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If your knee hurts and you are trying to tell whether it is arthritis or something else, an X-ray is usually the first and most useful test. Knee arthritis on X-ray shows a clear pattern: the cushion between the bones thins, small bony ridges form, and the bone underneath turns denser. In my practice, I read these films every week, and the picture they give, combined with a hands-on exam, is what tells me whether wear-and-tear arthritis is the cause or whether a torn cartilage, a ligament problem, or another condition is behind the pain.
How can you tell if knee pain is arthritis or something else?
The most reliable way to tell if knee pain is arthritis is a physical exam plus a standing X-ray, because arthritis leaves a specific footprint that other knee problems do not. Arthritis pain tends to build slowly over months or years, feels worse with activity and better with rest, and often comes with stiffness after sitting and a grinding or catching sensation called crepitus.
Other causes look and feel different. A meniscus (cartilage cushion) tear often follows a twist or squat and causes locking or a sharp catch. Ligament injuries usually start with a specific event and a feeling of the knee giving way. Inflammatory types of arthritis, such as rheumatoid arthritis or gout, tend to cause swelling, warmth, and morning stiffness that lasts well over 30 minutes.
Here is what I tell my patients: pain that has crept up over time, worsens with walking or stairs, and eases with rest points strongly toward osteoarthritis (the wear-and-tear form). Pain that started with a single injury, or that comes with fever, redness, or many swollen joints, points somewhere else. The exam narrows it down, and the X-ray confirms it.
What does knee arthritis look like on an X-ray?
Knee arthritis on an X-ray looks like four changes that a radiologist or surgeon can spot quickly: a narrowed joint space, bone spurs, denser bone under the joint surface, and small bone cysts. In advanced cases, the leg also starts to bow or angle. Cartilage itself does not show up on X-ray, so we read its health indirectly by the space between the bones.
Joint space narrowing: the first sign of knee arthritis on X-ray
Joint space narrowing is the main marker of cartilage loss and often the earliest sign. On a healthy knee, there is an even gap between the thighbone (femur) and shinbone (tibia). As the cartilage wears down, that gap shrinks, and in severe arthritis it can disappear entirely, leaving bone touching bone. The knee has three compartments (inner, outer, and behind the kneecap), and the inner compartment is the one most commonly affected.
Bone spurs (osteophytes)
Bone spurs, called osteophytes, are small bony ridges that grow at the edges of the joint as the body tries to stabilize a worn knee. They are one of the clearest signs of arthritis on film. When they grow large enough, they can limit motion or add to that catching feeling some patients describe.
Denser bone: subchondral sclerosis and cysts
Subchondral sclerosis is a bright white line of denser bone just under the joint surface. When cartilage no longer cushions the load, the bone underneath takes more force and responds by hardening. Nearby, small fluid-filled pockets called subchondral cysts can form. Both signal that the joint is carrying more stress than it was built for.
Alignment changes: bowlegged or knock-kneed
When arthritis wears down one side of the knee more than the other, the leg starts to angle. Inner-compartment wear pulls the knee into a bowlegged (varus) shape; outer-compartment wear can make it knock-kneed (valgus). These alignment shifts show clearly on a standing X-ray and matter a great deal when we plan treatment.
What do the knee arthritis X-ray grades 0 to 4 mean?
Knee arthritis X-ray grades run from 0 to 4 on the Kellgren-Lawrence scale, the system used worldwide since 1957 to describe how much arthritis is present. Your radiology report will usually list one of these grades, and it gives your surgeon and your insurer a consistent, documented measure of severity.
| Grade | What the X-ray shows |
|---|---|
| Grade 0 (none) | A normal knee. No joint space narrowing, no bone spurs. Any pain is coming from another cause. |
| Grade 1 (doubtful) | Possible tiny bone spurs and no definite narrowing. Often no symptoms; an early window for lifestyle steps. |
| Grade 2 (mild) | Definite bone spurs with possible slight narrowing. Cartilage wear is starting; a good time for conservative care. |
| Grade 3 (moderate) | Multiple spurs, definite narrowing, some sclerosis, and possible early bone deformity. Symptoms are often clear. |
| Grade 4 (severe) | Large spurs, severe narrowing (often bone-on-bone), marked sclerosis, and definite deformity. Surgery is commonly discussed here. |
After more than twenty years reading these films, I treat the grade as a starting point, not the whole story. It tells me how far the structural wear has gone; it does not tell me how much your knee is limiting your life.
