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Doctor examining patient's knee after partial knee replacement surgery
By In-house Team, Circle Health Group

What is a partial knee replacement?

A partial knee replacement is a procedure to replace part of the knee joint. It is also known as a unicompartmental knee replacement or unicompartmental knee arthroplasty. It can be used to treat the early stages of knee arthritis and involves replacing only the damaged part of the knee joint, instead of the whole knee.

How do our knees work?

The knee is the largest joint in the body and necessary for most activities.

Anatomy of the knee

Patient holding their knee in pain due to potentially needing partial knee replacement surgeryThe knee joint connects your thigh bone (femur) to your shinbone (tibia), and is made up of three bones: the femur, tibia and patella, held together by muscles, ligaments, and cartilage. The entire knee joint is surrounded by a tough capsule that protects the internal structures of the knee. The joint can be divided into three compartments:

  • The patellofemoral compartment — the front part of the knee under the kneecap
  • The medial compartment — the inside part of the knee
  • The lateral compartment — the outside part of the knee

Function of the knee

The knee is a type of joint known as a synovial hinge joint. It is vital for almost every type of movement and allows you to stand, walk, run, kick, and jump. The knee arguably takes more stress than any other area of the body and allows us to perform weight-bearing activities and lift heavy loads.

In this video, consultant orthopaedic surgeon, Mr Graeme Hopper talks through what a partial knee replacement is, and what to expect from having one.

Why might I need a partial knee replacement?

The most common reason for needing a partial knee replacement is damage to a part of your knee caused by osteoarthritis. The procedure can also be helpful if you have joint damage resulting from rheumatoid arthritis (RA) or post-traumatic arthritis.

Your consultant might also recommend a partial knee replacement if you have severe symptoms such as joint pain, swelling, stiffness and difficulty moving your knee that haven’t improved after trying nonsurgical treatments.

Who is a partial knee replacement suitable for?

Your consultant may recommend a partial knee replacement if only one of your knee compartments is damaged, such as by osteoarthritis.

The procedure is normally recommended for patients over 40 years of age with good mobility and range of motion and minimal pain at rest.

Partial knee replacement surgery may not be suitable for you if

  • You have damage to more than one component in your knee
  • You have osteoporosis
  • You are very overweight
  • You have inflammatory arthritis such as rheumatoid arthritis
  • Your knee is deformed or misshapen
  • You have significant stiffness in your knee joint
  • Your knee ligaments are not strong enough

The main benefits of a partial knee replacement are relief of long-term symptoms such as knee pain, stiffness and reduced mobility, increasing your independence and enhancing your quality of life.

Are there different types of partial knee replacement?

There are three types of partial knee replacement. Your consultant will decide which type of surgery is best for you based on which parts of your knee are damaged.

The three types of partial knee replacement are:

  • Unicondylar knee replacement — this is the most common type of partial knee replacement where only one knee compartment is replaced
  • Patellofemoral knee replacement — replaces the kneecap (patella) and the groove at the lower end of the thighbone (femur)
  • Bicompartmental knee replacement — replaces the inside (medial) compartment and the knee cap

What are the benefits of a partial knee replacement?

The main benefits of a partial knee replacement are relief of long-term symptoms such as knee pain, stiffness and reduced mobility, increasing your independence and enhancing your quality of life. 
Partial knee replacement surgery has many benefits over a total knee replacement, including:

  • The procedure preserves more of your healthy bones and ligaments, leading to a more natural feeling knee in the long term
  • Faster recovery
  • Shorter hospital stay
  • Less blood loss
  • Less postoperative pain
  • Lower risk of complications

What happens during a partial knee replacement?

Partial knee replacement surgery is normally carried out under general anaesthetic, meaning you’ll be asleep during the procedure. In some cases, you may be given a spinal or regional anaesthetic, which means you’ll be awake, but won’t feel any pain during the surgery. Your consultant will discuss the best type of anaesthetic for you before your surgery.

When the anaesthetic has taken effect:

  • Your consultant will make a small incision (cut) over your knee
  • The damaged bone and cartilage are removed from the knee joint
  • The prosthetic (artificial) pieces are inserted into the correct place in the knee joint and fixed with bone cement
  • The incision is closed with staples or stitches

Partial knee replacement surgery normally takes around an hour.

Are there any risks or complications?

