What is Knee Osteoarthritis?
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026
Quick Answer: What Is Knee Osteoarthritis?
Knee osteoarthritis is a condition in which the protective cartilage cushioning the ends of the bones in the knee wears down over time, so the bones rub together and cause inflammation and chronic pain. [1] It mainly results from aging and wear and tear, with injuries and obesity as risk factors. [1] [5] Treatment ranges from bracing and exercise to total knee replacement. [1]
What the research says
Exercise reduces knee OA pain and improves function, with benefits lasting for months. A Cochrane systematic review of 54 trials found that land-based exercise reduced pain by 12 points on a 100-point scale (95% CI 10 to 15) and improved physical function by 10 points (95% CI 8 to 13) right after treatment. Smaller benefits were still present 2 to 6 months after formal treatment ended (pain: 6 points, 95% CI 3 to 9), although many of the trials were at risk of bias (Fransen et al., British Journal of Sports Medicine, 2015 [2]).
Losing about 7% of body weight may be the point where pain relief becomes meaningful. A network meta-analysis of 13 randomized trials (2,800 adults with overweight or obesity and knee OA) found that diet plus exercise reduced pain more than control (-2.2 on a 0-20 scale, 95% CI -4.1 to -0.21). Significant pain relief may be expected once people lose at least 7% of their body weight (Shahid et al., Osteoarthritis and Cartilage, 2025 [3]).
PRP injections outperformed corticosteroid injections in one meta-analysis, but the evidence is still developing. Pooling 8 studies and 648 patients, platelet-rich plasma (PRP) reduced pain, stiffness, and functional limits more than corticosteroid injections at 3, 6, and 9 months. At 6 months, the difference equated to an extra 9.51-point reduction on the WOMAC scale (McLarnon & Heron, BMC Musculoskeletal Disorders, 2021 [4]). The Arthritis Foundation cautions that PRP is not FDA-approved for this use and that evidence is still emerging. [5]
Key Takeaways: Knee Osteoarthritis Facts
Feature | Details |
Medical Name | Knee Osteoarthritis (OA) |
Primary Cause | Degeneration of joint cartilage [1] |
Target Audience | |
Key Symptoms | Pain, stiffness, swelling, and grinding noises [1] |
Stages | Stage 1 (Minor) to Stage 4 (Severe) [1] |
Diagnosis | Physical exam and X-ray imaging [1] |
Treatment | Physical therapy, weight loss, injections, and surgery [1] |
Prognosis | Progressive; manageable with early intervention [1] |
What is knee osteoarthritis?
Knee osteoarthritis is the most common form of arthritis affecting the knee joint. [1] In a healthy knee, the ends of the femur (thigh bone) and tibia (shin bone) are covered with a smooth, slippery tissue called articular cartilage. This tissue acts as a shock absorber and allows the bones to glide effortlessly during movement. When this cartilage begins to thin and fray, the joint loses its protection, leading to the development of bone spurs and chronic inflammation. [1]
Because the knee joint carries the majority of the body's weight, it is particularly susceptible to the cumulative effects of daily stress. Knee OA is a lifelong condition that requires consistent management to prevent it from leading to significant disability.
What are the symptoms and stages of knee osteoarthritis?
Knee osteoarthritis usually develops gradually, causing pain, morning stiffness, grinding or popping and swelling, and providers often describe its progression in four levels. [1]
Common Symptoms
The onset of knee osteoarthritis is usually gradual, with symptoms worsening over several years. [5]
Persistent Pain: Discomfort that increases with activity and may persist even at rest. [1]
Morning Stiffness: A feeling of tightness in the joint that is most severe after waking or long periods of inactivity. [1]
Crepitus: A distinct cracking, popping, or grinding sensation when bending or straightening the knee. [1]
Joint Swelling: Puffy or inflamed appearance caused by fluid buildup in the joint capsule. [1]
The Four Stages of OA
There are no definitive stages of knee OA, but healthcare providers often use four levels to explain how advanced it is and to guide treatment decisions. [1]
Stage | Description | Typical Symptoms |
Stage 1: Minor | Very early wear and tear in the cartilage. [1] | Little to no pain; minimal cartilage loss. [1] |
Stage 2: Mild | Some cartilage wear, but enough remains to keep the bones from grinding together. [1] | Occasional pain and stiffness after a long day. |
Stage 3: Moderate | Cartilage is significantly reduced. [1] | Frequent pain during walking, squatting, or kneeling. [1] |
Stage 4: Severe | Cartilage is nearly gone; bone-on-bone contact. [1] | Severe pain, stiffness, and limited mobility. [1] |
What causes knee osteoarthritis, and who is at risk?
Knee osteoarthritis is primarily a "wear-and-tear" disease, but several factors can accelerate the breakdown of cartilage. [1]
Aging: The risk of developing OA increases as the body's ability to repair cartilage diminishes with age. [5]
Weight: Excess body weight puts significant mechanical stress on the knee joints. For every pound of weight gained, the knees experience four pounds of extra pressure. [5]
Previous Injury: Past ligament tears (like ACL injuries) or meniscus damage can change the joint's mechanics, leading to OA years later. [5]
Repetitive Stress: Jobs or sports that require frequent kneeling, heavy lifting, or high-impact jumping can wear down the joint prematurely. [1]
How is knee osteoarthritis diagnosed and managed?
