Study on sacroiliac joint diagnostics

Over the past 200 years, descriptions and concepts of the many integrated components of human sacroiliac joints (SIJ) and pelvic girdle systems have emerged. In particular, the concept of motion in the SIJ has undergone a slow, convoluted evolution. Although initial writings suggested that motion is normally present between the ilia and sacrum, this idea fell out of favor in the mid-20th century [37]. Now, current research supports the existence of a limited motion in the average range of 2–4° in all three planes of this joint, but only in a lying position [15].

The SIJs are highly specialized joints that permit stable (yet flexible) support of the upper body. In bipeds, the pelvis serves as a basic platform with three large levers acting on it (the spine and two legs). Thus, for bipeds submitted to gravity in an upright position, both the necessary tightness of the well-developed fibrous apparatus and the specific architecture of the SIJ result in limited mobility. Sacral movement involves the SIJ, and most likely directly influences the discs and the higher lumbar joints as well [38].

The SIJ appears as a typical joint from the second month in utero onwards and development of the joint cavity is completed by months 7–8. Examination of 200 anatomical specimens revealed that the bony surfaces of the joint are smooth until puberty [37]. At a later age, different combinations of bony ridges and grooves occur. The most frequent location of the ridges appears to be on the ilium. These ridges are not identical with osteoarthritis. However, the interdigitating symmetrical grooves and ridges [6] of the SIJ articular surfaces contribute to the highest coefficient of friction of any di-arthrodial joint. This property enhances the stability of the joint against shearing [37]. The keystone-like bony anatomy of the sacrum further contributes to stability within the pelvic ring. At its base, the sacrum is wider superiorly than inferiorly; it is also wider anteriorly than posteriorly, permitting the sacrum to act like a “wedge” towards caudally and dorsally between the ilia within the pelvic ring. This anatomical structure of the sacrum in humans is adapted to resist shearing from vertical compression (e. g., gravity) and anteriorly directed forces on the spine. Therefore, in an upright position, the mobility is even more restricted and the total degree of mobility is less than 1° [37].

Immediately after birth, the general orientation of the human SIJ is very similar to that of quadrupeds. The articular surfaces have the same angular orientation as the zygapophyseal joints of the lumbar vertebrae. Change begins as soon as the child starts to walk upright. The sacrum enlarges laterally, and the articular surfaces modify to a more complex adult curvature, resulting in the surface profiles of the joint bearing resemblance to a propeller-like shape. Comparative anatomical and paleontological research indicate that these changes are the result of mechanical factors, such as the supine position, body weight, load on the femur, and strain on the pubic symphysis [27].

Typically, the SIJ includes the sacral segments S1, S2, and S3, although inclusion of the complete S3 segment in the SIJ is not common for females [38]. In general, fusion of the sacral vertebra begins early in the second decade. The bony anatomy of the joint surface is highly variable in size, shape, and contour among individuals, and the shape of the joint changes markedly from infancy to adulthood [6]. The sacral auricular part is generally concave; however, often an intra-articular bony tubercle is present ventrally, in the middle aspect of the auricular surface of the sacrum. The iliac part is predominantly convex. Large variations of the auricular surfaces exist, resulting in intra-individual variations of motion axes.

The SIJ is unique in having elements of a combined synarthrosis and a diarthrosis—hence resulting in the term amphiarthrosis. The main portion of the joint is surrounded by a complex capsule and lined with cartilage (diarthrosis). Its shape is auricular, and “opens” posteriorly. The sacrum and ilia have an extracapsular, dorsally located articulation (synarthrosis), which is augmented by the vast iliosacral ligament (ISL) that provides considerable internal stability. Essentially, the SIJ is encased in a capsule that has a smooth anterior wall and irregular bands comprising the posterior wall. The capsule is innervated, at least from the dorsal lumbosacral rami (L5–S3) and is surrounded by several strong ligaments, such as the sacrotuberal ligaments, sacrospinal ligaments, long dorsal sacroiliac, and iliolumbar ligaments, which therefore influence its range of motion. In turn, these ligaments are related to a complex thoracolumbar fascia composite derived from the aponeuroses of several large muscles (like the paraspinal and the abdominal muscles) that surround the joint at a distance [37].

What is meant by the “dysfunction” of a joint that has so little mobility? Currently, there are no data to prove one or the other hypothesis—is it really the very small mobility, is it the affection of the capsule, or is it just a soft tissue reaction in segmental connection with the SIJ? Therefore, we rely on observations of pain and restriction in the region of the pelvic girdle and the related connective tissues.

