Partial Knee Replacement

Partial Knee Replacement

what is partial knee replacement

Partial Knee Replacement

Have you been suffering for some time with a painful knee, that is preventing you from leading a comfortable and active life?

If you have knee osteoarthritis in a single area (aka compartment) of your knee, a partial knee replacement may be a good option for you.

Partial knee replacement surgery is also known as uni-condylar replacement, hemi-knee replacement and unicompartmental knee replacement surgery.

Essentially, it’s a surgical procedure designed to replace a single area of an arthritic knee, and it’s considered to be less invasive than a total knee replacement, with a swifter recovery.


What is knee osteoarthritis?

Knee replacement surgery is typically carried out when a patient has exhausted all conservative forms of treatment for knee osteoarthritis.

Osteoarthritis is a form of wear-and-tear arthritis that affects the hard, shiny, articular cartilage that covers the ends of the joints.  Articular cartilage acts as a kind of shock absorber within a joint, enabling the smooth and slippery surfaces to glide easily over each other. When cartilage is worn or lost, bone becomes exposed, friction within the joint increases, and pain, inflammation, stiffness and swelling occurs.

There are three compartments within the knee. One is between the back of the kneecap (patella) and the front of the thigh bone (femur), and the other two compartments are between the ends of the femur and the shin bone (tibia). One is one the medial (inside) side of the knee, the other on the lateral (outside) side of the knee.

When osteoarthritis affects just one compartment of the knee, such as the medial compartment, a partial knee replacement may be a good option for a patient who is struggling despite physiotherapy, painkillers, and injection treatments. The vast majority of partial knee replacements are performed for isolated medial compartment disease.

medial knee osteoarthritis

Knee Osteoarthrits

Who is suitable for partial knee replacement surgery?

Partial knee replacement surgery isn’t for everybody who has knee osteoarthritis, but you this surgery may be an option for you if:


You only have osteoarthritis in a single compartment of your knee (typically the medial compartment).

  • The anterior cruciate ligament (ACL) in your knee is intact.
  • The medical collateral ligament (MCL) in your knee is intact.
  • The knee doesn’t have a significant bend or deformity (which can’t be corrected with partial knee replacement surgery).


In the past, partial knee replacements tended to be offered to people who were over the age of 60, and this was partly because longevity of the partial joint replacements wasn’t thought to be great in younger, more active patients.

Thanks to technological and surgical technique advances, partial knee replacements are lasting longer and longer; 70% of partial knee replacements last for 25 years. This means partial knee replacements are increasingly being offered to younger patients.



What are the advantages of a partial knee replacement?

A partial knee replacement only replaces a single compartment of the knee, preserving the other two compartments. There is less trauma to tissues, less blood loss, less pain after the surgery, a faster recovery, and typically a better range of movement in the knee, when compared to a total knee replacement. The incision length in a partial knee replacement is around 3-4 inches, compared with a much larger (e.g. 10 inch) incision required in a traditional knee replacement.


The younger patients I see who are seeking partial knee replacement surgery are often still working and they may have medial compartment osteoarthritis in both knees. If they lead active lives, or have a physical job, a partial knee replacement means a quicker recovery for them than a total knee replacement. Additionally, because the knee incision can be placed off-centre from the midline of the knee, kneeling is possible, which isn’t always the case after a total knee replacement.


In the older patients I meet with single compartment knee osteoarthritis, partial knee replacement is a less traumatic procedure to go through than a total knee replacement, which is important if the patient also suffers from other medical conditions.


Types of partial knee replacement

There are two kinds of partial knee replacement – known as fixed-bearing, and mobile-bearing. Both consist of a combination of metal and plastic components.

The fixed bearing partial knee replacement consists of a rounded femoral component that sits on top of a flat tibial component. Mobile-bearing replacements have a mobile plastic spacer that sits between the two components, which can rotate a little in the medial compartment (hence the term ‘mobile’ bearing).


The two different types each have their pros and their cons.

Mobile bearing partial knee replacements were originally introduced because previous generations of fixed bearing partial knee replacements tended to wear poorly, due to the high mechanical stress between the end of the femoral and tibial components. However, without very precise alignment and ligament balancing, mobile bearing partial knee replacements can dislocate (the plastic spacer pops out).

