Diabetes-related foot disease research in Aotearoa New Zealand: a bibliometric analysis (1970–2020)

Diabetes-related foot disease (DRFD) is one of the most devastating, but potentially avoidable complications of diabetes [1, 2]. DRFD is defined as a foot affected by infection, ulceration or destruction of tissues of the foot of a person with currently or previously diagnosed diabetes mellitus, usually accompanied by neuropathy and/or PAD in the lower extremity [3]. Diabetes-related foot ulcers are the most frequently recognised complication of DRFD and a major risk factor for, and nearly always precede, diabetes-related lower-extremity amputation (DRLEA) [4‐6]. DRLEA is one of the most substantial and debilitating consequences of diabetes [7].

Diabetes is common worldwide, affecting an estimated 10.5% of adults 20–79 years globally in 2021 with prevalence rates varying between countries [8]. In Aotearoa/New Zealand (NZ), in 2008/09, the prevalence of diabetes (diagnosed and undiagnosed) among those aged ≥15 years was 7.0% overall, and ethnic specific rates were 9.8, 15.4 and 6.1% among Māori, Pacific peoples and non-Māori non-Pacific peoples, respectively [9]. The age standardised rate for major DRLEAs in NZ is 6.4 per 100,000, which is almost double the rate for Australia and the United Kingdom [10, 11]. More than half (58%) of DRLEAs are attributable to diabetes [12] and Indigenous Māori are more likely to experience both major and minor DRLEA than their NZ European counterparts, with males bearing a higher burden [13‐15]. Gurney et al. demonstrated that Māori with diabetes were 65% more likely to undergo major DRLEA than NZ European/Other people with diabetes [12]. Internationally indigenous populations have poorer diabetes foot outcomes and higher rates of risk factors, which occur at a younger age compared with non-indigenous populations [16]. Understanding DRFD research quantity and quality in the NZ context is important, as Indigenous Māori people not only have high rates of DRLEA [13, 17] but also fare worse in many other diabetes-related health measures [15, 17].

Whilst the understanding of DRFD has been advanced over many decades based on international research, the contribution of locally NZ driven DRFD-related research appears to be limited [13, 15, 17]. Consequently, we do not know if NZ based DRFD research is targeting the areas specific to achieving a reduction in DRLEA and improved health outcomes. The objective of this study was to provide the first comprehensive bibliometric analysis of DRFD research generated by NZ based researchers in order to present a “big picture” of extant research. Specifically, the study aimed to identify underlying patterns in DRFD publications, author-specific contributions, the volume of scholarly work over time, the degree of national and international collaborations, and the major topics/areas of research focus.

The characteristics of the included studies are displayed in Table 3. A total of 140,489 publications were identified. Following application of the Scopus® search limiters [Article, Language (English), Country (NZ), Journal], 444 articles were assessed for inclusion (Fig. 1). After application of the study inclusion and exclusion criteria, 47 articles were included in the final analysis.

Bibliometric analyses are useful for inferring trends over time, themes researched, detection of the most prolific scholars and institutions and to present the “big picture” of research in a particular field [37]. The present study analysed the research quantity (i.e., publication output, areas of research focus and trends over time) and quality (i.e., the level of evidence, degree of collaboration, IF, and citation rates) of NZ DRFD-related research.

In line with an increasing worldwide volume of DRFD research [21] the number of NZ produced DRFD publications has steadily increased, albeit a relatively small increase, between 1988 and 2020. Notably, from 2006 onwards there was an increase in published articles with a peak of six new articles in 2018, and an increase in research growth and national collaboration. The underlying reasons for the increase in DRFD research are not attributable to any one factor but may have resulted from the increasing prevalence of diabetes in NZ [9] and the numerous diabetes quality of care strategies, policies and initiatives implemented in the early 2000s in NZ. Additional File 1 presents a timeline of policies/strategies/initiatives that may have potentially influenced NZ DRFD research. Notably during this period, the NZ Government strategy elevated the importance of diabetes with the release of The NZ Health Strategy (2001) [38]. Reducing the incidence and impact of diabetes was one of the 13 health objectives chosen for implementation in the short to medium term. Alternatively, the significant rise in the NZ-produced DRFD research may reflect the general worldwide trend of increasing scholarly activities across disciplines, including research focused on areas related to DRFD [39].

Whilst the significance of diabetes in NZ came to the fore with changes in health policy and strategy, research development prior to 2000 was hindered by limited research funding. In 2000, health research accounted for only 1% of the national health budget [40]. It was not until 2005 that the Health Research Council (HRC) of NZ became a Crown agent, charged with putting into effect government policy in relation to health research [41]. HRC now invests $NZ126 million a year into research studies, projects, and programmes [41]. The opportunities for NZ researchers to obtain funding have improved in the past 15 years, however, our results show DRFD research by NZ researchers is still poorly funded with only 32% of the included articles declaring research funding support. Most of these studies were funded by national organisations (DHBs, universities, HRC; n = 11, 23%) and represent studies that were largely observational. As these types of studies are of a lower level of evidence as characterised by the Oxford Centre for Evidence based Medicine levels of evidence [27], they are often considered insufficient to change clinical practice compared to RCTs that are considered to be the gold standard for demonstrating efficacy [42]. As shown by our analysis, there are few data related to DRFD disease derived from RCTs or interventional studies. Consequently, to bridge this gap, a medicine-based evidence approach may need to be adopted. The term medicine-based evidence, defined as a patient-centred approach to the evaluation of data that recognizes RCTs may not always yield higher-quality evidence than observational studies and/or provides high-quality evidence where RCT data are lacking [43]. In order for such an approach to be adopted, the development of comprehensive data registries and the generation of big data sets are required. This can only be achieved through further development of international research collaborations identified by this study and increased research funding from government organisations like the HRC of NZ. The impact of international research on NZ based provision of DRFD care must also be acknowledged. International research such as the Seattle Diabetic Foot Study [44], the North West diabetes foot care study [45], research examining multi-disciplinary-based diabetes foot ulcer care [46], and work from the Scottish Diabetes Foot Action Group in foot screening and risk stratification [47] has provided practice-changing evidence which is reflected in how diabetes foot care is provided in NZ.

