How to tell if your knees are healthy?

September 29, 2025 •

4 min read

According to the Centers for Disease Control (CDC), roughly 1 in 4 adults in the U.S. has arthritis, a condition that often affects the knees. It's never too early to start paying attention to your knees, and this guide explains how to tell if your knees are healthy by checking for signs of good joint function and stability.

Quick Summary

Several key indicators point to healthy knees, including a full and pain-free range of motion, stable movement without wobbling, and a lack of persistent stiffness, swelling, or grinding sounds. Assessing these signs can help you gauge your joint health and take preventive measures.

Key Points

Pain is a clear signal: Persistent knee pain during or after activity is a primary indicator that something is wrong with the joint.
Check your range of motion: You should be able to fully straighten and bend your knee without stiffness; reduced flexibility is a sign of poor health.
Look for instability: Healthy knees feel stable and secure, while wobbling or buckling under weight indicates weakness or ligament issues.
Heed abnormal sounds: While some clicking is normal, grinding, crunching, or painful popping often suggests damage to cartilage.
Watch for swelling and inflammation: Redness, warmth, or noticeable swelling are signs of inflammation that require attention.
Support your knees with strength: Strong quadriceps and hamstrings provide crucial support, absorbing impact and protecting the knee joint.

Understanding the Anatomy of a Healthy Knee

Your knee is a complex hinge joint, crucial for almost all movement, from walking to running and jumping. It consists of the femur (thigh bone), tibia (shin bone), and patella (kneecap), all surrounded by cartilage, ligaments, and tendons. In a healthy knee, the cartilage provides a smooth, low-friction surface for the bones to glide over, while strong ligaments hold the bones together and provide stability. Healthy knees allow for a full range of motion without pain or restriction, and are supported by strong surrounding muscles, which absorb shock and reduce stress on the joint itself.

5 Key Indicators of Healthy Knees

1. Pain-Free Movement

A healthy knee should move without pain during everyday activities. This includes walking, climbing stairs, squatting, or bending. Occasional soreness after a strenuous workout is normal, but persistent or sharp pain during or after activity is a red flag. Notice the location and timing of any pain; pain under the kneecap often signals patellofemoral issues, while pain on the sides can indicate ligament stress.

2. Full Range of Motion

Testing your knee's range of motion is a simple but effective way to gauge its health. Your knee should be able to fully straighten and fully bend without feeling stiff or restricted. A simple test is to sit on the floor with your legs extended and see if your knees can lie completely flat. Then, pull your heel toward your buttocks to test your flexion. Any noticeable difference between your legs or a significant restriction in motion is cause for concern.

3. Stability and Strength

Your knee should feel stable and supported, not like it will buckle or give way under pressure. Muscles like your quadriceps and hamstrings play a vital role in providing stability and protecting the joint. Weakness in these muscles can lead to instability and increased stress on the ligaments. Simple tests, like the single-leg squat, can reveal underlying weaknesses.

4. No Abnormal Sounds or Sensations

While some occasional popping or clicking, known as crepitus, can be normal, especially without pain, consistent grinding, catching, or painful snapping is not. These sounds can be a sign of worn cartilage or other mechanical problems within the joint. Pay attention to when these sounds occur and if they are accompanied by discomfort.

5. Absence of Swelling, Redness, and Warmth

Swelling is a clear sign of inflammation or fluid accumulation in the knee joint, often indicating an underlying issue. Similarly, redness and warmth to the touch can signal inflammation or even an infection. When checking for swelling, compare both knees; even a subtle difference can be significant.

Simple At-Home Tests to Assess Your Knee Health

1. The Single-Leg Squat Test

Stand in front of a mirror and balance on one leg.
Slowly lower yourself into a partial squat, keeping your knee aligned over your foot and not allowing it to turn inward.
If your knee wobbles inward or you feel unstable, it can indicate weak hip and thigh muscles, which contribute to knee health.

2. The Step-Down Test

Find a low step or platform (6-8 inches high).
Stand with one foot on the step and the other off the edge.
Slowly bend your standing knee, lowering the other foot toward the floor.
Observe how steady and controlled your movement is.

