Why is this question important?
Knee replacement is a common operation that involves replacing a damaged, worn, or diseased knee with an artificial joint made of metal and plastic.
Most surgeons prefer to carry out knee replacement surgery with the aid of a tourniquet - a tight band placed around the thigh that restricts blood flow to the knee.
Potential benefits of using a tourniquet include limiting blood loss during surgery and making it easier to conduct the operation. However, a tourniquet may increase the risk of pain and complications for patients after surgery. We reviewed evidence from research studies to find out about the benefits and risks of using a tourniquet in knee replacement surgery.
How did we identify and evaluate the evidence?
First, we searched for relevant, robust studies in the medical literature. We then compared the results and summarised the evidence from all studies. Finally, we assessed how certain the evidence was. To do this, we considered factors such as the way studies were conducted, study size, and consistency of findings across studies. Based on our assessments, we categorised the evidence as being of very low, low, moderate, or high certainty.
What did we find?
We found 41 studies that involved 2819 people (944 men and 1777 women) who were randomly assigned to have surgery with a tourniquet, or surgery without. This type of study, known as a randomised controlled trial, provides the most robust evidence about the effects of a treatment.
Studies were conducted in hospitals in Australia, Asia, Europe, and the USA. Each study involved between 20 and 166 people who were between 58 and 84 years of age. They were followed for between one day and two years after surgery.
Five studies were publicly funded, and one study received funding from a medical equipment manufacturing company. The other 35 studies did not receive specific funding or did not state who funded them.
The studies provided low to moderate evidence that:
- pain on the first day after surgery is probably worse with a tourniquet. On average, on a scale of 0 to 10 (higher scores = worse pain), people operated on with a tourniquet rated their pain as 5.81. People operated on without a tourniquet rated their pain as 4.56 (average difference: 1.25 points);
- knee function one year after surgery is probably similar with or without a tourniquet. On average, on a scale of 0 to 100 (higher scores = better functioning), people operated on with a tourniquet rated their knee function as 89.74. People operated on without a tourniquet rated their knee function as 90.03 (average difference: 0.29 points);
- satisfaction with treatment may be similar with or without a tourniquet. Six months after the operation, 94% of people operated on with or without a tourniquet were 'extremely' or 'very' satisfied with their treatment;
- there may be little or no difference in health-related quality of life with or without a tourniquet. On average, on a scale of 0 to 100 (higher scores = better quality of life), people operated on with a tourniquet rated their quality of life as 54.64. People who had surgery without a tourniquet rated their quality of life as 56.17 (average difference: 1.53 points); and
- serious adverse events such as blood clots in the leg or lung, infection, or re-operation other than to replace the artificial joint are probably more likely to occur with a tourniquet. Five per cent of people operated on with a tourniquet reported serious adverse events compared to 2.9% of people operated on without a tourniquet.
We do not know if using a tourniquet affects chances of needing a second operation to replace an artificial joint because available evidence is of very low certainty.
No studies investigated the effects of surgery with a tourniquet on people’s ability to process thoughts (cognitive function).
What does this mean?
Knee replacement with a tourniquet is probably slightly less beneficial, and is associated with greater risks, than surgery without a tourniquet.
How up-to-date is this review?
Evidence in this Cochrane Review is current to March 2020.
Moderate certainty evidence shows that knee replacement surgery with a tourniquet is probably associated with an increased risk of serious adverse events. Surgery with a tourniquet is also probably associated with higher postoperative pain, although this difference may or may not be noticeable to patients. Surgery with a tourniquet does not appear to confer any clinically meaningful benefit on function, treatment success or quality of life. Further research is required to explore the effects of tourniquet use on cognitive function and implant survival, to identify any additional harms or benefits.
If a tourniquet continues to be used in knee replacement surgery, patients should be informed about the potential increased risk of serious adverse events and postoperative pain.
Many surgeons prefer to perform total knee replacement surgery with the aid of a tourniquet. A tourniquet is an occlusive device that restricts distal blood flow to help create a bloodless field during the procedure. A tourniquet may be associated with increased risk of pain and complications.
To determine the benefits and harms of tourniquet use in knee replacement surgery.
We searched MEDLINE, Embase, and Cochrane Central Register of Controlled Trials (CENTRAL) up to 26 March 2020. We searched clinicaltrials.gov, the World Health Organization trials portal, and several international registries and joint registries up to March 2020.
