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Study Protocol

Study protocol: A systematic review and meta-analysis of risk factors for the first-ever foot ulcers in patients with diabetes.

[version 1; peer review: 1 approved with reservations, 1 not approved]
PUBLISHED 07 Jan 2025
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Abstract

Background

Diabetic foot ulcers (DFUs) are a serious complication of diabetes mellitus (DM), significantly contributing to mortality and morbidity in this population. Annually, approximately 18.6 million people with DM develop DFUs, with up to 34% experiencing a foot ulcer during their lifetime. DFUs are a leading cause of limb and life-threatening infections, lower limb amputations, and increased hospitalisations. Despite these public health challenges, there is a lack of research focusing on the primary prevention of DFUs, particularly the prevention of first-ever ulceration.

Objectives

To systematically review and synthesise research evidence and meta-analysis of previous research findings and derive conclusions regarding risk factors for the development of first-ever foot ulcers in patients with diabetes.

Methods and analysis

Four English and three Chinese databases will be utilised to identify eligible studies reporting risk factors for the first-ever foot ulcers in patients with diabetes. Two independent researchers will review the literature, extract relevant data, and assess the risk of bias of included studies using the Newcastle-Ottawa Scale. Pooled odds ratios (ORs) and standardised mean differences (SMD) with 95% confidence intervals (CIs) for nominal and continuous data will be calculated employing either a fixed-effects or random-effects model based on heterogeneity (I² < 50% for fixed-effects and I² > 50% for random-effects models). All statistical analyses will be conducted using Stata Software Version 16.

Systematic review registration

PROSPERO (CRD42024508855)

Keywords

Diabetes, Risk Factors, First-ever Foot Ulceration, Systematic Review

Introduction

Diabetic foot ulcers (DFUs) present a severe chronic complication of diabetes mellitus (DM). Due to the rising prevalence of DM, these complications are a major contributor to the burden on the global healthcare system. According to the International Diabetes Federation (IDF)1, the number of adults living with DM reached 537 million in 2021 and is projected to reach 643 million by 2030 and 783 million by 2045. Worldwide, about 6.3% of people with DM experienced a DFU, with up to 34% developing one during their lifetime2.

DFUs have a significant impact on individuals, family members and the healthcare system, as DFUs are associated with a high risk of hospitalisation, amputation, and mortality. Existing data indicates that approximately 20% of individuals living with a DFU required hospitalisation, with up to 20% of hospitalised patients undergoing amputation35. The mortality rate following incident DFUs stands at 49.1% at five years and escalates to 76.9% at ten years4. Additionally, DFUs admissions also incur the highest average per-patients medical costs compared to admissions with non-DFU-related DM patients68. A case-control study conducted in the U.S. revealed that the annual medical costs for each patient with DFUs range from $28,031 for Medicare to $26,881 for private insurance, making the cost for patients with DFU twice that of patients living with DM without DFUs6.

The first-ever foot ulcer is defined by the International Working Group on the Diabetic Foot (IWGDF) as “an ulcer occurring in a patient who has never before had a foot ulcer9. Identifying the risk factors for the occurrence of DFUs and providing evidence for prevention strategies is an important topic. Guo et al.10 and Huang et al.11 conducted systematic studies to pool risk factors for DFU recurrence. Another meta-analysis by Crawford investigated predictors for DFU occurrence, but this study did not differentiate between first-ever and recurrent cases12. Recently, a prospective study characterised first-ever and recurrence DFUs, highlighting differences in patients’ characteristics between these two groups13. In addition, it is worth noting that a history of ulcers serves as the primary predictor for the recurrence of DFUs14. Consequently, there is a need to explore the risk factors specifically associated with the first-ever foot ulcers to prevent their onset.

However, factors specifically associated with the first-ever foot ulcers remain unclear. Several studies1517 have investigated the risk factors associated with the first-ever foot ulcers in patients with diabetes, and there is significant diversity among the findings of these studies. For example, a retrospective study identified the duration of DM as a significant risk factor for the first-ever foot ulcers18, which contrasted with the results of another 8-year prospective study conducted in the UK17, which found no significant association between the duration of diabetes and the first-ever foot ulcers. Similarly, disagreements on age as a risk factor for the first-ever foot ulcers were found in the study of Panagoulias et al.19 and Adem et al.18, with the former study suggesting that patients who developed DFUs were older, while the latter study did not show a significant difference. Therefore, there is a need to synthesise and analyse existing evidence, specifically focusing on the risk factors for the first-ever foot ulcers in patients with diabetes.

