Table 1.

Original studies with NBF definitions in SpA

Author/year	Country	SPA Type	Diagnosis criteria used	Study design	Sample size (n)	Gender (M/F)	Age	Anatomical site	Definition
Petcharat et al. (2021) [22]	Thailand	AS and PsA	AS: Modified New York criteria PsA: Caspar Criteria	Cross-Sectional	AS: 153 PsA :166	171/148	45.5 (12.2)	Cervical and lumbar spine	‘Syndesmophyte was defined as bone growth originating from the vertebral endplate in the anterior one-quarter of the discovertebral space or from the anterior vertebral cortex’
Gonzalez-Lopez et al. (2017) [10]	Mexico	AS	New York criteria	Prospective/case–control	89	57/32	44.3 (11.4)a	Cervical/Lumbar	‘Syndesmophytes were defined as bony protuberances associated with ossification of the spinal ligaments without involvement of the intervertebral discs’.
De Bruin et al. (2016) [35]	Netherlands	AxSpA	ASAS	Cross-sectional	274	96/178	28.2 (9)a	All	‘The differentiation between osteophytes and syndesmophytes is based on the site of origin and the angle between the bony spur and the vertebral endplate; syndesmophytes originate at the ligamentous insertion and have a more vertical configuration’.
Gamez-Nava et al. (2016) [11]	Mexico	AS	New York criteria	Case–control	78	50/28	Male: 45 (26–63)b Female: 48 (23–64)b	Cervical/Lumbar	‘Syndesmophytes were defined according to the presence of ossification of vertebral ligaments of > 5 mm in radiographs’.
Baraliakos et al. (2014) [36]	Germany	AS	N/A	Cross-sectional	73	63/10	40.5 (10.5)a	Cervical/Lumbar	‘Assessment of syndesmophytes and differentiation from degenerative changes such as spondylophytes was made according to a recent proposal, where the former are considered by showing a growth parallel to the anterior vertebral side/anterior intervertebral ligament while the latter are considered by showing a growth parallel to the horizontal line’.
Haddad et al. (2013) [5]	Canada	PsA	CasparS	Prospective cohort	78	57/21	62.9 (8.9)a	Cervical/Lumbar	‘PsA-related changes (syndesmophytes) were considered if there was a growth angle of < 45° to the anterior vertebral side, while an angle > 45 was considered to be osteophytes’.
Baraliakos 2012 [37]	Germany	AS	mNew York criteria	Retrospective cohort	146	81/65	54.2 (12.3)a	Cervical/Lumbar	‘Measuring the horizontal angle of new bone formation on lateral spinal radiographs, AS-related changes (syndesmophytes) were assumed to typically show a growth angle of ≤ 45° to the anterior vertebral side, while a growth angle of > 45° was assumed to represent more DISH-related changes (spondylophytes)’.
Maejima et al. (2010) [23]	Japan	PsA	Caspar	Cross-sectional	25	18/7	N/A	All	‘Marginal syndesmophyte is classic and a thin syndesmophyte arises vertically from the annular attachment to the vertebral body. Non-marginal syndesmophyte is a vertically oriented or curvilinear syndesmophyte, often thick and chunky, arising from beyond the annular attachment to the vertebral body. Paravertebral ossification is ossification close to the vertebral body, but with a clearly defined gap between the margins of the ossification and the vertebral body’.
Chandran et al. (2009) [24]	Canada	PsA	N/A	Retrospective cohort	297	169/128	42.5a	All	‘Marginal syndesmophytes were recorded if the vertebral ossifications arose from the edge of the vertebral body and formed a fine vertical bridge, and paramarginal syndesmophytes were described when the ossification arose away from the edge of the vertebra and was board and coarse. Syndesmophytes were distinguished from osteophytes in that the latter, which originate from the cartilaginous endplate in response to degeneration of the disc, are wider, horizontally oriented and are associated with narrowed disc spaces’.
Baraliakos 2007 [38]	Germany	AS	mNew York criteria	Prospective	116	N/A	38.4a	All	‘Bony changes with an angle ≤45° to the anterior vertebral side were defined as syndesmophytes, in contrast with changes with an angle of >45°, which were defined as ambiguous syndesmophytes’.
Helliwell et al. (1998) [25]	UK	AS/PsA/IBD/ Reactive arthritis	AS = New York criteria ReA = Calin criteria		AS = 91, IBD = 31 ReA = 5 PsA = PsA		AS: 46a IBD = 48 PsA = 46 ReA = 43	All	‘Paravertebral ossification as defined and described by Bywaters and Dixon, ligamentous calcification (usually interspinous ligament), squaring of the anterior border of the vertebra without erosion/sclerosis, discitis (narrowing of disc space with erosion and new bone formation in adjacent vertebrae), spinal pseudarthrosis (a fracture line through a fused spine with reactive new bone formation at either side of the lesion), bamboo spine (complete ankylosis of vertebrae due to contiguous syndesmophyte formation) and ankylosis of zygoapophyseal joints. Syndesmophytes were classified as chunky or marginal based on their size and shape. Marginal syndesmophytes were defined as discrete vertically oriented areas of calcification extending from the corner of one vertebra to the next. Chunky syndesmophytes were defined as more extensive areas of calcification extending vertically from the vertebral corner included within this group were the non-marginal and ‘inverted comma’ syndesmophytes of McEwen et al.’
Hanly et al. (1988) [26]	Canada	PsA	NA	Cross-sectional	52	30/22	44 (23–70)b	All	‘Marginal syndesmophytes were recorded if the vertebral ossifications arose from the edge of the vertebral body and formed a fine vertical bridge and paramarginal syndesmophytes were described when the ossification arose away from the edge of the vertebra and was broad and coarse. Syndesmophytes were distinguished from osteophytes in that the latter, which originate from the cartilaginous end plate in response to degeneration of the disc, are wider, horizontally oriented and are associated with narrowed disc spaces. Paramarginal syndesmophytes were also distinguished from diffuse idiopathic skeletal hyperostosis (DISH) in that the latter condition occurs in four or more consecutive vertebrae, involves primarily the right side of the thoracic spine and is associated with normal sacroiliac joints’.

^aMean (s.d.).

^bMedian.

SpA: Spondyloarthritis; AxSpA: Axial Spondyloarthritis; ASAS: Assessment of Spondylo Arthritis International Society; ReA: Reactive arthritis; N/A: Not applicable.