Why Does One Knee Hurt More Than the Other?

One knee can hurt more than the other because the two joints may differ in arthritis severity, alignment, inflammation, muscle support, previous injury or daily loading. Even similar X-rays do not guarantee similar symptoms. Each knee should therefore be assessed separately before deciding whether both need the same treatment.

Why Does One Knee Hurt More Than the Other?

The knees look like a matched pair, but they do not have identical histories. A past injury may affect one side, one leg may be weaker, alignment may differ, and people often shift weight unconsciously. Pain also reflects inflammation and nervous-system sensitivity, not only the amount of cartilage visible on an X-ray.

Arthritis Can Be Uneven

Osteoarthritis may narrow one compartment of one knee more than the other. One side may also have more swelling, bone change or loss of movement. The NIAMS osteoarthritis overview describes osteoarthritis as a condition affecting the whole joint, including cartilage, bone, synovium, tendons, ligaments and the knee meniscus.

Imaging is only one part of the assessment. A knee with more severe radiographic change may sometimes be less painful than the other. Treatment should be based on symptoms, function, examination, alignment and imaging together. See the staged knee arthritis treatment pathway for that decision process.

Alignment Changes the Load

Bow-leg alignment tends to increase load through the inner knee, while knock-knee alignment may increase load through the outer knee. If deformity is greater on one side, standing and walking may provoke more symptoms there. Weight-bearing X-rays are often more informative than lying-down images when alignment and compartment narrowing are relevant.

Strength, Gait and Compensation

Pain can reduce use of one leg, which then loses strength and control. The other leg may compensate and eventually become overloaded. Assessment should compare both sides: quadriceps and hip strength, chair rise, walking pattern, balance and stair control.

A progressive programme may improve support and confidence when weakness or deconditioning is important. The guide to physiotherapy for knee pain explains when rehabilitation helps and when a lack of progress should trigger reassessment.

Previous Injury and Local Knee Problems

• An old fracture may have altered alignment or joint congruity.

• A previous ligament injury may leave instability.

• A meniscus or cartilage injury can affect one compartment more than the other.

• Kneecap tracking and patellofemoral load may differ between sides.

• A recent twist or fall may cause a new problem superimposed on existing arthritis.

Not every meniscus finding on MRI is the source of pain, particularly in adults with osteoarthritis. The history and examination should determine whether an imaging finding matches the patient’s actual symptoms.

The Pain May Come From Outside the Knee

Hip disease, lower-back problems and nerve irritation can refer pain toward the knee. Vascular problems and some systemic conditions can also mimic musculoskeletal pain. A clinician may therefore examine the hip, spine, circulation and neurological function when knee findings do not fully explain the symptoms.

What the Assessment Should Compare

• Pain location, onset and provoking activities in each knee.

• Swelling, warmth, stiffness, locking and instability.

• Range of movement and tenderness.

• Leg alignment and walking pattern.

• Strength and functional tasks such as stairs and chair rise.

• Weight-bearing X-rays when clinically appropriate.

• The response of each knee to previous exercise, medication or injections.

This side-by-side comparison prevents a common error: assuming that both knees require identical treatment merely because both show arthritis.

Does the More Painful Knee Need Surgery?

Not automatically. Many patients begin with education, activity modification, appropriate exercise, weight management where relevant and selected medicines. Injections may have a role for some people but do not reliably rebuild cartilage. Knee replacement is considered when pain and functional limitation remain unacceptable, the diagnosis is clear, imaging supports the problem and appropriate non-surgical care has not provided sufficient relief.

If surgery is being discussed, the knee replacement guide explains candidacy and shared decision-making. The less painful knee may need observation or non-surgical care even when it also shows arthritis.

When Unequal Knee Pain Needs Prompt Review

Seek urgent assessment after major trauma, or for inability to bear weight, an obvious deformity, a genuinely locked knee, a hot red swollen joint, fever or feeling systemically unwell. New calf swelling, chest pain or breathlessness also requires urgent medical attention.

The Practical Takeaway

Why one knee hurts more than the other is usually explained by a combination of structure, alignment, inflammation, strength and loading. Treat each knee according to its own symptoms and functional impact. A precise diagnosis is more useful than assuming that the worse-looking X-ray must be the worse knee.

Medical Review and References

Medically reviewed by Dr. Mayur Rabhadiya, orthopedic and joint replacement surgeon in Mumbai. Last reviewed: 16 July 2026.

• NICE NG226: Osteoarthritis in over 16s—diagnosis and management.

• NIAMS: Osteoarthritis overview.

• NHS: Knee pain and urgent warning signs.

This article provides general information and does not replace an individual orthopedic assessment.