Experimental characterization of motion resistance of the sacroiliac joint.

BACKGROUND: The human sacroiliac joint (SIJ) in vivo is exposed to compressive and shearing stress environment, given the joint lines are almost parallel to the direction of gravity. The SIJ supports efficient bipedal walking. Unexpected or unphysiological, repeated impacts are believed to cause joint misalignment and result in SIJ pain. In the anterior compartment of the SIJ being synovial, the articular surface presents fine irregularities, potentially restricting the motion of the joints. OBJECTIVE: To clarify how the SIJ articular surface affects the resistance of the motion under physiological loading. METHODS: SIJ surface models were created based on computed tomography data of three patients and subsequently 3D printed. Shear resistance was measured in four directions and three combined positions using a customized setup. In addition, repositionability of SIJs was investigated by unloading a shear force. RESULTS: Shear resistance of the SIJ was the highest in the inferior direction. It changed depending on the direction of the shear and the alignment position of the articular surface. CONCLUSION: SIJ articular surface morphology is likely designed to accommodate upright bipedal walking. Joint misalignment may in consequence increase the risk of subluxation.

Influence of size and shape of the auricular surfaces on subchondral bone density distribution in the sacroiliac joint.

The sacroiliac auricular surface has a variable morphology and size. The impact of such variations on subchondral mineralization distribution has not been investigated. Sixty-nine datasets were subjected to CT-osteoabsorptiometry for the qualitative visualization of chronic loading conditions of the subchondral bone plate using color-mapped densitograms based on Hounsfield Units in CT. Auricular surface morphologies were classified into three types based on posterior angle size: Type 1: >160°, Type 2: 130-160° and Type 3: <130°. Auricular surface size was categorized based on the mean value (15.4 cm2 ) separating the group into 'small' and 'large' joint surfaces. Subchondral bone density patterns were qualitatively classified into four color patterns: two marginal patterns (M1 and M2) and two non-marginal patterns (N1 and N2) and each iliac and sacral surface was subsequently categorized. 'Marginal' meant that 60-70% of the surface was less mineralized compared with the highly dense regions and vice versa for the 'non-marginal' patterns. M1 had anterior border mineralization and M2 had mineralization scattered around the borders. N1 had mineralization spread over the whole superior region, N2 had mineralization spread over the superior and anterior regions. Auricular surface area averaged 15.4 ± 3.6 cm2 , with a tendency for males to have larger joint surfaces. Type 2 was the most common (75%) and type 3 the least common morphology (9%). M1 was the most common pattern (62% of surfaces) by sex (males 60%, females 64%) with the anterior border as the densest region in all three morphologies. Sacra have a majority of surfaces with patterns from the marginal group (98%). Ilia have mineralization concentrated at the anterior border (patterns M1 and N2 combined: 83%). Load distribution differences related to auricular surface morphology seems to have little effect on long-term stress-related bone adaptation visualized with CT-osteoabsorptiometry. Higher iliac side mineralization was observed in larger joint surfaces and age-related morphomechanical size alterations were seen in males.

Topographic localization of the sacroiliac joint and superior gluteal artery branches on the posterolateral ilium.

Latrogenic vascular injuries at the posterior ilium during sacroiliac screw placements are not uncommon. Though intra-operative imaging reduces the risk of such injuries, anatomical localization of the sacral segments using discrete topographical landmarks is not currently available. This descriptive study proposes the use of an anatomical grid system to localize the sacroiliac articulation on the posterolateral ilium. It also investigates the positional variability of the branches of the superior gluteal artery (SGA) within areas defined by the grid. 48 dried adult hip bones were examined to determine the position of the sacral articular surface on the posterolateral surface of the ilium. A novel grid-system was defined and used to map the positions of the articulation of the first two sacral segments on the posterolateral ilium. Superficial and deep branches of the SGA were dissected in donor cadavers and their courses were virtually overlayed on the grid system. The grid system localized the sacral articular surfaces within a defined area on the posterior ilium. Arterial distributions indicated the presence of the superficial branch of SGA more frequently over the screw insertion area (at an intermuscular plane), while the deep branch ran closer to the ilium but antero-inferior to the screw placement areas. This study proposes a new topographical perspective of visualizing SGA branches with respect to the cranial sacral segments. Precise localization of vascular anatomy may help to reduce potential risk of injury during sacroiliac screw placements.

