The Structure of the Knee
The knee is one of the most commonly injured joints in the body. It is made up of three main bones and is quite complex in design. At first glance, it appears to be a simple hinged joint formed by the thigh bone (femur) connecting to the shin bone (tibia). However, there is more to the knee joint.
The end of the femur is made up of 2 rounded surfaces called femoral condyles. These sit in shallow cups at the top of the tibia and each surface is lined by smooth lubricated articular cartilage to enhance joint movement. A thicker layer of cartilage called the meniscus cushions the joint. It acts like a shock absorber and normally allows smooth movement of the joint. Cartilage cannot be seen on x-ray, but appears as a space between the two bones.
At the front of the knee joint, the patella (kneecap) sits in a groove at the lower end of the femur. A smooth cartilage lining allows the patella to glide up and down the end of the femur on knee movement.
The knee bones are held in place by strong bands of connective tissue called ligaments. The whole joint is enclosed by a synovial membrane capsule which manufactures lubricating synovial fluid to bathe the joint.
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What is a Total Knee Replacement?
There are two main types of knee surgery.
Total knee replacement (TKR): A total knee replacement is a surgical procedure where the diseased or damaged knee joint is replaced by a prosthesis (i.e. both femoral condyles are replaced). The knee replacement prosthesis can be made up of several components and the components can be made of various metal or plastic materials.
In a TKR, the end of the femur is removed and replaced with a metal shell. The top of the tibia is also removed and replaced, usually with a channelled plastic component with a metal stem. Depending on the condition of the patella, it may be remodelled (scraped) and a plastic "button” added to its under surface.
A uni compartmental knee replacement: This procedure is not as common as the TKR. In this procedure only one femoral condyle is replaced and the other condyle left undisturbed. The adjacent damaged cartilage is removed and a plastic component put in its place.
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Why would I need a Total Knee Replacement?
The main reason for a TKR is arthritis. Trauma and congenital conditions can also be triggers. Arthritis comes in many forms including rheumatoid arthritis and osteoarthritis; however the latter is the most common cause for knee replacement surgery.
Osteoarthritis results from wearing down of the cartilage surfaces, eventually causing bone to move on bone. This painful and debilitating condition is more likely to affect people as they get older or people who are inactive or obese.
Abnormalities of knee joint function resulting from fractures of the knee, torn cartilage and torn ligaments can also lead to degeneration many years after the injury. The mechanical abnormality
leads to excessive wear and tear - just like the out-of-balance tire that wears out too soon on
your car.
A TKR replaces your arthritic joint, replacing the damaged weight bearing surfaces. The design of a TKR helps to
1. Eliminate pain
2. Minimise wear and tear
3. Improve motion and function
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Is there an alternative to surgery?
A knee replacement should only be considered when pain and immobility are severe and all conservative treatments have been exhausted.
Such treatments can include:
• Over the counter medication like glucosamine with chondroitin can sometimes help reduce knee pain.
• Judicious use of anti inflammatory medication and analgesics can play a role.
• Orthoses, shoe modifications, braces and walking aids can also assist mobility.
• Weight loss and physical therapy can sometimes help to slow the progress of osteoarthritis.
• Joint injections can sometimes help reduce inflammation or replace joint fluid.
Who performs a TKR and where?
A TKR is performed in hospital by an orthopaedic (bone) surgeon. An anaesthetist will be present and an assistant surgeon will usually be in attendance. Most TKR surgery in Australia is performed in private hospitals.
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Before the procedure
You should quit smoking before a TKR or any major surgery. Smoking increases the risk of wound infections, pneumonia and blood clots. It can also slow down healing after surgery. Likewise, obesity can also lead to poor surgical outcomes. Weight loss achieved before surgery can reduce the risk of complications. Maintaining a healthy weight for life could also reduce future wear and tear on the prosthesis and increase its “lifetime.”
Your doctor will advise you to stop taking blood thinning agents like warfarin and aspirin. This can help to reduce the risk of blood loss during surgery. Your anaesthetist will decide whether you need a general or spinal anaesthesia. This will be based on your risk factors. It is important to discuss your medical history, other health problems, the medications you take and any allergies you have. Both the surgeon and anaesthetist need to know these things if they are to deliver the best possible outcome from your surgery.
