Low Back Pain (LBP) is often described as specific (clearly defined) or non-specific (not clearly defined). Specific LBP refers to symptoms cause by red flags such as tumor, fracture, cauda equina syndromes, infection etc., which is usually about 10% of LBP. Most (90%) LBP are classified as non- specific because a definite diagnosis cannot be achieved by current radiological means thus leaving a diagnostic vacuum [1]. Nevertheless, it has been reported that majority of nonspecific LBP originate from the intervertebral disc (50%), facet joints (20%) and SIJ (20%). Generally speaking, SIJ dysfunction refers to pain in the SIJ region that is caused by abnormal motion in the SIJ and it is divided into intra and extra articular dysfunction with the intra articular pathologies including the above mentioned red flags. Extra articular SIJ dysfunction is a disorder of abnormal joint movement and alignment owing to disruption of the posterior ligamentous support system [2]. This leads to recurrent hyper/hypo mobility, inflammation and in more severe cases, instability and recurrent subluxation that eventuate into pain in the low back, gluteal regoin, sciatic - leg, groin and hip. Other symptoms may include urinary frequency and transient numbness [3,4].

The prevalence of SIJ dysfunction in the population has been noted in the medical literature to be between 19.3% and 47.9%, it commonly affects women more than men, with an incidence of between 15% and 38% [5]. During pregnancy, the prevalence of posterior pelvic pain, which is pain, located distally and laterally to the lumbosacral junction, is approximately 20% and the SIJ dysfunction is more common in the presence of trauma, pregnancy, or in certain athletes [6-8].

Sacro-iliac joint dysfunction and leg length discrepancies are commonly associated with each other and that forms the bases for supine-long sitting or supine-to sit test. Bemis and Daniel found the supine-long sitting test result to be related to a diagnosis of iliosacral dysfunction or innominate torsion and study that investigated the prevalence of asymptomatic SIJ dysfunction, leg length discrepancy and the association between the two entities found 26.0% prevalence of asymptomatic SIJ dysfunction with real leg length discrepancy > or=0.5 cm which was significantly higher than the prevalence in those with apparent [9,10]. According to Laslett et al., if innominate test is positive and X-ray reveals the presence of a pelvic tilt, the diagnostic label should be right or left SIJ dysfunction with positive innominate test because the limb length discrepancy (real or apparent) needs to be addressed thereby highlighting the important relationship between SIJ dysfunction and leg length discrepancy [11].

Till date, the gold standard for the diagnosis of a symptomatic SIJ is fluoroscopically guided contrast enhanced intra-articular anesthetic block; however, false positive and false negative results are known to occur. For instance, where there is defect in the articular capsule, leakage of an anesthetic into adjacent areas may occur, and pain relief may be a reflection of an anesthetic effect of these structures rather than SIJ structures. This probability and the known effect of psychosocial influences on pain responses to invasive diagnostic procedures may lead false positive or false negative result. Similarly, intra-articular injection of anesthetic has the potential to wipe out SIJ pain when it originates within the joint cavity, but is unlikely to have anesthetic effect on structures outside or external to the joint. Thus, where peri-articular structures like ligaments and fascia are the actual pain generator, an intra-articular injection of local anesthetic into and confined to the joint space will also produce a false negative diagnostic result, whereas physical examination may correctly identify the periarticular and unanesthetized SIJ structure as pain generators [11,12]. In order to overcome this challenge, clinicians and researchers have evolved various provocative tests to identify LBP of SIJ origin, some of which include compression, distraction, Geaslen’s, thigh thrust, sacral thrust and supine-long sitting SIJ tests. These tests are generally known to be indirect in their application and appear stressful to the patient. However, the relative amount of exertion on the patient, how quick it is for the tests to detect (sensitive) and how clearly they can identify the absence of SIJ dysfunction (specific) is poorly understood. Further, early studies reported mixed results on the inter-examiner reliability of pain provocation tests, but subsequently, these tests have been shown to possess acceptable levels of reliability provided that they are highly standardized [13,14]. It is suspected that a test that directly targets the SIJ structures may be less stressful, more sensitive and specific in detecting SIJ pathologies at least of mechanical origin, hence the proposal of a Posterior Dimple Compression test (PDC).