Auricular surface morphology and surface area does not influence subchondral bone density distribution in the dysfunctional sacroiliac joint.

The subchondral lamella of the sacroiliac auricular surface is morphologically inconsistent. Its morpho-mechanical relationship with dysfunction (SIJD) remains unstudied. Here, the iliac and sacral subchondral bone mineralization is compared between morphological subtypes and in large and small surfaces, in SIJD joints and controls. CT datasets from 29 patients with bilateral or unilateral SIJD were subjected to CT-osteoabsorptiometry. Surface areas and posterior angles were calculated and surfaces were classified by size: small (<15 cm3 ) and large (≥15 cm3 ), and morphological types: 1 (>160°), 2 (130°-160°), and 3 (<130°). Mineralization patterns were identified: two marginal (M1 and M2) and two non-marginal (N1 and N2). Each sacral and iliac surface was subsequently classified. Dysfunctional cohort area averaged 15.0 ± 2.4 cm2 (males 16.2 ± 2.5 cm2 , females 13.7 ± 1.6 cm2 ). No age correlations with surface area were found nor mean Hounsfield Unit differences when comparing sizes, sexes or morphology-type. Controls and dysfunctional cohort comparison revealed differences in female sacra (p = 0.02) and small sacra (p = 0.03). There was low-conformity in marginal and non-marginal patterns, 26% for contralateral non-dysfunctional joints, and 46% for dysfunctional joints. The majority of painful joints was of type 2 morphology (59%), equally distributed between small (49%) and large joints (51%). Larger joints had the highest frequency of dysfunctional joints (72%). Auricular surface morphology seems to have little impact on pain-related subchondral lamella adaptation in SIJD. Larger joints may be predisposed to the onset of pain due to the weakening of the extracapsular structures. Dysfunctional joints reflect common conformity patterns of sacral-apex mineralization with corresponding superior corner iliac mineralization.

A patient-cohort study of numerical analysis on sacroiliac joint stress distribution in pre- and post-operative hip dysplasia.

In acetabular dysplasia, the cartilaginous roof on the acetabular side does not fully cover the femoral head, which may lead to abnormal stress distribution in both the femoral head and pelvis. These stress changes may have implications to the adjacent sacroiliac joint (SIJ). The SIJ has a minimal range of motion and is closely coupled to the adjacent spine and pelvis. In consequence, the SIJ may react sensitively to changes in stress distribution at the acetabulum, with hypermobility-induced pain. The purpose of this study was to investigate the stress distribution of the SIJ in acetabular dysplasia, and to gain insight into the cause and mechanisms of hypermobility-induced pain at the SIJ. Finite element models of pre- and postoperative pelves of four patients with acetabular dysplasia were created and analyzed in double leg standing positions. The preoperative models were relatively inflare, the sacral nutation movement, SIJ cartilage equivalent stress, and the load on the surrounding ligaments decreased with increased posterior acetabular coverage. Acetabular morphology was shown to affect the SIJ, and improvement of the posterior acetabular coverage may help normalize load transmission of the pelvis and thus improve the stress environment of the SIJ in acetabular dysplasia.

Relation of the lumbosacral trunk to the sacro-iliac joint.

This study aims to evaluate the relation between the lumbosacral trunk (LT) and the sacro-iliac joint (SIJ). In forty anatomic specimens (hemipelves) a classical antero-lateral approach to the SIJ was performed. The SIJ was marked at the linea terminalis (reference point A). Reference point B was situated at the upper edge of the interosseous sacro-iliac ligament. The length of the SIJ (distance A to B) and the distance between point A and the ventral branch of the fourth (L4) and fifth (L5) lumbar spinal nerves at the linea terminalis were measured. The SIJ had a mean length of 58.0 mm. The ventral branch of L5 was located closer to the SIJ in very long SIJs (mean length: ≥ 6.5 cm; mean distance: 9.8 mm) compared to very short joints (≤ 5 mm; mean distance: 11.3 mm). For the ventral branch of L4, very long SIJs had a mean distance of 7 mm and very short joints an average distance of 9.7 mm between point A and the nerve branch. A safe zone of approximately 1 cm to 2 cm (anterior to posterior) is present on the sacral surface (lateral to medial) for safe fixation of plates during anterior plate stabilization of the SIJ. Pelves with a shorter dorsoventral diameter of the most superior part of the SIJ apparently give more space for inserting plates.

