Skip to content
View commentaries on this research

This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

People with long-term illness are just as likely to benefit from knee or hip surgery as those without. However, they are more likely to have complications following surgery and to be readmitted within three months.

This study reviewed data from 70 studies to determine the chance of short-term harms and long-term benefits linked to 11 different co-existing health conditions (such as diabetes and cancer) following hip and knee replacement. Short-term outcomes included surgical complications, infections and readmissions and long-term outcomes included hip and knee function, revision surgery and quality of life.

Few studies were identified that looked at the long-term impact on joint function and quality of life, and those that did showed that the co-existing illnesses had little adverse effect on these outcomes.

The study suggests that taking into account these other illnesses can be helpful in assessing the risk faced by patients considering hip and knee replacement. This detailed data may help patients and the referring doctor discuss the risks.

Why was this study needed?

In the UK, over 210,000 hip and knee replacements were performed in 2017 at an average age of 68 for hips and 69 for knees. One in six of these people had an illness affecting their day to day life.

At the moment, little is known about how other illnesses influence the success of hip and knee replacement surgery. Previous research has focused on how age, gender, socioeconomic status and geography affect outcomes. This study set out to identify whether other illnesses can be identified as risk factors to help doctors decide who is likely to benefit.

What did this study do?

This meta-analysis of observational data looked at whether other illnesses are associated with safety and effectiveness outcomes of knee and hip replacement surgery. It included 70 studies from 13 countries including the UK covering 11 co-existing long-term conditions (comorbidities): cancer, depression, diabetes, diseases of the nervous system, heart disease, high blood pressure, kidney disease, liver disease, lung disease, poor circulation and stroke.

Five short-term outcomes (up to three months) and five long-term outcomes (one year after surgery) were used to report the safety and effectiveness of surgery.

Studies with fewer than 100 patients were excluded. There was variation between the studies, and only 13% were graded as high quality, using a recognised scale. Studies with negative results may also be missing, which means the results could be overestimating the effect on hip and knee replacement outcomes.

What did it find?

  • Overall, the likelihood of being readmitted to hospital after surgery was higher for patients with comorbidities (for eight out of the 11 conditions studied). The highest likelihood of readmission was in people with liver disease (pooled odds ratio [OR] 1.79, 95% confidence interval [CI] 1.36 to 2.35; 3 studies).
  • Patients with comorbidities were also at increased risk of dying within 90 days of surgery (for eight of the 11 conditions) and those with heart disease were most at risk (pooled OR 2.96; 95% CI 1.95 to 4.48; 4 studies).
  • The risk of surgical complications including infections and blood clots was higher overall in people with comorbidities, but there was no consistent trend for individual conditions.
  • Only 10 studies looked at the long-term impact of comorbidities on hip and knee function after surgery, and the results were variable across the 11 conditions. Five studies looked at health-related quality of life, but there was no consistent pattern between patients with or without comorbidities. Weak evidence from 12 studies suggested that people with comorbidities were more likely to need revision surgery (for six of 11 conditions).
  • Overall, the long-term risk of death tended to be higher for those with comorbid conditions, ranging from an OR of 1.38 (95% CI 1.05 to 1.80) for lung disease to 3.40 (95% CI 1.17 to 9.86) for liver disease. The wide margin of error, though, means there is less certainty about this outcome.

What does current guidance say on this issue?

NICE guidelines published in 2008 on managing osteoarthritis recommends that clinicians with responsibility for referring a person with osteoarthritis for consideration of joint surgery should ensure that the person has been offered at least the core (non-surgical) treatment options, which are:

  • access to appropriate information,
  • activity and exercise,
  • interventions to achieve weight loss if the person is overweight or obese.

Guidance recommends that patient-specific factors (including age, sex, smoking, obesity and other co-existing illnesses) should not be barriers to referral for joint surgery.

What are the implications?

This study suggests that long-term illness does affect the short-term safety of having a hip or knee replacement, but taking a longer view they are likely to benefit just as much from it as people without these other illnesses.

Other health conditions shouldn’t in themselves rule out joint replacement, but should be considered when discussing and advising people on the risks and benefits of possible surgery.

This observational study was unable to offer a clear view on exactly how each individual health condition might affect the short-term safety of surgery and was not designed to test what could be done to improve outcomes.

Citation and Funding

Podmore B, Hutchings A, van der Meulen J et al. Impact of comorbid conditions on outcomes of hip and knee replacement surgery: a systematic review and meta-analysis. BMJ Open. 2018;8(7):e021784.

This project was funded by the National Institute for Health Research (NIHR) Collaboration for Leadership in Applied Health Research and Care North Thames at Barts NHS Health Trust.


NICE. Osteoarthritis: care and management. CG177. London: National Institute for Health and Care Excellence; 2008.

Versus Arthritis. State of musculoskeletal health 2018. London: Versus Arthritis; 2018.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre

  • Share via:
  • Print article
Back to top