The posterior dimple (fossa lumbale laterale) is directly superficial to the SIJ and is formed by stretching the posterior sacroiliac ligament and the skin overlying the posterior superior iliac spine on the right and left respectively. It corresponds to the level of the second sacral vertebra [3]. The PDC test is a result of anecdotal observation and clinical experience (21 years) of the senior author (MOE), and involves the application of a graded (grades 1-3) postero - anterior force on the posterior dimple to provoke pain of varying intensities in the SIJ as an indicator of the presence and a pointer to the degree of dysfunction with or without associated apparent limb length discrepancy.

The standard of tests and measurement in physiotherapy practice specify that essential elements such as sensitivity, specificity and predictive values should be addressed when discussing diagnostic groups, to allow for interpretation. The purposes of this study therefore were to describe PDC test and to determine and compare the sensitivity, specificity and patient reported exertion associated with PDC, Gross Sacro-Iliac Joint Compression (GSIJC) and Distraction (GSIJD) and Supine Long – Sitting (SLS) test for SIJ dysfunction.

Subjects

Fifty three patients (24 males, 29 females; age range 19-90 years, mean age 54.3 yrs) with diagnosis of LBP seen in the Physiotherapy outpatient Departments of Obafemi Awolowo University Teaching Hospital Complex Ile-Ife and University College Hospital, Ibadan, Nigeria, were recruited for this study. These subjects represent patients who gave their consent to participate and pain elicited by at least one direction of trunk movement associated with or without buttock or lower limb symptoms. Patients with clear radicular signs, midline pain above the level of L5, history of lower limb trauma or hip pathology and those with metabolic/systemic diseases were excluded from this study.

Sacroiliac joint pain provocation tests

The tests employed in this study were: Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Compression (GSIJC) and Distraction (GSIJD) and Supine Long – Sitting (SLS). The GSIJC, GSIJD and SLS tests have been described previously [11,12,15-18]. The GSIJC and GSIJD tests were selected because Laslett et al. [11,16] observed that these tests were good predictors of a positive intra articular SIJ block, while SLS was selected because SIJ dysfunction is known to result in apparent limb length discrepancy (Figure 7) [3,16]. As mentioned earlier, PDC test is a graded (1-3) postero-anterior force applied on the indentation directly superficial to the SIJ in the right and left side respectively (Figure 1), with a view of provoking pain of varying intensities in the SIJ as an indicator (physical diagnosis) of the presence and a pointer to the degree of SIJ dysfunction. Pressure (compression force) is mild (C, grade 1) when the pain is severe (Numerical Rating (NR) 7-10), easily provoked and reflect a major SIJ dysfunction, medium (D, grade 2) when pain is moderate (NR 4-6), pointing to an intermediate level of SIJ dysfunction. Deep compression (E) is needed when the pain is mild (NR 1-3), reflecting a little dysfunction of the SIJ. Note that thumbs need to be superimposed for one to be able to generate enough compressive force to elicit mild pain. Compression of the SIJ will not elicit pain in the absence of SIJ dysfunction.

Figure 1: Posterior Dimple Compression Test Manual

Procedure

Patients with low back pain were screened on arrival on their respected clinic days, the purpose and procedures of the research was explained to each of the participants who met the inclusion criteria before obtaining their informed consent. The PDC (Figure 2), GSIJC (Figure 3), GSIJD (Figure 4) and SLS (Figure 4 and 5) tests were carried out in that order before receiving treatment. The semantic differential scale [19] was used to quantify pain intensity before and after the application of each tests while Borg’s scale [20] for rating of perceived exertion was used to assess the test induced exertion after each test. A tape measure (Butterfly, China) was used to quantify the degree of discrepancy after the SLS test (Figure 6). This study was approved by the ethics and research committee of the Institute of Public Health, Obafemi Awolowo University (IPHOAU/12/36).

Figure 2: Application of Posterior Dimple Compression Test to the Left Sacroiliac Joint

Figure 3: Sacroiliac Compression Test

Figure 4: Sacroiliac Distraction Test

Figure 5: Supine-Long Sitting Test stage 1-patient in supine lying and examiners’ two Thumbs on both Medial Maleoli.

Figure 6: Supine-Long Sitting Test stage 2-patient in Long Sitting position and examiners’ two Thumbs on both Medial Maleoli.

Figure 7: Measurement of apparent Limb Length Discrepancy

Data analysis

The descriptive statistics such as mean, standard deviation, frequency and percentage were used to summarize the gender as well as the clinical profile of the patient. GSIJ test was used as the gold standard such that results from other tests were compared to it. Two by two contingency tables were constructed and sensitivity, specificity, Positive and Negative Predictive Values (PPV & NPV), and Likelihood Ratios (LR) with 95% confidence intervals were calculated for each test. Sensitivity, specificity, PPV and NPV was calculated using standardized methods [21]. Receiver Operator Characteristic (ROC) curve is an overall measure of diagnostic efficacy and the curves combine sensitivity and specificity. Chi-square test of association was used to establish the correlation between gender and the distribution of positive and negative tests. Data entry and statistical analysis was performed using the statistical package for the social sciences (SPSS) software version 17.0 at an alpha level of 0.05.

The subjects in this study included 29 (55%) females (age range 19 - 90 years, mean age=59) and 24 (45%) males (age range 20 – 88, mean age=50 years), making a total of 53 (100%) patients (age range 19-90, mean age 54 years) with low back pain (Table 1). Majority of the patients had tertiary (N=34, 64%), secondary (N=9, 17%) and primary (N=2, 4%) education. Eight (15%) of the subjects did not have western education but were sufficiently knowledgeable to respond accurately to the rating of pain and exertion. Their pain duration ranged from 4 to 56 weeks and pain profile of subjects is presented in Table 2. Most of the patients (N=38, 72%) had pain that was barely strong (N=16, 30%), moderate (N=12, 23%) and mild (N=10, 19%). Others had strong (N=8, 15%), very mild (N=4, 8%), intense (N=2, 4%) and severe pain (N=1, 2%).

Table 1: Age and Sex distribution of the Respondents

Table 2: Pain Profile of Subjects (N=53)

It could be seen in Table 3 that true positive (PDC=19, GSIJD=12, SLS=14), false positive (PDC=14, GSIJD=3, SLS=5), false negative (PDC=2, GSIJD=3, SLS=7), and true negative (PDC=18, GSIJD=29, SLS=27) tests were recorded when compared with the result of the gold standard (GSIJC). The test for disease state as reflected in the ROC curve show that variable numbers of positive (PDC=33, GSIC=15, SLS=19) and negative (PDC=20, GSIC=38, SLS=34) tests result were obtained indicating the presence (positive) or absence (negative) of SIJ dysfunction (Table 4). The ROC had an Area Under Curve (AUC) of 0.738 (PDC), 0.782 (GSIJD) and 0.765 for SLS and a standard error of 0.069 (PDC), 0.072 (GSIJD) and 0.072 for SLS. The PDC test was the most sensitivity (0.91) followed by SLS (0.67) and GSIJD (0.57), while GSIJD test (0.91) was the most specific, followed by SLS (0.84) and PDC (0.56). The GSIJD test had the highest (0.80) PPV, then SLS (0.74) and PDC (0.58) followed, while PDC (0.90) had the highest NPV, followed by SLS (0.79) and GSIJD (0.76). The PLR was more in GSIJD (6.33) than in SLS (4.19) and PDC (2.10) while the NLR was equal in PDC and GSIJD (0.47) but less in SLS (0.39). The 95% confidence interval (Upper and lower bound) was highest in GSIJD (0.64, 0.92) followed by SLS (0.63, 0.91) and PDC (0.60, 0.87). Post test perceived exertion rating of subject (Table 5 and 6) shows that GSIJC was more physically exerting (14) on the patients than SLS (13), GSIJD (8) and PDC (7). The association between sex and sensitivity/specificity was generally insignificant (Table 7).

Table 3: Manual Assessment profile of respondents for Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Distraction (GSIJD) and Supine- Long Sitting (SLS) Tests using Gross Sacro-Iliac Joint Compression test as a Gold standard.

Table 4: Receiver operating characteristic Curve case processing summary for Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Distraction (GSIJD) and Supine-Long Sitting (SLS) Tests.

Table 5: Sensitivity, Specificity, Likelihood Ratios and Predictive Values for Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Distraction (GSIJD) and Supine-Long Sitting (SLS) Tests

Table 6: Post test Perceived Exertion of Patients for Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Compression (GSIJC), Gross Sacro-Iliac Joint Distraction (GSIJD) and Supine-Long Sitting (SLS) Tests.