Thus, we outline a systematic review and meta-analysis study protocol to estimate the risk factors contributing to the first-ever foot ulcers in patients with diabetes and offering evidence-based strategies for DFUs prevention.

Study objectives

The aim of this systematic review and meta-analysis is to estimate risk factors for the first-ever foot ulcers in patients with diabetes.

Research questions

What are the risk factors for the first-ever foot ulcers in patients with diabetes?

Methods

Protocol design and registration

The study protocol for this systematic review will adhere to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols guideline (PRISMA-P)19,20 (see Supplementary File S1). Meta-analysis procedures will align with the Meta-Analyses and Systematic Reviews of Observational Studies guideline (MOOSE)21. Furthermore, the protocol has been registered in the International Prospective Register of Systematic Reviews (PROSPERO) under the registration number CRD42024508855.

Data sourcing and search strategies

A comprehensive search strategy was devised to identify potential articles across seven databases: PubMed/Medline, Embase, Web of Science, the Cochrane Library, China Knowledge Resource Integrated Database (CNKI), Weipu Database (VIP), and Wanfang Database. The reference lists of the included studies will be examined for additional relevant studies, and citation tracking will be employed to identify further pertinent research. A research librarian was involved in formulating this search strategy. Our approach incorporated relevant keywords representing three core concepts: "diabetes mellitus", "diabetic foot ulcers", and "risk factors". Medical Subject Heading (MeSH) terms were employed in PubMed/Medline and the Cochrane Library to further refine the search for articles relevant to our topic. Boolean operators (OR, AND) and truncation (*) to capture variations in word endings and quotation marks (" ") for exact phrases were consistently utilised throughout the search strategy (see Supplementary data, File S2 for the search strategy).

Inclusion and exclusion criteria

Studies will be eligible if they report risk factors potentially contributing to the first-ever foot ulcers in patients diagnosed with either Type 1 or Type 2 DM. In this study, “first-ever foot ulcer” will be defined as “a foot ulcer occurring in a patient who has never before had a foot ulcer9. To be included, studies had to be retrospective or prospective cohorts, cross-sectional or case-control studies published in English or Chinese.

Due to limitations in translation capabilities, non-English/Chinese articles will be excluded. Additionally, intervention studies, review articles, case reports, letters, comments, meeting abstracts, studies not published in peer-reviewed journals, and incomplete or non-full text articles will be excluded due to duplication or limited quality of evidence (see Table 1).

Table 1. Inclusion and exclusion criteria.

Inclusion criteriaExclusion criteria
Patients diagnosed with either Type 1 or Type 2
diabetes mellitus
Foot ulcers due to causes other than diabetes mellitus
Articles reported factors contributing to the first-ever
foot ulcers in patients with diabetes.
Incomplete or non-full text articles
Articles in English or ChineseNon-English/Chinese language articles
Retrospective or prospective cohorts, cross-sectional
and case-control studies
Intervention studies, review articles, case reports, letters,
comments, meeting abstracts, or studies not published
in peer-reviewed journals.

Study selection procedure

The search results will be exported to Covidence data-management software for screening, and duplicates will be eliminated using the software's functionality. Two reviewers (Tao Y and Zhang D) will independently assess the titles and abstracts of all retrieved studies to exclude studies following the inclusion and exclusion criteria. Full texts of the remaining studies will be evaluated by two reviewers (Tao Y and Zhang D) for inclusion in the meta-analysis. Any discrepancies between the reviewers during the study selection process will be resolved through discussion until a consensus is reached. If necessary, a third reviewer (Liu YL) will be consulted to make the final decision.

Data extraction

Data will be extracted into a predefined Excel spreadsheet. Two reviewers (Tao Y and Zhang D) will independently extract and cross-check the extracted information. The following data will be extracted:

  • i. Study characteristics: last name of the first author, publication year, enrolment year, country, setting, study design and follow-up period (if applicable).

  • ii. Participants' characteristics include population, population size (DFUs/total), age, gender, type of DM, and duration of diabetes.

  • iii. Outcome: Estimated effects (e.g., relative risks (RRs), odds ratio (ORs), or hazard ratio (HRs)) for all risk factors for first-ever foot ulcers in patients with diabetes mentioned in included studies. For studies without reported risk estimates, raw data (e.g., means, standard deviations (SDs), median, inter-quartile range (IQR), and frequency data) will be extracted to calculate effect sizes.

Study quality and risk of bias

The methodological quality of the included studies will be assessed using the Newcastle-Ottawa Scale (NOS)22. This scale encompasses three main domains: selection of study groups, comparability of the groups, and assessment of outcome (for cohort studies) or exposure (for case-control studies). Total scores on the NOS range from 0 to 9 stars, with 6–9 stars indicating a low risk of bias, 4–5 stars indicating a medium risk of bias, and 1–3 stars indicating a high risk of bias. The quality of evidence for each risk factor and the incidence of first-ever foot ulcers will be evaluated using the Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) approach23.

