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Total Knee Replacement


Xray of a total knee replacement. The implant resurfaces the ends of the bones

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What is a Total Knee Replacement?

A Total Knee Replacement (TKR) or Total Knee Arthroplasty is a surgery that replaces the worn surfaces of an arthritic knee joint with artificial metal and plastic replacement parts.

The procedure is usually recommended for older patients who suffer from pain and loss of function from arthritis and have who have failed to achieve satisfactory relief from other more conservative methods of therapy. TKR can be done in younger adults if the symptoms are severe enough  but younger patients are tough on their joints so all other options should be explored first.

A typical knee replacement resurfaces the ends of the femur (thigh bone) and the tibia (shin bone) with metal. A plastic bearing is inserted between them and on the back of the patella (knee cap). The implants can be attached with bone cement of using cementless fixation. The Australian Orthopaedic Association National Joint Replacement Registry data shows that the best survivorship is when the tibial component is cemented. The femoral component can be fixed with or without cement with equally good longevity.


The diagnosis of osteoarthritis is made on history, physical examination & Xrays. An MRI is not an absolute necessity to diagnose arthritis but can be useful in terms of defining treatment options. There is no blood test to diagnose Osteoarthritis (wear & tear arthritis).


Why Consider a TKR?

The decision to proceed with TKR surgery is a cooperative one between you, your carers and your surgeon.

The potential benefits following surgery are relief of symptoms of arthritis. These include:

  • Severe pain that limits your everyday activities including walking, shopping, visiting friends, getting in and out of chair, gardening, etc.

  • Pain waking you at night.

  • Deformity- either bowleg or knock knees.

  • Stiffness.

Realising these benefits requires commitment and time. Prior to surgery you will usually have tried some conservative treatments such as simple analgesics, weight loss, anti-inflammatory medications, modification of your activities, canes, or physical therapy. Once these have failed it is time to consider surgery. Most patients who have TKR are between 60 to 80 years, but each patient is assessed individually and patients as young as 40 or old as 90 can undergo the procedure with good results.

How Long Will it Last?

Historically the lifespan of a TKR was limited by durability of the plastic (polyethylene) bearing. As this wore a huge number of small plastic particles were generated. This generated a response from the tissue around the knee that caused damage to the joint and eventually loosening of the implant. 

Polyethylene wear was greatly accelerated by the sterilisation process that left the plastic subject to oxidization in its packet. The longer it sat in its packet before being used the more rapidly it failed. This all happened before 1996 and it was this generation of implants that gave rise to the perception that TKRs are good for only 10 years.

Since that time there have been enormous improvements in the wear characteristics of polyethylene. Cross-linked polyethylene (XLPE) is now routinely used in many implants systems and rarely fails by wearing out.

The National  Joint Replacement Registry results show over 90% of TKRs unrevised at 20 years. The Registry also shows that if XLPE is used longevity is substantially improved and in fact infection rather than failure of the plastic is now the leading cause of revision, especially in men (see the figure below).


Before Surgery

TKR is a major procedure that should be undertaken under optimal conditions. This means that your general health needs to be assessed and any correctable problems dealt with prior to surgery. In most circumstances this will involve blood tests, an ECG and an echocardiogram. Ideally this should be done by your GP prior to you being referred for major surgery. This is especially important if you have a known heart condition and have not been seen by your cardiologist in the recent past. Dr McEwen will organize much of the appropriate testing to be conducted prior to your consultation if not already done. This is very important to minimize surgical risk to yourself. Take note of the following:

  • High Blood Pressure (Hypertension) should be controlled and stable.

  • Diabetes should be controlled and stable with blood sugar levels checked regularly.  A HBA1C of 7.0 or less is an optimal level to minimise the risk of an infection following a knee replacement.  An infection is a catastrophic problem should it occur and every attempt should be made to minimise the risk of this complication.  Optimal diabetic control is essential to this.

  • Any cardiac symptoms (chest pains, shortness of breath, palpitations) should be investigated and treated.

  • Sleep apnoea should be investigated and treated.