All surgery carries a risk of complications. Partial knee replacement is a generally safe procedure, but occasionally, complications may occur. Your consultant will discuss all the potential risks and complications of partial knee replacement with you before your procedure and make sure you are fully informed before deciding to go ahead.

Potential risks of partial knee replacement include:

  • Blood clots or deep vein thrombosis (DVT)
  • Chest infection
  • Adverse reactions to the anaesthetic
  • Infection inside the knee joint or at the incision site
  • Damage to the surrounding nerves
  • Damage to nearby blood vessels
  • Damage to the surrounding tissues such as the ligaments
  • The prosthetic implants may move, loosen or wear down
  • A build-up of scar tissue inside the knee
  • Reduced range of motion, instability of the knee joint or knee stiffness
  • The surgery may not relieve pain or other symptoms

What’s the recovery like?

Recovery from any type of surgery varies from person to person and depends on several factors, such as your age, general health, and activity level before surgery. You can help your recovery to go more smoothly by arranging for someone to help you for the first week or so after your procedure. You’ll be able to walk with a walker the day after your surgery, but can expect to need help with certain tasks such as bathing, housework, shopping and cooking. Prepare your home in advance by.

  • Stocking up on easy to prepare, non-perishable food
  • Prepare meals in advance that can be heated up
  • Install hand rails in the toilet and on the stairs
  • Put a bench or chair in the shower
  • Remove anything you could trip over like low tables, rugs and electric cables
  • Keep things you use regularly, like the TV remote control, glasses, books and medications, within easy reach

Depending on the job you do, you can expect to go back to work a week or two after your partial knee replacement. Your consultant can give you an accurate recovery timeline based on your individual circumstances.

You can expect to resume most normal activities in around six weeks, but it may take a few months to recover completely.

Your consultant will give you instructions on what to do during your recovery including pain management, wound care and exercises.

Pain management

It’s normal to have some pain and swelling after your knee replacement. Your consultant will prescribe medication to help manage any pain. Applying ice packs (or a bag of frozen peas) to your knee for around 20 minutes a few times a day will help relieve pain and swelling. Keep your leg elevated to or above the level of your heart to help the swelling go down.

Caring for your wound

Your healthcare team will give you instructions on caring for your surgical wound. Keep your incision clean and covered and follow instructions on changing the dressing. Check with your consultant when you can take a shower or bath. Seek medical attention as soon as possible if your surgical wound is showing signs of infection such as yellow or green discharge, redness, warmth, swelling, or an unpleasant smell.


Your physiotherapist will show you exercises to strengthen the muscles around your knee and prevent stiffness after your partial knee replacement. These exercises are an important part of your recovery and help you regain the function of your knee. You’ll need to have regular physiotherapy sessions for several weeks after your surgery.

How long your partial knee replacement will last may vary, but you can expect it to last for at least ten years and even up to 20 years.

How long does a partial knee replacement last?

How long your partial knee replacement will last may vary, but you can expect it to last for at least ten years and even up to 20 years.

Are there any alternatives to a partial knee replacement?

Non-surgical alternatives to a partial knee replacement include lifestyle changes, medication, injections, and physiotherapy.

Lifestyle changes

Some lifestyle changes you can try to ease knee pain include:


Over-the-counter painkillers such as paracetamol and non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen are normally the first medications recommended for knee pain. If these aren’t effective, your consultant may prescribe a stronger medication.

Knee injections

Steroids or corticosteroids work by reducing inflammation, which in turn reduces pain. A steroid injection is given directly into the knee joint and can relieve symptoms for several weeks or months.

Other injections, such as hyaluronic acid (hyaluronan) injections, may help lubricate the knee joint and relieve arthritis pain. Hyaluronan injections aren’t currently approved by NICE to treat osteoarthritis, but may be available privately.


Physiotherapy exercises focus on building muscle strength and increasing flexibility and range of motion. Your physiotherapist may also use techniques such as manual therapy, hydrotherapy, therapeutic ultrasound and transcutaneous nerve stimulation (TENS).


A partial knee replacement is an operation to replace part of the knee joint with a prosthesis. It is done to repair damage to the knee joint, normally caused by osteoarthritis.

Having a partial knee replacement can reduce symptoms of arthritis like pain and stiffness, improve your quality of life and allow you to return to doing the activities you enjoy.

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