Inter-examiner reliability of the diagnosis of cervical pillar hyperplasia (CPH) and the correlation between CPH and spinal degenerative joint disease (DJD)

Several authors recently proposed the concept of cervical pillar hyperplasia [1‐4]. Hyperplasia is identified on the neutral lateral cervical radiograph as parallel or posterior divergent lines drawn along the superior and inferior articular pillars (Figure 1b). The "usual" lordotic cervical curve requires these lines to converge posteriorly (Figure 1a) [2, 3]. The straightening effect of hyperplastic articular pillars on the cervical lordosis was suggested by Peterson and Wei [2] in 1987 and confirmed in 1999 [3]. These two studies were criticized by Harrison et al [5, 6] regarding the way pillar hyperplasia was determined, cervical lordosis was measured, and on a few other issues that were based on a misinterpretation of Peterson et al's article. In contrast to those critiques, Haas et al [7] reported that the measurement of each segment to determine the cervical lordosis, as suggested by Harrison et al would increase measurement errors. Furthermore, Peterson et al used Chamberlain's line to eliminate the effect of anterior head carriage in both the hyperplastic and the non-hyperplastic pillar populations. Flexion/extension studies were not necessary to define cervical pillar hyperplasia since it was detectable on the radiographic films most commonly used by primary physicians, the neutral lateral radiographs [3]. Therefore, to this point, both the concept of cervical pillar hyperplasia and its effect on the cervical lordosis seem reasonable [8]. This condition is of unknown aetiology and it may have clinical consequences that need to be determined.

Degenerative joint disease is a common, age-related [9‐12], multi-factorial condition with several theorized aetiologies including metabolic, mechanical, inflammatory, and genetic components [11, 13‐16]. It affects all joints, particularly those that experience chronic biomechanical stresses such as frequent repetitive use and strain, and constant weight-bearing.

The cervical/neck region is the human spine's most actively mobile part [17]. It has to support the permanent load of the head; therefore, progressive degenerative processes frequently affect it. This means that the intervertebral disc can become narrowed, develop osteophytes and have surrounding subchondral sclerosis in the condition called "degenerative disc disease" [12, 18]. It has been shown that there is a higher incidence of the development of disc space narrowing with the presence of anterior osteophytes on initial films, while posterior osteophytes are more commonly associated with the presence of an already narrowed disc space [19].

Both facet and uncovertebral joints can hypertrophy, sclerose and develop osteophytic spurs, in conditions described as facet arthrosis and uncovertebral arthrosis, respectively [12, 18]. Several grading systems have been developed to determine the degree of degeneration radiographically, using signs of subchondral sclerosis, joint space irregularity, decreased joint space and anterior and/or posterior osteophyte formation [9, 11, 12, 20‐22]. The degenerative condition that involves degenerative disc disease, facet arthrosis and/or uncovertebral arthrosis is defined as "degenerative joint disease (DJD)," osteoarthrosis, or cervical spondylosis (Figure 2 and 3). Such degenerative processes may have various clinical implications: they may cause limitation of head and neck mobility, with or without pain; occasionally, they can cause intervertebral foramen encroachment and central canal stenosis, which can result in nerve root or spinal cord compression (radiculopathy and myelopathy respectively) [11, 23‐26], and less commonly, extensive anterior osteophytosis can lead to dysphagia or even vocal fold paralysis [27].

The presence of osteoarthrosis is often confirmed using plain film radiographic findings, with the lateral view being the most informative [11]. Magnetic resonance imaging (MRI) and computed tomography (CT) are also useful diagnostic tools and can be used to determine the extent of soft tissue and bony involvement respectively. Although CT is the gold standard for detecting degenerative changes, plain film radiography is less expensive and more commonly used in primary contact clinical settings [11, 28].

There is some controversy in the literature over whether radiological findings are related, to a clinically important degree, to the patient's symptoms. In a recent long-term follow-up study, Gore [10] found that there might be a correlation between the patient's symptoms and radiographic findings. The subjects of his study who showed earlier degenerative changes at a particular level (C6-C7) were 4 times more likely to experience pain 10 years later compared to those without degenerative changes [10]. Most other authors, however, tend to dispute this finding [11, 29‐31]. A recent cross-sectional study of United Kingdom patients found that there is no statistically significant difference in pain or disability levels, between patients with and without radiographic evidence of degeneration in the cervical spine [32].

