Knee replacement surgery: who is it for and what is recovery like?

What is a knee replacement?

In knee replacement surgery (arthroplasty) the damaged ends of the bones in the joint are removed and replaced with metal and plastic parts. The most common type is a total knee replacement: the lower end of the thigh bone and the upper end of the shin bone are replaced, and in some people the back of the kneecap is covered as well ^[1].

A partial (unicompartmental) replacement is used when arthritis (osteoarthritis) affects only one half of the knee; the cut is smaller and recovery is usually quicker ^[1]. NICE recommends offering people whose osteoarthritis is confined to the inner part of the knee a choice between partial and total replacement, with a discussion of the benefits and risks of each ^[5].

Who is it considered for?

Surgery is not the first option. According to NICE, referral for joint replacement is considered when pain, stiffness, reduced function or progressive deformity substantially affect quality of life and non-surgical treatment such as exercise, weight loss and pain relief has not been enough or is unsuitable; the decision rests on clinical assessment, not on scoring systems ^[6]. Typical situations in which the operation is recommended are ^[4]:

• Severe pain or stiffness that limits walking, climbing stairs and getting up from a chair
• Pain that continues at rest, by day or by night
• Long-standing swelling that does not settle with rest or medicines, or bowing of the knee inwards or outwards
• Too little benefit from medicines, injections and physiotherapy

Assessment and getting ready

At assessment you are asked about your symptoms and general health, the knee is examined and X-rays are taken; blood tests or an MRI scan are requested only when needed ^[4]. The alternatives to replacement, expected benefits, risks, the possible need for more surgery in the future and the options for anaesthesia should be discussed with the patient ^[5].

A general health check is carried out several weeks before the operation, with any tests that are needed; the surgeon says which medicines to stop, and major dental treatment is best completed beforehand ^[4]. NICE recommends advice on exercises to do before and after surgery, weight management, diet and stopping smoking ^[5]. Arranging help at home for the first weeks, removing loose rugs and fitting handrails make things easier ^[4].

The operation and hospital stay

The operation is done under a general anaesthetic (asleep) or a spinal anaesthetic (numb from the waist down) and usually takes 1 to 2 hours ^[1][4].

According to NICE, rehabilitation should start on the day of surgery if possible and no later than 24 hours afterwards ^[5]; the first steps are taken with crutches or a walking frame ^[2]. Compression stockings and anticoagulant medicines may be advised to reduce the risk of blood clots ^[3][4].

Length of stay varies: the NHS states that people usually leave hospital 1 to 4 days after the operation ^[2]; OrthoInfo reports that some patients go home the same day while others stay overnight or longer ^[4].

Recovery and physiotherapy

Full recovery can take several months or longer; this varies with age and general health and is usually shorter after a partial replacement ^[2]. Before you leave hospital you are taught exercises to do at home ^[2][5]; people who struggle with daily activities, or who are not reaching their goals on their own, should be offered supervised rehabilitation ^[5]. The time frames given by the sources are general figures and vary from person to person:

• Walking: crutches or a frame at first, then one crutch and a stick; those who feel ready can try walking without an aid after about 6 weeks ^[2]
• Daily activities: most everyday activities can be resumed within 3 to 6 weeks ^[4]
• Driving: the NHS advises waiting at least 6 weeks after a total replacement or 3 weeks after a partial one ^[2]; OrthoInfo states that most people resume driving at about 4 to 6 weeks ^[4]
• Work: usually after about 6 to 12 weeks, depending on the type of work ^[2]
• Household tasks that involve heavy lifting or carrying: avoided for the first 3 months ^[2]

Risks and complications

Knee replacement is a common and safe operation; most people have no complications, and those that occur are usually minor and treatable. The risk depends on age and general health ^[3]. The main risks are:

• Infection: this can develop in the wound or around the implant days, weeks or even years after the operation. Wound infection is usually treated with antibiotics; deep infection may need further surgery ^[3][4]
• Blood clots: a clot can form in the leg veins (deep vein thrombosis); if it travels to the lungs (pulmonary embolism) the consequences can be serious ^[3][4]
• Stiffness: the knee may not bend well enough; this usually improves with physiotherapy ^[3][4]
• Persistent pain: a small number of patients continue to have pain after the operation ^[3][4]
• Wear and loosening: the implant surfaces can wear over time and the components can loosen ^[4]
• Injury to a nerve, blood vessel or ligament: this is not common ^[3][4]

How long does a knee replacement last?

With normal use, the plastic part of every knee replacement wears over time; excessive loading and excess weight can speed this up ^[4]. An analysis published in The Lancet in 2019, which pooled data from national joint registries, estimated that about 82% of total knee replacements and about 70% of partial replacements last 25 years; more information is needed to predict exactly how long a specific implant will last ^[7]. Another replacement may be needed later in life; the NHS states that this is not common ^[3].

Living with a knee replacement

Most people have much less pain and find everyday activities easier; however, a replacement does not allow you to do more than you could before the arthritis developed. Full movement of the knee often does not return; most patients can straighten the knee almost fully and bend it enough to climb stairs and get in and out of a car ^[4].

Low-impact activities such as walking, swimming, golf, cycling and dancing are suitable; most surgeons advise against sports that involve running and jumping ^[4]. Kneeling is sometimes uncomfortable but is not harmful ^[4]; during recovery, however, you should not kneel until your doctor says you can ^[2]. New or worsening pain, a limp or loss of function in a replaced knee needs orthopaedic assessment ^[5].

When not to wait

After the operation, seek care without delay if you have any of the following; they can be signs of infection or a blood clot ^[3][4]:

• A high temperature, chills or shivering
• Oozing or pus from the wound
• Redness, swelling, tenderness or pain in the knee that is not settling or is getting worse
• Increasing pain or swelling in the calf, or throbbing or cramping pain in the leg
• Sudden breathlessness or chest pain (a clot may have travelled to the lungs): go to an emergency department or call an ambulance

Sources

1. How a knee replacement is done. NHS (nhs.uk), 2026. nhs.uk
2. Recovering from a knee replacement. NHS (nhs.uk), 2026. nhs.uk
3. Complications of a knee replacement. NHS (nhs.uk), 2026. nhs.uk
4. Total Knee Replacement. American Academy of Orthopaedic Surgeons (OrthoInfo), n.d.. orthoinfo.org
5. Joint replacement (primary): hip, knee and shoulder (NG157). National Institute for Health and Care Excellence (NICE), 2020. nice.org.uk
6. Osteoarthritis in over 16s: diagnosis and management (NG226). National Institute for Health and Care Excellence (NICE), 2022. nice.org.uk
7. How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up. The Lancet (Evans JT, et al.), 2019. pubmed.ncbi.nlm.nih.gov