A Pilot Study on Feasibility of Ultrashort Echo Time T2* Cartilage Mapping in the Sacroiliac Joints.

PURPOSE: Assess feasibility of ultrashort echo time (UTE) T2* cartilage mapping in sacroiliac (SI) joints. METHODS: Prospective magnetic resonance imagings with UTE T2* cartilage maps obtained on 20 SI joints in 10 subjects. Each joint was segmented into thirds by 2 radiologists. The UTE T2* maps were analyzed; reliability and differences in UTE T2* values between radiologists were assessed. RESULTS: Mean UTE T2* value was 10.44 ± 0.60 ms. No difference between right/left SI joints (median, 10.52 vs 10.45 ms; P = 0.940), men/women (median, 10.34 vs. 10.57 ms; P = 0.174), or different anatomic regions (median range 10.55-10.69 ms; P = 0.805). Intraclass correlation coefficients were 0.94 to 0.99 (intraobserver) and 0.91 to 0.96 (interobserver). Mean bias ± standard deviation on Bland-Altman was -0.137 ± 0.196 ms (limits of agreement -0.521 and 0.247) without proportional bias (ß = 0.148, P = 0.534). CONCLUSIONS: The UTE T2* cartilage mapping in the SI joints is feasible with high reader reliability.

The association between sacral morphology and sacroiliac joint conformity demonstrated on CT-based bone models.

INTRODUCTION: Knowledge of the stress distribution on structures around the sacroiliac joint (SIJ) is required to treat or prevent SIJ disorders. The purpose of this study was to reveal the association between sacral morphology and SIJ conformity. MATERIALS AND METHODS: This cross-sectional study included 11 adult patients with unilateral SIJ pain who underwent computed tomography (CT) imaging of the pelvis. Bony coordinate systems for the sacrum and innominates were embedded using anatomical landmarks. Local coordinate systems for the auricular surfaces of the sacrum and innominate were also defined. Conformity of the SIJ was quantified by the offset of the coordinate systems between the auricular surfaces of the sacrum and innominate. Repeated measure ANOVA and multiple regression analysis were used for statistical analyses. RESULTS: There were large variations across subjects in sacral morphology and SIJ conformity. There were no differences in any of the six degrees-of-freedom positions or orientations of the bilateral sacral and innominate auricular surfaces between the symptomatic and asymptomatic sides. The SIJ downward rotation on the asymptomatic and symptomatic sides were 0.0 [-1.0, 1.1]° and 2.1 [1.2, 3.0]°, respectively. Smaller downward rotation of the sacral auricular surface based on the sacral bony coordinate system had significant association with the greater SIJ downward rotation (standard partial regression coefficient: -.44, p = .043). CONCLUSIONS: The results indicate that the morphology of the sacrum is associated with poor SIJ conformity and that separation of the superior portion of the SIJ can be a risk factor for SIJ pain.

[Pain generator sacroiliac joint : Functional anatomy, symptoms and clinical significance]. / Schmerzquelle Iliosakralgelenk : Funktionelle Anatomie, Symptome und klinische Bedeutung.

BACKGROUND: The sacroiliac joint is a common cause of low back pain. Due to variable symptoms, the diagnosis is often very difficult. For diagnosis, systemic disease, as well as pathologies in the hips and lumbar spine must be excluded. OBJECTIVES: To describe anatomy and function of the joint and underlying pathologies. To present the evidence of actual diagnostic and therapeutic options. MATERIALS AND METHODS: An extensive literature research was carried out on PubMed. RESULTS: The sacroiliac joint is an important and biomechanically complex joint. There are many controversial diagnostic tests to identify the sacroiliac joint as a source of pain. The cause of the dysfunction must be identified in order to treat it correctly and to prevent a chronification of the pain. The gold standard is conservative care. CONCLUSION: The sacroiliac joint must be included in the differential diagnosis in patients with low back pain. Diagnostic tests are often insufficient for the diagnosis of sacroiliac joint pain. Many of the current diagnostic and therapeutic options present weak evidence.