  • BMI should be less than 40 but preferably less than 35. BMI is a measure of obesity and is calculated by dividing weight in kg by the square of height in meters. For example someone who weighs 100kg and is 1.89m tall will have a BMI 100/1.89x1.89 = 100/3.57 = 28. The normal range for a BMI is 20-25. Every unit of body mass index over 25 carries some measurable additional risk of complication following a knee replacement.  This risk further increases with a BMI over 35 and then rises sharply over 40.  If your BMI is over 40 you should consider losing weight before seeking a total knee replacement.   This should be done with the aid of a nutritionist.

  • Smoking is very dangerous when combined with major surgery. It increases the risk of many serious complications and is one of the major risk factors for developing an infection following a total joint replacement and should be avoided at all costs. Smoking must be ceased prior to surgery. Dr McEwen will not undertake a TKR if you're smoking. This is for your benefit and your benefit only.

  • Staphlococcus aureus is the bacteria responsible for most TKR infections. 30-40% of people are colonised with the bug and walk into the operating theatre covered in it unless a decolonisation procedure is undertaken pre-operatively. This is dome with Betadine gargle painted into the nostrils and Phisohex skin wash for 5 days leading up to surgery. The most important application is on the day of surgery.

Many medications have an effect on bleeding, blood clotting and wound healing. Blood thinning medications  such as Clopidogrel, Warfarin, Pradaxa, Eliquis will need to be ceased prior to surgery. Aspirin is OK so keep taking it right up to surgery of you're on it. Dr McEwen will give specific instructions regarding this. Seek clarification well before surgery if unsure.

Cease any naturopathic or herbal medications 7 days before surgery.

Look after your skin. The skin on the leg being operated on must be free of cuts, scratches, grazes and bites.

Total Replacement: Text

How to Make a Fast Recovery

Learning what to do after your surgery should be learnt before surgery. After surgery you're on the clock in terms of making a fast recovery so any rehab learning curve needs to completed before the clock is ticking. Your habits and attention to detail after surgery have a huge effect of your risk profile, pain management and recovery timeframe. Functional rehab is all about using the way you naturally move around a house as your recovery strategy rather than doing hours of prescribed exercises. This is taught before surgery. Go to the Knee Replacement Exercise Page to get the detail.

The video in this section is very important and should be watched several times prior to surgery and used as a reference during rehab. 

Day of Surgery

You will be admitted to the hospital  on the day of your surgery 
Blood tests may be required on the day of surgery or the day before.
You will meet the nurses and answer some questions for the hospital records.
You will meet your Anaesthetist, who will ask you a few questions.
You will be given hospital clothes to change into and have a shower prior to surgery.
The operation site will be shaved and cleaned.
Approximately 30 minutes prior to surgery you will be transferred to the operating theatre complex.


Surgical Procedure

Surgery is performed under sterile conditions in the operating room under spinal or general anaesthesia. You will be positioned on your back and a tourniquet applied to your upper thigh but used for only a brief period to reduce injury to the thigh muscles. The surgery takes approximately two hours.

For a TKR to work well the prosthetic knee must mimic the patient’s pre arthritic knee as closely as possible. This means that the sizing, positioning and alignment of the TKR need to be matched as closely as possible to each patient’s anatomy within the tolerance limit of the chosen implant.  Sizing, positioning and aligning can be done in 4 ways:

  1. Conventional Instrumentation (Old School). Mechanical jigs are used around or through the centres of the femur and tibia. Cutting blocks are mounted on these jigs and the worn ends of the bones removed by cutting through these blocks.

  2. Computer Assisted Surgery. Position sensors are attached to the bones and used to teach a computer about the specific anatomy of the knee in a process called registration. A customized plan is developed to achieve optimal sizing, positioning and alignment. This plan is then executed using the computer to position the cutting blocks and to check that each step has been completed as per the plan. Used to its full extent Computer Assisted Surgery is a very powerful tool that predictably leads to better sizing, positioning and alignment compared to conventional instruments.

