Observational Studies in Orthopaedic Surgery: The STROBE Statement as a Tool for Transparent Reporting

Evidence-based medicine in orthopaedic surgery comprises predominantly observational studies. While the gold standard of study methodology is considered to be randomized controlled trials (RCTs), observational studies provide valuable information regarding disease prevalence and etiology, rare outcomes, and adverse treatment effects. Orthopaedic surgeons care for many diseases and injuries that are rare and will likely never be the subject of an RCT. Given the bias to which observational studies are prone, however, transparent reporting is imperative. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement is a checklist of items that can help clinician-scientists to improve the transparency with which observational studies are reported. We offer the following guidelines and examples for how the STROBE statement can be applied to reporting observational studies in orthopaedic surgery. Observational Studies Observational studies inform clinicians about disease etiology, natural history, prognostic factors, and treatment effectiveness1,2. The most common observational study designs include cohort, case-control, and cross-sectional studies. In a cohort study, subjects are divided into two groups, or cohorts: those with an exposure of interest and those without. The groups are then followed prospectively and are observed for an outcome of interest. In a case-control study, subjects who have experienced an outcome (cases) are matched with subjects who have not experienced an outcome (controls). The two groups are then studied retrospectively to determine a causal relationship between unmatched risk factors and the outcome of interest. In a cross-sectional study, each subject in a population is evaluated at a single point in time, often to calculate the prevalence of disease or to establish an association between risk factors and outcome. Observational studies, specifically, case series, predominate the surgical literature in both general surgery (46%) and orthopaedic surgery (88%)2-4. One reason for the high prevalence of observational studies is that, unlike in other fields of medicine, many questions in surgical subspecialties cannot feasibly or ethically be answered with RCTs. A candidate for surgery may not wish to be randomized to operative or nonoperative care, and a surgeon cannot feasibly be blinded to an operative procedure. Furthermore, surgical experience may affect the outcome of a new procedure and randomizing patients to surgeons with varying levels of experience may pose an ethical dilemma. While observational studies are more suitable than RCTs for studying rare outcomes, adverse treatment effects, and disease etiology, the clinician-scientist must recognize the limitations and biases of nonrandomized study designs. Observational studies are prone to bias, most notably confounding, sampling bias, and recall bias (Table I)5. Bias is any systematic error that causes an incorrect estimate of the association between an exposure and an outcome of interest. Unlike RCTs, observational studies do not benefit from the process of randomization, which balances confounders between groups. In case-control studies, unevenly balanced groups also may be the result of inherent differences between each group due to sampling bias. Cohort study designs are also susceptible to sampling bias in cases in which the sample does not represent the population from which it was drawn or the population at large. Retrospective observational studies are further prone to recall bias, which increases the potential for incomplete or biased data collection. Checklists that provide recommendations for how to report observational studies ensure that confounding, sampling bias, and recall bias are clearly recognized so that the strengths of nonrandomized studies can be appreciated. TABLE I - Confounding, Sampling Bias, Recall Bias5 Confounding factors: variables associated with both the exposure and outcome of interest Effect: May misrepresent the relationship between exposure and outcome Example: A clinician-scientist aims to study the effects of alcohol use (exposure) on time to fracture-healing (outcome). She includes fifty individuals who drink an average of more than two alcoholic beverages a day (cases) and fifty individuals who do not drink alcohol (controls). She finds that subjects who drink alcohol have an increased time to fracture-healing than the controls do. However, the subjects who drank alcohol were also more likely to smoke cigarettes. Smoking, which has been reported to increase fracture-healing time, is a confounding factor associated with both the exposure (alcohol use) and the outcome of interest (fracture-healing). Sampling bias: systematic error due to selection of study participants that do not represent the population from which they were drawn or the population at large Effect: Groups may have inherent differences due to how subjects were recruited; results may not be applicable to other populations Example 1: A clinician-scientist aims to study the association between activity level and osteoarthritis. He recruits high-activity-level subjects (cases) from a local fitness club and low-activity-level subjects (controls) by advertising in the local newspaper. During data analysis, he learns that the high-activity-level group was, on average, younger in age and had fewer comorbidities than the low-activity-level group. These inherent differences between groups may affect the results of his study. Example 2: An investigator reports the incidence of reverse shoulder arthroplasty with use of a database from one academic hospital. To estimate the incidence of reverse shoulder arthroplasty in the United States, a multicenter database with information from both private and academic hospitals in rural and urban locations throughout the country would more accurately represent the population at large. Recall bias: systematic error due to differences in the accuracy of or extent to which subjects recall a previous event Effect: May overestimate or underestimate the effect size of a risk factor Example: An investigator is interested in studying potential risk factors of osteosarcoma. He recruits 100 subjects with osteosarcoma and asks them to complete a detailed questionnaire about prior