Sex-based differences in human sacroiliac joint shape: a three-dimensional morphological analysis of the iliac auricular surface of modern Japanese macerated bones.

The human pelvis is one of the skeletons where sex differences are expressed, but few detailed studies have been conducted on sex-related differences in the sacroiliac joint morphology. Therefore, we conducted a three-dimensional morphological analysis evaluation of the sacroiliac joints to clarify the sex-related difference of the joint's morphology. Right-side macerated innominate bones of Japanese males (n = 100) and females (n = 70) whose ages at death were recorded were included in the study. Three-dimensional images were created from the subjects' iliac auricular surface images, and 16 measurement parameters were acquired on the basis of 11 defined measurement points. All measurement parameters were compared between the male and female groups. The values of the measurement parameters indicating the size of the iliac auricular surface were significantly larger in the male group than in the female group. In addition, the angle between the short and long arms of the auricular surface was larger in the male group. Furthermore, on the basis of the corrected values of the physical disparity, the long arm dimension of the iliac auricular surface was larger in the male group, while the short arm dimension was larger in the female group. The sex-based differences in the iliac auricular surface morphology that were confirmed in this study may reflect the sex-based differences in the sacroiliac joint function. The findings of this study may contribute to the elucidation of the pathophysiology of the sacroiliac joint dysfunction that frequently occurs in women.

Iliac auricular surface morphofunctional study in felidae.

Felids show remarkable phenotypic similarities and are conservative in behavioral and ecological traits. In contrast, they display a large range in body mass from around 1kg to more than 300kg. Body size and locomotory specializations correlate to skull, limb and vertebral skeleton morphology. With an increase in body mass, felids prey selection switches from small to large, from using a rapid skull or spine lethal bite for small prey, to sustained suffocating bite for large prey. Dietary specialization correlates to skull and front limbs morphology but no correlation was found on the spine or on the hind limb. The morphology of the sacroiliac junction in relation to ecological factors remained to be described. We are presenting a study of the overall shape of the iliac auricular surface with qualitative and quantitative analyses of its morphology. Our results demonstrate that body mass, prey selection, and bite type, crucially influence the auricular surface, where no significant effect of locomotor specialization was found. The outline of the surface is significantly more elevated dorso-caudally and the joint surface shows an irregular W-shape topography in big cats whereas the surface in small cats is smoother with a C-shape topography and less of an elevated ridge. Biomechanically, we suggest that a complex auricular surface increases joint stiffness and provides more support in heavier cats, an advantage for subduing big prey successfully during a sustained bite.

Frequency of anatomical variation of the sacroiliac joint in asymptomatic young adults and its relationship with sacroiliac joint degeneration.

INTRODUCTION: To evaluate the variations of the sacroiliac joint (SIJ) in asymptomatic young adults and their relationship to SIJ degeneration. MATERIALS AND METHODS: A total of 860 SIJs were retrospectively evaluated in 430 abdominal computed tomographies (CT) of abdominal pain cases. The study population consisted of 430 patients (176 female, 254 male) aged 20-45 years with abdominal pain. The anatomical variations of the SIJ were classified as (1) accessory sacroiliac joint, (2) iliosacral complex, (3) bipartite iliac bony plate, (4) semicircular defects, (5) crescent-like iliac bony plate, and (6) ossification center. The CT findings of SIJ degeneration included joint space narrowing, sclerosis, subcortical cysts, vacuum phenomenon, and osteophytes. Chi-square and cross tabulation tests were used for statistical analysis. RESULTS: The iliosacral complex was the most common (bilateral) anatomical variation (7.7%, n = 66). A total of 71 SIJ degenerations were detected in cases with anatomical variations. They were determined in 22 (2.6%) iliosacral complex, 19 (2.2%) bipartite iliac bony plate, 15 (1.7%) accessory sacroiliac joint, 6 (0.7%) semicircular defect, 5 (0.6%) crescent-like iliac bony plate, and 4 (0.5%) ossification center cases. CONCLUSION: We found that iliosacral complex was the most common SIJ variation in asymptomatic young adults and also that there was significantly more SIJ degeneration among subjects with anatomical variations of the SIJ than those without. SIJ degeneration was most common in subjects with the iliosacral complex variation.