Table 7: Association between sex and sensitivity/specificity for Posterior Dimple Compression (PDC), Gross Sacro-Iliac Joint Compression (GSIJC), Gross Sacro- Iliac Joint Distraction (GSIJD) and Supine-Long Sitting (SLS) Tests.

According to Rothstein [22], “All evidence has limitations, but whatever those limitations may be, data are far better than debates that are more about theology than they are about health care”. We described Posterior Dimple Compression (PDC) test then determined and compared the sensitivity and specificity of PDC, Gross Sacro-Iliac Joint Compression (GSIJC) and Distraction (GSIJD) and Supine Long – Sitting (SLS) test for SIJ dysfunction. The GSIJC test was used as the gold standard because previous studies have shown that it has the highest sensitivity (0.91, 0.69) when compared to the other provocative tests and is good predictors of a positive intra articular SIJ block [11,16]. Besides, it is to be noted that the GSIJC test is also known as iliac compression test for posterior SIJ ligament strain which is also part of the structures compressed using the PDC test. The only major difference here is that the posterior ligament is compressed directly using the thumb(s) during the application of PDC while it is stressed indirectly by iliac compression during the application of GSIJC test.

This study found that PDC (0.91) was more sensitive than SLS (0.67) and GSIJD (0.57), while GSIJD was more specific (0.91) than SLS (0.84) and PDC (0.56). In order to be able to discuss these findings, it is important to understand the nature and mechanism of origin of SIJ dysfunction. In an attempt to explain the mechanism of origin of SIJ dysfunction, DonTigny [3] explained that when the articular surfaces of the SIJ are altered in such a way as to allow the in nominate to slip vertically upward on the (lengthening) or the sacrum to slip vertically downward on the ilium (shortening) with fixation effectively preventing self correction by simple posterior rotation will lead to SIJ dysfunction. Also, an innominate that is rotated anteriorly and slipped upward will put tension on the oblique sacroiliac ligaments and tension/tenderness will be elicited over these ligaments at the point of their attachment. In addition, unusual postural stresses on the tissues lead to inflammation and subsequent liberation of substances capable of altering their excitability, thereby rendering the tissues responsive to noxious stimuli which it previously could not generate. It is the variable levels of pain generated by tissue strain from dysfunction that provocative test aggravate (positive test) where they exist and vice versa. Diagnosis of SIJ pathology may mean that either SIJ structures contain the pain generating tissues (intra articular red flags) or that the SIJ function or malfunction in such a way as to cause pain (extra articular soft tissue strain) [11]. It is the latter type of SIJ dysfunction that provocative tests are designed to detect so as to guide its therapy and it is the extent to which these test are able to detect the presence or absence of this pain that is open for discussion as sensitivity and specificity of diagnostic tools.

In signal detection, a Receiver Operating Characteristic (ROC) curve is a graphical plot which illustrates the performance of a binary classifier system as its discrimination threshold is varied [23]. It is created by plotting the fraction of the true positives (TPR=true positive rate) versus the fraction of false positives out of the negatives (FPR=false positive rate), at various threshold settings. It is the TPR that is referred to as sensitivity (in this case, how quick it is for the test to clearly detect SIJ pain/dysfunction). One minus the true negative rate is the specificity (i.e. The ability of the test to clearly identify the absence of SIJ pain/dysfunction). The current finding therefore point to the fact that PDC is the quickest test to use in detecting SIJ pain/ dysfunction with a good confidence interval (0.60, 0.87), while GSIJD is the test that can most clearly identify LBP patients that do not have SIJ pain/dysfunction (CI=0. 67, 0.92).

