No concept in the spine community is more widely used yet less well understood than "degenerative disc disease" (DDD). It has become a waste-basket description in which almost any spinal pathology can be categorized. Given its widespread use and unclear, inconsistent definition, continuing to use the term can result in miscommunication and misunderstanding among patients, spine care providers, and researchers. In order to better understand the wide range of definitions and use of the term DDD, Dr. Battié and colleagues from the ISSLS Degenerative Spinal Phenotypes Group performed a systematic review of the spine literature that included "degenerative disc disease" in the title from 2007-2016. They determined the frequency of articles using DDD in the title over time, categorized the definition in each study into eight categories, and also compared use of the term among different types of researchers (i.e. orthopedic spine surgeons, neurosurgeons, and others) and in different countries. Not surprisingly, they found a wide range of definitions of DDD. The most commonly used definition was no definition at all, which was the case in 30% of studies. Failing to define the term was most frequent in the surgical literature (40% of papers offered no definition) and papers from China (43% of papers). When defined, the most common definition was one based on disc degeneration on imaging studies (i.e. disc desiccation), found in 16% of studies. Interestingly, 14% of papers used the term in the context of radiculopathy or myelopathy, and this definition was generally used to describe cervical pathology (63% of cervical papers). In the lumbar studies, the most common definition included axial pain without radiculopathy (46% of lumbar papers). The use of the term DDD increased 189% over the course of the decade under study.
The authors have done a nice job presenting a formal analysis that demonstrated the broad and imprecise use of the term degenerative disc disease. These findings come as no surprise to readers of the spine literature, and the paper should serve as a call to use more precise diagnostic language or to at least clearly define DDD within the context of a study. The authors did not describe how they developed their taxonomy of definitions, and a formal process could have been used to create definitional categories. The current list is somewhat confusing and includes apparently overlapping categories like "disc degeneration causing axial pain" and "DDD with axial pain". A simpler system categorizing definitions as those based on radiographic findings alone, clinical findings alone, or a combination of radiographic and clinical findings may have been easier to understand. The search strategy also limited the included studies to those that had DDD in the title, which likely excluded many studies in which DDD was used as a diagnosis but was not in the title of the article. The persistent use of the term DDD likely reflects more of the spine community's lack of understanding of axial neck and back pain than the rhetorical imprecision of spine researchers. Despite decades of research on low back pain, the etiology of most cases of back pain remains unknown. The diagnosis of axial neck pain or back pain is essentially a black box, and some term is needed to describe these conditions. While DDD may be a poorly conceived term, using other terms to describe axial neck or back pain in the presence of age-related degenerative changes does not change the fact that we cannot determine the pain generator in most of these cases. I agree with the authors that the first step to coming to a better understanding of the cause and treatment of axial spine pain is to create a precise nosology of different spinal conditions so that researchers can accurately communicate about the populations and pathology they are actually studying. Unfortunately, DDD is likely ingrained in the spine lexicon and will probably not disappear from use regardless of how many papers urge its abandonment. However, researchers can agree to adopt more precise diagnostic terminology, and organizations like ISSLS can help with this process.
Please read Dr. Battié's article on this topic in the November 1 issue. Does this change how you view the term DDD? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor