Partial Knee Replacement

Introduction

In some patients, only part of the knee may be worn and thus a partial knee replacement is all that is required.

Knee anatomy

The knee is divided into three major compartments: The medial compartment (the inside part of the knee), the lateral compartment (the outside part), and the patellofemoral compartment (the front of the knee between the kneecap and thighbone).

If arthritis within a knee affects only one compartment, then there are some instances where a partial knee replacement might be appropriate.

Advantages

Replacing only part of the knee has the advantage of only needing to make a smaller incision which means scars will be smaller and healing times faster. There is also less pain after surgery and less blood loss. Also, because the bone, cartilage, and ligaments in the healthy parts of the knee are kept, the knee is likely to feel more natural.

Disadvantages

On the flip side, a partial knee replacement compared with total knee replacement entails slightly less predictable pain relief, and the potential need for more surgery if arthritis develops in the parts of the knee that have not been replaced.

Surgical procedure

Partial knee replacement is a type of minimally invasive surgery in that only the most damaged areas of cartilage from the joint are removed, and any healthy parts remain for continued use. Most often, partial knee replacements use implants placed between the end of the thigh bone and the top of the shin bone.

The operation typically lasts between 1 and 2 hours. First of all Mr Hull makes an incision at the front of the knee and explores the three compartments of the knee to make sure that the cartilage damage is definitely limited to one compartment and that your ligaments are intact. If your knee is unsuitable for a partial knee replacement, Mr Hull will perform a total knee replacement, a contingency plan which he will agree with you beforehand.

If your knee is suitable for a partial knee replacement, special saws are used to remove the cartilage from the damaged compartment of the knee. The ends of the femur and tibia are then capped with metal coverings which are held to the bone with cement. A plastic insert is then placed between the two metal components to allow for a smooth gliding surface.

Mr Hull uses the Oxford Unicompartmental knee replacement.  This is the most popular and well proven unicompartmental knee replacement in the UK.
Recent advances have seen the development of the Oxford ‘SIGNATURE’ unicompartmental knee replacement.  This uses pre-operative scans, to create personalized cutting jigs for use during surgery.
 
Mr Hull has recently been trained in this cutting edge technology, and is now offering this treatment to his patients.

Risks and complications

It’s good to be aware that there can be complications with this surgery, although serious ones are rare. As with all operations, there is a possibility of a reaction to the anaesthetic and excessive bleeding. A general anaesthetic may also make you feel temporarily sick after the operation.

Specific to knee replacements, there’s a small chance of infection around the prosthesis and sometimes this requires another operation to clean out the knee. Blood clots are another possibility, especially given that you won’t be able to move around much at first. To help prevent this, we will give you blood thinners.

Other less common concerns which nevertheless you need to be mindful about include pieces of fat in the bone marrow becoming loose, which can subsequently enter the bloodstream and get into the lungs, potentially causing serious breathing problems.

Nerves in the knee area may also be injured from swelling or pressure and can cause some numbness. In the longer term the joint may wear out or become loose, requiring it to be replaced again.  This is an especially important consideration for younger patients.

Preparing for surgery

Mr Hull will talk to you about how best to prepare for surgery which may include stopping taking any anti-inflammatory medications such as aspirin to reduce the risk of blood clots and stopping smoking if you are a smoker to minimize the risk of infection.

If you're having a general anaesthetic, you will be asked to follow fasting instructions. This means not eating or drinking, typically for about six hours beforehand.

Mr Hull may also ask you to wear compression stockings to help prevent blood clots forming in the veins in your legs.

Recovery

After the operation, you will need to rest until the effects of the anaesthetic have worn off. You may not be able to feel or move your legs for several hours after a spinal or epidural anaesthetic.

You may need some pain relief to help with any discomfort and it is also likely that we will give you an injection into your abdomen to help prevent blood clots forming in your legs, and possibly a short course of antibiotics to help prevent infection.

Our physiotherapist will also guide you daily about how to exercise to aid your recovery, exercises which you must continue for about two months when back at home.

In most cases, you can go home around 3 days after the operation and it’s possible to put weight on the knee immediately after surgery. You may need a walking aid for several days or weeks until comfortable enough to walk without assistance.

Exercises given by a physiotherapist are also essential to maintain your range of motion and restore your strength. Regular activities can usually be resumed 6 weeks after surgery.

Further information

For further information please contact Mr Peter Hull FRCS, Consultant Trauma & Orthopaedic Surgeon