The research collaboration post 2006 demonstrated marked growth with international and bi-national collaboration increasing. Bi-national authorship post 2006 may have been positively affected by increasing working relationships between DHBs, Primary Health Organisations (PHOs), and university research institutes, partially facilitated by health system restructures. Our data shows there has been a high level of bi-national collaboration since 2006, with 80% of national collaboration occurring between a DHB and university research institute/department. International collaborations indicate the increasing global reach of NZ based research and active exchange of knowledge and research skills.

Despite the increase in number of publications and increased national and international collaborations, the majority of the identified publications (87%) represent studies classified as basic/clinical research, which represents a lower level of evidence as per the Oxford Centre for Evidence-based Medicine (level 3 or 4 evidence) [48]. Based upon the Oxford levels of evidence rating, and the relatively low citations rates, the majority of identified NZ DRFD-related publications were categorised as of poor quality. Of the top five cited articles (contributing 46% of total citations), four were RCTs (one first-authored by an NZ researcher) and four were multi-centre studies first-authored and led by international researchers. The most cited articles were either multi-centre national or international RCTs representing high quality of evidence.

The median journal IF (4.31, IQR: 2.75–6.81) is reasonably high for included publications. A previous study by Al-Busaidi et al. investigating diabetic foot disease research in Gulf Cooperation Council countries that included 96 publications found a median IF of 0.15, compared to 4.31 from 47 NZ produced DRFD publications [21]. Analysis by SCI Journal in 2018 (https://​www.​scijournal.​org/​articles/​good-impact-factor) found that only 2% of journals have an IF of 10 or more, and 13% with IF of 4 or more. An IF greater than 3.29 places a journal in the top 20% of medical and health profession journals. Only five articles were published in journals with an IF of greater than 10. Of note, most publications were published in the New Zealand Medical Journal (n = 10, 21%), which does not currently hold an IF. IF is the most common metric for evaluating bibliometric impact of published research, however the value of the research is not necessarily reflected by the IF [21]. This finding is interesting as researchers often seek publication in so called higher impact/prestigious journals intending to improve their personal citation rate, and h-indices. Furthermore, academic staff promotions at universities often depend upon the publication of a certain number of articles in scientific journals [49]. However, it is possible authors may choose to publish in journals based on the intended audience/readership where the article may have the most context and/or clinical impact. This may be more common when authors have a clinical rather than purely academic background, where their driver may be to improve clinical outcomes rather than produce high ranked research outputs. Alternatively, the decision to publish in a particular journal may be dictated by the availability of funding to support the fees associated with publication. A combination of these factors may be likely reasons for many NZ authored DRFD articles being published in the New Zealand Medical Journal.

Categorisation of research by type found that there were a relatively even spread number of articles categorised as screening/prevention, management of diabetes-related foot complications, and epidemiological studies. However, of the studies categorised as screening/prevention none were interventional studies. With few studies aimed at improved care or prevention of diabetes-related foot ulceration/amputation, coupled with recent international calls to reduce foot ulcer incidence by at least 75% and local NZ health priorities to reduce health inequities for Māori, a shift in DRFD research priorities is essential [6]. Therefore, the first steps towards this goal are to evaluate the performance of health services aimed at the prevention and early detection of DRFD, and the ability of services to reduce inequities in access to services and health outcomes. This is a priority in NZ given the regional variation in DRLEA and significantly higher amputation rates for Māori [7, 12, 13].

The results of this study have several limitations that must be considered. All metrics were extracted based upon our pre-defined search terms, and data only from the Scopus® database, which may not include all publications that meet our inclusion criteria. Some peer-reviewed journals are not indexed in Scopus®. However, we also checked for additional publications by screening reference lists of identified articles from the initial search. As this study included only journal articles, our findings may not reflect all NZ DRFD literature. It is acknowledged there may be grey literature sources that reveal a number of NZ based quality-of-care improvement initiatives related to DRFD that are not published in peer-reviewed journals. Finally, journal IF was used to assess the quality of published research, which has been debated as a research quality indicator [21]. However, IF is the most commonly used and arguably the best existing metric for evaluating the bibliometric impact of published research [50].

DRFD articles authored by NZ researchers have increased over the past five decades. Despite NZ researchers increasing their global impact through collaborative networks, most of the research was classified as low-level evidence, with limited financial support and funding. Increased funding for interventional research is required to enable a higher level of NZ relevant, evidence-based, and practice-changing research to occur. Future research must focus on the NZ context and reducing inequalities in diabetes-related outcomes for Māori by specifically developing and evaluating interventions to better prevent, screen for, and manage DRFD in NZ.