knee pain on one side

Overview

Knee pain on one side (sometimes called unilateral knee pain) means discomfort, aching, or soreness felt in just one knee — on the inner side, outer side, behind the knee, or around the kneecap. The pain can range from a mild twinge to severe pain that makes it hard to put weight on the leg.

Yes. Knee pain is one of the most common joint complaints. It affects people of all ages and can happen after an injury, with overuse, or as a result of wear-and-tear.

It affects everyone, but the pattern is different by age. Young and active people often get pain from sports injuries. Older adults are more likely to notice gradual wear-and-tear changes. Children can also develop knee pain from overuse or growth-related conditions.

Symptoms

Common symptoms

• Pain on the inner or outer side of the knee, sometimes behind it
• Swelling, stiffness, or a feeling of tightness in one knee
• A catching, clicking, or grinding sensation when bending the knee
• Pain that gets worse with stair climbing, squatting, running, or prolonged sitting
• The knee feeling unstable, as if it might give way
• Tenderness when you press on the area

Symptoms in children

• A limp, or avoiding putting weight on one leg
• Pain that comes and goes during or after sport
• Swelling or bruising after a knock or fall
• Waking up during the night with knee pain

Symptoms in older adults

• A deep ache on the inner knee, often worse after activity
• Stiffness in the morning that eases after about 30 minutes
• A grating or grinding feeling when moving the knee
• Swelling that appears after walking more than usual

Causes

Main causes

• Ligament injuries: a sprain or tear of one of the knee’s side ligaments (the MCL or LCL) from twisting, a blow, or a sudden stop.
• Meniscus tears: damage to the wedge-shaped cartilage that cushions the knee, usually from a twisting movement while the foot is planted.
• Osteoarthritis: gradual thinning and wear of joint cartilage, often causing pain on the inner side of the knee in middle-aged and older people.
• Bursitis: inflammation of a fluid-filled sac near the knee, often from prolonged kneeling or kneeling on hard surfaces.
• Tendonitis: inflammation of a tendon, such as the patellar tendon, from repeated overuse or jumping.
• Iliotibial (IT) band friction: a tight band on the outside of the thigh rubbing against the knee, common in runners and cyclists.

Risk factors

• Being over 40
• Being overweight or carrying extra weight
• Participating in sports that involve jumping, pivoting, or sudden stops
• Jobs or hobbies with lots of kneeling, squatting, or climbing stairs
• Previous knee injury or surgery
• Weak thigh, calf, or hip muscles
• Worn-out or poorly fitted footwear

When to see a doctor

See a doctor urgently if:

• You cannot put any weight on the knee.
• The knee is red, hot, or severely swollen — with or without fever.
• You have had a previous knee replacement and then develop pain or swelling on that side.
• You are on blood-thinning medication and have a painful swollen knee after an injury.

Book a routine appointment if:

• Pain lasts more than two weeks despite simple self-care.
• The pain is getting worse or waking you from sleep.
• The knee gives way, catches, or locks repeatedly.
• You are 50 or older and have ongoing knee pain and stiffness starting gradually.

Diagnosis

A doctor will ask when the pain started, how it happened, and what makes it better or worse. They will compare both knees and check for swelling, tenderness, range of movement, and stability. This examination, along with your medical history, often gives a very clear picture of the cause.

Tests that may be done

• X-ray: helps look for arthritis, bone damage, or loose pieces of bone.
• Ultrasound: can show fluid, bursitis, or problems in tendons near the knee.
• Magnetic resonance imaging (MRI): creates detailed images of ligaments, cartilage, and other soft tissues, and is used when an internal injury is suspected.
• Blood tests: may be used to check for inflammatory arthritis or infection.
• Joint aspiration: a small sample of knee fluid is drawn out with a needle in rare cases, to check for infection, gout, or other crystal-related problems.

What to expect at your appointment

You should get a clear idea of the likely cause and a treatment plan at your first appointment. If there is still uncertainty, you may be referred for tests or to a physiotherapist or orthopaedic specialist. Most knee problems do not require surgery, and many people start feeling better within a few weeks.

Treatment

Treatment usually starts with conservative measures — meaning simple steps to reduce pain and let the knee settle. The plan almost always includes protecting the knee, using cold packs, and gradually building up movement and strength. Surgery is rarely the first option.

