When to worry about knee and leg pain?

October 2, 2025 •

3 min read

According to the CDC, over 20% of adults in the U.S. have some form of arthritis, a common cause of joint pain. Understanding the symptoms that suggest something more serious is at play is crucial for knowing when to worry about knee and leg pain.

Quick Summary

Several key symptoms indicate that knee or leg pain requires medical attention, including severe, sudden onset pain, swelling, numbness, and signs of infection like fever. It’s important to differentiate between minor aches and more serious issues that could signal a blood clot, nerve problem, or a significant injury.

Key Points

Immediate Concern: Seek immediate medical attention for sudden, severe pain, inability to bear weight, or visible deformity.
Blood Clot Signs: Be vigilant for signs of Deep Vein Thrombosis (DVT), which include swelling, warmth, and redness in one leg.
Nerve Damage Indicators: Numbness, tingling, or loss of sensation in the leg or foot are serious signs that require evaluation.
Infection Risk: Knee pain accompanied by fever or a general feeling of illness could signify a dangerous joint infection.
Chronic vs. Acute: Understand if your pain is a chronic issue needing a doctor's visit or an acute, emergency situation based on its onset and severity.
Listen to Your Body: Don't dismiss persistent or worsening pain, as it can indicate an underlying issue that needs professional diagnosis.

Differentiating Between Minor Discomfort and Serious Symptoms

Not all knee and leg pain warrants an emergency room visit. Often, aches are temporary, caused by overexertion or a minor strain, and will resolve with rest, ice, and elevation. However, recognizing the critical signs that signal a more serious underlying issue is key to preventing complications.

Red Flags That Require Immediate Medical Attention

Certain symptoms demand immediate professional evaluation. Ignoring these signs could lead to long-term damage or indicate a life-threatening condition.

Sudden, Severe Pain: Pain that comes on abruptly and is intense, especially after an injury or impact.
Inability to Bear Weight: If you cannot stand or put any weight on the affected leg or knee.
Deformation or Visible Injury: Any obvious change in the shape of the knee or leg, such as a severe bend or twist.
Significant Swelling: Swelling that appears rapidly and is accompanied by pain.
Numbness or Tingling: Loss of sensation or a 'pins and needles' feeling in the leg or foot, which can indicate nerve damage.
Inability to Straighten or Flex the Joint: A lock-up sensation or complete inability to move the knee joint through its full range of motion.

Other Warning Signs

While not always an emergency, these symptoms suggest a need to schedule an appointment with a healthcare provider for a thorough examination.

Pain that persists or worsens over several weeks.
Recurring pain that affects your daily activities.
Chronic swelling that does not improve.
A grinding or popping sound and sensation during movement.
Pain accompanied by a fever or general feeling of being unwell, which could point to an infection.

Potential Causes of Serious Knee and Leg Pain

Pain can stem from a variety of sources, from athletic injuries to underlying medical conditions.

Traumatic Injuries

ACL Tear: A common sports injury to the anterior cruciate ligament, resulting in instability and severe pain.
Meniscus Tear: A tear in the knee's shock-absorbing cartilage, often causing locking or clicking sensations.
Fracture: A break in one of the bones of the leg or kneecap, resulting in extreme pain and swelling.

Medical Conditions

Deep Vein Thrombosis (DVT): A blood clot in a deep vein, usually in the leg. Symptoms include swelling, pain, warmth, and redness.
Infection: A joint infection (septic arthritis) can cause intense pain, swelling, and fever. This is a medical emergency.
Severe Arthritis: Advanced osteoarthritis or rheumatoid arthritis can cause significant chronic pain and inflammation.
Sciatica: Nerve pain originating from the lower back that radiates down the leg.

Comparing Minor vs. Major Symptoms


Feature	Minor Pain/Strain	Major Injury/Condition
Onset	Gradual, often after specific activity	Sudden, often after trauma
Intensity	Mild to moderate, manageable	Severe, debilitating pain
Accompanying Symptoms	May have mild swelling or stiffness	Significant swelling, bruising, instability, numbness, fever
Ability to Bear Weight	Uncomfortable but possible	Difficult or impossible
Movement	Limited but possible	Severely restricted, locking
Recovery Time	Days to a couple of weeks with rest	Longer term, potentially requires surgery

When to Contact a Doctor vs. Seek Emergency Care

Knowing the difference between a situation that requires a routine appointment and one that needs immediate attention is crucial.

Call your doctor or a walk-in clinic if you experience:

Pain that doesn't improve with rest over a week.
Swelling that is persistent but not extreme.
A dull, aching pain that has been present for a while.
Pain that recurs after activity.

Go to the emergency room immediately if you:

Have signs of a blood clot (DVT): swelling, warmth, redness in one leg.
Cannot bear weight on your leg.
Have a fever with your knee pain.
See an obvious deformity or suspect a fracture.
Experience numbness or loss of sensation.
Suspect a septic joint.

It is always better to be cautious, especially if you have a pre-existing health condition or a history of blood clots. For more information on serious leg conditions, consult reputable sources like the Mayo Clinic.

Conclusion: Prioritizing Your Health

Understanding the signals your body sends is vital. While minor aches are a normal part of life, recognizing when to worry about knee and leg pain can be the difference between a minor setback and a serious medical emergency. Pay close attention to the severity of your pain, the presence of other symptoms like swelling or numbness, and your ability to function normally. When in doubt, seek professional medical advice. Early diagnosis and treatment can lead to better outcomes and a faster return to your daily activities.

Frequently Asked Questions

You should not ignore leg pain that is sudden and severe, accompanied by significant swelling, numbness, or a fever. Also, any pain that prevents you from bearing weight on your leg is a red flag.

You should see a doctor for leg pain if it persists for more than a week, recurs frequently, or is accompanied by other worrying symptoms like swelling, redness, or a visible change in your leg's appearance.

Yes, knee and leg pain can be a symptom of a blood clot (Deep Vein Thrombosis or DVT). Look for other signs like swelling, warmth, and redness, particularly in one leg. If you suspect a blood clot, seek immediate medical care.

Serious knee injury signs include intense, sudden pain, a popping sound at the time of injury, instability, severe swelling, and the inability to bend or straighten your knee.

Arthritis-related knee pain often starts gradually and may be accompanied by stiffness, especially in the morning or after periods of rest. It may also worsen with activity. A doctor can confirm the diagnosis.

While it's normal for minor strains to hurt with activity, pain that consistently worsens significantly with exercise or movement could be a sign of a more serious condition, such as a tear or advanced arthritis.

It is a medical emergency when pain is accompanied by fever, signs of a blood clot, extreme swelling, visible deformity, or loss of sensation. These symptoms suggest potentially life-threatening conditions.