Early diagnosis is essential for slowing the progression of knee OA. A healthcare provider will typically perform a physical examination to check for range of motion and joint stability before ordering imaging. [1]
Diagnostic Tools
How is knee osteoarthritis treated and cared for long term?
Lost knee cartilage cannot grow back, [1] but knee osteoarthritis symptoms can be managed with physical therapy, weight loss, braces, injections and, when needed, surgery such as knee replacement. [1]
Nonsurgical Approaches
For most patients, the first line of defense involves non-invasive strategies:
Physical Therapy: Strengthening the quadriceps and hamstrings to better support the knee joint. [1]
Weight Management: Reducing body weight to alleviate the mechanical load on the knees. [1] [5]
Assistive Devices: Using knee braces or orthotics to improve joint alignment. [1] [5]
Injections: Cortisone shots for immediate inflammation relief or gel injections (viscosupplementation) to provide lubrication. [1]
Surgical Interventions
When conservative treatments are no longer effective, surgery may be necessary. [1]
Conclusion
Knee osteoarthritis is a challenging condition, but it does not have to mean the end of an active lifestyle. By combining early diagnosis with a proactive management plan—including exercise, weight control, and medical guidance—most individuals can maintain their mobility and reduce chronic pain.
For more helpful health resources and visual guides, explore our infographic templates.
Frequently Asked Questions
Can knee osteoarthritis be cured?
No, it is a lifelong, progressive condition, but its symptoms can be managed effectively. [1]
Is walking good for knee OA?
Yes, low-impact exercise like walking helps maintain joint mobility and strengthens supporting muscles. [5]
What is the best exercise for knee OA?
Swimming and cycling are excellent because they are low-impact and do not put excessive stress on the joint. [1]
Does weather affect knee pain?
Many patients report increased pain during cold or damp weather, though the scientific reason for this is still debated.
What are bone spurs?
Bone spurs, or osteophytes, are bony lumps that grow on the edges of bones due to chronic friction and inflammation. [1]
Can I avoid surgery?
Many people manage knee OA without surgery through weight loss, physical therapy, bracing, and injections. Surgery is usually considered when nonsurgical treatments are no longer effective. [1]
What is crepitus?
Crepitus is the medical term for the grinding or popping sound heard when moving a joint. [1]
Does losing weight really help?
What is a Baker's cyst?
It is a fluid-filled swelling that develops at the back of the knee, often as a result of joint inflammation. [1]
Are knee injections painful?
Most patients experience only mild discomfort during the injection, which is often performed with a local anesthetic.
How long does a knee replacement last?
Many knee replacements last 15 to 20 years or longer, though this varies from person to person. [7]
Can young people get knee OA?
While less common, young people can develop OA, usually as a result of a severe joint injury.
What is the difference between OA and RA?
OA is caused by wear and tear, while rheumatoid arthritis (RA) is an autoimmune disease where the body attacks the joints. [6]
Should I use heat or ice?
Ice is best for reducing acute swelling, while heat can help relax stiff muscles and joints.
What is viscosupplementation?
It is a procedure where a thick fluid (hyaluronate) is injected into the joint to improve lubrication.
Can a knee brace help?
Yes, an "unloader" brace can shift weight away from the most damaged part of the knee. [6]
Is knee OA hereditary?
What is a total knee replacement?
It is a surgery where the damaged surfaces of the knee joint are replaced with metal and plastic parts. [6] [7]
Can supplements like glucosamine help?
Some people find relief with supplements, though there is no evidence to support using glucosamine or chondroitin. [6]
How is knee OA diagnosed?
It is primarily diagnosed through a physical exam and an X-ray of the knee. [1]
What is the "joint space"?
It is the gap between bones in a joint; narrowing of this space on an X-ray indicates cartilage loss. [6]
Can I still run with knee OA?
Running can put extra stress on an arthritic knee. Many doctors recommend lower-impact activities, or softer surfaces if you do run. [1] Ask your provider what is right for you.
What is an osteotomy?
It is a surgical procedure where the bone is cut and reshaped to realign the joint. [1]
Does knee OA affect both knees?
It can, though it often starts in one knee or is more severe on one side.
What are the signs of Stage 4 OA?
Severe pain, stiffness, a knee that may be hard to move, and bone-on-bone contact visible on X-rays. [1]
Can physical therapy regrow cartilage?
No, but it can strengthen the muscles that take the load off the joint.
What is a genicular nerve block?
It is an injection that targets the nerves around the knee to block pain signals.
How does obesity affect the knee?
Extra weight increases the mechanical load and releases inflammatory chemicals that damage cartilage. [5]
Can a past ACL tear cause OA?
Yes, joint injuries significantly increase the risk of developing OA later in life. [5]
What is "bone-on-bone" arthritis?
