The Short Version
Knee arthritis happens when the smooth cartilage covering the surfaces of the knee becomes damaged and wears down. It can cause pain, stiffness, swelling, difficulty walking, and problems with stairs or getting up from a chair.
The X-ray is important, but it is only part of the picture. Treatment should be based on how your knee feels, how it functions, what the examination shows, and how much it is interfering with your life — not simply on how bad an X-ray looks.
The Basics
What is knee arthritis?
Your knee is made up of three bones: the thighbone (femur), shinbone (tibia), and kneecap (patella).
Where these bones meet, their surfaces are normally covered by a smooth layer of cartilage. That cartilage allows the knee to move with very little friction and helps distribute forces across the joint.
Osteoarthritis develops when that cartilage becomes damaged and gradually wears away. As the joint changes, the knee may become painful, stiff, swollen, or less able to tolerate everyday activity.
People often call osteoarthritis "wear-and-tear arthritis." That is a useful shorthand, but the process is more complicated than simply wearing out a mechanical part. Age, genetics, previous injuries, alignment, body weight, prior surgery, and other factors can all contribute.
The knee has three compartments
Arthritis does not always affect the entire knee equally. We generally think about three areas, or compartments:
- Medial compartment: the inner side of the knee
- Lateral compartment: the outer side of the knee
- Patellofemoral compartment: the joint between the kneecap and the front of the thighbone
Some patients have arthritis mainly in one compartment, while others have changes throughout the knee.
Plenty of people have arthritic changes on an X-ray without severe symptoms. Others have pain and limitations that are much more significant than the X-ray might initially suggest. We have to put the entire picture together.
Symptoms
What does knee arthritis feel like?
Knee arthritis does not feel exactly the same for everyone. Some patients describe an ache. Others describe sharp pain with certain movements, stiffness after sitting, or a knee that simply does not move the way it used to.
Common symptoms include:
- Pain with walking or prolonged standing
- Difficulty going up or down stairs
- Pain getting up from a chair
- Stiffness after sitting or first getting up
- Swelling around the knee
- Loss of the ability to fully straighten the knee
- Difficulty bending the knee
- Grinding, catching, or crunching sensations
- Increasing difficulty with exercise, travel, work, or everyday activities
Where does it hurt?
The location of pain can sometimes give us clues about which part of the knee is most affected.
Arthritis on the inner side of the knee often causes medial knee pain. Arthritis on the outer side can cause lateral pain. Arthritis behind the kneecap may be especially noticeable with stairs, squatting, or getting up from a chair.
But symptoms do not always follow a perfect map. An arthritic knee may simply feel painful throughout the joint.
Can arthritis change the shape of the knee?
Yes. As arthritis progresses, some knees gradually become more bow-legged or knock-kneed. The knee may also lose motion and develop a flexion contracture, meaning it no longer fully straightens.
These changes can alter the way you walk and place additional stress on the surrounding muscles and joints.
Diagnosis
How is knee arthritis diagnosed?
Most of the time, diagnosing knee arthritis does not require an MRI.
I usually start with three things: your story, your examination, and standing X-rays.
Your symptoms matter
I want to know where the knee hurts, what activities make it worse, how long it has been bothering you, and what you have stopped doing because of it.
I also want to know what treatments you have already tried and whether they actually helped.
The examination matters
During the examination, I look at your walking pattern, alignment, swelling, tenderness, range of motion, stability, strength, and where movement reproduces your pain.
We also make sure the symptoms really seem to be coming from the knee. Hip problems, back problems, nerve irritation, and other conditions can sometimes cause pain that is felt around the knee.
Do I need an MRI?
Usually not when the question is whether you have established knee osteoarthritis.
Weight-bearing X-rays often provide the information we need. An MRI can be useful when the diagnosis is unclear or when we suspect a different problem that would change treatment.
In a knee that already has advanced arthritis on X-ray, an MRI often identifies additional findings — such as meniscus tears — without changing the underlying problem or treatment plan.
Understanding Imaging
What do my knee X-rays mean?
Cartilage does not show up directly on a standard X-ray. Instead, we look at the space between the bones as an indirect measure of how much cartilage remains.
As arthritis progresses, several changes may appear.
Joint-space narrowing
When cartilage becomes thinner, the visible space between the bones becomes smaller. In advanced arthritis, that space can disappear almost completely — what patients often hear described as "bone-on-bone" arthritis.
Bone spurs
The medical term is osteophytes. These are areas of additional bone that can form around an arthritic joint.
Hardening of the bone
You may hear the word sclerosis. This refers to increased density of the bone beneath the damaged joint surface.
Cysts
Small cyst-like changes can develop in the bone beneath the joint surface as arthritis advances.
Changes in alignment
Loss of cartilage can occur unevenly. Over time, this may contribute to bow-legged or knock-kneed alignment.
How I Think About It
We treat the patient, not the X-ray.
An X-ray can tell me how the joint looks. It cannot tell me how much the knee is interfering with your life.
I want the imaging, examination, symptoms, and your goals to tell the same story before we make a major treatment decision.
Treatment
What can I do about knee arthritis?
Having arthritis does not automatically mean you need a knee replacement.
If your symptoms are manageable, there are several nonsurgical options that can help reduce pain and keep you moving.
Stay active
Exercise is one of the foundations of knee arthritis treatment. The goal is not to completely rest the knee. It is to find forms of activity that you can tolerate and maintain.
