Abstract
Background
Sacroiliac joint dysfunction (SIJD) is a common cause of low back pain, yet no single clinical test is definitive. Diagnostic sacroiliac joint (SIJ) block is widely used, but the diagnostic value of sustained versus immediate pain relief remains unclear.
Objective
To compare the diagnostic accuracy of SIJ block immediately and 1 week after injection in patients with suspected SIJD and to determine the incidence of concurrent conditions influencing the final diagnosis.
Methods
We retrospectively reviewed 168 outpatients with low back pain and SIJ score ≥ 4 who received ultrasound-guided SIJ block using 2.5 mL of 1% lidocaine between 2019 and 2024. Pain relief was evaluated using the Pain Relief Scale immediately and 1 week post-injection. In patients without sustained block effects, additional imaging and selective blocks were performed. Diagnostic accuracy (sensitivity, specificity, and predictive value) was calculated at each time point.
Results
An immediate block effect was observed in 92.3% of patients; however, only 75.0% reported sustained relief at 1 week. Overall, 75.6% were diagnosed with SIJD alone, whereas 18.7% had SIJD concurrent with another condition. Immediate effect showed high sensitivity (0.99) but low specificity (0.30), whereas 1-week effect maintained high sensitivity (0.97) and significantly higher specificity (0.93).
Conclusions
The diagnostic utility of the SIJ block significantly improves when the effect is sustained 1 week after injection, as it excludes other etiologies. Immediate relief alone may be misleading, particularly in secondary SIJD. Notably, 1-week follow-up after SIJ block improved diagnostic accuracy and guided appropriate management.
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