Knee Replacement Surgery: Understanding Your New Knee and What to Expect During Recovery
Knee replacement surgery can make a significant difference to people whose lives have been restricted by knee pain. Walking, climbing stairs, getting out of a chair and enjoying everyday activities can become increasingly difficult when osteoarthritis damages the knee joint. When other treatments no longer provide sufficient relief, a knee replacement may offer an opportunity to improve mobility, reduce pain and regain independence.
However, having a knee replacement is a major operation, and recovery can be more challenging than people expect. It is not unusual to experience considerable pain, swelling and stiffness in the early weeks, even though the damaged arthritic surfaces have been replaced. Some people are surprised that their new knee can feel worse initially than the knee they had before surgery. It is often something that does not get explained to patients enough, prior to their surgery.
In this article, I will explain what happens to the knee in osteoarthritis, the differences between total and partial knee replacements, how the operation affects the ligaments and kneecap, and why your new knee needs time to recover. I will also cover practical advice on managing swelling, regaining movement and understanding the timescales involved in rehabilitation.
1. Understanding osteoarthritis of the knee
Osteoarthritis is a condition affecting the whole joint, rather than simply the wearing away of cartilage. The knee is formed by the thigh bone (femur), shin bone (tibia) and kneecap (patella). The ends of these bones are covered with articular cartilage, a smooth, resilient tissue that helps the joint move with minimal friction and distributes forces during activities such as walking and climbing stairs.
With osteoarthritis, the cartilage gradually changes and may become thinner or damaged. The underlying bone can remodel, small bony growths called osteophytes may develop, and the joint lining can become inflamed. The joint may produce excess fluid, leading to swelling, stiffness and pain. The muscles around the knee can also become weaker because pain makes it harder to remain active and use the leg normally.
Osteoarthritis does not affect everyone in the same way. Some people have considerable changes on an X-ray but relatively few symptoms, while others experience substantial pain and disability. Symptoms can fluctuate, with periods when the knee feels reasonably comfortable followed by flare-ups of pain and swelling.
Treatment initially focuses on managing symptoms and maintaining function through appropriate exercise, strengthening, activity modification and pain relief where suitable. However, if pain and stiffness continue to have a major impact on quality of life despite non-surgical treatment, knee replacement may be considered. The decision should be based on the person's symptoms and circumstances, rather than an X-ray alone.
2. What is a knee replacement?
Despite the name, a knee replacement does not involve removing your entire knee and fitting a completely new joint. It is more accurately described as a resurfacing operation. The surgeon removes the damaged joint surfaces and replaces them with artificial components, usually made from metal and a highly durable medical-grade plastic.
The artificial surfaces are designed to glide against one another as you bend and straighten your knee. The components may be fixed to the bone using bone cement or, in some cases, a design that allows bone to grow onto a specially prepared implant surface.
The aim is to replace the damaged surfaces responsible for much of the arthritis-related pain while restoring a functional, stable joint. However, the surrounding muscles, tendons, ligaments, nerves and other soft tissues remain important to how your new knee works.
There are two main types of knee replacement: total and partial. The most appropriate option depends on which parts of the joint are damaged, the condition of the ligaments, the stability of the knee and other individual factors.
3. Total knee replacement
A total knee replacement replaces the damaged joint surfaces across the main weight-bearing part of the knee. The surgeon removes the worn cartilage and a small amount of underlying bone from the end of the thigh bone and the top of the shin bone. Metal components are fitted to these surfaces, with a plastic insert between them to provide a smooth gliding surface.
The kneecap is moved aside during the operation to allow access to the joint. Depending on the circumstances and the surgical approach, the back of the kneecap may also be resurfaced with a plastic component. The kneecap itself is not removed; it remains in place and continues to move over the front of the artificial knee.
What happens to the ligaments?
This is an important part of understanding how a knee replacement works. Your natural knee relies on four main ligaments for stability: the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL) and lateral collateral ligament (LCL).
During a total knee replacement, the ACL is usually removed. The PCL may be retained or removed, depending on the implant design and the surgeon's approach. In a cruciate-retaining replacement, the PCL is preserved where suitable. In a posterior-stabilised design, the PCL is removed and the shape of the implant helps substitute for some of its stabilising function.
The collateral ligaments on the inner and outer sides of the knee are generally preserved because they are essential for controlling side-to-side movement and maintaining stability. The surgeon balances the soft tissues during the operation so that the knee is stable through its range of movement.
This is why a replacement is not simply a matter of inserting metal and plastic parts. The positioning of the components, the tension of the remaining ligaments and the balance of the surrounding soft tissues all contribute to how the new knee functions.
