Knee replacement surgery (arthroplasty) is usually necessary when a health condition or injury disrupts the normal working of the knee joint so that:
- your mobility is severely reduced
- you experience pain even while resting
How the knee should work
The knee joint acts as a hinge between the bones of the leg. It is really two joints. The major joint is between the thigh bone of the upper leg (femur) and the shin bone of the lower leg (tibia). The smaller joint is between the kneecap (patella) and the upper leg (femur).
A smooth, tough tissue called articular cartilage usually covers the ends of the bones within the knee joint. This protects the ends of the bones and allows them to slide smoothly over each other without pain or too much effort.
The synovial membrane that covers the other surfaces of the knee joint produces synovial fluid, which lubricates the joint, reducing friction to further help movement.
Replacing a damaged knee
Pain and difficulty moving the knee joint are common when the articular cartilage has become damaged or worn away. The ends of the bones start to rub or grind together, instead of smoothly sliding over each other.
Replacing the damaged knee joint with an artificial one can help reduce pain and increase mobility.
Osteoarthritis
The most common reason for knee replacement surgery is osteoarthritis.
Osteoarthritis in the knee occurs when the articular cartilage becomes damaged or wastes away through natural wear and tear. The bones have little or no protection to prevent them rubbing against each other when the knee moves, causing pain.
The bones may compensate by growing thicker and producing bony outgrowths to try to repair themselves, but this can cause more friction and pain. For more information, see the Health A-Z topic about Osteoarthritis.
Surgical alternatives to a knee replacement
There are alternative surgeries to knee replacement, but results are not as good in the long term.
Arthroscopic washout and debridement
An arthroscope (tiny telescope) is inserted through small incisions in the knee. The knee is washed out with saline and any bits of bone or cartilage are cleared away. It is not recommended if you have severe arthritis.
Microfracture
This is a keyhole (minimally invasive) operation in which small holes are made in the surface layer of bone with a small, sharp ‘pick’. This allows cells from the deeper, more blood-rich bone beneath to come to the surface and stimulate cartilage growth. It can be a good option if you have just a small area of damaged cartilage. However, the benefits are not well proven and the results are not as good as knee replacement for severe arthritis.
Osteotomy
This is an open operation in which the surgeon cuts the shin bone and realigns it so that weight is no longer focused on the damaged part of the knee. It is sometimes used for younger people with limited arthritis, where it may enable a knee replacement to be postponed. However, you will usually need a knee replacement at a later date, and the operation may make knee replacement surgery more difficult if it is needed.
Autologous chondrocyte implantation (ACI)
This is when new cartilage from your own cells is grown in a test tube and introduced into the damaged area. It is usually used for accidental injury to the knee rather than arthritis. As yet, ACI is only available as part of a clinical trial.
Mosaicplasty (cartilage replacement)
This is a keyhole (minimally invasive) procedure that involves transferring plugs of hard cartilage, together with some underlying bone from another part of your knee, to repair the damaged surface. Currently, it is only available as part of a clinical trial.
Non-surgical treatment options
Non-surgical options include:
- physiotherapy to improve the flexibility, mobility and strength of your knee joint
- painkillers to reduce pain in your joint so movement is easier
- anti-inflammatory medicines to reduce swelling within the joint, increasing mobility
- steroid injections into your joint to help relieve pain and swelling
- temporarily losing excess weight to reduce the strain on your knees, thereby reducing pain and improving mobility
- using walking aids, such as a cane or crutch
