Ligament-induced sacral fractures of the pelvis are possible

Sacrospinous and sacrotuberous ligaments influence in pelvis kinematics

The alteration in mechanical properties of posterior pelvis ligaments may cause a biased pelvis deformation which, in turn, may contribute to hip and spine instability and malfunction. Here, the effect of different mechanical properties of ligaments on lumbopelvic deformation is analyzed via the finite element method. First, the improved finite element model was validated using experimental data from previous studies and then used to calculate the sensitivity of lumbopelvic deformation to changes in ligament mechanical properties, load magnitude, and unilateral ligament resection. The deformation of the lumbopelvic complex relative to a given load was predominant in the medial plane. The effect of unilateral resection on deformation appeared to be counterintuitive, suggesting that ligaments have the ability to redistribute load and that they play an important role in the mechanics of the lumbopelvic complex.

Quantitative evaluation of the sacroiliac joint fixation in stress reduction on both sacroiliac joint cartilage and ligaments: A finite element analysis

BACKGROUND

The sacroiliac joint fixation is the last resort for patients with prolonged and severe joint pain. Although the clinical results of anterior fixations are conclusive, there exist several inevitable drawbacks with the surgical method such as the difficulty performing the surgery due to the presence of many organs. The posterior fixation technique has thus been developed to overcome those inconveniences. This study aims to assess in silico the mechanical environment following posterior and anterior fixations, focusing on stresses in both the sacroiliac cartilage and dorsal ligamentous part, as well as loads experienced by the pelvic ligaments.

METHODS

Sacroiliac joint cartilage, dorsal ligamentous part stresses and pelvic ligaments loads were evaluated with three types of fixation models. A vertical load of 600 N was applied, equally distributed via both acetabula when standing and sitting.

FINDINGS

Results show that the anterior sacroiliac joint fixation reduced von Mises stresses in the cartilage and dorsal ligamentous part and decreased ligaments loads more extensively than the posterior fixation when compared to the untreated model as a reference. However, the posterior fixation still remains the desirable and preferential treatment.

INTERPRETATION

The anterior sacroiliac joint fixation showed better performances compared to the posterior one; however, the lower invasive aspect of the latter is a fundamental clinical advantage which also has the possibility to be improved by considering various screws and cages configurations. This study provides a beneficial suggestion to improve the current fixation technique.

A comparison on the detection accuracy of ante mortem computed tomography vs. autopsy for the diagnosis of pelvic ring injury in legal medicine

A detailed knowledge on the exact morphology of pelvic injuries provided crucial information in understanding the mechanisms of injury and has influence on the natural course and subsequent mortality. However, forensic medical literature investigating pelvic fractures in detail is scarce to date. This case series aims to compare the accuracy in detecting pelvic injuries using autopsy and ante mortem computed tomography (CT). Nineteen deceased patients with CT scans of pelvic fractures were included retrospectively. Pelvic injuries were independently assessed by a board-certified radiologist (R) and a board-certified trauma surgeon (T), both using the ante mortem CT scans, and by a board-certified forensic pathologist using autopsy (A) results without knowledge of the CT scan findings. No patient had died causatively from a pelvic fracture. Most injuries of the pelvis were present in the pubic rami (16/18) and sacral bone (13/18), followed by the sacroiliac joint (9/18) and iliac bone fractures (8/18). Ilium fractures (A:100%;R:67%;T:67%) and injuries of the sacroiliac joint (A:83%;R:50%;T:42%) were best detected via autopsy. The diagnosis of sacral fractures (A:19%;R:94%;T:88%) and fractures of the pubic rami (A:67%;R:96%;T:96%) were most often missed in autopsy. The results show deficits in the assessment of the pelvic injury for both CT and autopsy. Autopsy was superior in detecting injuries of the sacroiliac joint, but inferior in detecting sacral and pubic bone fractures. For an encompassing evaluation of ligamento-skeletal pelvic injuries, the complementary use of both CT and autopsy is recommended.

In Silico Pelvis and Sacroiliac Joint Motion: Refining a Model of the Human Osteoligamentous Pelvis for Assessing Physiological Load Deformation Using an Inverted Validation Approach

Introduction. Computational modeling of the human pelvis using the finite elements (FE) method has become increasingly important to understand the mechanisms of load distribution under both healthy and pathologically altered conditions and to develop and assess novel treatment strategies. The number of accurate and validated FE models is however small, and given models fail resembling the physiologic joint motion in particular of the sacroiliac joint. This study is aimed at using an inverted validation approach, using in vitro load deformation data to refine an existing FE model under the same mode of load application and to parametrically assess the influence of altered morphology and mechanical data on the kinematics of the model. Materials and Methods. An osteoligamentous FE model of the pelvis including the fifth lumbar vertebra was used, with highly accurate representations of ligament orientations. Material properties were altered parametrically for bone, cartilage, and ligaments, followed by changes in bone geometry (solid versus 3 and 2 mm shell) and material models (linear elastic, viscoelastic, and hyperelastic isotropic), and the effects of varying ligament fiber orientations were assessed. Results. Elastic modulus changes were more decisive in both linear elastic and viscoelastic bone, cartilage, and ligaments models, especially if shell geometries were used for the pelvic bones. Viscoelastic material properties gave more realistic results. Surprisingly little change was observed as a consequence of altering SIJ ligament orientations. Validation with in vitro experiments using cadavers showed close correlations for movements especially for 3 mm shell viscoelastic model. Discussion. This study has used an inverted validation approach to refine an existing FE model, to give realistic and accurate load deformation data of the osteoligamentous pelvis and showed which variation in the outcomes of the models are attributed to altered material properties and models. The given approach furthermore shows the value of accurate validation and of using the validation data to fine tune FE models.

