The Stages of Knee Osteoarthritis

What are the stages of knee osteoarthritis?

Knee osteoarthritis is commonly divided into four stages, based on what an x-ray shows about the joint. In broad terms: early changes are subtle, with tiny bone spurs and near-normal cartilage; moderate stages show clear narrowing of the space between the bones as cartilage thins; and advanced, end-stage arthritis shows that space largely gone — the "bone on bone" picture — with larger spurs and changes in the bone itself 1Ref 1American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee osteoarthritis shows on x-ray as joint-space narrowing, bone spurs, and advanced 'bone on bone' change; it is managed nonsurgically first, with knee replacement considered when conservative care no longer controls symptoms.. Osteoarthritis is the most common form of arthritis and a gradual, years-long process, much like hip osteoarthritis in a neighboring joint 2Ref 2National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) (2023).Osteoarthritis.Osteoarthritis is the most common form of arthritis, a gradual degenerative joint disease driven by cartilage breakdown..

Kellgren-Lawrence grading is the common 0-to-4 x-ray scale used to stage osteoarthritis by joint-space narrowing and bone spurs.

The crucial thing to understand up front is what these stages are for. They describe the structural picture on imaging. They are a useful shorthand for clinicians, but they are not a verdict on how much you will hurt or a schedule for surgery. As the rest of this guide explains, the stage is only one input, and often not the most important one.

How the stages are graded — reading the x-ray

Staging is done by looking at a weight-bearing x-ray of the knee and judging a few features: how much space remains between the thigh bone and shin bone (a stand-in for cartilage thickness), whether bony spurs called osteophytes have formed at the joint edges, and whether the bone underneath has hardened or changed shape. Less joint space and more spurring push the grade higher 1Ref 1American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee osteoarthritis shows on x-ray as joint-space narrowing, bone spurs, and advanced 'bone on bone' change; it is managed nonsurgically first, with knee replacement considered when conservative care no longer controls symptoms..

A few points are worth knowing. The x-ray is taken standing, because lying down can make the joint space look falsely generous. "Bone on bone" is a real radiographic finding — the cartilage-shaped gap has closed — but it is a description of the film, not a measure of pain. And an x-ray is a snapshot: osteoarthritis usually progresses slowly, over years, and many knees change grade very gradually or plateau for long stretches. The grade tells you where the joint sits today, not how fast it is moving.

Why the stage doesn't decide how you feel

One of the most important and least intuitive facts about knee osteoarthritis is that the x-ray stage and the symptoms often do not match. Some people with advanced, bone-on-bone changes on film have modest pain and walk well; others with only mild-looking arthritis hurt a great deal and struggle with stairs. The severity of the picture is a loose predictor of the severity of the experience, not a tight one.

This has real consequences. It means a scary-sounding grade is not, by itself, a reason to panic or to rush toward surgery, and a mild grade does not mean your pain is imagined. It also means the goal of treatment is to change how the knee feels and functions — not to change the x-ray, which most treatments do not do anyway. Clinicians who manage arthritis well treat the person in front of them, using the stage as background rather than the headline. If you are noticing early knee arthritis, that discordance is good news: symptoms can improve even when the structure on film does not.

What actually changes treatment across the stages

Here is the part that surprises people: for most stages of knee osteoarthritis, the first-line treatment is the same. Whether the arthritis is early or moderate, the core of care is structured exercise, physical therapy, and — for those carrying extra weight — weight management. Land-based exercise reliably reduces knee pain and improves function, with benefits that last for months after a program ends 3Ref 3Fransen M, McConnell S, Harmer AR, et al. (2015).Exercise for osteoarthritis of the knee.Land-based therapeutic exercise reduces knee pain and improves physical function in knee osteoarthritis, with benefit sustained for 2-6 months after formal treatment ends., and clinical guidelines rate exercise, weight loss, and anti-inflammatory medication among the strongest-supported treatments at every stage short of joint replacement 4Ref 4American Academy of Orthopaedic Surgeons (AAOS) (2021).Management of Osteoarthritis of the Knee (Non-Arthroplasty), Third Edition — Clinical Practice Guideline.Strong evidence supports exercise/physical therapy, NSAIDs, and weight loss for nonsurgical management of knee osteoarthritis across stages short of replacement..

Within medication, anti-inflammatory drugs are among the better-supported options for symptom relief 4Ref 4American Academy of Orthopaedic Surgeons (AAOS) (2021).Management of Osteoarthritis of the Knee (Non-Arthroplasty), Third Edition — Clinical Practice Guideline.Strong evidence supports exercise/physical therapy, NSAIDs, and weight loss for nonsurgical management of knee osteoarthritis across stages short of replacement.. What does not change much with stage is the foundation: the exercise and weight work that helps a mild knee also helps a moderate one. Staging rarely moves someone off this base of care — it mostly informs when to add or consider other options.

Exercise, weight management, and anti-inflammatory medication are first-line at essentially every stage of knee osteoarthritis short of replacement 3Ref 3Fransen M, McConnell S, Harmer AR, et al. (2015).Exercise for osteoarthritis of the knee.Land-based therapeutic exercise reduces knee pain and improves physical function in knee osteoarthritis, with benefit sustained for 2-6 months after formal treatment ends.4Ref 4American Academy of Orthopaedic Surgeons (AAOS) (2021).Management of Osteoarthritis of the Knee (Non-Arthroplasty), Third Edition — Clinical Practice Guideline.Strong evidence supports exercise/physical therapy, NSAIDs, and weight loss for nonsurgical management of knee osteoarthritis across stages short of replacement..