Posture correctness of young female soccer players.

The objectives of the study were to evaluate the correctness of the body posture of female soccer players in the frontal plane from the back based on selected body points in two static positions (habitual and actively corrected) using a non-contact optical measurement method. Forty-two young women (aged 16-20) playing soccer in a sports club in Poland were examined and compared with controls. The spatial coordinates (x, y, z) of the selected body points were determined. Four points (OcL, OcR, PvL and PvR) were extracted and used to calculate vectors [Formula: see text] and [Formula: see text] for analysis. The results show that median of the pelvic line angle was positive (PvR was lower than PvL) in both groups. For the habitual posture, the absolute value of the difference between the 25th and 75th percentiles in the pelvic line was almost three times greater among the soccer players than the controls (ratio between soccer players and controls: 2.93). Static postural imbalances in female soccer players require diagnosis of the sacroiliac joints with analysis of lumbar-pelvic system support and inhibition in the context of myofascial connection integration. Exercises can be implemented to stabilize the lumbar-pelvis complex as prophylaxis for spinal overload during the training cycle.

A Systematic Review of the Normal Sacroiliac Joint Anatomy and Adjacent Tissues for Pain Physicians.

BACKGROUND: The sacroiliac joint (SIJ) forms a complex joint and has shown to be underappreciated in its involvement with lower back pain. Research efforts have intensified on SIJ anatomy and biomechanics because of its predisposing position to pain and dysfunction in individuals suffering from lower back discomfort. Previous work has focused on SIJ anatomy including bone and joint structure, innervation, as well as biomechanics and the treatment of SIJ pain. However, to date, no review exists describing the range of 'normal' anatomic features of the SIJ. OBJECTIVES: To describe the normal appearance of the SIJ and adjacent tissues, as opposed to 'abnormal' conditions involving SIJ morphology. It will also identify key areas that require further study because of lacking information or disagreement. STUDY DESIGN: A systematic literature review. SETTING: The research took place at the University of Otago, New Zealand. All published research on 'normal SIJ anatomy' available from MEDLINE, OVID, Scopus, Web of Science, PubMed, and Science Direct were included, available until December 2018, in English, French, and German. Subject areas included bony landmarks, joint type, bone morphology, ligamentous attachments, muscular and fascial relationships, blood supply, fatty infiltration, and morphologic variation. METHODS: Articles met the selection criteria if they contained specific information on SIJ anatomy, including bone morphology and architecture, ligaments, muscle attachments, innervation, vasculature, and the presence of fat. Biomechanics and kinematics related keywords were used as the literature often couples these with the anatomy. Keywords of individual articles were named as 'structures of interest.' RESULTS: A total of 88 primary and 101 secondary articles were identified in the time frame from 1851 to 2018. Primary articles provided quantitative data and detailed anatomic descriptions. Secondary articles did not focus specifically on the anatomy of the SIJ. Although research appeared to be in general agreement on bony landmarks, joint type, myofascial attachments, vasculature, and innervation of the SIJ, there was only part consensus on ligament attachments and cartilage structure. Information regarding bone density of the articulating surfaces of the SIJ is lacking. Despite its potential clinical significance, fatty infiltration within the joint lacks research to date. LIMITATIONS: Only the given databases were used for the initial search. Keyword combinations used for this review may not have been inclusive of all articles relevant to the SIJ. Work in languages other than the ones listed or work that is not available via the internet may be missing. CONCLUSIONS: This study provides an overview of normal SIJ structures, including all neuromusculoskeletal elements related to the joint. There is a lack of knowledge on the SIJ ligaments warranting further investigation. Furthermore, there are discrepancies in relation to the nomenclature, layers, attachment sites, and on the topographical relationships between ligamentous tissues and nerves. Subsequent studies on the quantification of fat and bone density in the SIJ have been suggested. These could be useful radiologic parameters to assess the condition of the joint clinically. This review may provide insight into the clinical signs and abnormal biomechanical features of the joint for the purposes of treating SIJ pain. KEY WORDS: Bone density, bony landmarks, fat infiltration, innervation, ligaments morphology, muscles, sacroiliac joint, vasculature.