Statistical analysis and meta-analysis

Statistical analyses will be performed using Stata Software Version 1624. When more than one studies report the same risk factor with consistent definitions, pooled ORs for nominal data and standard mean differences (SMD) for continuous variables will be computed. For the purpose of this study, RRs and HRs reported in the included studies will be treated as estimates of ORs. For studies that do not provide reported risk estimates, calculations will be carried out for both nominal data (ORs) and continuous variables (SMD) using the original data. Corresponding 95% confidence intervals (CIs) will be computed for all parameters. Descriptive presentation will be employed for lack of sufficient data within the literature or risk factors identified in only one study.

Heterogeneity among included studies will be assessed using the Cochran Q-test and the I2 test. A significance level of P < 0.10 for the Q-test will indicate potential study variance, recognising its limited power. Meta-analysis will be conducted using either a fixed-effects or random-effects model based on the absence (I2 < 50%) or presence (I2 > 50%) of statistically significant heterogeneity. A separate subgroup analysis based on study type and study quality will be conducted to explore the source of heterogeneity if at least ten studies reported a certain factor for first-ever foot ulcers. Sensitivity analyses by removing a single study at the time will be performed to examine the robustness of the pooled results. For meta-analyses that contain at least five studies, publication bias will be evaluated using a funnel plot, where asymmetry may indicate potential bias. Egger’s test will be employed to quantify the bias. To address potential bias, the trim-and-fill method will be used. A two-tailed P < 0.05 will be considered statistically significant.

Discussion

The aim of this systematic review and meta-analysis is to collect and statistically analyse all accessible data to identify potential risk factors for the first-ever foot ulcers in patients with diabetes. The outcomes of this study will enhance the current understanding of DFUs and equip healthcare professionals with information that could facilitate earlier identification of individuals at heightened risk of DFUs. Consequently, this could lead to the implementation of improved management strategies for diabetic patients predisposed to DFUs, potentially resulting in reduced mortality and alleviating the economic burden associated with DFUs.

Ethics and consent

Ethical approval and consent were not required.

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how to cite this article
Y T, D Z, MacGilchrist C et al. Study protocol: A systematic review and meta-analysis of risk factors for the first-ever foot ulcers in patients with diabetes. [version 1; peer review: 1 approved with reservations, 1 not approved]. HRB Open Res 2025, 8:1 (https://doi.org/10.12688/hrbopenres.13984.1)
NOTE: If applicable, it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Open Peer Review

Current Reviewer Status: ?
Key to Reviewer Statuses VIEW
ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 1
VERSION 1
PUBLISHED 07 Jan 2025
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Reviewer Report 26 Feb 2025
Bootan Hasan Ahmed, Case Western Reserve University, Cleveland, USA;  Nursing, Case Western Reserve University Frances Payne Bolton School of Nursing (Ringgold ID: 15735), Cleveland, Ohio, USA 
Not Approved
VIEWS 9
Abstract

In background, DFUs are a leading cause of limb and life-threatening infections, lower limb amputations, and increased hospitalizations should come after the first sentence as it the significance to the problem.
The study will be ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Ahmed BH. Reviewer Report For: Study protocol: A systematic review and meta-analysis of risk factors for the first-ever foot ulcers in patients with diabetes. [version 1; peer review: 1 approved with reservations, 1 not approved]. HRB Open Res 2025, 8:1 (https://doi.org/10.21956/hrbopenres.15349.r45374)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
Views
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Reviewer Report 07 Feb 2025
Ketan Dhatariya, University of East Anglia, Norwich, UK;  Elsie Bertram Diabetes Centre, Norfolk and Norwich University Hospitals NHS Foundation Trust, Norwich, England, UK 
Approved with Reservations
VIEWS 15
This is my review of the paper by Tao et al Study protocol: A systematic review and meta-analysis of risk factors for the first-ever foot ulcers in patients with diabetes

In the introduction the authors say that ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Dhatariya K. Reviewer Report For: Study protocol: A systematic review and meta-analysis of risk factors for the first-ever foot ulcers in patients with diabetes. [version 1; peer review: 1 approved with reservations, 1 not approved]. HRB Open Res 2025, 8:1 (https://doi.org/10.21956/hrbopenres.15349.r45141)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.

Comments on this article Comments (0)

Version 1
VERSION 1 PUBLISHED 07 Jan 2025
Comment
Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions

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