Response rates and respondent demographics

Although 43 of 68 potential respondents agreed to participate in the study (63%), only 17 respondents contributed at least one article of importance, for a response rate of 25%. Of the final respondents, six were between 41–50 years of age, ten were between 51 and 60, and one was 61 or older. In addition to possessing a clinical doctorate, nine held academic doctorates, six master’s degrees, and twelve bachelor’s degrees. Demographic characteristics of survey respondents are presented in Table 1.

Table 1 Respondent demographics of essential literature study Full size table

Article citation data

Respondents contributed 50 pieces of evidence (PE). Forty-one PE were mentioned at least once, with six articles mentioned by two or more respondents. Respondents categorized 26 as research, six as education, six as health care policy, and the remaining three as other. Additionally, forty were published within journals and one was a book. Recommended articles were published most often in the Journal of Manipulative and Physiological Therapeutics and The Spine Journal (Figure 2). Publications years for the recommended PE ranged from 1995 to 2011, with an emphasis on recently published journal articles. Seventeen (17) PE were published in 2005–2009 and 11 PE between 2010–2011 (Figure 3).

Figure 2 Recommended citations by journal. Full size image

Figure 3 Recommended citations by publication year. Full size image

Table 2 reports the 41 recommended PE. Citations are listed first by the number of recommendations by survey respondents and then by number of Google Scholar citations. Each PE also includes information about its accessibility. Lastly, a quotation from the recommending respondent is provided demonstrating the importance of the article for chiropractic professionals.

Table 2 Essential literature for the chiropractic profession: articles submitted, number of recommendations and justification, Google scholar citation frequency, and accessibility Full size table

Articles with multiple recommendations

Six distinct articles were recommended by more than one respondent. Six respondents recommended the article, “Effectiveness of manual therapies: the UK evidence report”, by Bronfort et al. [35]. A majority of the respondents noted the comprehensive nature of this systematic review of randomized clinical trials of spinal manipulation, mobilization and massage. This article addresses varying levels of evidence and cites 322 articles on spinal manipulation and other manual therapies as treatments for musculoskeletal, headache and non-musculoskeletal conditions in an organized and easily readable manner. One respondent wrote, “This is the most comprehensive systematic review of the literature pertinent to DCs for both musculoskeletal (MSK) and non-MSK conditions”.

Two respondents each recommended five additional studies [8, 36–39]. An article published in 2002 by Pickar [36], “Neurophysiological effects of spinal manipulation”, is one of the earliest publications making the list, confirming the author’s early attention to identifying the basic mechanisms of action underlying spinal manipulation and the relevance of the topic for doctors of chiropractic. One respondent wrote, “[the article] provides evidence based scientific rationale for the effects of spinal manipulation”.

Another basic science article, this one by Ianuzzi and Khalsa [39], “Comparison of human lumbar facet joint capsule strains during simulated high-velocity, low-amplitude spinal manipulation versus physiological motions,” was similarly recommended by respondents: “an important paper for mechanisms of action of spinal manipulation” and “demonstrated intrinsic biomechanical safety of lumbar spinal manipulation”.

The large population-based study by Cassidy et al. [37] “Risk of vertebrobasilar stroke and chiropractic care: results of a population-based case–control and case-crossover study”, demonstrated vertebrobasilar stroke as a very rare adverse event. This article is a relevant reference for chiropractic professionals who educate their patients, other healthcare providers and the media about the risks of chiropractic care. One respondent commented, “This presents the best evidence about the risk of stroke after cervical manipulation”.

A Cochrane Collaboration systematic review published by Walker and colleagues [38], “Combined chiropractic interventions for low back pain”, represented a rigorous, international, and interdisciplinary evaluation of the merits combined chiropractic therapies over spinal manipulation alone for pain and disability. Of this article, one respondent wrote, “This systematic review shows that usual chiropractic care is as effective as many other therapies for acute or sub acute low back pain”.

An article by Murphy et al. [8], “The establishment of a primary spine care practitioner and its benefits to health care reform in the United States,” presented a cogent health policy rationale for changing the role of chiropractors in the U.S. health care delivery system based on research evidence. Individuals interested in the evolution of the chiropractic profession should be familiar with this document, as a respondent commented, “This article outlines the need for a primary spine care clinician in the health care system, and highlights the qualifications of DCs to fill this niche”.

Literature with single recommendations

Of the 41 unique PEs, 34 were unduplicated articles or books mentioned by a single respondent. Six singly recommended articles address interdisciplinary clinical decision-making for the care of patients with low back pain [40–42, 50, 59, 72], while two texts highlight treatment approaches to neck pain and related conditions [45, 55]. Five articles report findings from clinical trials of manual therapies or spinal manipulation [43, 46, 53, 57, 60], while three other papers discuss either ineffective applications, [47, 65] or common side effects of manipulation [44]. Lastly, nine articles demonstrate chiropractic research priorities [30, 73, 74], analyze health policy issues for the chiropractic profession [14, 51, 69], or discuss evidence-based practice concepts for doctors and students of chiropractic [67, 70, 71]. That only one respondent mentioned each of these studies should not undermine their potential relevance to the chiropractic profession. Instead, many unduplicated references are important references on key concepts, evidence or issues for practicing doctors of chiropractic. For example, 10 recommended articles provide theoretical rationale or basic science evidence on the mechanisms of action of spinal or joint manipulation [48, 52, 56, 58, 61–64, 66, 68].

Scholarly impact

The secondary analysis of the scholarly impact of the recommended PEs revealed interesting patterns that may further assist doctors of chiropractic in selecting from among this list of essential literature for the profession (Table 2). The Google Scholar citation analysis identified some articles as highly referenced within the field of chiropractic and in associated disciplines. Researchers have cited some chiropractic research articles more than 100 times including work by Senstad et al. [44], Hurwitz et al. [45], Pickar [36], Cassidy et al. [37], Nelson et al. [46], Bronfort et al. [35] and Olafsdottir and colleagues [47]. Several articles in fields related to chiropractic, specifically regarding the interdisciplinary care of persons with back pain, also demonstrated very high citation rates [40–43]. These articles have clearly influenced how other researchers view the field. Other articles recommended as essential literature have received much less attention from researchers. This analysis of scholarly impact does not necessarily indicate the possible influence of any article among chiropractic educators, clinicians or students.

Article accessibility

The accessibility of scholarly articles also is an important factor for the dissemination, uptake, and clinical application of scientific knowledge. Many of the most highly cited articles were freely available as full-text articles on the Internet, either from the journal publisher or through the U.S. National Library of Medicine (NLM) and its PubMed Central (PMC) database of biomedical and life sciences literatures. For example, the articles with the broadest uptake by other authors were the low back pain clinical practice guidelines and the clinical prediction rule for identifying responders to spinal manipulation, three freely accessible articles published in Annals of Internal Medicine (Table 2). In contrast, articles published in Spine, The Spine Journal, and Journal of Manipulative and Physiologic Therapeutics were available only by subscription or direct purchase, at a cost of about $30 US per article. Perhaps not surprisingly, these articles also had lower overall citation rates from papers published in open access journals or those available from PMC. Of note, several of these articles were available on websites from individuals or institutions in possible violation of article copyright agreements.