Research activity amongst DCM research priorities

Systematic review and meta-analysis, otherwise known as research synthesis, are important tools to quantitatively summarise current knowledge about a topic. Their findings are fundamentally underpinned on the studies that they identify. Within the field of DCM, there is inconsistent disease terminology, with an absence of index terms or codes [7], which makes literature searching extremely inefficient. For this reason, and to support work by the Myelopathy.​org charity, a hand indexed database of primary clinical articles has been maintained.

The dataset was built using a search of Embase and MEDLINE for [“Cervical”] AND [“Myelopathy”]. It includes primary clinical human trials, in which DCM is the primary condition being addressed, with the full text available in English. Animal studies, case reports, letters, editorials, reviews, technical notes, commentaries, proposals and corrections were excluded.

The database was initially built on previous systematic reviews [2, 3] and initially contained all papers published up to December 31, 2015 [8]. The last update was performed on August 08, 2020. This updated database forms the basis of this study.

Each paper was assessed (by authors BG, HB, FB, RD, MK, CIPS, JQT) for alignment to the established research priorities. Each paper was allocated to one or more priorities, or deemed to be not aligned to any priority.

The following information was extracted for each paper: title, abstract, author names, country of corresponding author, year of publication, research theme (as per [8]), patient characteristics (number of patients, surgical vs. non-surgical treatment) and study design (prospective or retrospective, cohort or case-control, level of evidence).

In total, 2261 papers, with a total of 1,323,979 patients (median, 63 patients in the 2230 articles that reported an N), were included. Japan has published more papers (625, 27.6% of total) than any other country, whilst the USA studied the greatest number of patients (4,549,916). The aggregate global distribution of research activity is shown in Fig. 1 and per priority in Supplementary Data 3. Moreover, 727 (32.2%) papers reported a prospective design, whilst 806 (35.6%) studies reported a retrospective design. Furthermore, 728 (32.2%) papers had an unreported/unclear design.

Summary data for each priority are shown in Table 2. A substantial proportion (256/2261, 11.3%) of papers were not aligned to any priority. Those papers assigned to a priority were unevenly distributed. For instance, 1060/2261 (47%) of papers were assigned to priority #15 (predictors of outcome after treatment), whilst there were nine priorities that had fewer than 10 papers each (Table 3).

Median sample sizes for each priority are shown in Fig. 2. There was a statistically significant difference in the distribution of sample sizes between priorities (p = <0.001, independent-samples Kruskal-Wallis test).

The research activity in DCM over time is shown in Fig. 3 and Supplementary Data 2. Growth of research activity in the different priorities is significantly different (p = <0.001, Pearson Chi-squared test). For example, one priority (#21, management of mild DCM) had no papers published in the past 5 years, whilst another priority (#13, symptom management) had 33% of all its papers published in the past 5 years. Within the last 5 years, three priorities have shown consistent growth – #4 (assessment and monitoring), #9 (imaging techniques) and #15 (predictors of outcome after treatment).

This study was based on 2261 papers that form the entire literature in DCM over the past 25 years – a relatively small research output compared to other diseases of similar prevalence. Despite this, research activity has continued to grow since our last evaluation [8], with 968 new papers since January 1, 2016. In line with our previous findings, the focus of DCM research remains on surgery. In particular, the determinants of outcome after surgery (aligned with Priority #15) have been a particular focus. These determinants may include the choice and timing of the surgical procedure [6, 11, 12].

With the exception of Priority #15 (determinants of post-treatment outcome), the established research priorities have been under-represented. We found more papers not aligned to any research priority (‘/’, 256 papers) than aligned to any individual priority other than #15 and #4 (Table 3). This is emphasised when examining the most important priorities – the #1 priority (raising awareness) has only eight papers aligned to it, and the top ten priorities have only 780 papers between them, less than 35% of the 2261 included papers. Furthermore, there is inequality in research activity amongst the research priorities – both in cumulative counts (Tables 2 and 3) and in recent growth (Fig. 3).

It should be acknowledged that these priorities are newly established and reflect on-going clinical uncertainties. The literature included in this review spans 25 years, during which time the research priorities may have been different. For example, it is notable that during this period the evidence base for surgical management has increased significantly (as reflected within the AO Spine Guidelines [5]), which is in line with substantial research activity [8]. These findings therefore do not dismiss previous research but aim to highlight the present directions and knowledge translation gap. However, this example does highlight the logical correlation between a research focus and clinical progress, substantiating within DCM the premise and potential for research priority setting [1].

This paper therefore serves several roles. Firstly, it acts as a collection of research papers, comprising the entire current DCM literature, to serve as a reference for current research. Secondly, it indicates the magnitude of change required to address the research priorities, indicating which priorities in particular are under-researched. Both the established order of importance and the existing number of papers aligned to each priority may be used to guide researchers in choosing a topic for research. Thirdly, it acts as a baseline, against which the success of the AO Spine RECODE-DCM project, and in particular its KT strategy, may be measured against in the future.

As we have published previously [7], owing to the difficulties in indexing DCM literature, the results presented here are based upon an extensive hand search of the literature (title and abstract only). Whilst this may introduce an element of subjectivity – the reviewers must decide which papers meet the pre-established criteria and which do not and this is not always clear – this was the preferred approach to ensure a more comprehensive representation of the field. Given this breadth and the number of studies captured, we are confident that the overall findings are a true reflection of the DCM research field, although we note the need for reproducibility of methods in future research of this type. Establishing a clear set of disease codes to combat this problem is one of the aims of the AO Spine RECODE-DCM project and will help to address this for the future.