Injections — where they fit, and their limits

Injections are a common next step when exercise and medication are not enough, but the evidence asks for realistic expectations. A corticosteroid injection can calm a painful flare for a period of weeks, which can be genuinely useful for getting through a bad stretch or staying active. What it does not do is change the course of the arthritis.

Repeated cortisone injections, in particular, do not live up to their reputation. In a two-year randomized trial, giving a steroid injection every twelve weeks provided no better pain relief than a saline injection — and was associated with greater loss of cartilage on imaging 5Ref 5McAlindon TE, LaValley MP, Harvey WF, et al. (2017).Effect of Intra-articular Triamcinolone vs Saline on Knee Cartilage Volume and Pain in Patients With Knee Osteoarthritis: A Randomized Clinical Trial.Repeated intra-articular triamcinolone every 12 weeks for two years gave no better knee OA pain relief than saline and was associated with greater cartilage volume loss.. That does not make a single, well-timed injection useless, but it argues against leaning on them again and again as arthritis progresses. Injections are a tool for buying comfortable time, not a treatment that reverses the joint's decline.

Over two years, steroid injections every 12 weeks gave no more pain relief than saline and were linked to greater cartilage loss 5Ref 5McAlindon TE, LaValley MP, Harvey WF, et al. (2017).Effect of Intra-articular Triamcinolone vs Saline on Knee Cartilage Volume and Pain in Patients With Knee Osteoarthritis: A Randomized Clinical Trial.Repeated intra-articular triamcinolone every 12 weeks for two years gave no better knee OA pain relief than saline and was associated with greater cartilage volume loss..

Does arthroscopy help an arthritic knee?

For osteoarthritis, the answer from the evidence is mostly no. Arthroscopic surgery — the "clean-out" or "scope" — was once common for arthritic and degenerative knees, but a clinical practice guideline built on the trials issued a strong recommendation against arthroscopy for nearly all patients with degenerative knee disease, including those with mechanical symptoms or a degenerative meniscal tear 6Ref 6Siemieniuk RAC, Harris IA, Agoritsas T, et al. (2017).Arthroscopic surgery for degenerative knee arthritis and meniscal tears: a clinical practice guideline.A clinical practice guideline issued a strong recommendation against arthroscopy for nearly all patients with degenerative knee disease, including those with meniscal tears or mechanical symptoms.. On average it does not deliver lasting benefit over non-surgical care.

This matters because "my knee catches and locks" can feel like a mechanical problem a scope should fix, and because a degenerative meniscal tear often shows up on the MRI of an arthritic knee — where it is usually a feature of the arthritis, not a separate injury to be trimmed. There are specific exceptions, such as a true locked knee from a displaced tear fragment that physically blocks motion, but for the ordinary arthritic knee the sequence of care points toward exercise and weight management rather than the operating room.

When knee replacement is the right call

Total knee replacement is a highly effective operation for the right knee at the right time, and it belongs at the end of the sequence rather than the middle. The order that serves most people is a genuine trial of exercise, weight management, and medication first, with injections and other measures as needed — and surgery considered when those stop controlling the problem 1Ref 1American Academy of Orthopaedic Surgeons (OrthoInfo) (2024).Arthritis of the Knee.Knee osteoarthritis shows on x-ray as joint-space narrowing, bone spurs, and advanced 'bone on bone' change; it is managed nonsurgically first, with knee replacement considered when conservative care no longer controls symptoms.. Advanced arthritis on x-ray is part of the picture, but it is not the trigger by itself.

The indications that push toward replacement are about life, not just the film: pain that persists despite months of good non-surgical care, pain at rest or at night, and a steady loss of the ability to walk, work, sleep, and do the things that matter — usually with moderate-to-severe changes on x-ray to match. Whether knee replacement is worth it for a given person is a shared decision, weighing how much the knee is limiting you against how well conservative care is still holding. When a knee reaches that point, replacement reliably relieves pain and restores function for most people, though the recovery timeline runs over months of rehabilitation rather than weeks.

Tracking the knee — and catching it early

Because osteoarthritis changes slowly and the x-ray is a poor guide to how you feel, it helps to track function directly over time. A short, repeatable questionnaire can put numbers on pain, daily activities, and quality of life, so that you and a clinician can see whether a plan is working rather than relying on the memory of a good or bad week.

One widely used tool is the KOOS questionnaire, the Knee injury and Osteoarthritis Outcome Score, which measures pain, symptoms, daily function, sport and recreation, and knee-related quality of life. Completing something like the KOOS knee score before and after a few months of exercise gives an honest read on progress. Catching things early helps too: the early signs of knee arthritis — occasional stiffness after sitting, a little morning creakiness, mild soreness after activity — are exactly when exercise and weight management have the most room to work, long before anyone is talking about a "stage 4" knee. And if you are still sorting out whether arthritis is even the cause, making sense of knee pain begins with where and when it hurts.