Are we overcalling sacroiliitis on MRI? Differential diagnosis that every rheumatologist should know - Part I.

Diagnosing early spondyloarthritis remains a challenge in routine practice, especially in its axial (SpA) form. Magnetic resonance imaging (MRI) is capable of detecting early bone marrow edema (BME) in the sacroiliac joints (SIJs), a key criterion for the diagnosis of active SpA according to the "imaging arm" of the Assessment of Spondyloarthritis International Society (ASAS) classification. However, despite MRI having superior reliability compared to radiographs and being recognized as a crucial imaging biomarker of SpA, it has several limitations, including its limited specificity and sensitivity. Based on the established literature, there is currently an "overcall" of sacroiliitis on MRIs. In this setting, differential diagnoses and their imaging features come into play. In this two-part article, we will review both the imaging features that constitute a "positive" MRI in SpA and the most common differential diagnoses. In order to understand the pathophysiology of sacroiliitis and the spectrum of developing lesions, one needs to be familiar with the complex SIJs anatomy, both on radiographs and on cross-sectional imaging studies (particularly MRI). As such, in the first part of this article, we provide a brief background on anatomy and different imaging modalities used in this clinical setting and we review the imaging criteria for a "positive" MRI study of sacroiliitis in adults (imaging arm of the ASAS classification).

Are We Overcalling Sacroillitis on MRI? Differential diagnosis that every rheumatologist should know - Part II.

In the second part of this review article we will describe the imaging features of non- spondyloarthritis (SpA) pathologies that may mimic sacroiliitis on Magnetic Resonance Imaging (MRI), and that readers should be aware (part 2). Based on the established literature, there is currently an "overcall" of sacroiliitis on MRIs. In this setting, differential diagnoses and their imaging features come into play. In fact, non-SpA related sacroiliac joints (SIJs) pathologies are more commonly found than true sacroiliitis on MRI of the SIJs, even in patients with inflammatory type back pain. An imaging literature review, highlighting "easy-to-use" learning points regarding MRI interpretations in patients with suspected sacroiliitis and/or nonspecific lumbar back pain is presented. This two-part article aims to be a snapshot of the most common inflammatory versus non-inflammatory entities found on SIJs imaging studies in routine practice, while trying to keep this review article simple, educational and above all, practical.

Sacroiliac joint morphologic changes from infancy to adulthood.

BACKGROUND CONTEXT: Report of sacroiliac morphology changes during growth is limited in the literature and the interest of such morphology and its consequence for surgery is increasing. PURPOSE: Aims of this work are (1) to anatomically define the sacroiliac joint (SIJ), and (2) to assess the influence of growth on the sacroiliac morphology and the pelvic parameters. STUDY DESIGN: Forty-nine young subjects from 6 months to 18 years old (y/o) and 20 adults aged from 18 to 50 y/o were selected from our institutional patient database. METHODS: They underwent a computed tomography (CT) examination on a 128-MDCT (GE Healthcare Optima CT660). Transverse CT image datasets were reconstructed, anonymized, and segmented with ITK-SNAP. Landmarks and surfaces were selected and a SIJ orientation analysis was performed using costumed Python scripts. RESULTS: The subjects were divided into four groups: infants (1.9±1 y/o), children (6.9±1.7 y/o), adolescents (13.7±1.8 y/o), and adults (27.3±5.6 y/o). Differences between SIJ orientation were found significant between young subject groups for synovial sacrum SIJ orientation (p<.001) and iliac total SIJ orientation (p=.036). Both orientations of younger subjects were found significantly different from the adult group (p<.035). SIJ synovial sacrum and iliac total orientations correlated significantly with age (p<.03). All orientations correlated with pelvic incidence (p<.04) except for synovial sacrum SIJ orientation (p=.2). No gender or symmetrical differences were found significant in any group. CONCLUSIONS: Morphologic definition of the SIJ confirmed the independency of the gender during growth. Such results will be beneficial for the analysis and management of vertebral pathology.

Joint coordinate system for biomechanical analysis of the sacroiliac joint.

