Background In assessment of the modified Stokes Anklyosing Spondylitis Spinal Score (mSASSS), squaring is an important factor of scoring. However, the 1st sacrum (S1) is often underestimated in the assessment of mSASSS because it is difficult to evaluate squaring. Thus, we applied the concept of loss of anterior concavity to evaluate S1 score instead of squaring.
Objectives This study aimed to evaluate usefulness and reliability of S1 scoring using the concept of loss of anterior concavity and to evaluate its relationships with mSASSS and MRI in ankylosing spondylitis.
Methods The study group comprised 77 AS patients (67 males, 10 females; mean age 33.6 yrs) and 78 healthy controls (32 males, 46 females; mean age 56.3 yrs). Two experienced radiologists independently assessed the mSASSS on cervical and lumbar plain radiographies in AS groups and evaluated loss of anterior concavity of S1 in control and AS groups. And also, MR images were independently evaluated for signs of inflammation or structural changes of S1 in control and AS groups. S1 score between control and AS groups as well as its correlation with MR findings were statistically analyzed.
Results According to reader 1, loss of anterior concavity in the control group was found in 7 sacrum (8.9%) and in the patients group was in 27 (35%) on plain radiography. According to reader 2, loss of anterior concavity in the control group was found in 5 sacrum (6.4%) and in the patients group was in 39 (50.6%) on plain radiography. Interobserver agreement in S1 score was found to be nearly perfect (κ value: 0.854) on plain radiography. S1 score was significantly correlated with changes on MRI in AS group by both radiologists (κ value: 0.74). In AS group, the interobserver agreements for total mSASSS was very good (0.99 with ICC). And S1 score was found to be significantly correlated with total mSASSS by both radiologists (p<0.001).
Conclusions Loss of anterior concavity in S1 is a useful concept to assess S1 scoring and shows good reproducibility. And it is well correlated with MR findings in AS group. Thus, we should not overlook loss of anterior concavity in S1 which would to predict early spinal involvement of AS.
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Acknowledgements Disclosure of Interest: None declared
Disclosure of Interest None declared
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