Knee replacement surgery: Causes, risks, procedure, and recovery

What is knee replacement surgery?

Knee replacement surgery replaces nonfunctional parts of the knee joint with metal and plastic prostheses. The goal is to ease pain, restore function, and help patients return to everyday activities. 

Knee replacement becomes an option when nonsurgical treatments, such as medicines, injections, walking aids, or low-impact exercises, no longer relieve symptoms. 

Total vs partial knee replacement

A total replacement is considered if arthritis or injury has damaged the entire knee. It involves resurfacing the knee joint and replacing all three compartments (the inside and outside of the knee, and the front of the knee between the kneecap and the femur) with artificial parts. 

A partial knee replacement is an option if the damage is confined to one area of the knee. This surgery only replaces the damaged portion, leaving healthy ligaments, bone, and other parts intact. 

With smaller incisions and less discomfort, patients usually recover faster compared to those who’ve had a total knee replacement. 

When do people need a knee replacement operation?

Knee replacement surgery is often recommended when other treatments aren’t working and severe symptoms are making daily life difficult. The surgery can restore your independence and greatly improve your quality of life.

Factors contributing to the need for surgery may include:

• Arthritis and joint damage: Severe osteoarthritis wears away cartilage, causing bones to rub together, leading to pain, stiffness, and swelling. Rheumatoid arthritis, an autoimmune disease, can damage the joint lining, causing pain and restricted movement. Post-traumatic arthritis may develop after a serious injury, such as a fracture or torn ligament.

• Failed nonsurgical treatments: Surgery is considered when physiotherapy, exercise, weight management, medicines, joint injections, or walking aids no longer relieve pain or improve mobility.

• Injuries and deformities: Surgery can correct knee shape or restore function in patients with past injuries or knee deformities (such as bowing or instability). 

• Impact on daily life: Your doctor may also consider surgery if knee pain interferes with your sleep, work, or social activities.

Risks and potential complications

Knee replacement surgery is generally safe and effective, but like any operation, it carries some risks. Most complications are rare, and your medical team will take steps to reduce their likelihood. 

Common risks include:

• Infection. This can occur at the incision site or around the implant. Mild infections may be treated with antibiotics, but severe infections could require further surgery. The risk of infection after knee replacement is less than 1 in 100 patients.
• Blood clots. These can form in the leg veins. If a clot travels to the lungs, it can cause a potentially life-threatening pulmonary embolism. After surgery, you’ll be encouraged to move around and wear compression stockings. You may also receive blood-thinning medicine.
• Nerve or blood vessel damage. Although rare, nerves or vessels around the knee can be damaged during surgery. This may cause numbness, weakness, or pain. 
• Implant wear or loosening. The artificial joint parts can loosen or wear out over time, sometimes requiring revision surgery.
• Dislocation or fracture. The implant or bone around it may break or move out of position.
• Persistent pain or stiffness. Some people continue to experience pain, discomfort, or limited movement even after recovery.

Other possible risks include:

• Bruising and swelling, which may settle over several weeks
• Heart attack, stroke, or, very rarely, death
• Anaesthetic side effects 
• Post-surgery confusion
• Bladder issues.

Talk to your surgeon about any concerns before surgery so you understand your risks and how they can be managed.

Getting knee replacement surgery in New Zealand

In New Zealand, your knee replacement surgery may be paid for by the Accident Compensation Corporation (ACC), the public health system, or the private health system (paid out of pocket or through health insurance). 

Cover through ACC

The ACC may cover your knee replacement if surgery is required because of an accident. However, ACC does not cover knee replacements that are due to gradual wear and tear, aging, or medical conditions like arthritis.

The public health system

For situations not covered by ACC, the public health system provides free elective surgery. However, long waiting times and strict criteria mean it can be challenging to get on the wait list. Not everyone with knee pain will qualify, and those who do may have to wait several months or more than a year for treatment.

As of the end of January 2025, average wait times for knee surgery varied widely across hospitals, from 107 days (Christchurch Hospital) to 721 days (Southland Hospital).

