Association between radiographic damage of the spine and spinal mobility for individual patients with ankylosing spondylitis: can assessment of spinal mobility be a proxy for radiographic evaluation?
OBJECTIVE
To demonstrate the association between various measures of spinal mobility and radiographic damage of the spine in individual patients with ankylosing spondylitis, and to determine whether the assessment of spinal mobility can be a proxy for the assessment of radiographic damage.


METHODS
Radiographic damage was assessed by the mSASSS. Cumulative probability plots combined the radiographic damage score of an individual patient with the corresponding score for nine spinal mobility measures. Receiver operating characteristic analysis was performed to determine the cut off level of every spinal mobility measure that discriminates best between the presence and absence of radiographic damage. Three arbitrary cut off levels for radiographic damage were investigated. Likelihood ratios were calculated to explore further the diagnostic properties of the spinal mobility measures.


RESULTS
Cumulative probability plots showed an association between spinal mobility measures and radiographic damage for the individual patient. Irrespective of the chosen cut off level for radiographic progression, lateral spinal flexion and BASMI discriminated best between patients with and those without structural damage. Even the best discriminatory spinal mobility assessments misclassified a considerable proportion of patients (up to 20%). Intermalleolar distance performed worst (up to 30% misclassifications). Lateral spinal flexion best predicted the absence of radiographic damage, and a modified Schober test best predicted the presence of radiographic damage.


CONCLUSIONS
This study unequivocally demonstrated a relationship between spinal mobility and radiographic damage. However, spinal mobility cannot be used as a proxy for radiographic evaluation in an individual patient.
Wanders
A
A
University Hospital Maastricht, Department of Internal Medicine, Division of Rheumatology, PO Box 5800, 6202 AZ Maastricht, The Netherlands.
Landewé
R
R
Dougados
M
M
Mielants
H
H
van der Linden
Sj
S
van der Heijde
D
D
D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D008297:Male; D009068:Movement; D011336:Probability; D012372:ROC Curve; D011859:Radiography; D013131:Spine / Q000000981:diagnostic imaging* / Q000503:physiopathology; D013167:Spondylitis, Ankylosing / Q000000981:diagnostic imaging* / Q000503:physiopathology