Kellgren-Lawrence Grading System: What Grades 0–4 Mean for Your Knee Arthritis

By Dr. Jeffrey Peng, MD · Updated August 2026

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If you have been told you have knee arthritis, your doctor almost certainly used an X-ray and the Kellgren-Lawrence (KL) grading system to describe the severity. This system rates osteoarthritis from grade 0 (normal) to grade 4 (severe, bone-on-bone).

Understanding your grade is useful for treatment discussions. However, the most important thing I tell patients is this: the grade on your X-ray does not reliably predict how much pain or limitation you will have.

What Is the Kellgren-Lawrence Grading System?

The Kellgren-Lawrence system is the most widely used radiographic classification for osteoarthritis. Developed in the 1950s, it evaluates four features on X-ray:

• Joint space narrowing

• Osteophyte (bone spur) formation

• Sclerosis (increased bone density)

• Deformity of the bone contours

Each knee is assigned a grade from 0 to 4 based on the presence and severity of these findings.

KL Grade 0: No Osteoarthritis

A grade 0 X-ray shows no radiographic signs of osteoarthritis. Joint spaces in the medial, lateral, and patellofemoral compartments are well preserved. There are no osteophytes and no bony sclerosis. This is what a healthy knee looks like on imaging.

KL Grade 1: Doubtful Osteoarthritis

Grade 1 shows possible small osteophytes and doubtful joint space narrowing. The edges of the bone may appear slightly pointed — early bone spurs caused by increased mechanical stress and the beginning of cartilage breakdown. The joint space may still look preserved, but the underlying cartilage has already started to weaken.

KL Grade 2: Mild Osteoarthritis

At grade 2, X-rays show definite osteophytes and early joint space narrowing. Grades 1 and 2 are considered mild osteoarthritis.

Even at this stage, the biochemical environment inside the knee is deteriorating. Inflammatory markers, destructive enzymes, and toxic proteins are being released into the joint, progressively weakening remaining healthy cartilage.

This is an important window for intervention. Most high-quality clinical studies on osteoarthritis treatments focus on grades 1 and 2 because this is when therapies such as platelet-rich plasma (PRP) injections, structured exercise, and weight management have the greatest potential to slow progression.

KL Grade 3: Moderate Osteoarthritis

By grade 3, cartilage erosion is more substantial. X-rays demonstrate multiple osteophytes, more pronounced joint space narrowing, sclerosis of the underlying bone, and early deformity of the bone contours. This is often when patients first seek care because of increasing pain and functional limitations.

KL Grade 4: Severe (Bone-on-Bone) Osteoarthritis

Grade 4 represents severe disease with large osteophytes, significant or complete joint space collapse, marked sclerosis, and visible bone deformity. Treatment at this stage is primarily focused on symptom control. If pain cannot be managed with non-surgical approaches, knee replacement may eventually be considered.

How Many Knee Compartments Are Usually Affected?

When evaluating knee arthritis, physicians assess the three compartments separately: medial (inner), lateral (outer), and patellofemoral (kneecap).

A systematic review and meta-analysis published in Osteoarthritis and Cartilage found that approximately 50% of people with knee osteoarthritis have disease in only one compartment (most commonly the medial side). About 33% have two-compartment disease, and only 17% have tricompartmental involvement. In other words, three-quarters of patients do not have arthritis throughout the entire knee.

Do X-Ray Findings Predict Your Symptoms?

This is the most important clinical takeaway.

X-ray severity does not reliably correlate with symptom severity. In my practice I regularly see patients with grade 3 arthritis who are still running half marathons, and patients with grade 1 changes whose knees are so swollen they can barely walk.

The implications are clear:

• Having mild arthritis on X-ray does not mean you should wait until the disease reaches grade 3 or 4 before pursuing treatment. Early intervention is the best opportunity to slow progression and maintain function.

• Having moderate or even advanced radiographic changes does not mean your only option is a knee replacement. Many patients with significant X-ray findings continue to live active lives with the right combination of non-surgical treatments.

What matters most is treating the patient and their symptoms — not simply treating the X-ray.

Bottom Line

The Kellgren-Lawrence grading system is a useful way to describe the structural severity of knee osteoarthritis on X-ray. Knowing your grade helps frame the conversation about treatment options. But it should never be the sole factor that determines what you can or cannot do, or which treatments are appropriate for you.

If you have knee pain and want an evidence-based plan tailored to your specific grade, symptoms, and goals, I encourage you to schedule a consultation.

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References

1. Stoddart JC, Dandridge O, Garner A, Cobb J, van Arkel RJ. The compartmental distribution of knee osteoarthritis – a systematic review and meta-analysis. Osteoarthritis and Cartilage. 2021;29(4):445-455. doi:10.1016/j.joca.2020.10.011

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Medical Disclaimer: This content is for educational purposes only and does not substitute for the medical advice of a physician. Always consult your healthcare provider before beginning any new treatment program. The information presented reflects the opinion of Dr. Jeffrey Peng and does not represent the views of his employers or affiliated hospital systems.