Improvements in prosthesis technology and surgical techniques means that both fixed bearing and mobile bearing partial knee replacements have excellent outcomes, as demonstrated in a recent meta-analysis.

The fixed bearing partial knee replacement that I use has excellent long-term results on the UK National Joint Registry.

Shah Punwar in operating theatre

What happens during partial knee replacement surgery?

 On the day of the operation, you’ll come into hospital and you’ll be seen by myself and the anaesthetist, to check that all is well.  Most partial knee replacements are carried out under ‘regional’ anaesthesia, which avoids the potential risks and complications of a general anaesthetic. A spinal block injection numbs the nerves to the legs for several hours, and a light sedation will ensure you’re lightly a sleep, but able to breath on your own during the procedure.


A short incision (around 7cm in length) is made in a vertical line over the front part of the knee, just off centre, to allow access to the compartment of the knee which is being replaced. A minimally invasive ‘mid-vastus’ approach is used meaning that the quadriceps tendon is not split. This leads to a quicker recovery and faster ability to straight leg raise.


Accurately placed saw cuts are made to remove the damaged cartilage and bone, leaving a space ready to receive the new partial knee replacement components. Cement is used to ensure a good bond with the bone. The soft tissues and skin are then closed, and local anaesthetic is injected around the joint to help minimise pain after the surgery.



What’s the recovery like after a partial knee replacement?

 Some patients who undergo a partial knee replacement are able to go home on the same day, whilst other patients may stay overnight in hospital.


The recovery from a partial knee replacement is quicker than that of a total knee replacement. Most patients are able to walk without a stick or crutches after 3 to 4 weeks.  The knee will remain a little swollen for several weeks after the surgery, and there may be some discomfort from time to time. Physiotherapy is very important after the surgery to strengthen your leg, and to restore a really good range of movement and a natural gait. Most patients are back to their active lives by around 8 weeks, although I tell my patients to give it a good 6 months to experience the full benefits.


How successful are partial knee replacements?

Any surgery comes with potential risks, although much can be done to limit or prevent complications. The good news is that the satisfaction rate for partial knee replacements is as high as 95%.  Having a partial knee replacement cannot absolutely prevent the progression of osteoarthritis in other areas of your knee, but it will help to restore harmony and stability to the knee which may slow the wear in other areas.  Should osteoarthritis set in in other areas of the knee, it is entirely possible to ‘revise’ the partial knee to a total knee replacement.


Partial knee replacement surgery can be life changing for many patients, and if you’re struggling with the pain of knee arthritis, I can help.


Mr Punwar provided a partial knee replacement. He took over my diagnosis and discussed alternative to the original plan. He explained the pros and cons of each without any pressure. The whole process was exemplary. The surgical admission was like a well oiled machine. I woke from the operation feeling very comfortable. Pain relief was spot on. Within 48 hours, I was showering independently. Within 4 days, I was moving around the house without walking aids. 10 days later, I was walking outside - cautiously but with confidence. Of course, there is a fair amount of work to do to regain the flexibility and strength but it is such a joy to get out of a chair without the anticipation of feeling of pain. I now walk for sheer enjoyment as well as to get around. People think knee pain is just ... knee pain. However, it is many ramifications. Your exercise rate reduces. You start to take opportunities to sit rather than stand, to get the bus rather than walk. Reduced mobility impacted my ambitions and fitness, my sense of capability and available energy. It made me feel older than I actually am. This new partial knee is like having a new lease of life. I am looking forward to years of walking and cycling ahead of me. Mr Punwar's obvious surgical skill is matched with an excellent interpersonal manner. I have no hesitation in recommending him.


I saw Mr Punwar this afternoon and a member of his team as a followup from my operation for a uni-compartmental knee replacement in October. I was very happy with my treatment both for the operation and also today. I like that Mr Punwar is very direct in his approach, and as I know that in future I shall have to have surgery on my other knee, I will trust Mr Punwar to perform this operation at some time in the future.

Shahid Punwar white bg

Mr Shahid Punwar is a Consultant Knee & Hip Trauma and Orthopaedic Consultant.

To make an appointment:

020 8194 8541