It is currently not known whether the architecture of the articular pillars has any effect on regional biomechanics and subsequent degeneration. The hypothesis that was tested with our study was whether pillar hyperplasia accelerates the development of DJD, particularly in the intervertebral disc (IVD). The orientation of the facet joint in relation to the horizontal plane principally influences the axis around which flexion/extension occurs [33‐35]. A more horizontal facet compared to the plane of the superior endplate of the vertebral body will shift the instantaneous center of rotation anteriorly, resulting in an increased load on the IVD [36‐38]. It has also been shown that a flattened superior facet increases the risk of anterolisthesis (i.e. stress on the disc) [39]. Studies have shown that cervical pillar hyperplasia has an effect on the cervical curve [2, 3]. A straightening of the cervical curve results in a redistribution of the loads, favouring the facet joints, and therefore increasing the load on the IVD. An increase of the stress-load on the disc locally may enhance the degenerative process in the intervertebral compartment [40]. The presence of cervical pillar hyperplasia should consequently theoretically accelerate the degenerative processes of the IVD. We assumed that the degenerative processes would be a result of the cervical pillar hyperplasia and not the opposite, since cervical pillar hyperplasia has been observed at all ages.

No one has yet studied the prevalence of DJD in individuals with hyperplasia in comparison to those without. The purpose of this paper, therefore, was:

(1) to determine the inter-examiner reliability of detecting hyperplasia of the cervical articular pillars; and (2) to determine if there is a difference in the number of cervical spine levels showing signs of degenerative joint disease (DJD) in an age-matched sample with and without hyperplasia of the articular pillars at one or more levels, and hence, what the relationship is between cervical pillar hyperplasia and spinal DJD.

Cervical pillar hyperplasia is a recently described phenomenon of unknown aetiology. To date, the only promising data on the clinical relevance of hyperplasia is its possible effect on cervical spine lordosis [2, 3]. Having little information on cervical pillar hyperplasia allows for much speculation on the effect it may potentially have on cervical spine biomechanics; furthermore, it is important to determine whether this effect may or may not be of clinical significance. Theoretically, altered biomechanics of the spine could lead to degenerative changes and possible clinical consequences. It is currently not known to what degree, if any, cervical pillar hyperplasia contributes to the development of degenerative joint disease.

Our study found moderately strong agreement between two examiners in assessing cervical pillar hyperplasia. The moderate inter-examiner reliability achieved by the novices in this study coincided with the acceptable-to-good reliability (0.4–0.61) attained previously by Peterson [3]. It shows that the assessment of hyperplasia is an uncomplicated evaluation method, and therefore does not require expert skills. It should be noted, however, that in the study by Peterson, cervical pillar hyperplasia was assessed segmentally, and not globally; nevertheless, the fact that novice examiners performed the assessments of cervical pillar hyperplasia, and acceptable agreement was achieved, lends further credibility to the acceptability of the reliability of this diagnostic test.

Our study suggests that there is no clinically important difference between those with or without cervical pillar hyperplasia with respect to the prevalence of degenerative joint disease. This study also suggests that DJD is affected by age but not by gender, which concurs with previous studies [9‐12, 47]. Other known contributors to the development of DJD that were not tested in this study include trauma, genetic, metabolic, and inflammatory processes [11, 13‐16]. These results imply that cervical pillar hyperplasia is congenital, and allows the body to compensate for changes resulting from slightly aberrant biomechanics.

It should be noted that this study only looked at the presence/absence of DJD, and not its severity; thus there may indeed be a difference in the two groups if severity had been considered, but this has yet to be determined.

In our study, due to feasibility constraints, pillar hyperplasia was assessed globally in the cervical spine and considered to be present if even one cervical segment from C3 to C6 had a hyperplastic pillar. This definition may have resulted in more positive inter-examiner reliability than if segment-specific pillar hyperplasia had been assessed. Cervical pillar hyperplasia, as defined here, may possibly affect the biomechanics of the whole cervical spine; therefore, DJD was also assessed globally from C1 to C7.

Follow-up research should evaluate the segment-specific contribution of pillar hyperplasia to the development of DJD. Severity of DJD should perhaps also be considered. One of the limitations encountered when assessing films for cervical pillar hyperplasia was that the evaluation of C2-3 was not always adequate due to poor visualization. The same problem occurred at C1-2 while assessing for DJD. Another limitation of the study is using amateur examiners to detect cervical pillar hyperplasia and DJD; however, having a radiology expert re-evaluate each set of films likely minimized these problems.

Cervical pillar hyperplasia has shown evidence of being a credible phenomenon that requires further research. Its diagnosis appears to be easy to learn and reliable. This study indicated that, globally, cervical pillar hyperplasia does not appear to have an effect on the development of degenerative joint disease; however, because previous research suggests that cervical pillar hyperplasia affects the cervical lordosis, it is recommended that further research explore any segment-specific contribution of pillar hyperplasia to the development and severity of DJD.

Conception and design: CK Peterson, M Stupar, D Mauron

Generating and interpretation of data: D Mauron, M Stupar, CK Peterson

Statistical analysis and interpretation: D Mauron, M Stupar, CK Peterson

Drafting of the article: M Stupar, D Mauron

Critical revision of the article for important intellectual content: CK Peterson

Administrative, technical and logistic support: M Stupar, D Mauron