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Table 2 Hehne und Zielke classification in ankylosing spondylitis [9].

From: Pitfalls and complications in the treatment of cervical spine fractures in patients with ankylosing spondylitis

Type Definition Syndesmophyte characteristics Synonymes
I Dorsal ossification Simple ossification of the dorsal spine bodies, no syndesmophytes Spondylathritis type
Iia Incomplete anular ossification Tender, the anulus fibrosus ventrally with or without lateral syndesmophytes, without overlapping of the vertebral bodies (incomplete) Anulus-type
Iib Complete anular ossification As type IIa, but with syndesmophytes overlapping the vertebral disc (complete) Anulus-type
IIIa Partial ostotic ossification Thick and wide syndesmophytes, often with cortical- and spongiosa structure, corresponding the bamboo-type, but not present in all segments (incomplete) Ligament/sub-ligament type
IIIb Total ostotic ossification As type IIIa, but several thoracic and lumbar segments are affected Bamboo-spine