4. Partial knee replacement
A partial knee replacement is an option for some people whose osteoarthritis is concentrated in one compartment of the knee. The knee has three main compartments: the medial compartment on the inner side, the lateral compartment on the outer side, and the patellofemoral compartment between the kneecap and thigh bone.
If the arthritis is predominantly affecting one compartment, the surgeon may be able to replace just that area while preserving the healthier parts of the joint. For example, someone with advanced arthritis on the inner side of the knee but relatively healthy cartilage elsewhere may be suitable for a medial partial replacement.
Because less of the joint is replaced, a partial knee replacement can preserve more of the knee's natural structures. The ACL and PCL are generally preserved if they are functioning appropriately and the chosen procedure requires them. The collateral ligaments are also retained, and the kneecap is usually left intact because the operation does not routinely replace its joint surface.
A partial replacement may allow a smaller operation and faster early recovery than a total replacement in appropriately selected patients. However, it is not suitable for everyone. The surgeon needs to consider the extent of the arthritis, ligament function, alignment and stability of the knee. Arthritis may also progress in the compartments that have not been replaced, and further surgery may eventually be required.
Neither operation is automatically better. The aim is to choose the procedure most likely to provide a durable improvement in pain and function for that particular knee.
5. Why is knee replacement considered major surgery?
Although knee replacement is a common and well-established operation, it remains major orthopaedic surgery. The surgeon makes an incision at the front of the knee, works around the joint, removes damaged bone and cartilage, prepares the bone surfaces and accurately positions the artificial components.
The procedure affects more than the joint surfaces. The surrounding tissues are handled during surgery, small blood vessels are disrupted, and the body responds to the operation with an inflammatory healing process. The muscles around the knee can also become inhibited by pain and swelling, making it difficult to contract them effectively in the early stages.
The operation commonly takes around one to two hours, although the time varies. Patients are carefully monitored throughout the procedure, and the surgical team considers the risks associated with anaesthesia, bleeding, infection, blood clots, wound healing and other possible complications.
What anaesthetic is used?
Knee replacement can be performed under either a spinal anaesthetic or a general anaesthetic. With a spinal anaesthetic, medication is injected into the fluid surrounding the nerves in the lower back, temporarily numbing the lower half of the body. You may remain awake or be given sedation to help you feel relaxed or sleepy.
With a general anaesthetic, medication puts you to sleep for the operation. The anaesthetist will discuss the options with you and recommend an approach based on your health, preferences and the requirements of the procedure.
Additional pain relief may be provided through a nerve block or local anaesthetic injected around the joint and surrounding tissues. A nerve block temporarily reduces the transmission of pain signals from the area being treated. Some blocks can also temporarily weaken particular muscles, so the team considers this when planning early mobilisation.
These techniques are intended to improve pain control and support recovery, but they do not eliminate all post-operative discomfort. As the anaesthetic and nerve block wear off, pain may become more noticeable, which is why a planned pain-management strategy is important.
6. Why is my new knee so painful when the arthritis has been removed?
This is one of the most common questions people have after knee replacement. It can seem confusing: if the damaged cartilage and arthritic joint surfaces have been replaced, why does the knee still hurt so much?
The key is understanding that the operation removes the damaged joint surfaces, but it also creates a substantial healing process. The pain of osteoarthritis and the pain of recovering from surgery are not the same thing.
Before surgery, much of your pain may have come from the arthritic joint and the surrounding tissues. After surgery, that source of pain has been addressed, but the operation itself causes temporary tissue injury, inflammation and swelling. The skin, underlying tissues, bone and joint structures all need time to heal.
The body's inflammatory response is a normal part of healing. Chemicals released around the operated area make the local pain-sensitive nerves more responsive, so movements that might normally be comfortable can feel painful. Bending the knee stretches tissues that are swollen and healing, while contracting the quadriceps puts tension through the recovering area.
There is also a change in how your muscles work. Pain and swelling can inhibit the quadriceps, making it harder to straighten the knee and control the leg during walking. This can create a frustrating cycle: the knee hurts, the muscles do not work as effectively, movement becomes more difficult, and everyday activities require more effort.
The important message is that pain in the early stages does not necessarily mean the operation has failed or that the new joint is damaged. It often reflects the normal response to major surgery. However, severe or progressively worsening pain, particularly alongside increasing redness, wound problems, fever or rapidly increasing swelling, should not automatically be dismissed as normal recovery.
7. Why does the knee swell after surgery?
Swelling is common after knee replacement because surgery causes inflammation and disrupts small blood vessels and tissues around the joint. Fluid accumulates as part of the healing response, and some of it can move down into the lower leg and ankle under the influence of gravity.
Swelling can persist for weeks and may fluctuate with activity. You may notice that your knee feels more swollen in the evening, after walking or following a session of exercises. It may also feel tighter after sitting for a long period.