Some surgeons ask their patients to attend a hospital pre operative clinic where all of this is taken care of. It’s important to attend the clinic, have the pre op tests done and provide as much information as you can. It could help you to achieve the quickest recovery and best possible outcome from your procedure. It could even help save your life!
Use these helpful nib links (link to going to hospital questions) to find out more about what you need to know about your hospitalisation. Be sure to ask questions if you don’t understand what is being asked of you, or if you want to know more about the procedure. You are the most important person in this whole process!
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TKR – Brief description
There are two approaches to surgically replacing a knee.
1. Minimally Invasive approach
Although not commonly used in Australia, results overseas have been encouraging. The minimally invasive approach uses a shorter incision and is said to cause less trauma to muscles and other tissues. It is thought to lead to a shortened hospital stay, less post-operative pain and a more rapid return to normal activities. However, like all newer techniques, many doctors are waiting to see the long term results of this type of surgery.
2. Traditional approach
This is the more commonly used technique. The knee is flexed and usually an anterior incision is made to expose the knee. It can be 15 - 30cm long. The quadriceps muscles are split and the knee cap moved to one side.
The end of the femur and top of the tibia are then removed using cutting guides oriented to the long axis of the bones. Depending on the surgeon’s preference, the cartilages and some ligaments are removed. The new femoral and tibial prosthetic components are inserted into the cut ends of the bones. Cement may be used to gain adhesion of the prosthesis to the bone cavity. Alternatively, an uncemented procedure relying on bone ingrowth into the prosthetic components may be deployed. The way the bones are prepared, the size and type of prosthetic parts and the re-alignment of ligaments are all aimed to correct any pre-existing dysfunction and to achieve even weight bearing after the operation.
Once the joint is brought back into alignment and a drain is inserted into the site, the wound is then closed usually with absorbable sutures (stitches) or clips. The operation can take between 2 and 4 hours and intravenous antibiotics are given during and after your surgery to minimise infection risk. A urinary catheter is usually inserted for the first 24 hours after the operation as some people have difficulty urinating after an anaesthetic.
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Choices and Decisions
Talk to your surgeon
Although the surgeon is in the best position to decide which surgical approach, prosthetic components and fixation method to use, don’t be afraid to ask questions of the surgeon. After all it’s your body.
You could ask:
• What are the pros and cons of the various prosthetic components?
• Does the surgeon keep track of the lifespan of the prostheses he/she uses?
• How many of these procedures has the surgeon performed?
• How often do patients need repeat procedures?
• What national or international data has been collected on surgical outcomes using different prostheses and techniques?
Things you need to consider
About 90% of people have significantly improved quality of life after TKR – as measured in terms of mobility and pain relief.
You need to understand the pros and cons of the various alternatives and consider them against your expectations after the operation. For example:
• Do you need to be active (returning to physical work, caring for young grandchildren, getting back to dancing or bush walking)
• Are you looking at retiring or taking up a more sedentary occupation?
• How long will you be off work?
• How long before you can get in a car?
• How long before you can DRIVE a car? (there is a difference!)
Another decision to make at this time is whether you should enter a hospital-based rehabilitation programme after your surgery or whether you should return home with or without community-based rehabilitation.
Surgeons vary in their advice on these matters. Discuss the surgeon’s recommendations. Talk to your GP and family members or carers. Find out what services are offered in the community. Be proactive in this decision. Not everyone needs in hospital rehabilitation after knee replacement surgery.
Above all, talk with your surgeon. Most are more than happy to discuss your reasonable concerns. If not, then find another surgeon.
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Risks and Side Effects
Knee surgery carries risks – these include anaesthetic risk, infection risk, risk of blood clots and risk of bleeding or nerve injury. These conditions are preventable and treatable, but can also depend on your cooperation with pre and post-operative care (e.g. wearing compression stockings to prevent clots and mobilising as directed).
