Bilateral knee replacement means replacing both knee joints, either in one operation (simultaneous) or in two operations weeks or months apart (staged). Doing both at once means one anaesthetic, one hospital stay and one rehabilitation, and meta-analyses find fewer reoperations and lower cost, but a higher chance of blood transfusion and a small but consistent rise in death within the first year. Surgeons offer the simultaneous option to fitter patients and prefer staging for older people and those with heart, lung or kidney disease.
What does bilateral knee replacement mean?
Bilateral knee replacement means both knees are replaced, and the word that matters is whether it is simultaneous or staged. In a simultaneous bilateral replacement the surgeon replaces both knees in one sitting under one anaesthetic, usually one knee after the other, which Indian surgeons often call sequential simultaneous bilateral total knee arthroplasty (SSBTKA). In a staged bilateral replacement the knees are done in two separate operations, with a gap of weeks or months for the first knee to recover.
Each knee gets the same operation as a single replacement. MedlinePlus describes it: the surgeon removes damaged cartilage and bone and fits metal and plastic parts to the end of the thigh bone, the top of the shin bone and the back of the kneecap, under general or spinal anaesthetic, in about 2 hours per knee. The Cleveland Clinic says a total replacement covers all three compartments of the knee while a partial replacement covers only the damaged part.
Both knees need replacing when arthritis has worn both joints to the point where, as MedlinePlus puts it, pain disrupts sleep or normal activities and other treatments have not helped. The NHS lists what should have been tried first: weight loss, low-impact exercise and physiotherapy, pain relief medicines and steroid injections. Severe osteoarthritis in both knees is common in India, where the Mumbai series below drew 380 simultaneous bilateral patients from a single hospital in six years, so the simultaneous-or-staged question comes up often in an orthopaedic surgeon's clinic.
Who qualifies for both knees at once?
Patients who are fit apart from their arthritis qualify for simultaneous surgery; patients with significant heart, lung, kidney or liver disease are usually staged. A 2020 Mumbai cohort study in the Journal of Clinical Orthopaedics and Trauma, which followed 380 simultaneous bilateral and 754 single-knee patients from a tertiary hospital, lists the conditions that ruled patients out of simultaneous surgery:
- Active ischaemic heart disease or reduced heart pumping function.
- Breathlessness, poor exercise capacity or significant lung disease.
- Body mass index above 40.
- Kidney impairment (raised creatinine) or chronic liver disease.
- Poorly controlled diabetes.
- Previous stroke, or major peripheral vascular disease with stents or bypass.
The 2019 meta-analysis in Medicine states that its authors prefer staged procedures for elderly patients with moderate to severe symptoms in both knees, and advise caution in selecting simultaneous surgery for patients with cardiac comorbidities. The 2025 meta-analysis in Knee Surgery and Related Research notes that surgeons commonly exclude older patients and those with significant comorbidities, and that outcomes for higher-risk (ASA class 3) patients can be comparable at high-volume centres. None of the three meta-analyses pooled a specific age cut-off.
In practice this means a pre-operative assessment by a physician or cardiologist decides, not the patient's preference alone. The Mumbai hospital sent 8.2% of its simultaneous bilateral patients to intensive care against 2% of single-knee patients, so a hospital offering both knees at once should have an ICU and a blood bank on site.
What are the risks of simultaneous surgery compared with staged?
The risks that rise with simultaneous surgery are death in the first year, blood transfusion and, in older reviews, blood clots; the absolute numbers are small but consistent.
| Outcome, simultaneous vs staged | Result | Source |
|---|---|---|
| Mortality | OR 1.55 (95% CI 1.16 to 2.08); 0.66% vs 0.43% | Cureus 2023, 37 studies, 201,000 patients |
| First-year mortality | OR 2.43 (95% CI 2.02 to 2.92); no difference in hospital or year two | Knee Surg Relat Res 2025, 42 studies, 567,915 patients |
| Mortality | OR 1.41 | Medicine 2019, 18 studies, 92,782 patients |
| Blood transfusion in hospital | OR 3.99 (95% CI 3.10 to 5.13) | Knee Surg Relat Res 2025 |
| Deep vein thrombosis | OR 1.21 (95% CI 1.06 to 1.39) | Medicine 2019 |
| Pulmonary embolism | OR 1.39 (95% CI 1.16 to 1.67) | Medicine 2019 |
| Neurological complications, first year | OR 1.48 (95% CI 1.28 to 1.71) | Knee Surg Relat Res 2025 |
An odds ratio of 1.55 means the odds of dying were about 55% higher, from a low base: the Cureus review's 0.66% against 0.43% is roughly 1 extra death per 430 patients. The 2025 review found no significant difference in thromboembolic events overall, so the clot signal from 2019 is not settled.
