Does my blood sugar or A1c affect my knee replacement?

Last reviewed: September 29, 2026

Yes. People with diabetes whose blood sugar is poorly controlled have more infections after knee replacement. But there is no agreed A1c number above which surgery becomes unsafe.

For most people, diabetes raises the risk only slightly. In the Danish national registry, redo operations for infection within five years occurred in about 17 of every 1,000 knee replacements in people with diabetes, and about 14 of every 1,000 in people without it. The risk varied widely with age, weight and blood vessel disease. In a Utah study of hip and knee replacements, joint infection was more common with type 1 diabetes than with type 2: about 7 in 100 compared with 4 in 100.

A1c measures average blood sugar over about three months. Studies looking for a cut-off have found numbers from about 7.7% to 9.7%, and a large 2025 study found that A1c predicts infection poorly. Shorter-term blood tests may do better. In a study of 1,119 knee replacements, patients with a fructosamine level above 293 were about 11 times more likely to develop joint infection within 12 weeks. A1c cut-offs of 7% and 7.5% showed no link.

Guidelines differ. The American Diabetes Association recommends an A1c under 8% within three months before planned surgery, and blood sugar between 100 and 180 mg/dL around the time of surgery. It also says surgery should not be postponed on the A1c number alone. The American College of Rheumatology and the American Association of Hip and Knee Surgeons suggest delaying surgery to improve blood sugar control, without naming a number, and rate the evidence as low or very low. According to the American Academy of Orthopaedic Surgeons, surgeons should try to keep blood sugar under 126 mg/dL around and after knee replacement.

No trial has tested whether delaying surgery to lower A1c reduces infection. All of these studies are observational. They show a link, not proof that blood sugar itself is the cause.

In general:

• Ask your surgeon which blood sugar test and number they require before surgery.
• If your surgery is postponed, ask what number you need to reach.
• Work with the doctor who treats your diabetes to lower your blood sugar before surgery.
• Ask whether a fructosamine test would help in your case.

Drafted with AI assistance from published sources, reviewed and edited by Babak Sheikh, MD.

Sources:

• Anneberg M, et al. Clinical Profile and Risk of Periprosthetic Joint Infection After Total Knee Arthroplasty in Patients With and Without Diabetes. Bone Joint J. 2025. https://doi.org/10.1302/0301-620X.107B8.BJJ-2024-1424.R1
• Duensing I, et al. Patients With Type-1 Diabetes Are at Greater Risk of Periprosthetic Joint Infection. J Bone Joint Surg Am. 2019. https://doi.org/10.2106/JBJS.19.00080
• Tarabichi M, et al. Determining the Threshold for HbA1c as a Predictor for Adverse Outcomes After Total Joint Arthroplasty. J Arthroplasty. 2017. https://doi.org/10.1016/j.arth.2017.04.065
• Palmer RC, et al. The Limited Utility of Hemoglobin A1c as a Predictor for Periprosthetic Joint Infection Following Total Joint Arthroplasty. J Arthroplasty. 2025. https://doi.org/10.1016/j.arth.2025.01.004
• Shohat N, et al. 2019 John Insall Award: Fructosamine Is a Better Glycaemic Marker Compared With HbA1c in Predicting Adverse Outcomes Following Total Knee Arthroplasty. Bone Joint J. 2019. https://doi.org/10.1302/0301-620X.101B7.BJJ-2018-1418.R1
• American Diabetes Association. 16. Diabetes Care in the Hospital: Standards of Care in Diabetes—2026. Diabetes Care. 2026. https://doi.org/10.2337/dc26-S016
• Hannon CP, et al. 2023 ACR/AAHKS Clinical Practice Guideline for the Optimal Timing of Elective Hip or Knee Arthroplasty. J Arthroplasty. 2023. https://doi.org/10.1016/j.arth.2023.09.003
• American Academy of Orthopaedic Surgeons. Surgical Management of Osteoarthritis of the Knee, Clinical Practice Guideline. 2022. https://www.aaos.org/smoak2cpg

This is general information about what published research shows. It is not medical advice and it is not about your situation. Reading it does not create a doctor-patient relationship with me. I am a retired orthopedic surgeon and I do not see patients. Talk with your own doctor before changing anything about your care. If something feels suddenly or seriously wrong, get medical care promptly rather than waiting.

This page is provided as is. I make no guarantee that it is accurate, complete or current, and medical evidence changes. Use of it is at your own risk.

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