  3. Image derived instrumentation (patient specific tools).  With this technology, patient specific tools are manufactured using a 3D printing process based on a preoperative CT or MRI scan of the knee.  The CT or MRI is sent electronically to the prosthesis manufacturer and a provisional plan is sent back to the surgeon.  The surgeon then performs fine tuning of the intended implant position on line and the tools are subsequently 3D printed to produce this position when applied to the knee.  The tools are then discarded after completion of the procedure.  Image derived instrumentation has not been shown to improve longevity or accuracy of total knee replacement but it has advantages with respect to time and certainly reduces problems related to fat embolism that can occur with conventional instruments.

4. Robotic surgery for knee replacement has been a mainstream technology for partial knee replacement since 2014 and for total knee replacement since around 2018. There are a number of robotic systems available, each of which is linked to a specific prosthesis. Robotic surgery is a natural evolution of computer assisted surgery. In both techniques a virtual model of the knee is created and then a virtual knee replacement is done on a computer. This involves matching the virtual implants to the virtual skeleton and then adjusting the position of the virtual implants to optimise ligamentous tension to produce a balanced knee. Once definitive implant size and position is chosen then the plan needs to be executed. With computer assisted surgery the surgeon places cutting blocks on the skeleton, guided by the computer, so that when the cut is completed it matches the virtual plan. After each step, the executed cut is checked against the plan before moving to the next step. With robotic surgery, a robotic arm places the cutting block or the cutting tool under the surgeon's control. As with computer aided surgery, each step is validated against the virtual plan before moving to the next step. Robotic techniques are generally slightly more accurate than computer aided techniques in terms of reproducing the virtual plan. At the moment, the robots are essentially stupid and have to be told by the surgeon what to do. Within the next few years the robots will become progressively smarter and will evolve to a point where they make better decisions than a surgeon because they will be able to draw against the combined knowledge and experience of millions of cases rather than a surgeon, who even if very experienced, can draw against the knowledge and experience of a few thousand cases. Robotic surgery, like computer assisted surgery is no substitute for selecting the right patient for surgery, for optimising the patient for surgery, for selecting a good implant, for minimising surgical trauma to the knee or for enhancing the patient's recovery after surgery. It is very important that you be guided by your surgeon rather than by hype generated by the manufacturers and owners of the robotic systems. More information on robotic surgey can be found through the following links.

Dr McEwen uses Robotic surgery as the default technology for his total knee replacements.  

Accurate sizing, positioning and alignment make a successful TKR a possibility but constitute only one part of the formula for success.

























The remainder of the formula is ensuring that pain and swelling don’t get in the way of movement. This is called ENHANCED RECOVERY AFTER SURGERY. Many things contribute to this including:

  1. Spinal anaesthesia. A spinal anaesthetic is usually combined with a light general anaesthetic and has several advantages:

    •  It allows the patient to wake without pain and time for secondary pain relief measures to kick in before the limb becomes sensate again. 

    • It dramatically reduces the amount of anaesthetic medicine used so problems like nausea, vomiting, drowsiness and disorientation are much less likely to occur.

    • It allows the anaesthetist to the keep the blood pressure low and even so there is no need to use a tourniquet for long periods (see below).

  2. Limiting Tourniquet Time. A tourniquet prevents blood loss during the operation but causes pain, swelling and wasting of the thigh muscles. If the blood pressure is kept low and even a tourniquet is used for short periods only or not at all without increasing blood loss. Pain is reduced and control of the knee by the thigh muscles is better and recovers faster.

  3. Muscle Sparing Approach. There are several ways to surgically enter the knee. Each has its pros and cons. Muscle sparing approaches do less damage to the quadriceps so control of the knee is better and recovers faster.

  4. Periarticular Injection. The lining of the joint (synovium) is very sensitive and is the source of much of the pain, swelling and scarring after TKR. A periarticular injection of painkillers and anti-inflammatory drugs into the synovium and other tissues around the knee during the TKR reduces pain, swelling and scarring and is particularly effective when combined with a spinal anaesthetic and a cryocuff.

  5. Cryocuff. A cryocuff is a mobile, patient operated ice delivery system that reduces pain and swelling. The cryocuff is applied to the knee after wound closure and will be operational long before the spinal anaesthetic wears off.

