Knee Replacement Surgery: What Are the Types, and Does Alignment Matter?
Knee replacement surgery replaces damaged joint surfaces with metal and plastic parts. There are total and partial options. How well a knee replacement works in the long term depends heavily on how well the new joint lines up with your hip, ankle and spine. Standard scans done lying down often cannot show this.
Key points
- Knee replacement surgery removes worn cartilage and bone and replaces them with artificial surfaces.
- Total and partial replacements suit different patterns of damage.
- Alignment of the whole leg, from hip to ankle, affects how the new joint wears over time.
- Standing imaging shows alignment under real weight-bearing load, unlike scans done lying down.
- An EOS scan uses about 90% less radiation than a standard X-ray, around ten times less.
Knee replacement, also called knee arthroplasty, is one of the most common planned operations in the UK. It is usually considered when osteoarthritis or other joint damage causes pain and stiffness that no longer respond well to treatment without surgery.
But surgery is only part of the picture. Your knee does not work on its own. It sits between your hip and your ankle, and the angle of your whole leg affects how forces pass through the replacement. Getting that alignment right, both before and after the operation, can make a real difference to how long the new joint lasts and how well you move.
What are the different types of knee replacement?
There are two main types. A total knee replacement resurfaces all three compartments of the joint. A partial (unicompartmental) replacement resurfaces only the damaged compartment and keeps healthy bone and ligament tissue.
All three compartments (inner, outer, kneecap) are resurfaced. Suitable when damage is widespread.
Only the worn compartment is replaced. Keeps more natural tissue and may allow quicker recovery.
A second operation to replace or repair a worn or loosened implant. Less common, but checking alignment is especially important.
Your surgeon will recommend the type that suits your pattern of damage. In every case, the position and angle of the implant within your leg matter greatly.
How do you know if knee replacement is right for you?
A knee replacement is usually considered after options without surgery, such as physiotherapy, weight management and medicine, have been fully tried. Common signs that you may be suitable include persistent knee pain that limits daily activities, stiffness that makes walking or climbing stairs difficult, and pain that disturbs your sleep.
However, a damaged knee on a scan does not automatically mean surgery is the best next step. It is important to first understand how your knee fits within your overall posture and leg alignment.
Thinking about a knee replacement? A standing whole-body scan can show your surgeon exactly how your leg lines up under load.
Book a free video consultationWhy does whole-body alignment matter for knee replacement?
Alignment matters because the forces travelling through your knee replacement are shaped by the position of your hip above and your ankle below. If your leg is not straight, one side of the implant takes more load than the other. Over time, this can lead to faster wear or loosening.
Your body is a connected chain from your feet to your head. A tilted pelvis, a stiff hip or a flat foot can all change the angle at which force meets your knee. Pain often appears away from its true cause because the body compensates. For example, a hip that rotates inward may push the knee outward and put uneven stress on the joint surface.
Standard imaging, such as an X-ray or MRI done lying down, relaxes the muscles and removes gravity. This can hide alignment problems that only show when you are standing and bearing weight. A surgeon planning a knee replacement needs to see the real, loaded position of your leg, not the relaxed position you take while lying on a table.
A note on MRI. EOS imaging is excellent at showing bones, joints and alignment under load. For soft tissue detail, such as ligaments, cartilage or meniscus tears, MRI is usually the better tool. The two work well together, and each answers different questions.
How does an EOS scan help before or after knee replacement?
An EOS scan takes a full-length, weight-bearing image of your entire body, from head to feet, in a single standing exposure. This gives your surgeon a true picture of your mechanical axis, the line from your hip centre through your knee to your ankle, while gravity and your muscles do their normal job.
Before surgery, this helps with planning the correct implant position. After surgery, it shows whether the replacement sits at the intended angle and whether your overall leg alignment has improved.
The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. You stand inside an open cabin for a few seconds. There is no tunnel and no need to lie down.
To learn more about how standing imaging works, see our EOS scan overview.
What affects knee replacement recovery time?
Recovery from knee replacement surgery differs from person to person. Common factors include your general fitness, your weight, the type of replacement and how well you follow your rehabilitation. Most people return to everyday activities within a few months, though full recovery can take longer.
Alignment plays a role in recovery too. If the implant is well aligned within your leg, forces spread evenly across the joint surface. This supports smoother movement and may reduce the risk of complications later on. A standing scan after the operation can confirm that the replacement sits as planned under real weight-bearing conditions.
ScanAlign is a diagnostic imaging clinic. We do not perform surgery or provide treatment. We provide the imaging that helps your surgeon or physiotherapist make better-informed decisions about your care.
Before you start treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in your pelvis, your legs or your spine changes what will actually help.
- Are considering a knee replacement and want full alignment data for your surgeon
- Have had a replacement and want to check the implant position under load
- Have ongoing pain after a previous replacement
- Want a low-radiation standing image of your whole leg
- Need soft tissue or ligament assessment (MRI is usually better)
- Have sudden knee locking, giving way or severe swelling: see your doctor or go to the emergency department
- Have numbness, weakness or loss of bladder or bowel control: seek urgent medical attention
For details on scan safety and preparation, see our FAQs page. The price for patients travelling from abroad is confirmed during the free video consultation.
Frequently asked questions about knee replacement
Knee replacement surgery, also called knee arthroplasty, removes damaged cartilage and bone from the knee joint and replaces the surfaces with metal and plastic parts. It is most commonly done for severe osteoarthritis.
A total knee replacement resurfaces all three compartments of the joint. A partial replacement only resurfaces the damaged compartment and keeps healthy bone and ligaments. Your surgeon will recommend the option that suits your pattern of wear.
Recovery varies. Most people return to everyday activities within a few months, but full recovery and the return of full strength can take up to a year. Fitness, body weight and rehabilitation all play a part.
If the mechanical axis of your leg, the line from hip to ankle, is not straight, forces spread unevenly across the implant. Over time this can lead to faster wear on one side. Checking alignment while you stand and bear weight gives the most accurate picture.
An EOS scan is a standing, full-body X-ray that captures your skeleton from head to feet in one image. It shows the true weight-bearing alignment of your leg. This helps surgeons plan implant position and check results after surgery.
Yes. The EOS system uses about 90% less radiation than a standard X-ray, around ten times less. It is a quick, open scan with no tunnel.
No. You can book directly yourself. The first step is a free video consultation, where a specialist radiographer reviews your situation and confirms whether a scan is suitable for you.
The price for patients travelling from abroad is confirmed during the free video consultation, and you can find more answers on our FAQs page.
They answer different questions. EOS shows bones, joints and alignment under load. MRI is excellent at soft tissue detail, such as ligaments, meniscus and cartilage. Many patients benefit from both.
Yes. Metal implants show on the EOS image. A standing scan is a useful way to check implant position and whole-leg alignment after surgery, especially if you are having ongoing discomfort.
Thinking about knee replacement?
A free video consultation with a specialist radiographer can help you understand whether a standing alignment scan is right for your situation, before you plan your trip to London.
Book a free video consultationWritten by Abbas Dhami (Specialist Diagnostic Radiographer)
Sources
- National Joint Registry (NJR). Annual reports on knee replacement outcomes in England, Wales, Northern Ireland and the Isle of Man. njrcentre.org.uk
- NHS. "Knee replacement." NHS conditions guidance. nhs.uk/conditions/knee-replacement
- Paley D. Principles of Deformity Correction. Springer, 2002. Widely referenced textbook on mechanical axis planning in lower-limb surgery.
This page is general information and not a diagnosis.
ScanAlign is the trading name of CoreMed Solutions Ltd and operates under The Harley Street Hospital's CQC licence.