health habits. Some of the subjects cannot recall of the details of their prior health habits; others provide biased answers because they are worried that their actions were responsible for the development of osteosarcoma. Checklist for Observational Studies: The STROBE Statement In order to practice evidence-based orthopaedic surgery, a reader must critically appraise the published research, understand the strengths and weaknesses of the study, and determine if the reported results and conclusions apply to other clinical situations. The research paper must clearly describe the research question, the study population, how the study was designed to answer the question, and whether the research methodology and analysis were appropriate to reach the author’s conclusions. As described above, observational studies are prone to bias, and it is often challenging for readers to understand if a study population (and therefore the study’s conclusion) is truly representative of clinical practice. Authors of observational studies not only must clearly report their research design and conduct but also must examine and disclose potential factors that may threaten the validity and applicability of their findings. The STROBE initiative was established in 2004 in an effort to improve the quality of reporting of observational research (Table II). A multinational group of methodologists, researchers, and journal editors met to develop recommendations intended to help investigators write “a clear presentation of what was planned, done, and found in an observational study.”6 The STROBE initiative further aimed to assist reviewers and editors when evaluating such studies for publication and to guide readers when interpreting and applying a published study’s results and conclusions. The resulting checklist has been adopted by many of the current orthopaedic journals, including The Journal of Bone and Joint Surgery, which the STROBE statement in to in TABLE - The STROBE of be in of Observational Studies and the study’s design with a in the or the in the an and balanced of what was and what was found the and for the reported including any design of study design in the paper the and including of and data Cohort the and the and of selection of of the and the and of case and the for the of cases and the and the and of selection of participants Cohort matched studies, and of and matched studies, and the of controls case outcomes, potential and effect if applicable each of of data and details of of of if is more than one group Bias any to potential of bias size how the study size was at variables how variables were in the describe which were and including those to for confounding any to examine and how data were Cohort how to was how of cases and controls was describe of sampling any of individuals at each of for in the study, and for at each use of a data of study participants and information on and potential confounders of participants with data for each of interest Cohort time average and data Cohort of outcome or time in each exposure or of exposure of outcome or results if and their clear which confounders were for and they were when variables were of risk into risk for a time other of and and results results with to study limitations of the study, into of potential bias or both and of any potential bias a of results of results from studies, and other the of the study results information the of and the of the for the study if for the study on which the is information for cases and controls in case-control studies if for and groups in cohort and cross-sectional An and each checklist and and published examples of transparent The STROBE checklist is in with on the of at of at and Epidemiology at on the STROBE is at with of STROBE The the reporting of observational studies in (STROBE) guidelines for reporting observational studies. The STROBE statement is an checklist of recommendations that are considered for transparent reporting of cohort, case-control, and cross-sectional studies. the are general to of observational studies and are include a of study of potential confounders and bias, and guidelines for reporting study limitations and to to the STROBE Statement The STROBE statement is not intended a for investigators to improve study it is a for to improve the quality and of research findings. to the STROBE statement the in potential bias inherent to the study design and the reader to recognize the limitations of the study’s results and conclusions. The following checklist is a guide intended to assist investigators in of observational studies. the checklist is aimed at the development of a the checklist the of the study and in variables and data have been and can increase of and prior to data may increase the validity of observational studies. to the STROBE checklist in the design of a study will in the development of a suitable and will help to study and research and the We include an of STROBE statement including examples from published observational studies in The Journal of Bone and Joint that to be suitable examples of checklist The may in their to the STROBE however, that the transparent The following provide and examples of checklist and 1: and the study’s design with a in the or The research the reader what research was to a case-control, or Example: with for in the and Observational in the an and balanced of what was and what was The is a exposure to the study and must clearly and the details of the study. of the be with The the reader what the study is about and it is the the study the report the of the study in and the the and of the study. the and for the reported. The of the paper be to the do to and is on what was not be a of the literature or a of previous but an of the of including any A study’s aims the and of the study. the study’s the reader to if the study were suitable to the Example: of study was to further the between and that between and cross-sectional would when the shoulder was with the shoulder and that the of differences would with of study design in the to the STROBE study design be at the of the or at the of the The of observational study case-control, or be clearly Cohort studies include the exposure of the case-control studies include information regarding the population from which the subjects were and cross-sectional studies include the point in time which the study