| Vol. 1 Issue 20 |
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September 23, 2010 |
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In this issue we examine articles from the following journals: Journal of Bone and Joint Surgery and the journal Annals of Internal Medicine. In addition, in the “critical analysis” section we’ll take a closer look at the specific topic of another way to look at confounding variables as they apply to these articles. And finally, please join us for an online discussion of these and other articles on our eTalk page. |
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PODIATRY JOURNAL REVIEW |
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WHY did the authors undertake this study?
Although the negative effects of smoking on post-operative outcomes are well established, the unique aim of this study was to evaluate the effects of smoking cessation following emergent orthopedic fracture repair. The study authors hypothesized that initiating a smoking cessation program following emergent orthopedic extremity fracture repair would decrease the development of post-operative complications.
HOW did they attempt to answer this question?
The primary outcome measure of the study was the development of a post-operative complication within 12 weeks of surgery.
Inclusion criteria of the population cohort were patients with acute extremity fracture requiring operative repair that smoked (at least two cigarettes per day) and who were willing to participate in the study. Patients were then randomized into control and interventions groups, with intervention consisting of a 6-week smoking cessation program (frequent meetings, education and encouragement, as well as free nicotine substitution).
WHAT were the specific results?
A statistically significant difference was found between the control and intervention groups with respect to the proportion of patients who developed at least one post-operative complication (38% versus 20%, respectively; p = 0.048).
HOW did the authors interpret these results?
From these results, the authors concluded that the initiation of a smoking cessation program following surgery may help to reduce the development of complications following acute extremity fracture repair.
There are several other review articles in this issue that readers may find both beneficial and interesting. Zhao et al examine the effects of a lubricating-type chemical compound on reducing adhesions following tendon surgery in a canine model. Mangat et al use an ultrasound technique to examine healing changes in the Achilles following tenotomy in the treatment of clubfoot. Monument et al take a close look a joint capsule fibrosis following trauma. Yepes et al used a cadaveric arterial perfusion study design to demonstrate the cutaneous vascular supply in the area of the Achilles tendon with specific reference to incision placement. And Woon provides two cases of hallux IPJ dislocation, interestingly, about the same amount of case studies provided in the original and classic Jahss article with respect to 1st MPJ dislocations.
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MEDICAL JOURNAL REVIEW |
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WHY did the authors undertake this study?
Hemoglobin A1c (HbA1c) values are known to be not only associated with long term glycemic control, but they have also been associated with long term diabetic complications including lower extremity manifestations. It has also been established that HbA1c values tend to be higher in black patients compared to white patients in the United States, but this difference has always been attributed to differences in diabetes control. The aim of this study is to determine whether race, as an independent variable, affects HbA1c values.
HOW did they attempt to answer this question?
Data from 2 glucose control trials, and from over 3000 patients, was collected with respect to patient demographics and several measures of glycemic control. These measures of glycemic control were then compared to the HbA1c value.
WHAT were the specific results?
After factoring out and adjusting for all measures known to affect HbA1c values, black patients were still found to have higher HbA1c values when compared to white patients. This difference was statistically significant in patients with normal glucose tolerance (0.13 percentage points; p<0.001), pre-diabetes (0.21 percentage points; p<0.001) and with the diagnosis of diabetes (0.47 percentage points; p<0.013).
HOW did the authors interpret these results?
The authors of this study were unable to determine why black patients had higher HbA1c values, and caution that this may limit the use of the HbA1c test for diagnosis and treatment. There were also unable to determine why differences appear to increase as glucose intolerance worsened.
There are several other review articles in this issue that readers may find both beneficial and interesting. Shaukat et al provide a systematic review for the management of lactose intolerance. Ito et al examine the cost-effectiveness of medical preventative therapy in men at risk for hip fracture. And Goldfine et al investigate the effect of salsalate (a salicylate prodrug) on diabetic glycemic control.
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CRITICAL ANALYSIS OF THE LITERATURE |
Let’s take a closer look at the topic of confounding variables as they apply to these articles, specifically the Ziemer et al HbA1c study. Put most simply, a confounding variable is something that could potentially affect the outcome measures and results of a study, but at the same time, wasn’t specifically studied in a given research design. The design of the HbA1c study not only provides a good example of a confounding variable, but the authors also do an excellent job in recognizing this weakness of their study.
We know from this and previous studies that there are black-white differences in HbA1c levels. For whatever reason, black patients tend to have consistently and statistically significant higher HbA1c levels when compared to white patients. “For whatever reason” is an example of a confounding variable. We know that there is a difference, but up until this time, no one has been able to determine why this difference exists. Although studies have attempted to evaluate as many different variables as possible, none of these variables have been able to explain the difference. We hypothesize that there is some “variable” out there that will explain this difference, but it has “confounded” researchers up until this point.
The Ziemer et al study attempted to find this variable by closely examining measures of glycemic control. In fact, tables 1, 2 and 3 in their study are full of variables and outcome measures that could potentially explain this difference. However, although they found that the black-white differences in HbA1c levels increased with worsening glycemic control, it did not explain why the difference exists in the first place. Because the outcome measures and variables that were examined in this study did not account for the difference in HbA1c levels, this study had a confounding variable.
This example also demonstrates one of the reasons that prospective studies are generally superior to retrospective studies when viewed from a critical analysis standpoint. When data is collected prospectively, the researchers are able to determine ahead of time exactly what information they want to collect. They are able to hypothesize about as many variables and outcome measures as they can think of before the data collection period. When data is collected retrospectively, like in a retrospective chart review, the researchers are essentially stuck with whatever information has already been recorded. They obviously can’t go back in time and say, collect pre-operative AOFAS scores from a patient that has already been operated on. A retrospective study design dramatically increases the chance of having some type of confounding variable because the researchers can only use data that has already been recorded.
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DISCUSSION
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Please join us for an online discussion of these topics: |
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I hope you find PRESENT Journal Club a valuable resource. Look out for the eZine in your inbox. Please do not hesitate to contact me if there is anything I can do to make this a more educational and clinically relevant journal club. |
Andrew Meyr, DPM
PRESENT Podiatry Journal Club Editor
Assistant Professor, Department of Podiatric Surgery,
Temple University School of Podiatric Medicine,
Philadelphia, Pennsylvania
[email protected]
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