  6. Multimodal Analgesia. A combination of drugs are used to manage pain and ensure reasonable sleep after the TKR.

          7. Vitamin C. Vitamin C works as an antioxidant to reduce inflammation         and as a co-factor in collagen crosslinking which can help reduced scarring.


Dr McEwen employs all these strategies routinely. All TKR patients will discharge with a cryocuff which is returned after 2 weeks. You will walk the day of surgery and the vast majority of patients will be home the day after surgery. This does not mean that there will be no pain or swelling but that pain will be manageable with good first aid (elevation / ice / compression).

Bilateral TKR. Knee osteoarthritis frequently affects both knees. Having both knees replaced at the same time has some advantages but also some increased risks and is not applicable to all situations. All patients having both knees replaced will walk the day of surgery and on generally walk out of hospital within 2-3 days.

Outputs from robotic-assisted surgery

How Long in Hospital

The last 10 years has seen a tremendous evolution of "Rapid Recovery"protocols around total knee replacement. Day surgery total knee replacement is a reality for suitable patients and the typical stay in hospital is one  day.

Because the time in hospital a short it is very important to learn how to manage the knee at home long before the surgery. If you are reading this website then that is exactly what you are doing.

Probably the most important thing to understand is that the patient runs the show after discharge and in many ways is master of their own destiny in terms of their experience after discharge. The key is to keep swelling around the knee to a minimum. Rest, ice, compression and elevation (toes above nose) is the key to the whole shooting match. A recently replaced knee that is not overly swollen is completely manageable at home without large quantities of painkillers. Approximately 30% of patients are narcotic free after discharge and most of the rest use small quantities of narcotic for a few nights to help with sleep. Mobility and an exercise program is important but it must not drive swelling. The protocols outlined on the Knee Replacement Exercises page are  specifically designed to reduce the risk of stiffness and blood clots without driving swelling in the wrong direction. 

After Surgery

Getting over major surgery without any problems requires an active approach to prevent problems rather than reacting to problems once they occur. The rule with prevention is “the sooner the better”. Therefore there are a few things the patient should actively take responsibility for:

  1. Ice therapy. Turn over the water in the cryocuff at least hourly unless sleeping.

  2. Blood Clot Prevention. Drink plenty of fluids. Do calf pump exercises when lying or sitting. Be prepared to be out of bed a few hours after surgery. Being up quickly is the most important.

  3. Pain Control. Don’t let pain ramp up. As soon as you are aware that pain is increasing let the nursing staff know. Much less painkiller is required to keep pain away compared to beating severe pain into submission.

The nursing staff will assist you with these issues but remember to actively take control of your own well-being.

Physiotherapy begins the day of surgery and will be a daily event until discharge. The aim is to have you independently mobile and self caring as quickly as possible. A wheelie-walker is used to aid balance and is much easier to use than crutches.

The criteria for discharge are a dry wound, good pain control with oral medications, no high temperatures and a pass mark from the physiotherapist including on stairs. Many will achieve this within 24 hours and nearly all within 48 hours. Make sure you have your discharge envelope with scripts, information sheets and appointment card when you leave. 

Remember that swelling is the enemy of movement. Use the cryocuff and keep the leg up. Lots of small walks around the house followed by periods of elevation and ice is the correct approach.

Sleep in whatever position is most comfortable as long as the knee is elevated. DO NOT sleep only on your back with the knee straight early on as it will result in more swelling and pain.

The wound should be clean and dry. Notify Dr McEwen immediately if this is not the case. Do do with a photo through My Mobility.

You will have a postoperative appointment scheduled for 2 weeks after the surgery. No sutures will be removed at this time as they are all under the skin .An experienced musculoskeletal physiotherapist will see you at the same time so leave plenty of time for this. There is no need for supervised physiotherapy between discharge from hospital and your appointment. 

Sleep disturbance is very common after TKR and tends to persist  after walking is easy. No drug will make this normal. The fastest way to sleep well is to get movement quickly so structured physiotherapy can stop. This allows the knee to settle much faster.

Risks and complications

As with any major surgery, there are potential risks involved. The decision to proceed with the surgery is made because the advantages of surgery outweigh the potential disadvantages.

It is important that you are informed of these risks before the surgery takes place.

