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Knee pain when bending: common causes and what helps

Written by Elliot Stubbs, BSc (Hons) Physiotherapy, 13 years in MSK practice. Updated 14 October 2026.

Knee pain when bending or squatting is most often caused by irritation around the kneecap (patellofemoral pain), a sore tendon, wear-related changes such as osteoarthritis, or irritation of the meniscus, the cartilage cushion inside the joint. Where the pain sits gives useful clues, and most of these problems respond well to the right exercise. Swelling that appears quickly, a knee that locks, or one that gives way are the signs that need a proper assessment sooner.

Why does my knee hurt when I bend it?

Bending the knee under body weight, in a squat, on stairs or getting up from a low chair, puts a lot of pressure behind the kneecap and through the tendons at the front of the knee. If any of these structures are irritated, or not yet strong enough for what you're asking of them, bending is where you feel it first.

Often there's no single injury, just a change in activity, such as a new exercise class, more running, or a weekend of kneeling for DIY. So the answer is usually rebuilding the knee's capacity, not protecting it forever.

What does the location of the pain tell you?

Location isn't a diagnosis, but it helps.

Front of the knee

An ache around or behind the kneecap, worse with squats, stairs and after sitting with your knees bent, is typical of patellofemoral pain, often called runner's knee. Pain in one spot just below the kneecap, especially with jumping, points more towards the patellar tendon, which joins the kneecap to the shin. See our guide to runner's knee for more.

Inside of the knee

Pain along the inner joint line, sometimes with catching, twisting pain or discomfort in a deep squat, can come from the meniscus. In people over about 45, a gradual ache here with morning stiffness is often linked to osteoarthritis, which commonly affects this side of the knee first.

Outside of the knee

Pain that appears at a consistent point into a run or ride is often linked to the iliotibial band (ITB), a thick band of tissue down the outside of the thigh. The outer meniscus can also hurt here, usually after a twist.

Back of the knee

Tightness or fullness behind the knee on full bending is sometimes a Baker's cyst, a fluid-filled swelling that usually reflects something else in the joint, such as arthritis or a meniscus problem. New pain, swelling and warmth in the calf is different and needs prompt medical advice (see below).

Does it matter if your knee swells, locks or gives way?

• Swelling. Swelling within a few hours of a twist or impact can mean bleeding inside the joint, seen with some ligament injuries, and needs assessing promptly. Swelling that builds gradually, often the next day, is more typical of an irritated joint or meniscus.
• Locking. A brief catch that frees itself is common. True locking, where the knee gets stuck and won't fully straighten, can mean a piece of meniscus is caught and should be assessed.
• Giving way. Occasional buckling from pain or weak thigh muscles usually improves with strengthening. Repeated giving way after a twisting injury, especially with a pop at the time, can point to a ligament injury.

Safe self-checks you can do at home

These won't tell you exactly what's wrong, but they give you, and a physiotherapist, useful information:

• Is one knee more swollen or warmer than the other?
• Can you straighten and bend the sore knee as fully as the other?
• Note which movements bring it on: stairs, squatting, kneeling, or long spells of sitting.
• Notice how it behaves over 24 hours. Pain that settles by the next morning is a different picture from a knee that's stiffer and more swollen the next day.

There's no need to force a deep squat or twist the knee to test it.

What can you do now to ease knee pain when bending?

Complete rest eases pain for a while, but leaves the knee less able to cope when you return to normal activity. A better approach is to find a level the knee tolerates:

• Reduce rather than stop. Squat to a shallower depth, use a handrail on stairs, and break up long spells of sitting.
• Keep moving. Walking on flat ground, swimming or cycling with the saddle raised slightly are often well tolerated.
• Start gentle strengthening. Straight-leg raises, shallow wall sits or sit-to-stands from a higher chair keep the thigh muscles working.
• Use a simple pain guide. Mild discomfort that settles within 24 hours is generally fine. Pain that's sharp, keeps climbing or is worse the next day means ease back a step.
• Comfort measures. Ice or heat can help short term, and a pharmacist can advise on pain relief.

How does physiotherapy help knee pain?

An assessment works out what's most likely driving the pain and screens for anything that needs a different route. Most knee problems don't need a scan.

• A clear explanation, so you know what's safe to keep doing
• Progressive strengthening of the thigh, hip and calf muscles
• Gym-based rehab, such as leg press, split squats and step-downs, progressed as the knee improves
• Hands-on treatment where it helps ease pain and stiffness short term
• Activity changes while things settle, and a plan back to what matters to you

Sessions are 1:1 in a fully equipped gym. If your knee isn't progressing, or the assessment suggests something more significant, you'll be advised to see your GP, who can arrange further tests or a specialist opinion on other options such as injections or surgery.

How long does knee pain when bending take to settle?

It depends on the cause and how the knee responds. As a rough guide, kneecap pain and meniscus irritation without locking often improve over several weeks to a few months of consistent exercise. Tendon problems tend to be slower, often three months or more. Arthritis pain tends to flare and settle, so the aim is long-term management with strength and activity rather than a one-off fix.

Knee pain physio in Wymondham

If you're in Wymondham, Norwich or South Norfolk and your knee has been sore when bending for more than a couple of weeks, or keeps flaring up, an assessment gives you a clear plan. Appointments are Tuesday evenings, 6:15pm to 9:00pm, at Suggs Gym. An initial assessment is £65 for 45 minutes, follow-ups £55 for 30 minutes (see pricing). No GP referral is needed, so you can book directly or call 07730 013625.

Frequently asked questions

This guide is general information written by a physiotherapist, not a substitute for individual assessment. If you have any of the warning signs above, seek medical help promptly.