Osteoarthritis

Written by Dr Sheila Strover on March 14, 2025

Osteoarthritis of the knee is the most common form of knee arthritis.

Sketch of the knee joints showing bone-on-bone contact where joint cartilage has been lost.
The circled area shows where the joint cartilage covering of the bones has worn away, and now there is 'bone-on-bone' (which leads to osteoarthritis).
X-ray to show how one side of the knee joint has lost joint cartilage and is now 'bone-on-bone'.
X-rays normally show the joint cartilage as a 'space' between the bones, as cartilage does not usuallty show up on X-ray. You can see on the one side that the cartilage spacer has disappeared, and the joint is now 'bone-on-bone.

Symptoms of knee osteoarthritis

Osteoarthritis begins with breakdown of the joint cartilage at the ends of the bones.

Classical symptoms include pain at rest, reduced exercise tolerance, joint swelling and eventual joint deformity.

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Diagnosing osteoarthritis of the knee

Usually knee osteoarthritis begins in one part of the knee (what we call a 'compartment'), such as the contact area between femur and tibia on the one side. Only later does it tend to progress to involve the other compartments.

This gives the patient the option to try to arrest progression by suitable intervention, such as wearing an unloader brace or having a uni-compartmental knee replacement.

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Photograph taken during arthroscopy to show destruction of the joint cartilage.
Joint surfaces of tibia and femur within the knee joint, showing Grade IV damage.

If one looked inside the joint via arthroscopy one would see damage to the usually silky joint cartilage breakdown.

Classical imaging signs include joint line narrowing, bone spurs, bone cysts and areas of increased bone density (sclerosis).

The concept of compartmental arthritis

The bones of the knee actually have three areas of articulation, not one. The two rounded condyles of the femur make articulate separately with the flattened tibia.

The kneecap or patella has a third area of articulation with the femur. Each of these is really a separate 'joint', which we call a 'compartment'. Arthritis may initiate at different times in these compartments, depending upon those factors that have triggered it off, such as a damaged meniscus just on the one side.

So it is helpful if the surgeon can intervene and improve function in the one compartment, before the changed mechanics of the knee causes arthritis to affect the other compartments also.

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How is knee osteoarthritis managed?

Doctors tend to take different approaches in the management of osteoarthritis depending on their particular line of interest:

For example, a general practitioner may tend to look at general factors such as weight and diet, a rheumatologist may prescribe anti-inflammatories, including steroids, and knee surgeons tend to take a mechanical approach and try and sort out any structural problems. 

Early osteoarthritis is managed conservatively with anti-inflammatory medications, removal of fluid in the joint and injections into the knee. As deformity progresses, minor procedures might be performed, such as removal of bone spurs, but later deformities may be indications for osteotomy, unicompartmental knee replacement or total knee replacement.

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The Clinical diagnosis of knee osteoarthritis is "Knee pain for most days of the prior month, in addition to at least 3 of the following:

- crepitus on active joint motion

- morning stiffness less than 30 minutes’ duration

- age older than 50 years

- bony enlargement of the knee on examination

- bony tenderness of the knee on examination

- no palpable warmth."

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