Degenerative Disc Disease: What's in a Name?

Michele C. Battié, PhD; Anand B. Joshi, MPH, MD; Laura E. Gibbons, PhD

Disclosures

Spine. 2019;44(21):1523-1529. 

In This Article

Results

The search limited to 2007–2016 for the term degenerative disc disease specifically in the title of publications resulted in 437 publications after initial duplicate removal. The final primary study sample for review comprised 402 publications after 13 book chapters, 11 remaining duplicates, 5 retracted or withdrawn articles, 3 erratum, 1 sound recording, and 2 unavailable articles were omitted. The majority of the publications were full-length research articles (69·9%), followed by proceedings (18·9%), and the remainder comprised research newsletter articles, narrative reviews, other reports, and editorials and letters in indexed research journals.

The term degenerative disc disease was featured as the object of study in publication titles with increasing frequency in the scientific literature over the decade under review (Figure 1). Its appearance specifically in the title increased during the last 3 years of the decade by 89%, as compared to the first 3 years (Figure 1).

Figure 1.

Number of publications by year (2007–2016) in the primary sample in which degenerative disc disease appeared specifically in the title

Countries and Disciplines of Origin

Using the primary sample (n=402), the published work on degenerative disc disease emanated from 42 countries, with the largest contributors being the United States (39·8%) and China (13·2%). Fifteen of the 28 member states of the European Union together contributed 20·2% of the publications on the topic, with Switzerland contributing 4·5%, and Turkey 4·0%. All other identified countries of origin contributed less than 3% each to the total number of publications. The corresponding or lead authors were also from a wide variety of disciplines and organizations, but were most commonly orthopedic surgeons (41·8%), followed by neurosurgeons (23·6%).

Accordingly, degenerative disc disease was studied most commonly in the context of spine surgery (52·2%), followed by basic science (15·4%), interventions other than surgery (11·2%), and reports of occurrence rates and associations of various phenomena deemed relevant to degenerative disc disease as revealed in cross-sectional and descriptive studies (9·7%). The lumbar region was nearly three times more commonly the focus of papers on degenerative disc disease (61·0%) than was the cervical region (22·4%). The remaining papers studied multiple or unspecified spinal regions, or used animal models.

Degenerative Disc Disease Case Definitions

Degenerative disc disease was defined or operationalized in many different ways, with no one definition used in the majority of publications (Table 1). Of the eight broad definitional categories, most frequently the term was used without any further definition provided (30·1%), such as "degenerative disc disease for which surgery was performed" or simply "degenerative disc disease." In other instances, case definitions specifically included radiculopathy or myelopathy, such as "one symptomatic, focal, contained, herniated disc … radicular pain [must be] concordant with image findings …,"[7] or "symptomatic cervical disc disease causing intractable, debilitating radiculopathy"[8] (14·4%), or only included axial pain (5·5%), such as "chronic back pain" accompanied by common but variable degenerative changes.[9]

Degenerative disc disease was often equated with disc degeneration (e.g., Pfirrmann grade or disc desiccation, narrowing or bulging) regardless of the presence or absence of symptoms (15·4%), or with other specific imaging findings (4·5%), such as disc herniation or lumbar spondylolisthesis with adjacent segment stenosis. In 12·7% of publications, degenerative disc disease was defined as disc degeneration as a cause of back or axial pain, with half of these defined specifically as a painful disc or discogenic pain (e.g., "positive discography at operated levels").[10] In another 7·2% of the publications, degenerative disc disease represented a mix of broad ranging degenerative or pathological findings and diagnoses. For example, one study cited evidence of degenerative disc disease as "radiographic evidence of mild to moderate osteophyte formation of vertebral endplates, loss of disc height …, herniated nucleus pulposus, loss of water content on MRI …, or vacuum phenomenon, associated with a history of back and/or radicular pain that is severe, ongoing, and recurrent."[11] In another study, degenerative disc disease comprised "spondylosis, spondylolisthesis, stenosis, disc herniation, degenerative scoliosis, standalone DDD, or discogenic back pain, all with mention of degeneration."[12] This variability was also seen within the countries from which the related research originated (Table 2).

Cervical Versus Lumbar Degenerative Disc Disease

The most notable differences occurred in the definition of degenerative disc disease and the context in which it was studied when comparing the full-length journal articles on cervical vs. lumbar regions (Figure 2). The vast majority of articles on cervical degenerative disc disease were written in relation to surgery (82·8%), while this was not the case in the lumbar region (46·3%). Also, it was much more common for the operational definition of degenerative disc disease to specifically include radiculopathy or myelopathy in the cervical region (62·5%) than in the lumbar region (5·1%). Conversely, definitions involving disc degeneration, "discogenic" pain, and only axial pain were commonly used for the lumbar region (45·7%), but were rare for the cervical region (1·5%). Furthermore, none of the papers on cervical degenerative disc disease used a broad range of degenerative findings and diagnoses to define the condition, while this was the case for 18·3% of papers on the lumbar region.

Figure 2.

Percentage of all full-length articles on cervical versus lumbar degenerative disc disease (DDD) using the various case definition categories

Use of "Degenerative Disc Disease" in Orthopedics, Neurosurgery, and Other Disciplines

When looking at full-length journal articles coming from neurosurgery vs. orthopedics, the majority by both groups focused on degenerative disc disease in the context of surgery (63·5% vs. 61·2%, respectively). However, a greater portion of the publications from neurosurgeons was of longitudinal outcomes studies (36·5%) and a lesser portion was randomized clinical trials (2·7%) than those from orthopedists (18·7% and 9·0%, respectively). The articles by neurosurgeons were more commonly of the cervical region than was the case for orthopedists (35·2% vs. 23·9%), and more commonly included radiculopathy in the clinical case definition (29·7% vs. 14·9%). Conversely, the case definition of "degenerative disc disease for which surgery was performed" was used in a higher proportion of articles led by orthopedists than neurosurgeons (26·9% vs. 14·9%). Differences in case definitions were more apparent when comparing surgical vs. other disciplines (Table 3). In particular, surgeons were more likely to use the term degenerative disc disease without further explanation (40·5%) or specifically with radiculopathy or myelopathy (22·4%) than were other disciplines (18·8% and 5·7%, respectively).

Study Types or Designs

As an indication of the types of research being conducted on the topic of degenerative disc disease, the subset of full-length research publications was reviewed with respect to study type or design. Longitudinal or outcomes studies were most common (20·6%), followed by narrative reviews (15·7%), systematic reviews (12·1%), gene expression or association studies (10·0%), descriptive or cross-sectional studies (9·3%), clinical trials other than randomized controlled trials (8·5%), randomized controlled trials (6·1%), case reports (5·0%), nongenetic basic science studies (e.g., biomechanics/modeling) (4·6%), methodological studies (e.g., measurement) (2·5%), and others (5·7%).

Growth in Articles Including "Degenerative Disc Disease" Relative to Other Spine-related Articles

There was greater relative growth in the number of articles using the term, degenerative disc disease, from 2007–2016 when compared with growth in the number of other spine-related articles using the broad terms of cervical spine or lumbar spine (Figure 3). When comparing increases from the first 3 years to the last 3 years of the decade, the number of articles in which the term degenerative disc disease appeared in the title, abstract, or keywords increased by 74%, relative to increases of 23% and 24% for cervical spine and lumbar spine, respectively.

Figure 3.

The graph depicts the relative growth in the number of publications from 2007–2016 using the term degenerative disc disease, cervical spine, or lumbar spine in the title, key words or abstract, as the percentage change in the number of papers published since 2007.

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