Etiology of Pseudarthrosis in Ankylosing Spondylitis: What Is the Main Cause?

One of the well-known complications in advanced ankylosing spondylitis (AS) is the development of Andersson lesion (AL)1. Subsequently, various reports with conflicting terminology appeared in the literature. Spondylodiskitis , which implies inflammatory etiology, was used by some authors2,3,4. Others have used the terms destructive vertebral lesion 5,6,7,8 or spinal pseudarthrosis 9,10. The terminological diversity alludes to the varied purported etiologies surrounding AL. The etiologies of extensive AL have been well documented in literature. Various etiologies for the development of AL in patients with AS have been postulated, including infection, inflammation, and trauma. Current consensus is that infection is no longer considered a cause of the AL, because of the lack of positive culture results. Subsequently, etiology of the AL has been open to an ongoing debate between inflammation and trauma. AS is characterized by spinal inflammation, and it is not surprising that many authors have focused on the inflammatory etiology of AL. Anterior spondylitis such as Romanus lesion comprised marginal erosion of the anterior vertebral corners related to inflammation of the attachment sites of anterior annulus fibrosus (AF) and anterior longitudinal ligament (ALL) in patients with AS8. The erosion becomes enclosed by a sclerotic rim and further healing results in the formation of syndesmophytes, finally resulting in a complete ankylosed segment. It has been postulated that AL might be exceptional extensions of this inflammatory process3,8,11,12. … Address correspondence to Dr. S. Lee, Department of Radiology, Hanyang University Hospital for Rheumatic Diseases, 17 Haengdang-Dong, Seongdong-Gu, Seoul 133-792, Republic of Korea. E-mail: radsh{at}hanyang.ac.kr