Private surgery

If you can’t get on the public waiting list or your pain means you simply cannot wait, private surgery is another option. The benefits of going private include faster treatment and more choice about when and where you have the operation. The downside is the high cost of knee surgery, which can range from $25,000 to over $33,000.

Having medical insurance can make a big difference. The best private health insurance plans may pay for some or all of your surgical expenses. It’s also possible that other types of insurance cover already in place could help pay towards your costs (for more information, see How insurance can help with knee surgery). Check with your insurer or broker to confirm what you’re covered for.

Knee replacement procedure

Before surgery

Stay healthy

• Keep active with gentle walking or other exercises
• Eat well and maintain a healthy weight
• Stop smoking and limit alcohol before and after surgery, as these can impact your healing and recovery
• Practise deep breathing to keep your lungs healthy.

Take your tests and check your medicines

• You will undergo diagnostic tests to make sure you’re ready for surgery. These may include blood and urine tests and an ECG
• Tell your doctor about all medications and supplements
• Follow your doctor’s instructions on what medications to take and which ones (including supplements and herbal remedies) to stop before the surgery
• Complete any major dental work before surgery.

The night before

• Don’t eat or drink after midnight unless told otherwise
• Pack your hospital bag and key documents.

Prepare for recovery

• Ensure someone can bring you home from hospital
• Arrange help with meals, bathing, laundry, and shopping
• Create a living space on one level to avoid climbing stairs
• Install grab rails, use a shower chair, and remove loose rugs.

During surgery

You’ll change into a gown and be made comfortable before your anaesthetic. You'll receive either:

• A spinal or epidural anaesthetic – you won’t feel anything from the waist down
• A general anaesthetic – you’ll be asleep throughout the surgery.

The operation usually takes one to two hours. Your surgeon will:

• Make a small cut over your knee
• Remove the damaged bone and cartilage
• Fit smooth metal and plastic parts to restore your joint.

Your knee will then be closed and gently bandaged.

After surgery

You’ll wake up in the recovery area, where nurses will monitor you closely. Once you’re stable, you’ll move to your hospital room, or sometimes go home the same day. Most people stay in hospital for two to four nights, although this can be shorter or longer depending on your health and the complexity of the surgery.

Your team will help reduce complication risks and keep you comfortable through:

• Blood clot prevention: walking early, compression stockings, and sometimes blood thinners
• Wound care: clean dressings and advice on or help with showering
• Pain control: a mix of medicines to keep pain manageable.

Going home
You’ll be given exercises, wound care advice, prescriptions, and follow-up details. Most people return to daily activities within a few weeks, gaining strength and confidence as they recover.

Knee replacement recovery and rehabilitation

Recovery at home

• Keep the wound clean and dry. Do not soak the incision until it has fully sealed 
• Watch for warning signs like fever or chills, increased pain, redness or swelling, drainage or heavy bleeding from the wound, calf or leg pain or swelling, and call your doctor if these appear. Also, contact a healthcare provider if you experience chest pain, shortness of breath, ongoing nausea, or worsening flexibility
• Eat a balanced diet, consider fibrous foods, and drink plenty of fluids, as these can help with healing and managing constipation
• Make your home safe. Remove tripping hazards, like loose rugs and cords. Add grab rails in the bathroom and along stairs 
• Keep snacks, water, and commonly used items within easy reach at waist height to avoid bending or stretching
• Use the mobility aid you were given, such as crutches or a walker, until your healthcare team says it is safe to stop. As your strength and balance improve, you’ll gradually rely less on walking aids until you can finally walk on your own without a limp 
• Keep moving to build muscle strength and prevent joint stiffness. Follow the home exercise plan from your physiotherapist. Short, regular walks on even ground are best, especially in the first few weeks
• Talk to your doctor before engaging in sports, strenuous activities, or taking short or long flights
• Let your GP or dentist know you have a knee replacement before any future surgery or dental work.

What is the recovery time for knee replacement?

