Roughly 30 million people have diabetes in 2015, and that number is expected to increase to 50 million by 2050. This is a medical condition here to stay. Its important for TJA surgeons to think about in all patients because the CDC believes about 30% of cases are currently undiagnosed.
Diabetes is defined as: fasting blood glucose > 126 mg/dL, or random blood glucose > 200 mg/dL, or HgA1C > 6.5% (HgAIC is average blood glucose levels over preceding 8-12 weeks
There are some initial studies that suggest diabetes is associated with DJD as diabetic patients undergo TKA at a younger age (although the association between diabetes and obesity, a known risk factor for premature arthritis, makes it less clear whether diabetes is an independent risk factor) .
Diabetes is a risk factors for Periprosthetic Joint Infection in patients undergoing TJA, with reports of 2x to 4x higher rates of infection compared to nondiabetics  . Additionally, insulin dependent diabetics have greater risk than noninsulin dependent diabetes. About 8.5% of patients undergoing TJA have diabetes. Additional risks associated with diabetes are widespread due to its systemic effects on the body, particularly in promoting renal and cardiopulmonary disease .
The target is a Hemoglobin A1C < 7.0. 
While this threshold is associated with better outcomes, it is likely that glucose control exists along a spectrum of risk, similar to obesity, with a dose-dependent association to infection and wound complication. This concept was suggested in a study by Harris et al.  that looked at Veteran’s Health Database (over 20% of TJA patients had diabetes) and showed that lower HgbA1C correlated with lower complications along a continuum from 5 to 9, with almost linear correlation between HgbAC1 and complication rates. Yet even diabetics with well-controlled HgbAIC appear to present with an elevated risk of complications. 
These findings suggest that all diabetics need to be councilled for increased risk of TJA, but also that 7% should not represent a hard-stop for performing surgery, and that HgbAIC should play a role as one variable in determining the risk/benefit balance of surgery. Giori et al have demonstrated the challenge that many patients have in obtaining HgbAIC levels below 7.0% and have recommended accepting a level of 8.0% in many cases .
Additional studies have found that perioperative glucose levels are more predictive of acute complications than the prior 2-3 months of glucose control, as represented by HgbAIC    . These studies suggest that even nondiabetic patients with postoperative glucose levels over 140 (which can result from steroid administration, excessive fluids containing glucose, postsurgical stress, or poorly controlled underlying diabetes) are at 3x increase risk for infection.
The key is to optimize patients toward a target HgbA1C around 7.0% (even if there is increasing evidence to suggest that this one value is not a hard stop for surgery), while providing tight pre-op and post-op glucose control .
Perioperative Glucose management for diabetics:
Preop: hold the short-acting insulin and oral medications on the morning of surgery. Give half dose of long-acting insulin, and allow insulin pumps to continue during morning of surgery.
Postop: Resume the patients optimized insulin protocol as a regular diet is begun. Start oral medications the following morning (postop day 1). Ensure proper hydration and kidney function the next morning before starting metformin. All patients, including non-diabetics, should have glucose checked postop day 1. Early wound complications (< 30 days) are associated with in-hospital blood glucose levels with an average over >200 mg/dL, or when levels spike over 260. A target between 140 – 180 mg/dL appears acceptable to avoid complications .
1. King, K.B., et al., Veterans with diabetes receive arthroplasty more frequently and at a younger age. Clin Orthop Relat Res, 2013. 471(9): p. 3049-54.
2. Marchant, M.H., Jr., et al., The impact of glycemic control and diabetes mellitus on perioperative outcomes after total joint arthroplasty. J Bone Joint Surg Am, 2009. 91(7): p. 1621-9.
3. Iorio, R., et al., Diabetes mellitus, hemoglobin A1C, and the incidence of total joint arthroplasty infection. J Arthroplasty, 2012. 27(5): p. 726-9 e1.
4. Jain, N.B., et al., Comorbidities increase complication rates in patients having arthroplasty. Clin Orthop Relat Res, 2005(435): p. 232-8.
5. Rizvi, A.A., S.A. Chillag, and K.J. Chillag, Perioperative management of diabetes and hyperglycemia in patients undergoing orthopaedic surgery. J Am Acad Orthop Surg, 2010. 18(7): p. 426-35.
6. Harris, A.H., et al., Hemoglobin A1C as a marker for surgical risk in diabetic patients undergoing total joint arthroplasty. J Arthroplasty, 2013. 28(8 Suppl): p. 25-9.
7. Stryker, L.S., et al., Elevated postoperative blood glucose and preoperative hemoglobin A1C are associated with increased wound complications following total joint arthroplasty. J Bone Joint Surg Am, 2013. 95(9): p. 808-14, S1-2.
8. Giori, N.J., et al., Many diabetic total joint arthroplasty candidates are unable to achieve a preoperative hemoglobin A1c goal of 7% or less. J Bone Joint Surg Am, 2014. 96(6): p. 500-4.
9. Maradit Kremers, H., et al., Diabetes mellitus, hyperglycemia, hemoglobin A1C and the risk of prosthetic joint infections in total hip and knee arthroplasty. J Arthroplasty, 2015. 30(3): p. 439-43.
10. Chrastil, J., et al., Is Hemoglobin A1c or Perioperative Hyperglycemia Predictive of Periprosthetic Joint Infection or Death Following Primary Total Joint Arthroplasty? J Arthroplasty, 2015. 30(7): p. 1197-202.
11. Adams, A.L., et al., Surgical outcomes of total knee replacement according to diabetes status and glycemic control, 2001 to 2009. J Bone Joint Surg Am, 2013. 95(6): p. 481-7.
12. Mraovic, B., et al., Perioperative hyperglycemia and postoperative infection after lower limb arthroplasty. J Diabetes Sci Technol, 2011. 5(2): p. 412-8.