articleKnee ReplacementSigns You May Need a Knee Replacement
Most people with knee arthritis don’t need surgery any time soon — and surgery is rarely the first step. But it helps to recognize when arthritis is genuinely limiting your life, because with a knee replacement, you largely decide when it’s time. The decision is driven by your pain, function, and quality of life — not by an X-ray.
Read articleArthritis & Joint PainBone Spurs in the Hip and Knee: What Do They Really Mean?
Patients often panic when they hear “bone spur,” picturing a sharp piece of bone causing their pain. In reality, bone spurs (osteophytes) are usually not the main problem — they’re a sign that the joint has been under abnormal stress for years. Bone is living tissue that adapts to load (Wolff’s Law), and a spur is the body’s attempt to stabilize a worn or poorly-moving joint. The real source of pain is almost always the underlying arthritis — cartilage loss, bone-on-bone contact, inflammation, and abnormal mechanics — which is why removing a spur alone rarely helps.
Read articleHave questions about your hip or knee?
Schedule a consultation with Dr. Harb to discuss your options and build a plan to get you back to an active life.