ABSTRACT
Background: Sacroiliac joint (SIJ) pain presents as
a deep and somatic pain, predominantly affecting the lower back and buttock and
referring down the leg, sometimes as far as the foot. Given that the features
of SIJ pain are non-specific and that this referred pain is similar to lumbar
facet joint and lumbar disc pain, diagnostic
local anesthetic injections (diagnostic blocks) into the SIJ are used to identify the source of pain. Despite wide use,
little is known about the false positive rate of a single diagnostic sacroiliac
(SI) block and the requirement for a control block. Objective: To determine
whether a control SI block is necessary and to monitor the false positive rate
for a single injection. Study Design: A prospective and observational study was
conducted as part of a practice audit, with data collected over 3.5 years at
the authors’ private practice. Patients & Methods: Under fluoroscopic guidance, 1408 consecutive
patients presenting with prominent deep somatic pain over the SIJ region
were sterilely injected with anesthetic into the SIJ and/or the deep interosseous ligament (DIL). Pain was measured on the
11-point Numerical Rating Scale (NRS) prior to injection and incrementally over
the following 1- 2 weeks. Fully completed and unequivocal data sets were available for 1060 patients. Decreases in pain
scores (of >80%) at >2 hours of post-injection were indicative of
SIJ pain and recorded as a positive SIJ block. Results: Of 1060 patients
receiving a first SIJ diagnostic block, 680 (64.1%) recorded a positive result.
Subsequently, 271 positive patients and 22 who were negative for SIJ pain opted
to receive a second control block. SIJ pain diagnosis was confirmed in 237/271
(87.5%) of those with an initial positive
response, while 18/22 patients (81%) had their initial negative result
confirmed. The false positive rate of a single block is therefore
calculated at 12.5%, and on a contingency table analysis, a single anesthetic
SIJ injection has diagnostic accuracy of 87.03%, with high sensitivity (98.3%),
when compared with a second control diagnostic block. Limitations: All
injections were performed at one clinical centre. A proportion (348/1408) of
initial patients did not return fully completed pain records or had equivocal
responses (≥80% pain relief, but transiently, for ≤30 min) and were excluded
from further analysis. Conclusion: Given the observed high rates of accuracy in
this study, it is reasonable to suggest the
use of one diagnostic block as the criterion standard for assessing the
SIJ as the source of a patient’s pain.