Unicompartmental (Partial) Knee Replacement

What is it?

Your knee joint has three separate components – the medial (inside part of the knee), lateral (outside part of the knee) and patellofemoral (front of the knee between the femur and kneecap). Partial knee replacement surgery – which involves resurfacing whichever compartment of the knee has been damaged by arthritis – is performed through a smaller incision than with a total knee replacement and it retains all of the healthy bone and cartilage, as well as the ligaments around your knee. It is a quicker procedure than a total knee replacement, which means you are likely to recover faster and with less post-operative pain. However, there are some disadvantages and not every patient is suitable. Your orthopaedic surgeon will discuss your individual circumstances with you and advise whether or not a partial knee replacement is an option.

Who might need it?

You will only be offered knee replacement surgery if you are experiencing severe pain and loss of function in your knee due to a condition like arthritis and only when other, less invasive treatments have been tried and are no longer effective. If you have knee arthritis that only affects one of the compartments of your knee, you may be able to have a partial knee replacement. You will not be offered this type of surgery if you have arthritis affecting your entire knee joint or if there is ligament damage or extensive stiffness in the knee. People with inflammatory arthritis are also unsuitable for a partial knee replacement.

What to expect

You will undergo an orthopaedic assessment to check the condition of your knee, your general state of health and suitability for a partial knee replacement. Normally, if the pain is focused on the inside or outside of your knee, you may be offered a partial knee replacement but if the pain affects your entire knee or is at the front of your knee (under your kneecap), you may be more suited to a total knee replacement. Prior to surgery, you will have an X-ray and you may also have an MRI scan to assess the condition of your bones and cartilage. Most partial knee replacements are performed under general anaesthetic, which means you will be asleep throughout, but in some cases you may be able to have an epidural so you will be awake but numb from the waist down.

Partial knee replacement surgery takes between one and two hours. The surgeon will make an incision in the front of your knee and remove any damaged cartilage and bone. These will be replaced with a metal implant that recreates the surface of the joint. A plastic spacer is placed in between any metal components to create a smooth surface so the joint can move in a natural way. At the end of the operation, the incision will be closed and you will be moved to the recovery room where you will be closely monitored as you come round from the anaesthetic.

After surgery, you will be given painkillers. You can begin putting weight on your new knee immediately but you will need to use crutches or a walker for a few weeks until you feel confident enough to walk without assistance. A physiotherapist will recommend exercises to help you rebuild your strength and mobility and you will see your orthopaedic surgeon a few weeks after surgery to check you are making a good recovery.

Benefits of unicompartmental (partial) knee replacement surgery

If you are experiencing debilitating knee pain due to osteoarthritis or severe injury, a partial knee replacement can be a life-changing operation. Outcomes are generally good, with studies showing excellent results in the medium to long-term for patients of every age. Compared to a total knee replacement, patients undergoing a unicompartmental knee replacement tend to have less blood loss and a lower risk of post-surgical infection and blood clots. Because more of your natural knee is retained, a unicompartmental knee replacement may feel more natural than a total knee replacement and the knee may bend more easily.

The main disadvantage of a partial knee replacement compared to a total knee replacement is that there is a greater possibility that you will need to undergo further surgery in the future if the arthritis spreads to other components of your knee. There are the normal risks associated with any surgical procedure, which includes the risk of developing an infection or blood clots. Your surgeon will discuss potential risks with you prior to your surgery.