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Hemoglobin A1c in Diabetic Patients Undergoing Total Joint Arthroplasty
Nicholas J. Giori, MD PhD
VA Palo Alto Health Care System, Palo Alto, CA
Palo Alto, CA
Funding Period: January 2011 - December 2011
Diabetes and osteoarthritis are the third and fourth most common health conditions treated by the Department of Veterans Affairs. Advanced osteoarthritis of the hip and knee is treated with total joint arthroplasty. Given the aging United States population and the durability and success of total joint arthroplasty, it has been projected that total hip and knee arthroplasty procedures in the U.S. will grow 174% and 673% respectively between 2005 and 2030. Diabetics make up approximately 22% of the total joint arthroplasty patients in the VA system. Diabetes is a known risk factor for postoperative complications following total joint arthroplasty, and recent data has shown that poorly controlled diabetes further increases that risk. Compared to well controlled diabetics, poorly controlled diabetics undergoing total joint arthroplasty have a greater than 3-fold increased risk of stroke, a greater than 2-fold increased risk of wound infection, and a greater than 3-fold increased risk of death. A VA study found that elevated preoperative hemoglobin A1c (greater than 7%) in diabetic patients before major non-cardiac surgery is associated with a greater than two-fold increase in postoperative infection. Data on patients undergoing cardiac surgery reveals that preoperative hemoglobin A1c greater than 7% is associated with increased risk of a range of postoperative complications and death. However, it is unknown if this threshold (7% elevation) is optimal for identifying total joint replacement candidates who are at high risk of complications and who may benefit from preoperative intervention to improve diabetes control. It is also unknown how difficult it is for a poorly controlled diabetic to achieve a hemoglobin A1c of 7%, and whether achieving improved hemoglobin A1c preoperatively reduces postoperative complication rates. As complications are costly, personally to the veteran and financially to the healthcare system, it is vital to understand if preoperative intervention for control of diabetes is possible and effective in minimizing complications following joint replacement procedures.
The aims of this study were as follows:
1.To assess the use of hemoglobin A1c as a clinically accessible and useful marker of surgical complications in veteran total joint arthroplasty patients.
2.To assess whether preoperative referral to primary care for intervention to reduce hemoglobin A1c is a barrier to receiving surgical treatment for osteoarthritis.
3.To estimate surgical complication rates in patients referred to primary care for diabetic control prior to total joint arthroplasty.
Aim 1. We conducted a retrospective cohort study on veterans having total joint arthroplasty over a four year period (FY06-FY09). Demographic, surgical, and other clinical data (e.g., comorbidities) were obtained from the VA National Patient Care Database (NPCD) and the National Surgical Quality Improvement (NSQIP) database. Preoperative hemoglobin A1c data were obtained from the laboratory file of the Decision Support System (DSS). The functional relationship between hemoglobin A1c and surgical complications was estimated using propensity score weighted mixed effects regression models. The sensitivity and specificity of various threshold values were evaluated.
Aim 2. We conducted a retrospective cohort study of patients presenting at the VA Palo Alto for primary total hip or knee arthroplasty from October 1, 2004 to September 30, 2010. We identified all diabetic patients who presented to our orthopedic clinic with a diagnosis of hip or knee osteoarthrosis and were deemed candidates for primary hip or knee replacement using the NPCD outpatient records. Then, for each patient, we extracted from the DSS laboratory file all hemoglobin A1c values from October 1, 2004 to September 30, 2010. The presenting hemoglobin A1c was defined as the nearest documented hemoglobin A1c value prior to the date that the orthopedic surgeon determined that the patient was a candidate for total joint arthroplasty. Electronic medical charts for these patients were reviewed to determine whether their scheduled surgery was delayed, reason(s) for delay, whether the patient was referred back to primary care for diabetic control, whether the patient achieved an A1c value of 7% or less, and how long it took to achieve that value and become a candidate for surgery.
Aim 3. For patients in the VA Palo Alto cohort who eventually underwent total joint replacement, we planned to estimate their complication rates and compare them to a matched nationally-based cohort of patients who had surgery with hemoglobin A1c greater than 7%. Going into this study, we understood that the numbers of patients would be limited and the results would likely be descriptive.
Aim 1: During the study period, 6,088 VA patients with a diabetes diagnosis underwent total joint replacement and also had a presurgical hemoglobin A1c lab value and were included in the VASQIP sample. We first evaluated if patients with presurgical hemoglobin A1c values >7% had greater odds of complications, number of complications, and 30-day mortality compared to patients with values <7%, controlling for demographic, clinical, and surgical characteristics as well as the number of days prior to surgery that the hemoglobin A1c value was recorded. Patients with presurgical hemoglobin A1c values >7% had 24% increased odds of any surgical complication (OR = 1.24, 95%CI = 1.03 - 1.49) and a 68% increased odds of 30-day mortality (OR = 1.68, 95%CI = 1.01 - 2.79). Presurgical hemoglobin A1c values were not significantly related to number of surgical complications (p<.09).
We used these models to examine the functional form of the relationship between presurgical hemoglobin A1c values and complications. Data suggest that the risk of complications rises linearly from approximately 8.13% at HbA1c of 6.5% to 9.33% at HbA1c of 7.5%, but is relatively flat for higher values.
Aim 2: Over the 6 year period of the study, we identified 435 diabetic patients who were felt to be candidates for total joint replacement. Of these, 59 were delayed for a reason that included a presenting hemoglobin A1c greater than 7%. Of these 59 patients, 35 achieved a hemoglobin A1c less than or equal to 7%, while for 24 patients, this goal was unreachable. Thus 6% of diabetic patients, who are, from an orthopedic standpoint, candidates for total joint arthroplasty, will find the 7% cut-off value of eligibility for joint replacement surgery to be an impossible barrier. If the cut off A1c value is raised to 8%, then only 2% of diabetic joint arthroplasty candidates would find this barrier to be insurmountable.
Aim 3: Of the 35 patients in the local sample who were initially delayed from surgery pending better diabetic control, and who managed to reduce their hemoglobin A1c to less than or equal to 7%, and who received surgery, only nine were sampled by VASQUIP. Therefore, we only had data on complications and outcomes for nine local patients. Among these nine patients, only one had a complication. The fact that VASQUIP selected so few of our local patients unexpectedly reduced our already small expected sample size to a truly unusable number. In the RRP proposal, we acknowledged that this aim would have low power and would therefore be exploratory. As it turned out, we were unable to do any meaningful work on this aim. However, the results from Aim 1 and 2 are extremely useful and promise to influence practice even without results from Aim 3.
This work was informally presented at the annual meeting of the Association of VA Orthopedic Surgeons meeting in San Francisco, CA and was the subject of much discussion. Springing from this work is a study group that was formed to look at all modifiable risk factors in joint replacement surgery with the aim of establishing a standard set of criteria to be applied across the VA system for joint replacement eligibility. In addition, we anticipate publishing these data in orthopedic journals of high clinical impact in the coming year. The papers are written and only waiting approval from VASQIP before they will be submitted for publication. Reducing complications (and thus costs) without unduly limiting access to care is a major goal of this work and will be the subject of future research.
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DRA: Diabetes and Other Endocrine Disorders
MeSH Terms: none