Complications can be medical (general) or local complications specific to the knee.

Medical complications include those of the anaesthetic and your general well being. Almost any medical condition can occur so this list is not complete. Complications include:

  • Allergic reactions to medications.

  • Blood loss requiring transfusion with its low risk of disease transmission.

Local Complications

  • Infection. Infection can occur with any operation. In the knee this can be superficial or deep. Superficial infections are treated with antibiotics. Deep infections always require surgical treatment as well as antibiotics. Deep infection is an uncommon but very serious complication and many measures are employed during the course of having a TKR to prevent it. In most cases of deep infection the joint can be salvaged but in certain circumstances the TKR will need to be removed and another implanted after the infection is cured.

  • Blood Clots (Deep Venous Thrombosis).These can form in the calf muscles and can travel to the lung (Pulmonary embolism). These can occasionally be serious and even life threatening. If you get calf pain or shortness of breath at any stage, you should notify your doctor. As with infection, many measures are employed to prevent this complication. These include compression stockings, calf compressors, IV fluids, blood thinning medications but by far the most important is early mobility.

  • Stiffness in the Knee (Arthrofibrosis). As discussed above implant positioning and control of pain and swelling are important if the TKR is to bend well. Other factors including how well the knee bent before surgery and diligent attention to physiotherapy and home exercise are also important. If there is poor progression of movement of the TKR in the first 4-8 weeks after surgery a manipulation under anaesthesia may be required to break down scar forming in the joint.

  • Neurovascular injury (Damage to nerves and blood vessels). All the major nerves and vessels that pass the knee are within a centimetre of the surgical envelope of a TKR. Great care is taken to avoid damage to these important structures. The Common Peroneal Nerve (CPN) is the most commonly but rarely injured but even this occurs rarely. Injury to the CPN (usually caused by swelling rather than direct injury) causes a foot drop. In most cases this recovers spontaneously over a period of weeks / months.

  • Wear. The plastic liner eventually can wear out over time. Improvements in the mechanical properties of the plastic have extended the useful lifespan of a TKR and in most circumstances it is likely that the implant will function beyond 20 years.

  • Numbness. The skin on the outside edge of the incision will be numb after the surgery. Most people are very aware of this in the first 6 months after surgery. The sensation of numbness fades with time but probably never returns absolutely to normal.

  • Heart attacks, strokes, kidney failure, pneumonia, bladder infections Complications from nerve blocks such as infection or nerve damage.

  • Serious medical problems can lead to ongoing health concerns, prolonged hospitalization or rarely death.


Very commonly severe knee arthritis is associated with changes in the shape and length of the limb. Both are corrected at the time of a TKR. If both knees are deformed and only one is corrected there will be noticeable asymmetry of limb shape and length. This persists only until the other knee is replaced and is not an issue at all if both knees are replaced at the same time.

The National Joint Replacement Registry

The Australian Orthopaedic Association set up the registry 20 years ago. Virtually every TKR done in Australia over the last 20 years is recorded in the registry. If the joint is revised that also is recorded. The registry produces an annual report that is accessible at

An abbreviated report put together fo patients by the registry in available here.

The registry examines prosthetic survivorship against many factors and helps guide the profession in terms of the most effective prosthetic combinations. The registry also provides individual surgeons with their individual data.

Only the surgeon can access this data but you can and should ask your surgeon to disclose his data so that you know how your surgeon compares to the average. 


Surgery is not a pleasant prospect for anyone, but for some people with arthritis, it could mean the difference between leading a normal life or putting up with a debilitating condition. Surgery can be regarded as part of your treatment plan—it may help to restore function to your damaged joints as well as relieve pain.

TKR is one of the most successful operations available today. It is an excellent procedure to improve the quality of life, take away pain and improve function. In general, over 90% of knee replacements survive more than 20 years, depending on age and activity level.

Surgery is only offered once non-operative treatment has failed. It is an important decision to make and ultimately it is an informed decision between you, your surgeon, family and medical practitioner.

Although most people are  happy with their new knee, complications can occur and you must be aware of these prior to making a decision. If you are undecided, it is best to wait until you are sure this is the procedure for you.

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