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Not all Patients with Diabetes have the Same Risks: The Association of Perioperative Glycemic Control with Deep Postoperative Infection Following Knee Arthroscopy in Patients with Diabetes

Objectives: Diabetes mellitus has been associated with an increased risk for postoperative infection following numerous orthopaedic surgical procedures including arthroscopy; however, among patients with diabetes, the level of perioperative glycemic control may affect the risk of postoperative infection. Diabetic patients with ideal glycemic control in the perioperative period may have a lower risk of infection than those patients with higher average glucose levels. The primary goal of the present study was to evaluate the association of perioperative glycemic control as demonstrated by hemoglobin A1c (HbA1c) in patients with diabetes with the incidence of deep postoperative infection requiring a subsequent procedure following knee arthroscopy. The secondary objective was to calculate a threshold level of HbA1c above which the risk of postoperative infection after knee arthroscopy increases significantly in patients with diabetes. Methods: A national administrative database was queried for patients who underwent knee arthroscopy, including arthroscopic meniscectomy and/or repair, shaving chondroplasty, arthroscopic-assisted cruciate ligament reconstruction, and debridement from 2007-2014. Patients with procedures performed for infection and patients with a prior diagnosis of septic knee arthritis were excluded. Patients who met these criteria with diabetes mellitus and a perioperative HbA1c level checked within 3 months of surgery were identified; these patients were then stratified into six mutually exclusive groups based on their HbA1c: 1) HbA1c 0 - 5.99, 2) HbA1c 6 - 6.99, 3) HbA1c 7 - 7.99, 4) HbA1c 8 - 8.99, 5) HbA1c 9 - 9.99 and 6) HbA1c > 10 mg/dL. The incidence of deep infection requiring operative intervention within 1 year for each HbA1c group, including both open and arthroscopic irrigation and debridement (I&D), were identified using CPT and ICD-9 codes. A receiver operating characteristic (ROC) analysis was performed to determine an optimal threshold value of the HbA1c above which the risk of postoperative infection was significantly increased. Results: 11,384 patients who underwent arthroscopic knee procedures with diabetes and a perioperative HbA1c recorded in the database were included in the study. The overall rate of infection requiring subsequent I&D within 1 year postoperatively was 0.37% (42 of 11,384). The rate of deep infection stratified by HbA1c group is pictured in Figure 1. The rate of infection ranged from a low of 0.24% in patients with HbA1c < 6 mg/dL up to 1.23% for patients with HbA1c > 10 mg/dL (P < 0.001). The results of ROC analysis are depicted in Figure 2. The inflection point of the ROC curve corresponded to an HbA1c level between 8.0 and 9.0 mg/dL (P = 0.004, AUC = 0.63, specificity = 73%, sensitivity = 50%). Conclusion: The risk of deep postoperative infection requiring surgical intervention following knee arthroscopy in patients with diabetes mellitus increases significantly as the perioperative HbA1c increases. ROC analysis determined that a perioperative HbA1c above 8.0 mg/dL could serve as a threshold for a significantly increased risk of deep postoperative infection following knee arthroscopy.