The Indian data point the same way. In the Mumbai series (both knees against one knee), transfusion was 4% against 0.3%, cardiac complications 1.6% against 0.4%, deep infection 0.8% against 0%, and mortality 0.8% against 0.3%, not statistically significant; function scores were comparable.
All three meta-analyses warn that nearly every included study was retrospective, so healthier patients were probably steered towards simultaneous surgery and the true added risk may be larger than these figures show.
What are the benefits of doing both knees at once?
The benefits are one anaesthetic, one hospital stay, one rehabilitation, fewer second operations and lower total cost. The 2025 meta-analysis found reoperation odds of 0.65 (95% CI 0.61 to 0.69) with simultaneous surgery, lower in-hospital joint infection (OR 0.59, 95% CI 0.40 to 0.89), fewer periprosthetic fractures in the first year (OR 0.46), and a mean in-hospital cost saving of US$7,063 across four studies. The 2019 Medicine review likewise found lower odds of deep infection (0.71, 95% CI 0.63 to 0.80) and respiratory complications (0.76, 95% CI 0.66 to 0.88), with no difference in cardiac complications or revision.
The practical benefit is time. The NHS timeline for one knee runs 1 to 4 days in hospital, about 6 weeks on crutches or a stick, 6 to 12 weeks off work and several months to full recovery; a staged patient goes through that twice, with the second operation typically scheduled once the first knee is strong. In the Mumbai series the median stay was 4 days for both knees against 3 days for one.
For an Indian family the cost of two admissions, two sets of pre-operative tests and two periods of a carer's leave is real. Whether that saving is worth the added first-year risk is the trade-off the last section is about.
How long is recovery after bilateral knee replacement?
Recovery follows the same milestones as a single knee, with both knees healing at once, so the calendar is shorter than two staged recoveries. The NHS milestones give the frame: walking with a frame or crutches from the first day, home in 1 to 4 days, compression stockings for at least 6 weeks, stitches out at about 10 days, walking without an aid at about 6 weeks, driving after 6 weeks, work at 6 to 12 weeks and no heavy housework for 3 months. MedlinePlus puts full recovery at 4 months to a year, and the Cleveland Clinic says pain is worst in the first few weeks.
With both knees done, expect:
- A longer hospital stay (median 4 days in Mumbai against 3) and a higher chance of a night in ICU.
- A higher chance of transfusion, so the hospital checks haemoglobin beforehand.
- Exercises for both knees from day one, under a physiotherapist.
- Help at home in the first weeks: the NHS says no cross-legged sitting for 6 weeks and no kneeling until cleared.
> See a doctor the same day if either calf becomes painful or swollen, you have fever, or a wound oozes. Call 112 if you have chest pain or difficulty breathing, which can mean a clot in the lung.
The NHS says a knee replacement lasts about 25 years, and the 2019 Lancet meta-analysis found 82% of total knee replacements still in place at 25 years.
How should you decide between simultaneous and staged?
Decide on your medical fitness first and your convenience second, with the surgeon, an anaesthetist and, if you have heart disease, a cardiologist in the room. The evidence supports a simple rule: with no significant heart, lung, kidney or liver disease, controlled diabetes and a BMI under 40, simultaneous surgery at a high-volume hospital with an ICU is a reasonable choice that saves time, money and a second operation. If you are elderly or have those conditions, the authors of the 2019 Medicine review prefer staging, and the Mumbai hospital would have staged you.
Questions to ask the surgeon:
- How many simultaneous bilateral replacements do you and this hospital do a year, and what are your transfusion and ICU rates?
- Which of my conditions would move me to the staged list?
- What is the blood clot prevention plan, and for how long?
- If staged, what gap between the two knees do you plan, and why?
- What is the total cost of both routes, including a second admission and physiotherapy?
Infection is the complication that leads to further surgery in either route. A 2024 meta-analysis of 3.66 million knee replacements put the rate at 0.83% to 1.08% per knee, so two knees carry roughly twice the chance of one; the 2025 review found in-hospital infection lower with simultaneous surgery, so the route itself does not add to that.
Compare hospitals on ICU, blood bank and volume. This guide is general information from the sources listed below, not medical advice; a registered doctor makes decisions with you.
