How to Get Your Knee Straight After Knee Replacement
- Tom Morgan, Chartered Physiotherapist
- Aug 9
- 3 min read
Regaining full knee straightening after a total knee replacement is just as important as getting the knee bending again.
A knee that remains slightly bent during standing and walking can change your gait, increase the work required from the quadriceps and make everyday mobility feel more tiring. This is why extension receives such a strong emphasis in the first weeks.
Why does the knee struggle to straighten?
Swelling, pain, hamstring tightness and quadriceps inhibition can all make the knee rest in a slightly flexed position. Some people also go into surgery already lacking full extension because of long-standing arthritis.
Why extension matters for walking
During normal walking, the knee needs to straighten as the foot contacts the ground and the body moves over the leg. If it remains bent, you may develop a persistent limp or feel as though the leg never fully supports you.
Early extension is important
The handbook prioritises near-full passive extension from the first days after surgery and aims for full or very close to full active extension during the early weeks.
This is because a persistent extension deficit can become more difficult to change once the tissues settle.
Avoid keeping a pillow directly under the knee
A pillow directly under the knee can feel comfortable, but it encourages the joint to remain bent. When elevating the leg, the guide instead suggests supporting under the calf and ankle so the knee can rest straighter.
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Quadriceps activation
Quadriceps sets help restore the muscle's ability to actively straighten and stabilise the knee. Tighten the front of the thigh and gently press the knee towards the bed or floor, holding briefly before relaxing.
Quality of contraction is more important than simply completing a large number of repetitions.
Heel prop or passive extension work
Some rehabilitation programmes use a heel prop, where the ankle is supported and the knee is allowed to relax towards straight. This should be performed according to your physiotherapy advice and stopped once full extension is consistently achieved.
Terminal knee extension
As strength improves, resisted terminal knee extension can help train the final part of straightening in a more functional standing position. This is typically introduced later than the very early static exercises.
Do not force through sharp pain
A stretch or muscular effort is expected. Sharp pain is not a target. If extension work repeatedly causes a major flare in pain or swelling, the exercise dose or technique may need reviewing.
When should you get help?
If you still have a meaningful extension deficit and it is not improving, speak to your physiotherapist. A worsening limp, rapidly increasing stiffness or loss of movement that you previously had should also be reviewed.
When should you seek further advice?
Recovery is rarely a perfectly straight line, but new or rapidly worsening symptoms should not simply be pushed through. Contact your surgical team, GP or physiotherapist if pain, swelling, movement or function is moving in the wrong direction rather than gradually improving. Seek urgent medical attention for symptoms such as sudden breathlessness or chest pain, marked one-sided calf swelling, a hot increasingly red joint with fever, sudden loss of function, or other symptoms your surgical team has told you require urgent review.
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This article provides general information and does not replace advice from your own surgeon, physiotherapist or medical team. Recovery varies between individuals and any specific restrictions or weight-bearing instructions from your surgical team should take priority.
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