Example 1: of the study was to determine whether patients with a of have an increased of following and surgery with a cohort of patients to whether patients with with the of a of or are at a risk for than are patients with or patients Example 2: of patients who at of two were to that were for and were to a with use of published by with only those patients a of in the group to or cohort group was matched to a group of patients who had arthroplasty at the a time but who were not with prior to the and including of and data collection. A detailed report of and how data were a so that readers can determine if the results are applicable to other and Example: study was in the of Orthopaedic and at the in an May and prospectively patients who were of age or with a new of were prospectively with use of a case report to and information regarding and the group from which the population was population or and the of and studies include the for case and groups. Example: database for patients was in the of Orthopaedic and was in in order to include a representative sample from the population controls for the study. of only one was in the study if he or had been for a of was not not with any for the of the and were the for the group and the that the case and groups and the and groups are and be and the of subjects in each group be reported. Example: and May 100 patients who had been and for a of the study and were matched with a cohort of 100 The was on the of age and The cohort of was in the order in which they to and of the and the to be for outcomes, potential and effect if A clear of variables such outcomes, and confounding variables the reader to understand the author’s and to determine if the results of the study are applicable to other Example: was an that was with of and treatment with was with of treatment by or surgical was the and risk factors were considered potential each of of data and details of of the of if is more than one group. The in which a is and will affect the validity of the study. The of the data and the to the data must be clearly such that a reader and reach the The potential for confounding and bias is in observational studies, and the to and effects. outcome will with the of the and in the of the will the of the outcome describe the that were to and The data may be if the or The describe the validity or of the data and and describe any to their or their analysis for Example: was for standard of the and the and order to the of studies of the and were also and with the reported in the Bias any to potential of bias. As above, observational studies are prone to bias due to inherent in the studies results that from in a systematic in the of patients and in data may bias when data from or are of a into a cohort or group can to of if a is into a when the only may be in a cohort of patients on the of and the observed risk of the Authors potential of bias and estimate the and of the effect on the Example 1: studies that had been were evaluated by the at the time of the were by the A who was not the and was to bias in Example 2: were by the orthopaedic potential bias was that have been had an blinded the how the study size was The sample size must be large to differences or if they sample size are they be other factors sample such a be Example 1: sample size not be the was However, the incidence of in the controls to be and the estimate of the risk for the patients to be increased a sample size of individuals group would be to risk Example 2: analysis that a sample size of patients for each of the would provide to a of in the the how variables were in the describe which were and or of the data must be the is divided into groups, groups must be may have in the analysis of the Example: was and patients were to the of the of if the was if it was to and if it was The STROBE statement includes a of recommendations for reporting the to and the These recommendations are on the and study design and must be considered at the point of the data and the of a study is the of and investigators to understand the of confounding, bias, and to their study’s validity and the study Authors describe and the following items are at the most common with the and analysis of observational research for Confounding confounding when two groups of subjects are if they are when in is an between the groups. The observed relationship between the (exposure) and the outcome can be due to factors that both the exposure and the outcome and the observed relationship of interest and threaten the validity of any conclusions The investigator about any potential confounding such or analysis be to and for to and for confounding be clearly reported. analysis to for a in a of the study The reader must be to understand when the was or analysis may to biased Furthermore, the results from a analysis must be such in the report to data to studies and any study or database a study to selection bias. While it is to include only patients with complete data on variables of is to the of bias. Authors the data and understand the in which data are not appropriate to with the data and describe clearly in their is further by the of study and is on that the study subjects are with each other or representative of a population how to was to is a truly event and is a of bias in cohort studies. with complete may be from those with incomplete to more patients than the analysis of patients with complete will underestimate the relationship of interest. that a cohort is followed for the development of and that only patients with one of are who of a a than one not be for the analysis, and the observed of would be an of the of is to of patients who reach the of the study from those who have not and to report how to was analysis, of how cases and controls were In order to conclusions from a of two groups, the two groups to be is a process by which potential confounding variables are and cases and controls are on the of factors such that the groups are the with to is associated with limitations and is not In order for the reader to if the matched design was the clearly describe and was and describe the An of the of and a of the bias that may have from be the sampling The of most clinical studies is to the of a representative sample of subjects in order to a about a population of cross-sectional studies use a sampling to subjects from a These are