On the one hand, structural changes exist in the bony parts of the joint, the synovia, and the capsule, which are caused either by long-lasting mechanical overcharge in the sense of degenerative osteoarthritic changes altering the mechanics by osteophytes. Alternatively, pathological autoimmune-reactive processes (by inflammation) also lead to a structural change of the joint, in the most severe situation represented by a synostotic fusion (i. e., ankylosing spondylitis). These changes are not reversible. However, they only occur in a small proportion of patients with respective complaints. On the other hand, the vast majority of patients present a reversible dysfunction during the examination, which sometimes disappears spontaneously, but more often will dissolve only after external influence (mechanical, medication, etc.).

Similar to the intervertebral joints and using the forces of compression or distraction, these reversible dysfunctions have the property to react to a respective mechanical provocation with a diminution of pain in at least one direction.

The reversible SIJ dysfunction follows the pattern of a complex arthro-neuromuscular reaction as an answer to nociception [4]. This complex nocireaction comprises the segmentally organized muscles that show a painful protective contraction, as well as the vast ligamentous apparatus of the pelvis that will develop painful insertions (here from segments L5–S3).

Last but not least, the multilayered collagenous fibers have to reorient themselves according to the altered direction of mechanical load within the system of the deep fascia of the abdominal, back, and leg muscles. In addition, a densification of the fascial layers through physical forces or biomechanical processes will occur that reduces the gliding, with the result that a spontaneous return to normal function is impeded [28, 29].

Which changes occur in the joint itself? Even today, we can only answer this question hypothetically. Based on the abovementioned data, it is quite plausible that the grooves and ridges that form themselves individually in every person during upright walking on the corresponding surfaces will always move in the same way, they will follow a uniform pattern.

In case external influences disturb this pattern, the grooves and ridges will no longer fit, leading to a disturbance of the movement—perhaps similar to a train that has been derailed. We can usually influence this biomechanical part of the complex nocireaction by mobilizing the joint partners (sacrum and ilium) in a direction previously established to be pain-free or just by separating them from each other.

The very successful manual therapeutic techniques to treat SIJ-related pain based on a reversible dysfunction that we teach today follow this hypothesis. Therefore, it is an indispensable precondition for treatment to differentiate between structural damage and reversible dysfunction by diagnostic steps, and furthermore to identify the pain-free direction of any movement in the latter. Although this sounds plausible, in daily practice it is not so easy.

Therefore, SIJ diagnostics remain difficult and uncertain. There is no typical pain pattern; there are substantial contradictions in the analysis of the innervation [10‐12, 14, 24, 27]. Today, there is still no gold standard in SIJ diagnostics. Even Rx(fluoroscopically)-guided intraarticular injections do not have reliable results [9]. Many irritation zones/points have been described [5]. The clinical examination of function is not reliable and reproducible [21, 25, 26]. In addition, we have to take into consideration that the perception of pain at a certain point of the anatomy does not mean that the nocigenerator of this pain is exactly where the brain locates that pain. This means that a chronic pain in the area of the SIJ may also be a referred pain of any nocigenerator in any structure segmentally innervated from L5 to S3 [23]. Is there reliable information from the clinical findings at all? In this respect, the publications are conflicting and not unanimous [2, 8, 13, 19, 20, 32‐34, 40]. Nevertheless, these studies present some general ideas:

The real functional mobility of the SIJ in a supine position is a complex three-dimensional nutation and counternutation movement of the sacrum towards the ilium in the range of 2–4°. This can only be tested in a lying position, using a helicoidal axis that varies largely even between the SIJs of the same person [3].

The axis even depends on the actual function (standing on both or one leg, lying in supine or prone position; [15]). During the nutation, the base of the sacrum moves cranially and anteriorly, and during counternutation, the tip of the sacrum moves caudally and anteriorly. During aging, the mobility decreases in men. In young subjects and in the horizontal position of the body we find 4°, in older men only 2°.

With only 2–4° of three-dimensional mobility in a supine position and less than 1° in an upright position, it is very difficult to produce clinically reliable signs of articular movements. In fact, clinical manual movement tests are completely unreliable for the SIJ [39]. Commonly used diagnostic tests are 1. the standing-flexion test (also called bending-forward-test or Gillet-test or Piedallu-test) and 2. the spine-test (also called hip flexion test or stork-/flamingo-test). Unfortunately, these tests have low reliability [22] and low reproducibility [21]. Sturesson et al. checked these tests in 22 patients with severe SIJ pain using radio-stereometric analysis (RSA). The results show minimal change of movements during the test, and no differences between symptomatic and asymptomatic sides. When the pelvis is loaded in a one-leg standing position while flexing the contralateral leg, patients are physically challenged, which leads to bilateral increased force closure of the SIJ [1, 3, 30]. During this test, no SIJ motion occurs. The visibly changing position of bony landmarks like the upper posterior iliac spine (SIPS) that is apparently derived from the SIJ is in fact a movement of the external pelvis relative to the hips. This gives the manually perceived but misleading illusion that the SIJs are moving [30]. Perhaps these functional tests react positively in the presence of SIJ dysfunction by changing the behavior of the connective tissues of the whole pelvic girdle.