We included randomised controlled trials (RCTs) comparing knee replacement with use of a tourniquet versus without use of a tourniquet and non-randomised studies with more than 1000 participants. Major outcomes included pain, function, global assessment of success, health-related quality of life, serious adverse events (including venous thromboembolism, infection, re-operation, and mortality), cognitive function, and survival of the implant. Minor outcomes included blood loss, economic outcomes, implant stability, and adverse events.
Two review authors screened abstracts and full texts, extracted data, performed risk of bias assessments, and assessed the certainty of the evidence using the GRADE approach.
We included 41 RCTs with 2819 participants. Trials included from 20 to 199 participants. Mean age ranged between 58 and 84 years. More than half of the RCTs had unclear risk of selection bias and unclear risk of performance and detection bias due to absence of blinding of participants and surgeons.
Major outcomes
Pain: at postoperative day 1, pain (on a scale from zero to 10, with higher scores indicating worse pain) was ranked at 4.56 points after surgery without a tourniquet and at 1.25 points (MD) higher (95% CI 0.32 higher to 2.19 higher) with a tourniquet (8 studies; 577 participants), for an absolute difference of 12.5% higher pain scores (95% CI 3.2% higher to 21.9% higher) and a relative difference of 19% higher pain scores (95% CI 3.4% higher to 49% higher) with a tourniquet. Evidence for these findings was of moderate certainty, downgraded due to risk of bias. Knee replacement with a tourniquet probably led to higher postoperative pain scores at day 1, although this difference may or may not be noticeable to patients (based on a minimal clinically important difference (MCID) of 1.0).
Function: at 12 months, tourniquet use probably makes little or no difference to function, based on an MCID of 5.3 for Knee Society Score (KSS) and 5.0 for Oxford Knee Score (OKS). Mean function (on a scale from 0 to 100, with higher scores indicating better outcomes) was 90.03 points after surgery without a tourniquet and was 0.29 points worse (95% CI 1.06 worse to 0.48 better) on a 0 to 100 scale, absolute difference was 0.29% worse (1.06% worse to 0.48% better), with a tourniquet (5 studies; 611 participants). This evidence was downgraded to moderate certainty due to risk of bias.
Global assessment of success: low-certainty evidence (downgraded due to bias and imprecision) indicates that tourniquet use may have little or no effect on success. At six months, 47 of 50 (or 940 per 1000) reported overall successful treatment after surgery without a tourniquet and 47 of 50 (or 940 per 1000) with a tourniquet (risk ratio (RR) 1.0, 95% CI 0.91 to 1.10) based on one study with 100 participants.
Health-related quality of life: at six months, tourniquet may have little or no effect on quality of life. The 12-Item Short Form Survey (SF-12) score (mental component from zero to 100 (100 is best)) was 54.64 after surgery without a tourniquet and 1.53 (MD) better (95% CI 0.85 worse to 3.91 better) with a tourniquet (1 study; 199 participants); absolute difference was 1.53% better (0.85% worse to 3.91% better). Evidence was of low certainty, downgraded due to risk of bias and small number of participants.
Serious adverse events: the risk of serious adverse events was probably higher with tourniquet; 26 of 898 (29 per 1000) reported events following surgery without a tourniquet compared to 53 of 901 (59 per 1000) with a tourniquet (RR 1.73, 95% CI 1.10 to 2.73) in 21 studies (1799 participants). Twenty-nine more per 1000 patients (95% CI 3 to 50 more per 1000 patients) had a serious adverse event with a tourniquet. Forty-eight (95% CI 20 to 345) participants would need to have surgery without a tourniquet to avoid one serious adverse event. This evidence was downgraded to moderate certainty due to risk of bias.
Cognitive function: one study reported cognitive function as an outcome; however the data were incompletely reported and could not be extracted for analysis.
Survival of implant: it is uncertain if tourniquet has an effect on implant survival due to very low certainty evidence (downgraded for bias, and twice due to very low event rates); 2 of 107 (19 per 1000) required revision surgery in the surgery with a tourniquet group compared to 1 of 107 (9 per 1000) without a tourniquet group at up to two years' follow-up (RR 1.44, 95% CI 0.23 to 8.92). This equates to a 0.4% (0.7% lower to 7% more) increased absolute risk in surgery with a tourniquet.