A total knee joint replacement is an operation to remove damaged parts of the knee joint and replace them with metal and plastic parts. The aim of the surgery is to relieve pain and restore function to the joint.
This is a common operation undertaken in New Zealand as planned (non-urgent) surgery in both public and private hospitals, typically involving a 5-7 day hospital stay. If the operation is done in a private hospital and paid for by the patient or through health insurance, the cost is likely to be between $23,600 and $29,000.
Why have knee replacement surgery?
Severe knee pain or stiffness that limits daily activities (eg: walking, climbing stairs, getting in and out of chairs) is the main reason that knee replacement surgery may be recommended. Other reasons are knee pain at rest and knee deformity. These problems are likely be the result of osteoarthritis or rheumatoid arthritis.
Most people who undergo total knee replacement are aged 50 to 80 years. However, eligibility for knee replacement surgery is primarily based on a person’s level of pain and disability, not their age.
An orthopaedic surgeon will assess the need for a knee replacement taking into account medical history and symptoms, physical examination (especially knee range of motion, stability, strength, and alignment), blood tests, x-rays or magnetic resonance imaging (MRI) scans of the damaged knee.
A knee replacement is a major operation and there are many things you should discuss with your surgeon, including the risks and benefits of the surgery.
An artificial knee joint (prosthesis) has smooth surfaces that replace the worn surfaces within the knee joint. The prosthesis is made of metal alloys and hard plastic components that fit together during surgery. The procedure usually takes about 2 hours.
Surgery begins with an incision being made over the front of the knee joint. The surgeon will expose the knee joint, loosen the muscles and ligaments surrounding it, and turn the kneecap out of its place. The worn surfaces within the joint, including the back part of the kneecap, are removed and the ends of the bones are precisely reshaped. The components of the artificial knee joint are then attached to the bone ends using specialised bone cement and fitted together. The muscles and ligaments are repositioned and, if necessary, the ligaments are adjusted to achieve the best possible knee function.
Knee joint replacement surgery can be performed under a spinal or general anaesthetic. This will be discussed with the surgeon and anaesthetist prior to surgery and a decision made as to which is most appropriate.
At the completion of the surgery, a tube will be inserted to drain excess fluid from the new joint. The surgeon then closes the layers of tissue and the skin with stitches and a dressing is placed around the knee.
Antibiotics are given during and after the operation to prevent the development of infection in the new joint. A blood transfusion may also be required.
Measures to prevent the formation of blood clots and reduce leg swelling may be prescribed. These may include compression stockings, inflatable leg coverings (compression boots), and blood thinning medication. Foot and ankle movement also is encouraged immediately following surgery to encourage blood flow in the leg muscles, which also helps to prevent leg swelling and blood clots.
After surgery, your surgeon and a physiotherapist or physical therapist will provide recovery and movement guidelines. Initially these include passive exercises, and progress to gentle knee-bending exercises and walking. Ongoing exercises are designed to increase the range of motion of the new joint and to strengthen the surrounding muscles, particularly the thigh muscle (quadricep). Strength in the quadricep will help to keep the knee joint stable, therefore protecting the new joint.
The success of the surgery depends on following the recovery and movement instructions while in hospital and on carrying out the prescribed exercises when at home.
The time spent in hospital can vary from about 5 to 7 days. Crutches will need to be used for up to 6 weeks after the operation. By 6 weeks, the majority of people should be able to return to a range of normal activities, including driving.
Risks of surgery
As with any surgical procedure there are risks involved with total knee joint replacement. As well as general risks of infection and risks associated with anaesthesia; risks specific to this surgery include:
- Blood clots can form in one of the deep veins in the leg (deep vein thrombosis or DVT).
- The legs may not be the same length after the operation
- Nerves can be injured from swelling or pressure resulting in permanent pain, numbness, or loss of function
- The knee prosthesis may become loose and require further surgery.
It is usual to see the surgeon 2 to 6 weeks after surgery to assess recovery. Long-term follow up may also be recommended in order to monitor the wear of the artificial knee joint.
It may be that replacement (revision) of the artificial knee joint is required if it loosens and becomes painful. Most modern total knee replacements last at least 15 years if properly cared for and not subjected to too much stress.
Excessive activity or weight speeds up the normal wear of the replacement joint and may cause it to loosen and become painful. Therefore, people are advised not to engage in high-impact activities such as running, jogging, skiing, and jumping after the surgery. Instead, low-impact activities, such as walking, swimming, playing golf, light hiking, cycling, and dancing, are recommended.
American Academy of Orthopaedic Surgeons (2020). Orthoinfo: Total knee replacement (Web Page). Rosemont, IL: American Academy of Orthopaedic Surgeons. https://orthoinfo.aaos.org/en/treatment/total-knee-replacement [Accessed: 25/06/20]
Mayo Clinic (2017). Knee replacement (Web Page). Rochester, MN: Mayo Foundation for Medical Education and Research. https://www.mayoclinic.org/tests-procedures/knee-replacement/about/pac-20385276 [Accessed: 25/06/20]
NHS (2019). Knee replacement (Web Page). Redditch: National Health Service (NHS) England. https://www.nhs.uk/conditions/knee-replacement/ [Accessed: 25/06/20]
Palmer, S.H. (2020). Total knee arthroplasty (TKA) (Web page). Medscape Drugs and Diseases. New York, NY: WebMD LLC. https://emedicine.medscape.com/article/1250275-overview [Accessed: 25/06/20]
Southern Cross Annual Report Summary (2020). How much does it cost? www.southerncross.co.nz/annualreport
Last Reviewed – June 2020