What Is Knee Osteoarthritis?

Knee osteoarthritis (OA) is a degenerative joint condition where the protective cartilage between the bones gradually wears down. As cartilage thins, the bones begin to rub together, causing pain, stiffness, swelling, and reduced mobility. OA is progressive — meaning symptoms typically worsen over time — but the rate of progression varies widely from person to person.

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OA is extremely common in adults over 45 and is one of the leading causes of knee pain during walking, standing, and daily activities.

The 4 Stages of Knee Osteoarthritis

Stage 1: Early Wear
Small cartilage changes, occasional mild discomfort.

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Stage 2: Mild OA
Cartilage thinning becomes visible on X-ray; symptoms appear during activity.

Stage 3: Moderate OA
Cartilage significantly worn; daily activities like walking or stair climbing become painful.

Stage 4: Severe OA
Very little cartilage left; bone-on-bone contact; pain can occur even at rest.

Common Causes of Knee OA

• Age-related wear

• Previous knee injuries (meniscus, ACL, MCL)

• Repetitive heavy activity or long-term sports

• Genetics and joint shape

• Obesity

• Joint misalignment (bow-leg/varus or knock-knee/valgus)

Medial vs Lateral vs Patellofemoral OA

Medial Compartment OA (most common)

Pain on the inside of the knee; often linked to bow-leg alignment (varus).

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Lateral Compartment OA

Pain on the outer side of the knee; often linked to knock-knee alignment (valgus).

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Patellofemoral OA

Pain around or behind the kneecap; worse with stairs, squatting, or sitting long periods.

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What Is Tricompartmental Osteoarthritis?

Tricompartmental OA affects all three compartments of the knee — medial, lateral, and patellofemoral.

This type is more advanced and often leads to:

• stiffness throughout the knee

• reduced mobility

• difficulty walking long distances

• pain during all weight-bearing activities

Because the entire knee is involved, offloading braces and stabilizers become essential for pain reduction and mobility.

Most Common Symptoms of Knee OA

• Morning stiffness

• Pain during walking or prolonged standing

• Swelling after activity

• Clicking or grinding sensations

• Difficulty climbing stairs

• Pain when straightening or bending the knee fully

• Locking or instability

Why Knee OA Pain Gets Worse at Certain Times

Morning Pain

Stiffness after inactivity due to inflammation buildup overnight.

Pain Walking or Standing

Weight-bearing increases joint compression on areas where cartilage has worn down.

Pain Going Up or Down Stairs

Knee joint forces increase 2–4× during stair climbing.

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Pain After Sitting

“Start-up pain” occurs when stiff tissues suddenly move again.

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Pain During Cold Weather

Temperature changes can affect joint fluid and inflammation levels.

Night Pain

Inflammation peaks after a full day of activity, causing discomfort before sleep.

How Knee OA Is Diagnosed

Doctors usually diagnose OA using:

• Medical history and symptom review

• Physical exam

• X-rays (to check cartilage space, bone spurs, alignment)

• MRI (only if other injuries are suspected)

When To Seek Medical Evaluation

• Sudden knee swelling

• Severe instability or buckling

• Sharp locking pain

• Symptoms worsening quickly

• Unsure whether symptoms are OA or something else

(General educational information — not medical advice.)

Non-Surgical Treatments That Help OA

These methods can reduce pain and slow progression:

Weight Management

Even 10 lbs of extra weight adds ~40 lbs of pressure on the knee joint.

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Physical Therapy

Strengthens supporting muscles to reduce joint load.

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Low-Impact Exercise

Walking, cycling, swimming.

Medications

NSAIDs, topical creams, supplements like turmeric or glucosamine.

Bracing

Re-distributes joint forces to reduce pain (covered in detail below).

Injections

• Cortisone

• Hyaluronic acid

• PRP (varies by patient)

When Surgery Is Considered

• Partial knee replacement

• Total knee replacement

Surgery is usually a last resort when symptoms severely limit quality of life.