The aim of this study was to evaluate the diagnostic value of a new clinical test for SIJ arthropathy, the PSIS distraction test, and to compare it to commonly used clinical tests.
Within our population of patients with confirmed SIJ arthropathy, the PSIS distraction test was found to be of high sensitivity, specificity and therefore a very good accuracy.
While other common clinical tests as pelvic compression, pelvic distraction, Gaenslen test, Thigh Thrust, and Faber test also showed a good specificity, their sensitivity was poor (< 35%).
This is in accordance with previously published data, even though the range of reported values for sensitivity and specificity is broad [6–9] and some of these studies lack control groups [8]. In a large systematic review, Szadek et al. analysed SIJ provocation tests (compression, distraction, thigh thrust, Gaenslen’s test, and Patrick’s sign/Faber test) and observed significant heterogeneity and inconsistency. They assumed the use of different thresholds for a positive reference standard of sufficient pain relief to be partly responsible for this [7].
Some authors reported an association [9, 13, 14] between patient-reported pain in the area of the posterior superior iliac spine (PSIS) and SIJ-generated pain. Still, a clinical test applying a force on the PSIS combining the knowledge of patient-reported pain with movement of exclusively the SIJ has not been described, so far.
The presence of pain-transducing nerve fibers in the SIJ and its adjacent ligaments is known [12, 15]. In this context is important to know that the innervation of the sacroiliac joint is almost exclusively derived from the sacral dorsal rami [16, 17]. The immediate anatomical vicinity of these neural structures and the PSIS could be an explanation for the good diagnostic value of the PSIS distraction test we observed. Similar to the supra- and infraorbital exits of the trigeminal nerve, the PSIS might serve as a pressure point to test the sensitivity of the sacral dorsal rami innervating the SIJ. However, a distinctive mapping of the nociceptive areas in the SIJ to strengthen this hypothesis has not been described in the literature.
Even though our study design was useful to differentiate between cases and the controls, the results need caution to some limitations. The clinical value of the PSIS distraction test was investigated on base of a case–control design. Since the case group consisted of patients with a SIJ arthropathy confirmed by an infiltration, this might especially influence the sensitivity values.
The commonly used SIJ provocative test are known to be subject to considerable inter- and intraobserver variabilities [7]. Information on this issue for the PSIS distraction test is not given by our study. We are convinced, however, that the simplicity of the PSIS distraction test procedure makes a high inter- and intraobserver variability unlikely.
The examiners were not blinded for the non-symptomatic volunteers in the control group. This might be a potential source of bias and in this case partially explain the good specificity. In contrast, examiners were not able to predict the results of the SIJ infiltration in the group of patients with SIJ pathology.
Further validation by prospective, blinded multi-investigator trials with a larger cohort is needed to confirm this assumption.
We did not differentiate on symptom duration before treatment. Pain mechanisms are different in acute, sub-acute or chronic pain and hyperalgesia in patients with a chronic pain syndrome is a possible confounding factor.
As many others [5, 8, 13, 14], our study used SIJ infiltration under fluoroscopic monitoring as reference test. The topography of the sacroiliac joint space is variable as well as irregular and even with the use of radiopaque agent to prove the intraarticular position of the needle, there is a notable probability of an extraarticular infiltration leading to a false-negative test result. Thus, it has been not definitely proven if the tenderness of the PSIS is really caused by an intraarticular pathology or rather a periarticular (i.e. ligamenteous) problem. CT-guided infiltration may be used in future studies to avoid this vagueness.
Therefore, while the PSIS distraction test is not entirely validated trough this study, strong evidence on its clinical value is given. In contrast to the commonly described provocative tests, it can be performed with the patient standing and is easy to perform during clinical routine. Thereby, it provides a quick and robust decision guidance towards the need for more invasive diagnostics as SIJ infiltration.