This swelling is important because it affects more than the appearance of the knee. Fluid within and around the joint can restrict bending, make straightening more difficult and reduce the ability of the quadriceps to contract effectively. A swollen knee often feels tight and heavy, and movement may become more uncomfortable.
What can you do to manage swelling?
The aim is to reduce unnecessary swelling while continuing to move enough to recover strength and mobility. Helpful strategies include:
Elevate your leg when resting. Support the leg comfortably and, where possible, raise it to help fluid return from the lower limb.
Use a cold pack if appropriate. Wrap it in a thin towel and apply it for around 15–20 minutes, or follow the advice from your surgical team. Never place ice directly on the skin.
Keep moving little and often. Short walks and gentle ankle movements can help maintain circulation, provided you follow your prescribed rehabilitation plan.
Pace your exercises. Avoid doing so much that your knee becomes substantially more swollen and painful later that day or the following morning.
Follow your medication and compression advice. Take prescribed medication as directed and use compression garments only as advised by your healthcare team.
Rest is important, but complete inactivity is not the goal. A balance of movement and recovery helps you gradually rebuild function without repeatedly overloading the healing knee.
New calf pain or swelling requires urgent medical assessment because it may indicate a blood clot. Sudden breathlessness or chest pain requires emergency assessment; call 999.
8. Why is movement so stiff when the knee is new?
It is tempting to expect a new artificial joint to bend and straighten smoothly straight away. However, the movement you experience depends on much more than the artificial surfaces themselves.
In the early stages, swelling increases the pressure within and around the joint. The healing tissues become sensitive, and your quadriceps muscles may struggle to contract normally. Pain can also make you instinctively protect the knee, reducing how far you are willing or able to move it.
The joint may therefore feel tight, heavy and resistant when you try to bend it. Straightening can also be difficult, particularly if swelling and quadriceps weakness make it hard to control the leg.
This is why rehabilitation focuses on both bending and straightening. Regaining extension helps you stand and walk efficiently, while improving flexion supports activities such as sitting, getting into a car and climbing stairs.
Gentle, regular practice is generally more useful than repeatedly forcing the knee through severe pain. Exercises such as heel slides, quadriceps contractions and supported knee-straightening work are commonly included in rehabilitation, but the precise programme should be guided by your physiotherapist.
Progress is not always linear. You may achieve a little more movement one day and find the knee stiffer the next because swelling has increased. The aim is to build movement gradually while keeping symptoms manageable.
9. How long until my new knee feels like my own?
This is an understandable question, particularly when the knee feels unfamiliar during the early weeks. You may notice tightness, altered sensation around the scar, clicking from the artificial joint or a feeling that the knee does not yet move naturally.
Although some people make rapid progress during the first few weeks, recovery continues well beyond the initial post-operative period. Pain and swelling often improve gradually, while strength, balance, confidence and walking endurance take longer to rebuild.
As a general guide, many people notice substantial improvements over the first three months, but it can take six to twelve months for the knee to feel more settled and natural, and some people continue to improve beyond this. Total knee replacement recovery can take several months or longer, while partial knee replacement recovery is often quicker. Individual experiences vary considerably.
It is also important to recognise that a replacement may never feel exactly like your original knee. Some people continue to notice stiffness, a numb area around the scar or an awareness of the artificial joint, particularly when kneeling. The aim is to achieve a comfortable, stable and functional knee that allows you to return to the activities that matter to you.
What can help you recover?
Consistent rehabilitation, appropriate pain management and gradually increasing activity are important. Use your walking aids until you can walk safely without a pronounced limp, complete the exercises prescribed by your physiotherapist, and allow time for rest between activities.
Avoid judging your progress against someone else's recovery. Your starting strength, general health, pain levels and individual response to surgery all influence how quickly you improve. If movement is not progressing, stiffness is substantial or pain is worsening rather than settling, speak to your physiotherapist or surgical team.
Final thoughts
Knee replacement surgery can be life-changing for people whose osteoarthritis has significantly affected their quality of life. However, it is a major operation, and the new joint needs time to settle while the surrounding tissues heal and the muscles regain their strength.
Understanding what happens during surgery can help explain why pain, swelling and stiffness are normal parts of early recovery. The artificial joint may be in place, but the body still needs time to adapt to it.
From a physiotherapy perspective, recovery is about more than achieving a particular knee bend. It involves regaining strength, walking safely, improving confidence and gradually returning to the activities that make everyday life meaningful. Patience, consistency and an appropriate rehabilitation programme can help you make the best possible progress.
This article is for general educational purposes and does not replace individual medical advice. Always follow the instructions provided by your surgeon and physiotherapist, particularly regarding weight-bearing, exercises, wound care and post-operative complications.
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