Everyone heals at a different pace. Younger or fitter people may move ahead more quickly, but it’s important not to push too hard. Older adults or those with other health conditions may take longer and need extra support. 

Most people resume basic daily tasks within 3 to 6 weeks and driving at 4 to 6 weeks after surgery. Those with sedentary jobs may be able to return to work between 6 and 8 weeks, while returning to physically demanding jobs may take longer. 

Knee surgery outcomes

Most people enjoy a significantly better quality of life after their knee replacement surgery. Chronic pain is eased, mobility improves, and daily tasks, like climbing stairs or walking, become easier. Many patients regain independence and return to hobbies they had given up, such as cycling, swimming, or gardening. 

Limitations

It is important to have realistic expectations. A new knee can improve motion, but may not restore it fully. Most people can straighten their leg and bend it enough to climb stairs or get into a car, but deep bending or squatting may remain difficult. 

You may notice some stiffness or numbness around the incision. Kneeling can feel uncomfortable, though it is not harmful. Some people also hear clicking in the knee when moving - this is normal and usually fades over time.

How long do knee replacements last?

Modern knee replacements are very durable. Most still work well after 15 years, and many last 20 years or longer. However, the implant may eventually wear out and need a revision surgery. Factors such as age, activity levels, and overall health can influence how long your new knee lasts.

Protecting your new knee

You can help extend the life of your knee replacement by:

• Taking part in regular, light exercises to keep the joint strong
• Avoiding falls and using support when needed
• Following your surgeon’s advice about dental care, including antibiotics if recommended
• Attending regular check-ups.

Activities after knee replacement

After recovery, you can enjoy low-impact exercise like walking, swimming, golf, and cycling. These keep you mobile without stressing the joints. Avoid high-impact activities, such as running, basketball, or contact sports. By making the right choices, you can protect your new knee and enjoy many years of comfortable movement.

How insurance can help with knee surgery

Knee replacement surgery can be life-changing, but it is also expensive if you need to go private. In New Zealand, the public system offers knee replacements, but strict criteria and long waiting lists mean you could be left in pain for months or even years. 

Having the right insurance can ease both the cost of private surgery and the wait, so you can focus on getting back to your work, hobbies, and everyday life sooner.

Health insurance

If you have comprehensive private health insurance, your policy may cover many or all of the costs related to your surgery, including hospital stay, surgeon’s fees, and diagnostic tests. With private cover, you often get faster access to surgery, shorter waits, and sometimes the choice of your surgeon or hospital. 

However, ‘everyday’ health insurance plans don’t usually cover big-ticket procedures, like knee arthroplasty. Consult an insurance adviser and consider the ins and outs of a health insurance product before you purchase it.

Also note that if your knee surgery is due to a pre-existing condition, it may be excluded from your cover. It's a good idea to have your insurance plan in place before you develop health problems, rather than later.

Other types of insurance

Health insurance isn’t the only form of cover that could support you. Depending on your situation, other types of insurance may provide financial benefits, which you can use for private surgery, home modifications, or to replace the income you lose due to your health condition.

• Trauma insurance – pays a lump sum if you’re diagnosed with a covered condition, such as severe rheumatoid arthritis
• Total and permanent disability insurance – provides a payout if you suffer a permanent disability that prevents you from returning to your occupation
• Income cover or mortgage protection insurance – pays a monthly benefit if your condition keeps you off work, helping you stay on top of your medical bills, housing payments, and living costs.

Why work with an insurance broker 

Because everyone’s health and financial situation is unique, choosing the right insurance product can be confusing. Policywise can help by comparing policies, clarifying how insurers handle pre-existing conditions, and ensuring your cover offers adequate support if you need costly procedures or develop serious health conditions later on. It’s also a good idea to get cover before health concerns arise, so you’re not limited by exclusions or stand-down periods.

RECOMMENDED READINGS

What type of insurance do I need?

Long waiting lists in NZ's public health system

Knee replacement cost in NZ: Prices, wait times, and insurance

Knee care tips for Kiwis

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