Self-care at home

• Rest the knee from painful activities for 24–48 hours, but try gentle movement as soon as possible.
• Use a cold pack wrapped in a towel for 10–15 minutes, several times a day, during the first two days.
• Elevate the leg on a stool or cushions to help reduce swelling.
• Wrap an elastic bandage or use a light knee sleeve for support during the day, but remove it at night.
• Try to keep a pain-free range of motion: sit on a chair and gently straighten and bend the knee.
• Avoid high-impact activities until the pain settles — swimming, cycling, and walking on flat ground are gentler.

Medical treatments

If self-care is not enough, a healthcare professional may recommend a structured physiotherapy programme to strengthen the muscles around the knee and improve balance. They might also suggest a walking aid, a supportive sleeve or brace, or a course of anti-inflammatory treatment that is applied to the skin or taken by mouth, if appropriate for you. In some cases, a doctor may offer a corticosteroid injection to reduce inflammation — this is always discussed and agreed with you first. Your doctor, pharmacist, or physiotherapist can explain what is suitable and safe for your specific situation.

When is surgery considered?

Surgery is considered only when other treatments have not worked, or when there is a major injury such as a complete ligament tear or a locked meniscus. If an operation is proposed, an orthopaedic surgeon will explain exactly what would be done, the expected recovery time, and the risks. Many people with even significant knee pain avoid surgery by following a good rehabilitation plan.

Living with this condition

Living with knee pain on one side means working with the knee rather than against it. Use a steady (hand) rail on stairs, avoid kneeling on hard floors, and take brief rest breaks during long standing tasks. Plan activities so you alternate sitting and moving, and let pain guide you — if an activity pushes the knee into ache, take a break and do something gentler.

Lifestyle tips

• Keep moving every day, even if it is only a short walk around the house.
• Choose low-impact activities such as swimming, stationary cycling, or chair-based exercises.
• Aim for a healthy weight — losing even a small amount of weight can reduce knee load.
• Wear supportive shoes with good cushioning and flat, flexible soles.
• Do the exercises a physiotherapist gives you — even after symptoms improve, this helps prevent recurrence.

Diet and exercise

No diet cures knee pain, but a balanced diet supports tissue healing and helps you maintain a healthy weight. Include plenty of vegetables, fruit, lean protein, whole grains, and water. Regular gentle exercise avoids stiffness and strengthens the muscles that protect the knee. If you have a condition like gout, your doctor may advise specific dietary changes, but do not cut out foods before speaking to them.

Mental health and emotional wellbeing

Living with pain can be exhausting and frustrating, and it is completely normal to feel anxious or low at times. Try to keep connections with family and friends, share how you feel, and ask your healthcare team about psychological support if the pain is affecting your mood. In a crisis, always reach out: contact your local mental health crisis service or call your local emergency number — you do not have to cope alone.

Prevention

You cannot prevent every knee injury, but you can greatly reduce your risk. Strengthen the muscles around your knees (thighs, calves, and hips), warm up properly before sport, use good technique, and increase training loads gradually. If you already have knee pain, staying at a healthy weight and keeping active protects the joint from further strain.

Vaccines

There is no specific vaccine for knee pain. However, staying up to date with routine vaccinations is part of overall health and can help prevent infections that might occasionally spread to a joint.

Screening programmes

There is no national screening test for knee pain. If you know you have osteoarthritis or another joint condition, regular check-ups with your doctor and a personalised exercise plan are the best way to monitor things.

Complications

If left untreated

• Repeated 'giving way' episodes, which make falls more likely.
• Long-term muscle weakness and stiffness in the affected leg.
• A torn meniscus may fail to heal and can cause the knee to lock or lead to increased arthritis over time.
• Untreated joint infection or major injuries can permanently damage the knee.

Long-term outlook

The outlook is generally positive. Most knee pain on one side — even if it takes weeks to fully settle — improves with simple measures and rehabilitation. For longer-term conditions like arthritis, the aim is to manage symptoms, keep you moving, and protect the joint for as long as possible. Many people live active, comfortable lives with the right support.

Find support

International organisations

• Versus Arthritis ↗
• Arthritis Foundation ↗

Local organisations

• NHS UK – Knee pain information ↗ · United Kingdom

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