Sacroiliac joint (SIJ) biomechanics have been described in both in vitro and in vivo studies. A standard for joint coordinate systems has been created by the International Society of Biomechanics for most of the joints in the human body. However, a standardized joint coordinate system for sacroiliac joint motion analysis is currently still lacking. This impedes the comparison across studies and hinders communication among scientists and clinicians. As SIJ motion is reported to be quite limited, a proper standardization and reproducibility of this procedure is essential for the interpretation of future biomechanical SIJ studies. This paper proposes a joint coordinate system for the analysis of sacroiliac joint motion, based on the procedure developed by Grood and Suntay, using semi-automated anatomical landmarks on 3D joint surfaces. This coordinate system offers high inter-rater reliability and aspires to a more intuitive representation of biomechanical data, as it is aligned with SIJ articular surfaces. This study aims to encourage further reflection and debate on biomechanical data representation, in order to facilitate interpretation of SIJ biomechanics and improve communication between researchers and clinicians. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res.

The sacro-iliac joint: A potentially painful enigma. Update on the diagnosis and treatment of pain from micro-trauma.

The sacro-iliac joint (SIJ) located at the transition between the spine and the lower limbs is subjected to major shear forces. Mobility at the SIJ is very limited but increases during pregnancy and the post-partum period. Familiarity with the anatomy and physiology of the SIJ is important. The SIJ is a diarthrodial joint that connects two variably undulating cartilage surfaces, contains synovial fluid, and is enclosed within a capsule strengthened by several ligaments. This lecture does not discuss rheumatic or inflammatory diseases of the SIJ, whose diagnosis relies on imaging studies and blood tests. Instead, it focuses on micro-traumatic lesions. Micro-trauma causes chronic SIJ pain, which must be differentiated from hip pain and spinal pain. The diagnosis rests on specific clinical provocation tests combined with a local injection of anaesthetic. Findings are normal from radiographs and magnetic resonance imaging. Non-operative treatment with exercise therapy and stretching aims primarily to strengthen the latissimus dorsi, gluteus, and hamstring muscles to increase SIJ coaptation. Other physical treatments have not been proven effective. Radiofrequency denervation of the dorsal sensory rami has shown some measure of efficacy, although the effects tend to wane over time. Patients with refractory pain may benefit from minimally invasive SIJ fusion by trans-articular implantation of screws or plugs, which has provided good success rates.

Physiological in vitro sacroiliac joint motion: a study on three-dimensional posterior pelvic ring kinematics.

The sacroiliac joint (SIJ) is a well-known source of low back and pelvic pain, of increasing interest for both conservative and surgical treatment. Alterations in the kinematics of the pelvis have been hypothesized as a major cause of SIJ-related pain. However, definitions of both the range and the extent of physiological movement are controversial, and there are no clear baseline data for pathological alterations. The present study combined a novel biomechanical setup allowing for physiological motion of the lumbosacral transition and pelvis without restricting the SIJ movement in vitro, combined with optical image correlation. Six fresh human pelvises (81 ± 10 years, three females, three males) were tested, with bodyweight-adapted loading applied to the fifth lumbar vertebra and both acetabula. Deformation at the lumbopelvises was determined computationally from three-dimensional image correlation data. Sacroiliac joint motion under the loading of 100% bodyweight primarily consisted of a z-axis rotation (0.16°) and an inferior translation of the sacrum relative to the ilium (0.32 mm). Sacroiliac joint flexion-extension rotations were minute (< 0.02°). Corresponding movements of the SIJ were found at the lumbosacral transition, with an anterior translation of L5 relative to the sacrum of -0.97 mm and an inferior translation of 0.11 mm, respectively. Moreover, a flexion of 1.82° was observed at the lumbosacral transition. Within the innominate bone and at the pubic symphysis, small complementary rotations were seen around a vertical axis, accounting for -0.10° and 0.11°, respectively. Other motions were minute and accompanied by large interindividual variation. The present study provides evidence of different SIJ motions than reported previously when exerted by physiological loading. Sacroiliac joint kinematics were in the sub-degree and sub-millimeter range, in line with previous in vivo and in vitro findings, largely limited to the sagittal rotation and an inferior translation of the sacrum relative to the ilium. This given physiological loading scenario underlines the relevance of the lumbosacral transition when considering the overall motion of the lumbopelvis, and how relatively little the other segments contribute to overall motion.