Background/Purpose: One of the hallmark characteristics of the disease is new bone formation that manifests as syndesmophytes and spinal fusion. Spinal fusion results from bridging syndesmophytes extending across a discovertebral unit. The true impact of radiographic spinal fusion on function and spinal mobility is still debated. We studied the location and number of bridging syndesmophytes and their relation to spinal mobility measures.

Methods: The following patients were included from a longitudinal observational AS cohort: (i) patients who met the NY criteria for AS, (ii) who had complete sets of X-rays, and (iii) who had available spinal mobility measures including cervical rotation, lateral lumbar flexion and Schober’s test. Schober’s test and lateral lumbar flexion reflects thoracolumbar spine mobility. Cervical rotation reflects cervical spine mobility. Trained rheumatologists did all spinal measurements. Bridging syndesmophytes were scored in the anterior corners of cervical and lumbar vertebrae. Two expert rheumatologists scored X-rays. A third expert reader settled discordant results. Demographics, clinical data and BASDAI were recorded. The independent effects of bridging syndesmophytes on mobility were assessed by multivariable regression after controlling for other clinical variables.

Results: From the cohort of 800 AS patients, 113 had bridging syndesmophytes in the cervical or lumbar or both vertebrae. Ninety-two patients had cervical and 47 had lumbar bridging syndesmophytes. The mean age and disease duration of the patients was 47±11.3 and 21.6±11.4 years respectively. 86.7% of the patients were male and B27 was present in 75%. The number of cervical bridging syndesmophytes showed moderate negative correlations with cervical rotation in patients with both active and inactive disease states (r=-0.56 and -0.59 respectively). Similarly lumbar bridging syndesmophytes had moderate inverse correlations with lateral flexion and Schober’s measurements (r=-0.41 and -0.38 respectively). The total number of syndesmophytes and the degree of limitation of the spine both cervical and lumbar movements showed restrictions as the number increased (Table 1). In regression models where age, sex, disease duration, increased acute phase response and B27 was included the strongest predictor for the cervical rotation, lumbar lateral mobility and Schober’s was the number of cervical (β=-0.59) or lumbar bridging syndesmophytes (β=-0.42 for lumbar side flexion and -0.37 for Schober’s).

Conclusion: Bridging syndesmophytes independently influenced spinal mobility. The study also provides reference values regarding the location and number of syndesmophytes and their respective impact on spinal mobility. Table 1:Association between localization, number of bridging syndesmophytes and degree of limitation

* Continuous variables are presented with median (min-max) values

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/can-bridging-syndesmophytes-independantly-affect-spinal-mobility/