Why does the X-ray grade not always match your pain?
The X-ray grade does not always match your pain because the film measures structure, not symptoms. Higher grades do track with worse pain on average, but there is real scatter. I have patients with grade 4, bone-on-bone knees who walk and golf comfortably, and others with grade 2 changes who are in daily, limiting pain.
This is why I never treat the scan alone. What I care about is how your knee affects your day: the stairs you avoid, the sleep you lose, the walks you have given up. The grade informs the plan; your symptoms and goals drive it. If you want to understand where your knee sits and what fits, our overview of nonsurgical joint pain treatment is a good next read.
Why do knee arthritis X-rays need to be weight-bearing?
Knee arthritis on X-rays should be taken standing, with your full weight on the knee, because that is the only way to see the true joint space. When you lie down, the load comes off the joint, the gap can look near-normal, and mild or moderate arthritis can be underestimated. Standing puts the joint under real physiological load and reveals how much cartilage is actually left.
A standard knee series for arthritis usually includes a standing front-to-back view, a side view, and a view of the kneecap. Sometimes a slightly bent-knee standing view is added to catch early cartilage loss at the back of the joint. The whole study takes only a few minutes and needs no preparation.
An X-ray is enough to diagnose and stage most knee arthritis. I order an MRI only when the X-ray looks normal but symptoms persist, when I suspect a meniscus or ligament tear alongside the arthritis, or when the diagnosis is unclear.
When should you see a knee specialist in Franklin or Nashville?
See a knee specialist when knee pain starts limiting the things you care about, rather than waiting until the joint is bone-on-bone. Cartilage does not grow back, so the realistic goals are to slow the arthritis and control the symptoms, and both are easier before pain reshapes how you move. Early does not mean surgery; for most people, the first steps are strengthening, weight management, activity changes, and medication as needed.
At the Bone and Joint Institute of Tennessee, I see patients from Franklin, Nashville, Columbia, Spring Hill, and across Middle Tennessee who simply want to know what is causing their knee pain and what to do about it. If your knee has been aching for weeks, catching, swelling, or keeping you from stairs and sleep, that is the right time to get it looked at. When conservative care has run its course, we can talk through options from injections to total knee replacement.
You do not need a referral to be seen. You can request an appointment with Dr. Calendine online, or call the office at (615) 791-2630. Our clinic is at 3000 Edward Curd Lane, Franklin, TN 37067.
This article is for educational purposes only and is not a substitute for professional medical advice. Reading of any X-ray should be done by a qualified clinician. Always consult a licensed healthcare provider about your own knee pain, imaging, and treatment options. Individual results vary.
References
- Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis. Annals of the Rheumatic Diseases. 1957;16(4):494-502.
- Kohn MD, Sassoon AA, Fernando ND. Classifications in brief: Kellgren-Lawrence classification of osteoarthritis. Clinical Orthopaedics and Related Research. 2016;474(8):1886-1893.
- Bedson J, Croft PR. The discordance between clinical and radiographic knee osteoarthritis: a systematic search and summary of the literature. BMC Musculoskeletal Disorders. 2008;9:116.
- Hayashi D, Roemer FW, Guermazi A. Imaging for osteoarthritis. Annals of Physical and Rehabilitation Medicine. 2016;59(3):161-169.
- Kolasinski SL, Neogi T, Hochberg MC, et al. 2019 American College of Rheumatology/Arthritis Foundation guideline for the management of osteoarthritis of the hand, hip, and knee. Arthritis and Rheumatology. 2020;72(2):220-233.
- American Academy of Orthopaedic Surgeons. Arthritis of the Knee. OrthoInfo. Reviewed 2024. https://orthoinfo.aaos.org/en/diseases–conditions/arthritis-of-the-knee/