Several studies have checked the reliability of SIJ tests. In general, pain provocation tests seem to be more reliable than functional tests in the diagnosis of SIJ dysfunction without structural lesion [35, 39]. The most frequently used tests are the compression test, the femur-thrust test, the pelvic torsion test, the FAbER test (for flexion, abduction, and external rotation; [17]), and the hip extension test [35]. Based on this specific differential diagnosis, the results of manual therapy for SIJ-related gluteal and leg pain in a prospective single-blinded trial were better (72% success) than those of injections (50%) or physiotherapy (20%; [36]).

In Germany, physicians have been competent in the use of manual medicine (MM) and have been teaching the method for 65 years. They have developed these tests through empirical observations and good practical results. Nobody has ever evaluated these tests in comparison to other diagnostic techniques. Therefore, in the world of evidence-based medicine and reliability studies, evaluation of these tests in comparison to each other has become inevitable. The described approach uses three steps to identify SIJ dysfunction, including an exact medical history and a neurological examination:

This is a diagnostic study with the primary aim of evaluating the interrater reliability between two independent examiners with respect to the principles of the three-step diagnosis. The secondary aim was to evaluate the validity of the three-step diagnosis compared to the already evaluated SIJ testing procedures (here: FAbER test, pelvic torsion test, femur-thrust test). In the case of the two pain provocation tests of the Physicians’ Seminar for Manual Therapy of Spinal and Periperal Joints (MWE; checking a gluteal irritation point for pain-free direction cranial–caudal and ventral–dorsal) reaching sufficient reliability in Cohen’s kappa [7], these two tests were to be added to the set of tests, reaching a set of five tests that are reliable for SIJ diagnostics.

Generally, the magnitude of Cohen’s kappa coefficients for the agreement of the two raters is interpreted as follows: kappa values between 0 and 0.20 indicate poor agreement, values between 0.21 and 0.40 indicate sufficient agreement, values between 0.41 and 0.6 are interpreted as a substantial agreement, and kappa coefficients above 0.61 are interpreted as almost perfect agreement [16].

Although 168 subjects signed the informed consent to participate, 7 had to be excluded from evaluation as they did not fulfill the inclusion criteria, mainly because they were too old or too heavy. Of the included subjects, 82 (50.9%) were male, 79 (49.1%) were female. The mean age was 44.4 ± 8.9 years, the mean weight was 76.3 ± 13.4 kg, the mean height was 174.6 ± 10.0 cm, and the mean BMI was 24.8 ± 3.1 kg/m². The general physical examination found in 3 (1.9%) subjects a pathologic condition in the central nervous system, 9 (5.6%) with cardiac problems (high blood pressure), 2 (1.2%) with asthma, 1 (0.6%) with nephrologic problems, 11 (6.8%) had previous gastric ulcers, and 11 (6.8%) had thyroid disorders. They were included nevertheless, as all of them used the respective medication to control their specific problems.

In 8 (5.0%) subjects there were signs of some nerve root compression, but none from the lumbosacral region, so they were not excluded. Another 31 (19.3%) showed signs and symptoms of intervertebral dysfunction in the segments T12 to L5, which was also not a criterion for exclusion.

For the three functional tests (standing forward flexion, spine test, and checking the variability of leg lengths), we did not expect good results for interrater agreement. They are not based on real mobility within the SIJ, but rather on connective tissue reactions. Therefore, they may probably but not reliably be related to SIJ dysfunction. Although the observed kappa values were not poor for each of these functional tests, the 95% CI was too wide to allow an appropriate interpretation. Nevertheless, the observed kappa values for the FAbER test and the pelvic torsion test were almost equal to the data from the references [18]. In our study, we only found similarly good and precise results for the femur-thigh thrust as for the pain provocations to the gluteal muscular irritation. All results are compiled in Table 1.

These results show that SIJ diagnosis using the gluteal irritation in combination with the pain provocation in the cranial–caudal plane as well as in the ventral–dorsal plane have an almost perfect kappa coefficient and are even more reliable than the already examined tests.

We accepted the precondition [18] that there is a need for at least three positive tests out of five for the diagnosis of SIJ dysfunction. Using the pain provocation test cranial–caudal, pain provocation test ventral–dorsal, FAbER test, pelvic torsion test, and femur thrust test, the interrater reliability for one of the possible three diagnoses (no SIJ dysfunction, dysfunction right SIJ, and dysfunction left SIJ) was evaluated: