Comorbidity-Related Risks

Part of The Joint Replacement Guide — Phase 3: Understanding the Risks · Article 17 of 44 · Hip & Knee

Key Points

A comorbidity is a health condition that exists alongside the joint problem being treated.
Existing conditions can affect the risks of surgery, anaesthesia and recovery, but the effect varies considerably between individuals.
NICE advises that a comorbidity should not, by itself, prevent referral for consideration of joint replacement.[1]
Referral and suitability for an operation are different decisions. An unstable or insufficiently assessed condition may occasionally make postponement or an alternative treatment safer.
Diabetes, heart or lung disease, kidney disease, frailty, anaemia, sleep apnoea and medicines that affect immunity or blood clotting may all require additional planning.
Do not stop or change prescribed medication yourself. The plan should come from the appropriate clinical team.

What Does “Comorbidity” Mean?

Comorbidity simply means another health condition that exists alongside your arthritis. Many people considering joint replacement have more than one long-term condition.

Risk is rarely determined by one diagnosis alone. The team will consider:

how severe and stable each condition is;
how the conditions interact;
your medicines;
your mobility and functional capacity;
frailty and nutritional health;
the proposed operation and anaesthetic;
the support available during recovery; and
what matters most to you.

The purpose is to understand your individual circumstances and make an appropriate plan—not to label everyone with the same diagnosis as having the same risk.

Referral Is Not the Same as Proceeding Immediately

NICE recommends that people with osteoarthritis should not be excluded from referral for joint replacement because of comorbidities.[1] Referral allows a specialist to assess the likely benefits, risks and alternatives.

This does not mean that surgery must always proceed immediately. An active or unstable condition—such as a recent serious cardiac event, uncontrolled heart failure, an acute chest infection or another significant illness—may make elective surgery unsafe at that time.

If postponement is recommended, the team should explain:

the specific concern;
whether the problem can be treated or stabilised;
what support or specialist review is needed;
when the decision will be reconsidered; and
whether another treatment should be considered.

The decision should be individualised rather than based only on the name of a condition or a numerical threshold.

Diabetes

Diabetes can increase the risk of infection, wound problems and abnormal blood-sugar levels around surgery. Risk is affected by the type of diabetes, recent control, medication, complications of diabetes and other health conditions.

Preoperative assessment usually includes review of HbA1c, which reflects average blood-sugar control over recent weeks. Hospitals may use target ranges as part of their pathway, but an HbA1c value is not a complete assessment or a universal pass/fail test.

An individual plan should cover:

diabetes medicines and insulin;
fasting instructions;
glucose monitoring;
treatment if glucose becomes too high or low;
eating and drinking after surgery; and
management of diabetes-related kidney, nerve or circulation problems.

Some diabetes medicines require special arrangements before surgery. Do not omit or alter them unless the team has given you clear instructions. CPOC and Diabetes UK provide specific guidance for perioperative diabetes care.[2]

Body Weight and Nutritional Health

Higher BMI is associated with an increased risk of some complications, particularly infection and wound problems. However, BMI is an incomplete measure and should be considered alongside fitness, fat distribution, muscle strength, nutrition and other conditions.

NICE states that overweight or obesity should not, by itself, prevent referral for joint replacement.[1] If weight management would improve health or reduce risk, support should be realistic and non-stigmatising.

Being underweight, losing weight unintentionally or having poor nutritional intake can also increase concern about healing, muscle loss and recovery. Rapid dieting immediately before surgery may be counterproductive if it causes loss of muscle or inadequate nutrition.

Heart and Circulatory Conditions

Relevant conditions may include:

coronary artery disease or a previous heart attack;
heart failure;
heart-valve disease;
an abnormal heart rhythm;
high blood pressure;
previous stroke or transient ischaemic attack;
peripheral vascular disease; and
a pacemaker or implanted defibrillator.

A diagnosis does not automatically require cardiology referral or extensive testing. The need for further assessment depends on symptoms, stability, functional capacity, previous investigations and the proposed operation.

Report new or worsening chest pain, unexplained breathlessness, fainting, palpitations or ankle swelling promptly. These symptoms may require investigation before elective surgery.

The team will also review medicines affecting blood pressure, heart rhythm and clotting. Do not stop aspirin, anticoagulants or heart medication without explicit advice.

Lung Disease and Sleep Apnoea

Asthma, chronic obstructive pulmonary disease, pulmonary fibrosis and other respiratory conditions can affect breathing during and after surgery.

Preparation may include:

checking whether symptoms are stable;
reviewing inhaler technique and treatment;
treating an active respiratory infection;
smoking-cessation support;
planning the anaesthetic and postoperative monitoring; and
arranging respiratory review when clinically necessary.

Obstructive sleep apnoea can increase sensitivity to sedatives and opioid painkillers. Tell the team if you have diagnosed sleep apnoea, use CPAP or have symptoms such as loud snoring, witnessed pauses in breathing or marked daytime sleepiness. If you use CPAP, follow the hospital’s instructions about bringing the equipment with you.

Kidney Disease

Kidney function affects fluid balance and the safe use or dosing of several medicines. These can include anti-inflammatory painkillers, some antibiotics, tranexamic acid and certain anticoagulants.

The team may review blood tests, adjust medication and monitor fluid balance and kidney function around the operation. Avoid taking additional anti-inflammatory medicines or supplements without checking that they are safe for you.

Dialysis patients or people with advanced kidney disease may require joint planning between the surgical, renal and anaesthetic teams.

Immunosuppression and Inflammatory Disease

Some conditions and treatments alter the immune response. Examples include:

rheumatoid or psoriatic arthritis;
systemic lupus erythematosus;
inflammatory bowel disease;
treatment following an organ transplant;
chemotherapy or some cancer treatments;
long-term corticosteroids;
biologic medicines; and
other disease-modifying antirheumatic drugs.

The balance is not simply between “continue” and “stop”. Continuing some medicines may increase infection risk, while stopping them may cause a serious disease flare or threaten a transplanted organ.

Guidance for inflammatory rheumatic disease recommends continuing some medicines and temporarily withholding others, with timing determined by the particular drug, condition and operation.[3] Transplant and cancer treatments require advice from the relevant specialist.

Never stop corticosteroids suddenly unless a clinician has given you a safe plan. Long-term steroid use may also affect how steroids are managed around the operation.

Anaemia

Anaemia is associated with an increased risk of transfusion and other complications after major surgery. If it is found, the cause should be investigated rather than assuming that every case is due to iron deficiency.

Treatment may involve iron, vitamin B12, folate or management of another underlying condition. CPOC recommends identifying and treating anaemia as early as possible in the surgical pathway.[4]

Do not start high-dose iron without advice, as it is not appropriate for every type of anaemia.

Previous Blood Clots or Bleeding Problems

Tell the team if you have:

previously had a DVT or pulmonary embolism;
a known clotting or bleeding disorder;
a history of significant bleeding;
a close family history of unexplained blood clots; or
ongoing anticoagulant or antiplatelet treatment.

Joint replacement temporarily increases blood-clot risk, while anticoagulants can increase bleeding. The team must balance both risks and provide an individual plan for interruption, bridging where appropriate, restarting treatment and postoperative clot prevention.

Frailty, Mobility and Cognitive Health

Frailty is not the same as age. It describes reduced physiological reserve and the ability to recover from illness or surgery. It can occur in younger as well as older people.

Frailty, falls, memory problems and reduced independence may affect:

the risk of delirium or other complications;
rehabilitation;
length of stay;
medication management; and
the support required after discharge.

Assessment may lead to additional preparation, therapy input, medication review or comprehensive geriatric assessment. The aim is to plan appropriate care and support informed decision-making.[5]

Mental Health and Chronic Pain

Anxiety, depression, severe mental illness, cognitive difficulties and longstanding pain can affect preparation, pain management and recovery. They do not automatically make someone unsuitable for surgery.

Tell the team about mental-health treatment, previous difficulties in hospital, high-dose opioid use or medication that could interact with anaesthesia. Planning additional communication, psychological support or specialist pain input can make care safer and more manageable.

Bringing the Information Together

Preoperative assessment may involve nurses, anaesthetists, pharmacists and therapists. Depending on your needs, the team may seek advice from cardiology, respiratory medicine, diabetes services, rheumatology, renal medicine, geriatrics, haematology or another specialist.

Not every patient requires all these reviews. Unnecessary referral and testing can delay treatment without improving safety. Additional assessment should answer a specific clinical question or lead to a change in care.

For people with complex health needs, planning may include:

additional monitoring;
a particular anaesthetic or pain-management approach;
changes to medication;
a higher level of postoperative care;
a longer or shorter hospital pathway;
additional rehabilitation or home support; or
a further shared decision-making consultation about surgery and alternatives.

Understanding the ASA Classification

Anaesthetists commonly record an ASA Physical Status classification. This describes overall health before anaesthesia, ranging from ASA I for a healthy patient to higher categories for increasingly significant systemic disease.[6]

The ASA classification is not:

a pass/fail grade;
a complete surgical-risk assessment;
a percentage chance of a complication; or
a judgement about whether joint replacement is worthwhile.

Although a higher ASA category is associated with greater risk across groups of patients, it cannot predict an individual outcome by itself. The anaesthetist must also consider the proposed procedure, functional capacity, frailty and other clinical information. Formal risk calculators may be used when a numerical estimate would assist planning and shared decision-making.[7]

What You Can Do

Before pre-assessment:

prepare a complete list of prescribed medicines, over-the-counter products and supplements;
include doses and how often you take them;
report allergies and previous reactions to medicines or anaesthesia;
describe your conditions honestly, including recent changes;
bring relevant specialist letters if requested;
tell the team about previous blood clots, bleeding or hospital complications; and
ask for written instructions about which medicines to take or withhold.

Contact the team if your health changes significantly while you are waiting—for example, if you develop a new infection, chest pain, worsening breathlessness, a hospital admission or a major change in medication.

The Bottom Line

A comorbidity is relevant because it may change risk and the care you need—not because the diagnosis automatically excludes you from treatment.

The appropriate questions are:

What benefits might joint replacement provide?
What risks are particularly relevant to me?
Which risks can reasonably be reduced?
What additional planning or support is needed?
Would postponement improve safety, and how will that decision be reviewed?
Are the risks of delaying or not having surgery also being considered?

This article provides general information and does not replace individual advice. Discuss all health conditions, medicines and supplements with your surgical and anaesthetic teams. Do not stop prescribed treatment unless the responsible clinical team tells you to do so.

References

National Institute for Health and Care Excellence. Osteoarthritis in over 16s: diagnosis and management. NICE guideline NG226. London: NICE; 2022. Recommendations 1.6.1–1.6.4. Available from: https://www.nice.org.uk/guidance/ng226/chapter/Recommendations
Centre for Perioperative Care, Diabetes UK. Perioperative care of people with diabetes undergoing surgery. Updated October 2023. London: CPOC; 2023. Available from: https://www.cpoc.org.uk/guidelines-and-resources/guidelines/guideline-diabetes
Goodman SM, Springer BD, Chen AF, et al. 2022 American College of Rheumatology/American Association of Hip and Knee Surgeons guideline for the perioperative management of antirheumatic medication in patients with rheumatic diseases undergoing elective total hip or total knee arthroplasty. J Arthroplasty. 2022;37(9):1676–1683. doi:10.1016/j.arth.2022.05.043. Available from: https://rheumatology.org/perioperative-management-guideline
Centre for Perioperative Care. Guideline for the management of anaemia in the perioperative pathway. Updated 2025. London: CPOC; 2025. Available from: https://www.cpoc.org.uk/guidelines-and-resources/guidelines/anaemia-perioperative-pathway
Centre for Perioperative Care, British Geriatrics Society. Guideline for perioperative care for people living with frailty undergoing elective and emergency surgery. London: CPOC. Available from: https://www.cpoc.org.uk/guidelines-and-resources/guidelines/perioperative-care-people-living-frailty
American Society of Anesthesiologists. Statement on ASA Physical Status Classification System. Schaumburg, IL: ASA. Available from: https://www.asahq.org/standards-and-practice-parameters/statement-on-asa-physical-status-classification-system
Royal College of Anaesthetists. Guidelines for the provision of anaesthesia services for the perioperative care of elective and urgent care patients 2025. London: RCoA; 2025. Available from: https://www.rcoa.ac.uk/gpas/chapter-2
Centre for Perioperative Care. Preoperative assessment and optimisation for adult surgery. London: CPOC. Available from: https://www.cpoc.org.uk/preoperative-assessment-and-optimisation-adult-surgery

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