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Insight on the Clinical Significance of Baastrup’s Disease: from Kissing Spine to Interspinous Bursitis 2013

Category General Spine Austin C. Bourgeois, MD, BS
Hunter Pearson
Patrick Barlow
Dwayne John
Ted Chang, MD, BA
Geoffrey Laing, MD, BS
Purpose Back pain is nearly ubiquitous, affecting up to 84 percent of adults patients and representing the second most common reason for physician visits in the United States.1,2 There are many structures in the lumbar spine that can produce such pain; the relatively less common of which are the spinous processes, lumbar spine osteophytes, and anomalous lumbosacral articulations.3   Back pain resulting from spinous process pathology has been described as early as 1825, but remains of uncertain significance and prevalence.4 Mayer of Bonn first portrayed spinous processes as a source of back pain in 1825.  He noted fluid-filled cavities interposed between adjacent lumbar spinous processes that were hypertrophied and had developed neo-facets.  The radiologic manifestations of these findings were described by Brailsford in 1929, who coined the term “kissing spines”.  It was not until 1933 that Baastrup provided both a radiological and clinical explanation of the syndrome.4 Since this time, Baastrup’s disease has remained a pain generator of unknown clinical significance.  This is at least partially attributable to the lack of adequate research correlating anatomic, imaging, and clinical factors.  This study examines the prevalence of lumbar interspinous bursitis* on routine, non-contrast MRI and its concomitance with facet hypertrophy, degenerative disc disease, vertebral body compression fracture, and listhesis on both a same-level and aggregate basis. *The authors acknowledge that this phenomenon is truly a neo-bursitis. Materials & Methods IRB approval was obtained.  A retrospective review was conducted via Softek Illuminate software, examining 862 patients who had undergone both prior non-enhanced magnetic resonance imaging (MRI) of the lumbar spine and either computed tomography (CT) or lumbar spine radiograph (DX).   CT and DX images were reviewed for presence of hypertrophied, intimately approximated spinous processes with reactive sclerosis (“kissing spine”).  Non-enhanced sagittal short tau inversion recovery (STIR) MR images of the patient subset with “kissing spine” were analyzed for evidence of interspinous bursitis. Each lumbar spine MRI was evaluated on a level-by-level basis for qualitative degree of degenerative disc disease (DDD) and facet hypertrophy (FH). The presence of listhesis, compression fracture, and spondylolysis were also analyzed. Results Of the 862 patients reviewed, 103 (11.9%) had “kissing spine” changes by lumbar spine CT or DX. 17 of these 103 patients had evidence of lumbar interspinous bursitis (16.5%), which affected a total of 22 levels.  Lumbar interspinous bursitis was most common at the L4/5 and L5/S1 (equal incidence, n=9), accounting for the overwhelming majority cases (81.8%). Interspinous bursitis was not associated with severe same-level FH or DDD at any lumbar spine level. Fisher’s Exact test was used to examine the association between fracture incidence, DDD, FH and indication of bursitis. The prevalence of bursitis was 6/25 (24%) in those with fracture versus 11/75 (14.7%) in those without fracture. This corresponds to an OR for fracture of 1.84 (95% CI=.60 – 5.62), p=.357. Conclusion Baastrup’s disease refers to a disease spectrum in which lower lumbar spinous processes hypertrophy and undergo repetitive mechanical friction.  This leads to interspinous ligamentous degeneration, adventitial recruitment, and ultimately produces neo-bursitis in a small patient subset.  Since degenerative changes and hypertrophied spinous processes (“kissing spine”) are nearly ubiquitous in an elderly population, many hypothesize that Baastrup’s is a merely harbinger of global aging-related degenerative changes. We propose that the interspinous bursitis component of the Baastrup’s spectrum is present in a small proportion of patients and likely corresponds with more advanced disease. In contrast to the belief of several authors, our data suggest that lumbar interspinous bursitis may be associated with a lesser degree of degenerative change on a level-by-level basis.  There is suggestion of a positive correlation between interspinous bursitis and compression fracture at any level, possibly related to altered lumbar spine mechanics and load-bearing. Unfortunately, a much larger sample size would be require to prove statistical significance for any of the measured variables.  Furthermore, the study is inherently biased to certain age and sex demographics.  Future research that examines larger patient samples and incorporates therapeutic solutions may help to delineate whether Baastrup’s disease is a stand-alone source of lumbar pain. References
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