Most total knee replacement surgery can be expected to result in good and comfortable knee function for 10-15 years and sometimes longer, but it can be dependent upon the age and activity level of the patient. On rare occasions the surgery doesn’t work. Increased pain and ongoing immobility can be the result. This can be caused by loosening of the prosthesis, fracture at the site of the prosthesis, joint infection or some other complication. Sometimes a repeat surgery is needed sooner than anticipated. Knee stiffening can also be an adverse surgical outcome, although the great majority of patients will eventually bend their knee past 90 degrees. In fact, most will achieve at least 110 degrees.
Although these factors are sometimes out of everyone’s control, you can minimise your risk by being in the best health possible before your operation and keeping your weight under control and staying fit after the procedure. You should follow the pre-op and post-op advice given by your doctor, nursing and physio staff. But remember to ask questions if you are unsure about anything. Everyone involved in your procedure wants it to be a long term outstanding success.
Immediately after the operation
You will be sent to the recovery room whilst the anaesthetic wears off. You will then return to the ward with your pain relief taken care of. Your wound will usually have a dressing or waterproof film over it and you will be left to rest for the next day or so.
It is important to start moving about as soon as you are able and with the support and supervision of trained staff. This can help to reduce the risks of clots and chest infections. A physiotherapist will show you exercises to strengthen your muscles and will “fit” you for a walker or crutches. They can also advise you about returning to sport or other activities.
In the first couple of weeks, protected weight bearing with a walking frame or crutches is required. It can take 2 weeks or longer sometimes for the quadriceps muscles to heal and restrengthen and the full range of movement of the prosthetic joint to be achieved. Sutures or clips are usually removed 10 days after your operation.
Discharge from the orthopaedic ward usually occurs around 7 days after your operation as you should be able to bend your knee to at least 90 degrees by this time. Your discharge date is also determined by level of home support available and whether a hospital based rehabilitation programme has been recommended.
It can take 6 weeks and sometimes longer to return to full weight bearing and often a walking stick will be needed. It may take up to 3 months or longer for your knee to return to its normal function.
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General tips after TKR
Your surgeon and GP will give you all the information you need, but here are some general tips.
• Your surgeon will usually arrange check-ups at 6 weeks, 3 months, 6 months and one year after your operation. After that, a knee check up every two years with an x-ray is a good idea.
• Keep your weight under control and keep physically fit if possible
• Antibiotics should be given if you have any major bowel, bladder or dental surgery – otherwise germs in the blood stream may attach to the knee prosthesis meaning it may have to be removed.
• Metal prostheses can set off airport security alarms.
What does nib cover me for?
The hospital you choose, your health cover policy and hospital excess, and if you’re still serving waiting periods are just some of the things that affect how much your procedure will cost.
You should always contact nib BEFORE your procedure to ensure you’re covered.
Your out of pocket expenses may be minimised if you:
• Choose an nib agreement private hospital or public hospital
• Ask your doctor in advance if they’ll treat you as an nib MediGap patient, and if other people performing the procedure (e.g. anaesthetist) will be charging nib MediGap rates as well.
More information about Going to Hospital.
This procedure is INCLUDED only on the following nib health insurance covers:
• Top Cover
• Young at Heart Mid
• Young at Heart Top
• Premier Plus
• Just Hospital*
* Benefit Limitations apply if you are new to Private Health Insurance. During your first 24 months of cover (but after standard hospital waiting periods have been served) this procedure is subject to ‘Benefit Limitations’. This means that the benefits payable on these services are limited to Public Hospital Benefits only.
This procedure is EXCLUDED on:
• Basic Saver
• Basic Plus
• Family Basic Saver
• Family Plus
• Mid Plus
At nib agreement private hospital and public hospitals, this procedure is fully covered for hospital costs on
Note: These covers are no longer available for sale
• Gold
• Couples Plus
• Singles Plus
• Premier 65% and Premier 85%
• Essentials
• Top Private Hospital
• Executive R
And, if the doctors and anaesthetists charge nib’s MediGap rate, there should be no out of pocket expenses for these services.
If you are on Public Hospital or Public Hospital Plus Extras, you will be fully covered if you are admitted to a public hospital, provided you are treated as a day patient. If your admission requires an overnight stay, or you are admitted to a private hospital, you will have out of pocket expenses.
Note: This information should not replace the advice given to you by your doctor or other health care providers.
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