often and include of the that the are representative of a Authors clearly the that were to subjects so that readers can understand how the sampling the and of the are to determine if the results of an analysis are with those with or or These the in a to determine the effects of the on the results and can be to confounding, selection bias, or bias to an observed Authors describe any the were done, and describe what were Example: analysis the of the conclusions a of and outcome the of one or variables in were the other and outcome variables were with analysis a of of at the of individuals at each of the the of patients who were who were for who were who were in the study, who had complete and who were for the for at each the use of a reporting the reader to recognize potential of selection bias. Authors report the of participants at each of the study and and include information about subjects who were to be or who were to Example: A is an for data regarding In a detailed from the study information at each of the study from to of 1: from the study, information at each of the study from to of with with nonoperative treatment for results in the randomized and observational Bone Joint the of the study participants and information on and potential the of participants with data for each of interest. for a of the of Example: In the study by the retrospectively evaluated the to a cohort of patients who of in order to the of time to treatment with A clear in the that patients not have a data point for the of and that patients not have data for at one of the the to be associated with the to patients from the The in the information on for subjects who would have been for in the study have selection Cohort the bias resulting from to to the of for the outcome data and to how many patients not reach and Example: the two had of to for clinical and patients had been to The patients had a complete clinical operative and a of of and to and were in the In the data about the study population be reported. cohort and cross-sectional studies, outcome data include the of or the of time for each outcome of interest. case-control studies, information regarding the of exposure for case and groups be Example: can and clearly outcome the outcome data for a cohort study in which the of is reported for each for the population and a population of subjects with TABLE - of in Cohort and in the of of of patients surgery surgery disease use was of in and a of patients with and Bone Joint and if and their clear which confounders were for and they were both and the reader to determine how confounding factors the and of The which confounding factors were or and Example: In a study of describe how the variables were in the and were and the following data were for each of of of surgery, and time in We variables other studies have associated them with In the the data from both a and those variables with found on that, when for and only to a of an to and the use of to were associated with increased of when variables were the of if a is divided into groups. In the further the and or for each group if analysis a also be Example: the study however, the patients in the to group a risk of about to with the group of patients who was a were increased of but the was not for and for and of risk into risk for a time risk is often more to other populations than but in such the risk of an adverse risk may provide more information to the reader than risk the may to a and increase the of the results by including of both and other that were of and and for a and regarding Example: The in is an from the of the the for In the of the the analysis that a to in with if the was if only of patients treatment and only if treatment the incidence of by more than and if patients were results with to study the study readers of the of the study and whether or not the results or their Example: study, aimed to the between the and the of an We one and and on of a large of subjects with varying of of the of study is that is a between the and the of the limitations of the study, into of potential bias or both the and the of any potential bias. The of the paper include a detailed of the limitations of the that the of a study to potential bias and confounding is of the study design and the of potential bias be that were to bias and confounding be the effects of factors on the observed a of the results of results from studies, and other The inform readers the study into the literature and how the results can be and applied to other Example: the study to any clinical benefit in association with the use of treatment for patients who had a in the level from on to surgery for the treatment of a In with previous studies on that the practice of to orthopaedic surgery in patients who are not surgery is of the of the study The investigators any between the study population and a more general population that may threaten the of the results to a Example: multicenter study cohort may not be representative of the population of patients who The are the of which may be to those of the average the of and the of the for the study if for the study on which the is is a association between the of and the conclusions of many research of of be clearly described so that the reader can the or of and inherent to the of the Example 1: study was by the Orthopaedic and and The was also in by the for and on from the for and Example 2: of research for or of one or more of the or for from Observational studies, including case-control, cohort, and cross-sectional study are in the orthopaedic literature and provide information about disease etiology, natural history, prognostic factors, and treatment study however, are prone to bias, most notably confounding, sampling bias, and recall bias. Authors must recognize the limitations of observational studies and potential biases that threaten the validity and applicability of their findings. The STROBE statement is a checklist that is designed to assist clinician-scientists in reporting observational studies. examples from The Journal of Bone and Joint Surgery, have on the STROBE statement to provide a for orthopaedic surgeons reporting observational studies. We have STROBE checklist items that improve transparent reporting by potential bias and a for the results of an observational study.

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