In all provocative tests, the examiner is looking for the movement or maneuver that alter the symptom or to determine if the usual pain that brought the patient to the hospital is produced or aggravated [15,24]. This is also the intension of PDC test, however, just like tension tests (straight leg raise, prone knee bend etc), GSIJC, GSIJD (gapping or transverse anterior stress test of anterior sacroiliac ligament strain) and SLS (innominate slip test of SIJ dysfunction) test are indirect using the movement of the limb, trunk, or ilium to stress (not compress) the SIJ. Consequently, these tests are not able to load the SIJ structures (skin, fascia, ligament, and the synchondrosed posterior articular surface) directly and alone without loading other structures that may also be pain generators. It is because of this weakness that indirect tests are incapable of discriminating between pathology in the SIJ and those from nearby structures that are also stressed. The reason for high sensitivity of PDC test may then be associated with previous observation of researchers and clinicians that healthy tissue, nerve/nerve root does not produce pain when compressed or stretched and that previously sensitized/traumatized or inflame nerve/nerve root or tissue, is tender to touch [25-27]. In addition, Cyriax [15] had noted that “if a lesion appears to lie at, or near, one joint, this region must be examined for signs identifying its site. It is equally essential for the adjacent joints and structures about them to be examined so that by contrast, their normality can be established”. Therefore, by comparing PDC test result for both SIJs, positive test may be balanced by a corroborative negative test to enhance its sensitivity during examination of LBP patients.

Over the years, different authors have alluded to some challenges affecting sensitivity, specificity, validity and reliability of provocative tests as follows: Kokmeyer et al. [24] had pointed out that some training is needed to ensure correct application of sufficient force to adequately stress the SIJs. Laslett and Williams [16] suggested that due to the large size and lack of mobility of the SIJs, a large amount of force has to be exerted in the correct direction to adequately stress the structures otherwise a false negative result will be returned. Also, if the stress is applied to the incorrect location, the SIJ may not be stressed and pain may arise from other tissues leading to a false positive result. They reminded clinicians that clinical examination may not be able to clearly diagnose a condition due to illness behavior, severe pain, body size, structure and shape inability to identify land marks, and poor palpatory skills. It is also to be noted that surrounding tissues and joints such as the lumbar facet joints, sacrospinous and iliolumbar ligaments may be strained because the force needed to stress the SIJ is large [28]. However, it is widely believed that the commonly used tests for SIJ dysfunction do have diagnostic value especially when used in the context of specific clinical reasoning [9,11,16,17].

Furthermore, there is an ongoing focus on identification of painful SIJ structures based on the patient’s history, area of pain, clinical examination findings (result of provocative test and composite of tests) and diagnostic blocks [11,16,29,30]. All of these have their strength and weakness as pointed out earlier. For instance, proponents of palpatory test as sufficient for mechanical diagnosis of SIJ dysfunction rely on the knowledge that there are a number of key clinical indicators regarding painful area and behavior which provide an important insight into the different mechanisms underlying and driving a pain disorder, allowing the classification to be made [17,29,30]. Also, the presence of localized and anatomically defined pain in the SIJ associated with specific and consistent mechanical aggravating (during compression) and easing (after compression) suggest that physical and mechanical factors are likely to dominate the SIJ disorder resulting in a primary peripheral nociceptive drive. However, correlation between clinical examination and pathoanatomical findings is critical to determine the significance of each provocative test in relation to the disorder.

This study also examined the relative exertion perceived by patients during these provocative tests and the influence of sex on their sensitivity and specificity. It was observed that PDC (7.2) and GSIJD (7.5) tests were the least exerting and GSIJC (13.9) and SLS (13.0) were the most exerting tests. It should be noted that rating of perceived exertion is a way of measuring physical activity intensity level during the tests and it reflect how hard the patient felt his or her body was working including increases in heart rate, respiratory rate, sweating and fatigue 20. The result reveals that patients felt extremely light exertion during PDC and GSIJD tests while they found GSIJC and SLS tests somewhat hard. Going by the theory that human beings have inherent dislike of work, one will be tempted to conclude that patients will always prefer PDC and GSID to GSIJC and SLS test for SIJ dysfunction and pain. Internet search indicate that there have been no study that assessed the test induced exertion of patients undergoing provocative tests for SIJ dysfunction and pain, nor had the influence of gender on sensitivity and specificity of these tests been studied. Our data stands as evidence that patient’s test induced exertion vary according to the work done during the test and should be of interest to the tester as it may influence test outcome. However, gender have no effect on sensitivity and specificity of SIJ provocative tests among patients with LBP as gender did not significantly affect the number of patients that tested positive or negative to these tests.

PDC test is the least exerting and more able to identify the proportion of LBP patients having SIJ dysfunction while GSIJD is more able to identify the proportion of Patients with LBP without SIJ dysfunction but exert more stress on the patient without gender bias. This is without prejudice to the influence of skill on test results.

The kind assistance of Bose Arilewola and Chidozie Mbada is thankfully acknowledged.