Walking, cycling, swimming, water exercise, and other low-impact activities can be useful depending on your symptoms.
Strengthening and physical therapy
Strong muscles around the hip and knee help support the leg. A home exercise program or formal physical therapy can improve strength, motion, balance, and function.
Physical therapy cannot regrow missing cartilage, but it can help you function better with the joint you have.
Weight management
If you are carrying excess weight, even modest sustained weight loss can reduce the load placed across the knee and may improve pain and function.
This is not about blaming someone for having arthritis. It is one tool we can use to reduce stress on a painful weight-bearing joint.
Anti-inflammatory medication
Topical or oral nonsteroidal anti-inflammatory medications may help with pain when they are medically safe for you.
They are not appropriate for everyone, particularly patients with certain kidney, stomach, heart, bleeding, or medication issues. Your physician can help determine whether they are appropriate for you.
Braces and a cane
A knee brace may help some patients, particularly when arthritis is concentrated in part of the knee. A cane can also decrease stress on a painful knee and improve mobility.
Corticosteroid injections
A corticosteroid injection can provide short-term pain relief for some patients. The amount and duration of relief vary from person to person.
An injection does not reverse the arthritis. I think of it as a tool for controlling symptoms when that tool makes sense for the individual patient.
What about gel injections?
Hyaluronic acid injections — often called gel injections — are sometimes used for knee arthritis. Current orthopedic guidelines do not recommend them for routine treatment because the average clinical benefit has been inconsistent.
Do I have to try everything before considering surgery?
No. Treatment should make sense for the individual patient.
Nonsurgical treatment is appropriate when it is helping you maintain an acceptable quality of life. The goal is not to accumulate a checklist of treatments simply so you can say that you failed them.
If these treatments are keeping you comfortable and active, that is a success. If they are no longer doing that, it may be reasonable to discuss what comes next.
Making the Decision
When is it time to consider knee replacement?
There is no single X-ray, pain score, or age that tells every patient when it is time for knee replacement.
I generally want several pieces of the picture to line up:
- Your symptoms are consistent with the arthritic knee
- X-rays show arthritis significant enough to explain those symptoms
- Pain or stiffness is meaningfully limiting your quality of life
- Reasonable nonsurgical treatments are no longer giving you acceptable relief
- You understand what knee replacement can and cannot do
- You feel ready to proceed with surgery
You do not have to wait until you can barely walk.
I do not think the goal is to prove how much pain you can tolerate.
At the same time, knee replacement is major surgery and should not be performed simply because an X-ray shows arthritis.
The right time is when the arthritis is affecting your life enough that the expected benefit of surgery makes sense to you after considering the alternatives and risks.
A Useful Question
How much of your life are you changing because of your knee?
Have you stopped walking for exercise? Avoided stairs? Turned down a trip? Stopped golfing? Changed how you shop? Started planning your day around where you can sit down?
Those changes often tell us more about the real impact of arthritis than a pain score alone.
What does knee replacement actually do?
A knee replacement removes the damaged joint surfaces and replaces them with artificial components designed to create a stable, smoothly moving joint.
The goal is to relieve arthritic pain, improve function, and help you return to activities that knee arthritis has made difficult.
If you are considering surgery, the next step is understanding what the operation actually involves.
Common Questions
Frequently asked questions
Does bone-on-bone arthritis mean I need surgery?
No. It means the cartilage loss is advanced in that part of the knee. Whether you need surgery depends on your symptoms, function, examination, goals, and whether nonsurgical treatment is still giving you an acceptable quality of life.
Can cartilage grow back?
Established osteoarthritis does not currently have a treatment that reliably restores the knee to normal cartilage. Many treatments can improve symptoms, but they do not reverse advanced arthritis.
Do I need an MRI before knee replacement?
Usually not. If standing X-rays already show advanced arthritis and the symptoms and examination fit, an MRI often does not add information that changes the treatment plan.
My MRI says I have a torn meniscus. Is that the problem?
It depends. Meniscus tears become increasingly common as a knee becomes arthritic and may be part of the overall degenerative process rather than a separate problem that needs to be fixed.
The imaging has to be interpreted in the context of your age, symptoms, examination, and the amount of arthritis already present.
Will a knee injection make the arthritis worse?
A corticosteroid injection is used to reduce symptoms, not to cure arthritis. Like any treatment, injections have potential benefits and risks, and the timing and frequency should be discussed with your physician.
Am I too young or too old for knee replacement?
Age is only one part of the decision. Younger patients have more years in which an implant could eventually wear or require revision, while older patients may have additional medical considerations.
The decision is better based on the severity of the arthritis, its impact on your life, your overall health, and the expected benefit of surgery rather than an arbitrary birthday.
Key Takeaways
What I want you to remember
- Knee arthritis is the progressive loss and deterioration of the cartilage within the knee joint.
- Arthritis can affect one part of the knee or several compartments.
- Standing X-rays are usually more useful than MRI for evaluating established knee arthritis.
- The severity of an X-ray does not automatically determine how much treatment you need.
- Exercise, strengthening, medication, weight management, braces, walking aids, and injections can help selected patients manage symptoms.
- Knee replacement becomes reasonable when arthritis is significantly affecting your life and nonsurgical treatment is no longer providing acceptable relief.