Sacroiliac joint dysfunction: hypomobility and hypermobility

I read with interest the article by Ribeiro et al. [1] that was recently published in this journal. The authors performed a prospective study with a sample composed of individuals of both sexes. The objective was to evaluate the construct validity and determine the intra- and inter-rater reliabilities of the clinical tests that evaluate the sacroiliac joint (SIJ): standing flexion test (STFT) and sitting flexion test (SIFT). The assumption on which their research is based is to consider SIJ dysfunction caused by hypomobility [1]. However, their assumption is incorrect.

SIJ is a complex joint (a synovial portion and a diarthrodial portion) that develops near the first three segments of the sacrum, where the sacral surface is generally concave, while the iliac portion is convex; its morphology is very subjective and can change from individual to individual, based on age and gender [2, 3]. We can functionally represent the joint as a part consisting of anatomical interlocking of the articular surfaces (grooves and ridges or form closure), which allows passive stabilization, and a portion of coincident compressive forces (muscles and ligaments or force closure), with the latter allowing dynamic stabilization [3].

The joint is innervated by fibers from L5-S3, with the presence of myelinated and unmyelinated fibers, with encapsulated endings within the joint; the axons of the fibers can be classified as type C and type A-delta fibers, with a high sensitivity of nociceptive response to some biochemical substances (neuropeptide P and calcitonin gene-related polypeptide) [2]. SIJ is highly sensitive to mechanical variations.

SIJ falls as a cause and trigger in low back pain, with a primary cause rate between 15 and 30%, regardless of gender and race [3, 4]. There are many causes of joint pain, such as repetitive asymmetrical movements in rotation, pregnancy, obesity, direct trauma or previous lumbar/sacral surgery, systemic inflammatory and/or degenerative diseases, a discrepancy in the length of the legs, and genetic conditions (Marfan, Ehlers-Danlos) [3, 4]. The biomechanical conditions that can lead to SIJ dysfunction and consequent pain (symptomaticity) or painlessness (asymptomaticity), limiting or increasing the millimeters related to the joint range of motion, are hypomobility and hypermobility, respectively [3], [4], [5], [6].

The biomechanical behavior of excess or lack of joint mobility falls under the designation of dysfunctional SIJ. The clinical presentation is variable. The pain can be localized in the medial and distal areas of the posterior superior iliac spine; the pain can present different behaviors (dull, sharp, shooting), or mimic distant problems, such as radiculitis up to the posterior portion of the thigh, buttock, groin, and abdominal area [3].

In clinical practice, the evaluation of a problem at the SIJ passes first through some provocative tests or test clusters, which can be carried out in groups of three of the following: the Faber test or Patrick test, the thigh thrust test or posterior shear test, the Gaenslen test, the compression test, the distraction test, the Yeoman test, and the Trendelenberg test [3, 4]. The application of these tests in groups can provide approximately 35% positivity in identifying SIJ as the source of the patient’s dysfunction [7].

A more precise and diagnostic evaluation takes place thanks to the use of guided ultrasound with injection of a mix of drugs (anesthetic and steroids or platelet-rich plasma only), within the SIJ; the positive diagnosis for joint dysfunction is symptomatic resolution for approximately 75%, with a certainty of diagnosis of approximately 87.3% [3, 8, 9]. The ineffective response to ultrasound injection could lead one to think that the source of pain is the joint capsule or the presence of a previous SIJ fixation surgery [3]. Other evaluations utilizing clinical instruments, such as CT, MRI, X-rays, and scintigraphy, are too confusing and yield conflicting results [3].

SIJ can depend on joint hypermobility and hypomobility, and assessments of SIJ may not be entirely precise and sure. The study carried out by Ribeiro et al. [1] does not take into consideration the possibility of a hypermobile sacroiliac, without specifying whether the individuals enrolled for the research had joint hypermobility or hypomobility; the result is negatively linked to a very reduced clinical thickness. Considering the importance of this articulation and the multidisciplinary interest that this anatomical portion possesses, it would be advisable to carry out further research with a broader assumption and well-specified assessments.