🩺Diabetes and Surgery
Making sure your diabetes is well-controlled will significantly reduce your risk of complications after knee replacement. If you have diabetes, the month before surgery are an important time to optimise your blood sugar.
The link between blood sugar and healing
High blood sugar impairs the immune system and slows wound healing, increasing the risk of surgical site infection.
Most anaesthetic teams look for a HbA1c level below 69 mmol/mol before proceeding with elective joint replacement surgery, as above this the risks of serious complications- which may be life-threatening- is high. However, recent studies have shown that the risk of infection after joint replacement starts to increase significantly when the HbA1c is above 58 mmol/mol. Optimising your diabetes control may therefore substantially reduce your risks. If you start the process of getting your diabetes controlled early, it is often possible to bring your HbA1c level down to acceptable levels within months through a change in diet, lifestyle and medications which your medical team will be able to advise on.
Preparing your diabetes for surgery
Review your medication and monitoring routine with your GP or diabetes team well ahead of your surgery date. If you haven't had a recent HBA1c level, it is worth getting this done soon so you know your current level.
Bring an up-to-date list of your medicines, insulin doses and recent HbA1c results to your pre-assessment appointment.
Why does diabetes affect knee replacement surgery?
High blood sugar affects the body's ability to heal. When glucose levels are raised over time, the tissues around a surgical wound recover more slowly and the immune system does not respond as effectively to bacteria.
- Slower wound healing
- Reduced immune function
- Increased inflammation
- Poor collagen production
- Increased infection risk
- Increased kidney complications
- Reduced tissue healing
What is HbA1c?
HbA1c measures your average blood glucose over approximately the previous three months.
Unlike a single blood sugar reading, it gives doctors an overall picture of your diabetes control — which is why it is used to guide decisions before surgery.
| HbA1c | Meaning |
|---|---|
| Below 42 mmol/mol | Normal |
| 42–47 mmol/mol | Prediabetes |
| 48 mmol/mol or above | Diabetes |
Many hospitals aim for an HbA1c below approximately 53–58 mmol/mol (7.0–7.5%) before elective knee replacement, although targets should always be individualised by your diabetes and surgical teams.
Why surgeons check HbA1c before surgery
Blood sugar control is one of the strongest predictors of how well you will recover from a joint replacement. That's why your team may arrange an HbA1c test in the months leading up to your operation.
A large UK study involving over 9,400 hip and knee replacements found that, compared with patients without diabetes, people with diabetes had:
- 50% higher overall complication rates
- More than double the risk of deep surgical wound infection
- Over twice the risk of urinary tract infection
- Nearly 60% higher risk of acute kidney injury or electrolyte problems
The study also showed that complication risk increased progressively as HbA1c rose — even in people with prediabetes.
Does improving diabetes control help?
Yes. One of the most encouraging findings from recent research was that patients whose HbA1c improved back into the normal range before surgery had complication rates that were almost the same as people without diabetes.
Improving blood sugar control before surgery can bring surgical risk close to that of patients without diabetes — meaningful change, not perfection, is what makes the difference.
Possible complications
Infection
Elevated blood glucose weakens the immune system and increases the risk of prosthetic joint infection at the surgical site.
Wound healing
Wounds tend to heal more slowly when blood sugar is raised, which can mean more dressing changes and a longer recovery.
Blood clots
Diabetes is associated with a higher risk of deep vein thrombosis (DVT) after surgery, particularly in the first few weeks.
Kidney problems
Diabetes can increase the risk of acute kidney injury after an operation, especially when combined with dehydration or certain medications.
Does this mean I shouldn't have surgery?
Absolutely not. Most people with diabetes achieve excellent pain relief and improved mobility after knee replacement.
The aim is not to deny surgery but to reduce avoidable risks by improving diabetes control beforehand — so that you get the best possible result from a very successful operation.
How can I improve my diabetes before surgery?
- Take medications exactly as prescribed
- Monitor blood glucose regularly
- Eat a balanced diet
- Lose weight if appropriate
- Stay physically active
- Attend diabetes reviews
- Work with your GP or diabetes specialist if your HbA1c is above target
Never stop diabetes medication without medical advice. Your GP or diabetes team can help you adjust safely in the weeks before surgery.
What happens on the day of surgery?
The team will monitor your blood sugar during and after your operation. Some diabetes medications may need to be adjusted or stopped prior to surgery but you will be given clear information about this.
Your healthcare team will monitor:
- Blood glucose
- Fluids
- Kidney function
- Wound healing
What does the evidence show?
- Diabetes increases the risk of infection, kidney injury and other complications after knee replacement.
- Complication risk rises progressively with higher HbA1c — including in prediabetes.
- Improving HbA1c into the normal range brings complication rates close to those of people without diabetes.
- Individualised targets, agreed with your diabetes and surgical teams, matter more than a single universal cut-off.
Key takeaway
Good diabetes control before knee replacement is one of the most effective ways to reduce complications.
Improving your HbA1c lowers the risk of infection, improves wound healing and helps your body recover after surgery.
Even if you have diabetes, knee replacement remains an excellent operation when your condition is well managed.
References
- Holleyman, R.J., Clarkson, M., Shenfine, A., Martin, K., Prentis, J., Bowditch, M., Rayman, G., Judge, A. and Reed, M.R. (2025) Association between preoperative glycaemic control (HbA1c) and early outcomes following primary hip and knee arthroplasty. Bone & Joint Journal, 107-B(6), pp. 615–624.
- Vaishya, R., Patralekh, M.K., Misra, A. and Vaish, A. (2025) Outcomes of total knee arthroplasty in people with diabetes: An overview of systematic reviews and meta-analysis. Journal of Orthopaedics, 65, pp. 336–345.
- Shohat, N., Muhsen, K., Gilat, R., Rondon, A.J., Chen, A.F. and Parvizi, J. (2018) Inadequate glycemic control is associated with increased surgical site infection in total joint arthroplasty: A systematic review and meta-analysis. Journal of Arthroplasty, 33(7), pp. 2312–2321.
This article is for general education and does not replace advice from your surgical, anaesthetic or diabetes team.
Practical tips
- Do not stop diabetes medication without medical advice.
- Aim for consistent, gently improving blood sugar readings in the weeks before surgery.
- Flag hypoglycaemic episodes to your team — dosing may need to be adjusted around the operation.