In England and Wales there are approximately 160,000 total hip and knee replacement procedures performed each year.
A total joint replacement is exactly what is says on the tin – it is a surgical operation to replace your own joint with an artificial joint. The “total” means that both joint surfaces are replaced. Sometimes only one component, half of the joint, will be replaced – a “hemi arthroplasty” . This is often seen in hip surgery following a fall, for example, where only the ball of the femur (or thigh bone) is replaced and the socket remains the patient’s own. Sometimes only one side of the knee joint will be replaced. The most common joints to be replaced are the hip and the knee, in roughly equal numbers. Shoulder and ankle replacements are most usually done for Rheumatoid Arthritis sufferers, and small joint replacements like toes and fingers can be done for arthritis. The joint replacement components are traditionally metal on one part of the joint with plastic on the other, but in some circumstances, a surgeon may suggest metal for both components, or even ceramic. This choice will depend on many factors, including your age and mobility and how you are likely to use the joint after replacement. In the hip, resurfacing is also available which is a less extensive type of joint replacement and sometimes favoured by surgeons for younger people.
How are the new joint components fixed in place?
Joints can either be fixed with special cement, or they can be tightly fitted in position (like carpentry) without cement. A cemented joint is used more often in older people or less active patients, and in people with “weak” bones. The cement holds the new joint to the bone. An un-cemented joint is often recommended for younger, more active people and those with good bone quality. These may take longer to heal, because it takes longer for bone to grow and fix the prosthesis in place. These patients may therefore need to use crutches and limit the weight they can put through the joint for the first 6 weeks until the bone has grown around the prosthesis to hold it firmly enough in position to hold the entire body weight. Your surgeon will advise you on this.
How long do they last?
New hip joints generally last at least 10 to 15 years, although this time can vary considerably in individuals. It is possible that younger patients may need to have the same joint replaced more than once in their lifetime, and surgeons therefore prefer to choose not to cement in these patients.
This is a link to a very nice hip replacement explanation video (no blood I promise!) with extra information
Why do people have a hip or knee joint replacement?
The only real reason is pain, especially night pain, although these patients will also suffer limitation to walking and loss of joint movement in certain directions.
The usual causes are Osteoarthritis – so-called ‘wear and tear arthritis’, where the cartilage inside a joint becomes worn away, leading to the bones rubbing against each other, Rheumatoid arthritis – this is caused by the immune system mistakenly attacking the lining of the joint, resulting in pain and stiffness, or a hip fracture – usually from a fall. However, in some cases a hip replacement may be necessary in children or younger adults whose hips are incorrectly formed (hip dysplasia).
The purpose of a new joint is to relieve pain, improve your function, and improve your mobility and quality of life.
Rehabilitation after your operation
Knee replacements are more complex anatomically than the hips and require more rehabilitation. This is because the hip is a deep stable ball and socket whereas the knee joint is flatter in surface. The 2 bones are supported and stabilised by ligaments, muscles and tendons. Of course, immediately after surgery, it will be sore, but it is important to get up and around as soon as possible (within the first 24 hours), and your hospital physio will come to help you do this. When I worked in hospitals, I remember visiting patients to get them up the first day after surgery and they would look at me and say “but I only had it done yesterday!” as though this was a misunderstanding on my part, and surely they should stay in bed for at least 5 days? The joint is stable from day 1 and the risks to health by staying in bed (chest or urinary tract infections, DVTs or bedsores) are much greater than getting up on a strong new joint. These days most patients are home in 5 days or so. Physio to restore mobility, strengthen muscles that may have been weak for some years, and re-educate the walking pattern will begin on day 1. Hydrotherapy (physio in a swimming pool) can be very useful.
Total hip replacement patients typically do very well with 6-8 weeks of rehabilitation. Total knee replacements generally take longer due to the different anatomy. Usually about 3 months after the operation the knee begins to feel normal, with another 6-9 months before you will begin to forget you’ve had it done. The replacement knees are unable to bend as much as a real knee does, with a 90 degree bend being the minimal acceptable functional amount (to allow you to sit in a car) and most eventually bending to 110 – 125 degrees. (A normal knee joint bends about 140 degrees.) It is fine to kneel on the knee once it is comfortable to do so.