It is a term used for Stage 4 OA, where the cartilage is almost completely gone. [1]
Are there new treatments for knee OA?
Research into stem cell therapy and new types of injections is ongoing.
How long is recovery after knee surgery?
Recovery from a total knee replacement usually takes several months of dedicated physical therapy. [7]
Can knee OA cause depression?
Chronic pain and loss of mobility are significant risk factors for anxiety and depression. [1]
What is articular cartilage?
It is the smooth, white tissue that covers the ends of bones where they come together to form joints.
Does a "locked" knee mean OA?
A locking sensation can be a symptom of OA or a related issue like a meniscus tear.
What is the meniscus?
The meniscus is a C-shaped piece of tough, rubbery cartilage that acts as a shock absorber between the shinbone and thighbone.
Can I drive after a knee injection?
Most people can drive themselves home, though you should follow your specific doctor's advice.
What is "unloading" the joint?
It refers to techniques (like bracing or weight loss) that reduce the pressure on a specific part of the joint.
Is knee OA more common in men or women?
It is more common in women, [5] especially after the age of 50.
What is the role of inflammation in OA?
While primarily degenerative, OA involves low-level inflammation that contributes to pain and joint damage.
Can I use a cane?
Using a cane on the opposite side of the painful knee can significantly reduce the load on the joint.
What is PRP therapy?
Platelet-rich plasma (PRP) therapy uses a concentration of the patient's own platelets, injected into the joint to try to ease pain and inflammation. Evidence is still emerging, [5] so discuss it with your doctor.
Does knee OA affect sleep?
Severe pain can make it difficult to find a comfortable position, leading to sleep disturbances.
What is a "partial" knee replacement?
It is a surgery that replaces only one of the three compartments of the knee joint.
Can knee OA be prevented?
While not entirely preventable, maintaining a healthy weight and protecting your joints can reduce the risk. [1]
What is the synovium?
The synovium is a thin membrane that lines the joint and produces lubricating fluid.
Does knee OA cause redness?
While it can cause swelling, significant redness and heat may indicate an infection or a different type of arthritis.
How do I know if my knee pain is OA?
If the pain is worse with activity and accompanied by morning stiffness, OA is a likely cause. A healthcare provider can confirm the diagnosis.
What is "crepitus" a sign of?
It is a sign that the joint surfaces are no longer smooth, often due to cartilage loss.
Should I see a specialist?
An orthopedic surgeon or a rheumatologist is the best specialist to manage advanced knee OA.
Related Reading
Knee Brace: Types, Uses and How to Wear One explains knee brace types and how to use them.
PEMF Therapy: What Pulsed Electromagnetic Field Therapy Does explains PEMF therapy and what research shows.
Using a walking aid safely: How to Use a Cane: Sizing, Walking, Stairs and Safety Tips
Learn more in our guide to Genicular Artery Embolization (GAE) for Knee Osteoarthritis: How It Works, Procedure and Recovery.
Knee X-Ray: Why It's Done, What It Shows and What to Expect explains the X-ray used for knee injuries, pain and arthritis.
Patellar Grind Test (Clarke's Sign): Checking Kneecap Pain explains the knee exam that checks for cartilage problems under the kneecap.
References
Cleveland Clinic. Knee Osteoarthritis. Cleveland Clinic. Last updated January 30, 2025. https://my.clevelandclinic.org/health/diseases/21750-osteoarthritis-knee
Fransen M, McConnell S, Harmer AR, et al. Exercise for osteoarthritis of the knee: a Cochrane systematic review. Br J Sports Med. 2015;49(24):1554-1557. PMID 26405113. https://doi.org/10.1136/bjsports-2015-095424
Shahid A, Thirumaran AJ, Christensen R, et al. Comparison of weight loss interventions in overweight and obese adults with knee osteoarthritis: a systematic review and network meta-analysis of randomized trials. Osteoarthritis Cartilage. 2025;33(4):518-529. PMID 39233046. https://doi.org/10.1016/j.joca.2024.08.012
McLarnon M, Heron N. Intra-articular platelet-rich plasma injections versus intra-articular corticosteroid injections for symptomatic management of knee osteoarthritis: systematic review and meta-analysis. BMC Musculoskelet Disord. 2021;22(1):550. PMID 34134679. https://doi.org/10.1186/s12891-021-04308-3
Arthritis Foundation. Osteoarthritis. Arthritis Foundation. Accessed October 30, 2026. https://www.arthritis.org/diseases/osteoarthritis
American Academy of Orthopaedic Surgeons (AAOS). Arthritis of the Knee. OrthoInfo. Accessed November 5, 2026. https://www.orthoinfo.org/diseases--conditions/arthritis-of-the-knee
MedlinePlus. Knee joint replacement. MedlinePlus Medical Encyclopedia. Last updated August 27, 2024. https://medlineplus.gov/ency/article/002974.htm
Disclaimer
This information is for educational purposes only and does not constitute medical advice. Always seek the counsel of a qualified healthcare professional regarding any medical condition or emergency. If you are experiencing a life-threatening emergency, call 911 or your local emergency services immediately.
Comments