3. The Range of Motion Check

Sit on the floor with your legs straight out in front of you.
Place a pillow or rolled-up towel under your ankle.
Gently use your leg muscles to press the back of your knee down toward the floor.
If you can't fully straighten your knee to touch the floor or feel significant discomfort, your range of motion may be restricted.

Comparison: Healthy vs. Unhealthy Knee Symptoms


Indicator	Healthy Knee	Unhealthy Knee
Pain	Minimal to no pain during regular activity.	Persistent pain, soreness, or sharp twinges, especially with movement.
Movement	Smooth, controlled motion through a full range.	Stiffness, limited range of motion, or a feeling of catching or locking.
Stability	Feels solid and secure, with no feeling of giving way.	A sense of instability, wobbling, or the knee buckling under weight.
Sounds	Quiet joint, or occasional, painless popping.	Frequent, painful grinding, crunching, or snapping noises.
Appearance	Normal temperature and size, no visible swelling.	Swelling, redness, warmth to the touch, or visible deformity.

Protective Factors for Long-Term Knee Health

Maintaining healthy knees goes beyond just spotting problems; it involves proactive care. Here are some crucial lifestyle factors that support long-term knee health:

Maintain a Healthy Weight: Every extra pound of body weight adds four pounds of pressure on your knees. Keeping your weight in a healthy range significantly reduces stress on the joints.
Stay Active with Low-Impact Exercise: Regular movement helps nourish the joint cartilage and strengthens the supporting muscles. Focus on low-impact activities like walking, swimming, and cycling, which are gentle on the knees.
Strength Train: Strong quadriceps, hamstrings, and glutes act as natural shock absorbers for your knees. Include exercises like leg raises, hamstring curls, and gentle squats in your routine.
Ensure Proper Footwear: Supportive shoes are critical for maintaining proper foot and leg alignment, which reduces stress on your knees. Wear appropriate footwear for your activities and replace worn-out shoes promptly.
Listen to Your Body: While movement is key, so is rest. Recognize when you need to slow down or take a break to avoid overtraining and injury.

Conclusion

Being proactive about your knee health is a wise investment in your future mobility and quality of life. By regularly checking for a pain-free, full range of motion, stability, and the absence of abnormal symptoms like swelling or grinding, you can stay ahead of potential issues. Remember that consistent pain, instability, or major swelling warrants a consultation with a healthcare professional. Through mindful exercise, weight management, and attention to your body's signals, you can protect and maintain your knees for years to come. For more information on the structure and function of the knee joint, consult the American Academy of Orthopaedic Surgeons.

Frequently Asked Questions

Low-impact exercises like walking, swimming, and cycling are excellent for knee health. They strengthen the muscles around the knee without placing excessive stress on the joint. Incorporate strength training for your quadriceps and hamstrings, as well as regular stretching to maintain flexibility.

Occasional, painless cracking or popping (crepitus) is often normal and can be caused by gas bubbles in the joint fluid. However, if the sounds are frequent, painful, or accompanied by grinding, catching, or stiffness, they could indicate a cartilage or meniscal issue and should be evaluated by a doctor.

Excess body weight puts significant pressure on your knees. Studies show that every pound of extra weight adds four pounds of pressure to your knees when walking. Maintaining a healthy weight is one of the most effective ways to reduce stress on your joints and prevent issues like osteoarthritis.

Improve knee stability by strengthening the surrounding muscles, particularly the quadriceps, hamstrings, and glutes. Regular exercise, including leg raises, gentle squats, and lunges with proper form, can help. Practicing balance exercises and wearing supportive footwear also play a key role.

You should see a doctor if you experience persistent pain that doesn't improve with rest, marked swelling, an inability to fully bend or straighten your knee, a visible deformity, or if your knee feels unstable or buckles under you. Sudden, severe pain or pain with a fever also warrants immediate medical attention.

Yes, proper footwear is crucial for knee health. Supportive shoes help maintain proper alignment of your feet and legs, which minimizes the amount of stress transferred to your knees. Choosing the right shoe for specific activities, such as running or hiking, is also important.

To check for swelling, sit with your legs extended and relaxed. Compare the size and appearance of both knees. Use the back of your hand to feel for warmth and gently press around the kneecap. Excess fluid can make the area feel puffy, and a firm tap on the kneecap may make it bob up and down.