In-silico pelvis and sacroiliac joint motion-A review on published research using numerical analyses

BACKGROUND

Computational models of the human pelvis have become highly useful tools to assess mechanisms of injury, diagnostics and treatment options. The purpose of this systematic literature review was to summarize existing pelvic computer models, to assess their comparability and the measures taken for experimental validation.

METHODS

Research on virtual simulations of the posterior pelvis and sacroiliac joint available from the ISI Web of Knowledge, PubMed and Scopus databases available until January 2018 were included.

FINDINGS

From a total of 3938 articles, 33 studies matched the criteria. Thirteen studies reported on experimental biomechanics, of which seven were parametric. Thirteen studies focused on pelvic injury and surgery, three were clinical case reports. One study assessed the effects of lumbar surgery on the sacroiliac joint, three studies on diagnostics and the non-surgical treatment of the sacroiliac joint. The mode of load application, geometry, material laws and boundary conditions varied vastly between the studies. The majority excluded the lumbosacral transition as part of pelvic biomechanics, and used isotropic linear elastic material properties. Outcomes of the analyses were reported inconsistently with negative impact on their comparability, and validation was commonly conducted by literature with varying agreement of the loading conditions.

INTERPRETATION

Comparability and validation are two major issues of present computational biomechanics of the pelvis. These issues diminish the transferability of the in-silico findings into real-life scenarios. In-vitro cadaveric models remain the realistic standard to account for the present computational analyses which simplify the complex nature of musculoskeletal tissues of the pelvis.

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.

Pelvic orthosis effects on posterior pelvis kinematics An in-vitro biomechanical study

The sacroiliac joint (SIJ) is a well-known source of low back pain, with increasing interest for both conservative and surgical treatment. Alterations in pelvis kinematics are hypothesized as a contributor to SIJ pain and pelvic orthoses one treatment option, but their effects on the pelvis are poorly understood. Alterations in movement patterns induced by the application of pelvic orthoses were determined in five human cadaveric pelvises. Deformations were obtained from the lumbosacral transition and the bilateral SIJ, using digital image correlation and a customized routine to compute the movements within the pelvis. Significant alterations were found for the movements at the SIJ, in particular a vast increase in axial (x-axis) rotation, accompanied by increased inferior (y-) translation of the sacrum relative to the ilium. Movement patterns at the lumbosacral transition changed, causing increases in axial rotation and decreased inferior translation of L5 relative to S1. Using a physiologic mode of load application gives novel insights into the potential effects of pelvic orthoses. The results of these in-vitro experiments vary markedly from previous experiments with loading limited to two or less axes. Furthermore, the influence of pelvic orthoses on the lumbosacral transition warrants further investigation.

Effects of Cutting the Sacrospinous and Sacrotuberous Ligaments

The sacrospinous (SS) and sacrotuberous (ST) ligaments form a complex at the posterior pelvis, with an assumed role as functional stabilizers. Experimental and clinical research has yielded controversial results regarding their function, both proving and disproving their role as pelvic stabilizers. These findings have implications for strategies for treating pelvic injury and pain syndromes. The aim of the present simulation study was to assess the influence of altered ligament function on pelvis motion. A finite elements computer model was used. The two-leg stance was simulated, with the load of body weight applied via the fifth lumbar vertebra and both femora, allowing for nutation of the sacroiliac joint. The in-silico kinematics were validated with in-vitro experiments using the same scenario of load application following SS and ST transection in six human cadavers. Modeling of partial or complete ligament failure caused significant increases in pelvis motion. This effect was most pronounced if the SS and ST were affected with 164% and 182%, followed by the sacroiliac and iliolumbar ligaments with 123% and 147%, and the pubic ligaments with 113% and 119%, for partial and complete disruption, respectively. Simultaneous ligament transection multiplied the effects on pelvis motion by up to 490%. Unilateral ligament injury altered the motion at the pelvis contralaterally. The experiments presented here provide strong evidence for the stabilizing role of the SS and ST. A fortiori, the instability resulting from partial or complete SS and ST injury merits consideration in treatment strategies involving these ligaments as important stabilizers. Clin. Anat. 32:231-237, 2019. © 2018 Wiley Periodicals, Inc.

Symphyseal fixation in open book injuries cannot fully compensate anterior SI joint injury-A biomechanical study in a two-leg alternating load model

INTRODUCTION

In open book injuries type Tile B1.1 or B1.2 also classified as APC II (anteroposterior compression), it remains controversial, if a fixation of the anterior ring provides sufficient stability or a fixation of the posterior ring should be included. Therefore the relative motion at the sacroiliac joint was quantified in a two-leg alternating load biomechanical pelvis model in the intact, the injured and the restored pelvis.

METHODS

Fresh-frozen intact (I) pelvises (n = 6) were subjected to a non-destructive cyclic test under sinosuidal axial two-leg alternating load with progressively increasing amplitude. Afterwards an open book injury (J) including the anterior ligament complex of the left sacroiliac joint, the sacrospinal and sacrotuberal ligaments (Tile B1.1) was created and the specimens were retested. Finally, the symphysis was stabilized with a modular fixation system (1-, 2- or 4-rod configuration) (R) and specimens were cyclically retested. Relative motion at the sacroiliac joint was captured at both sacroiliac joints by motion tracking system at two load levels of 170 N and 340 N during all tests.

RESULTS

Relative sacroiliac joint movements at both load levels were significantly higher in the J-state compared to the I-state, excluding superoinferior translational movement. With exception of the anteroposterior translational movement at 340N, the relative sacroiliac joint movements after each of the three reconstructions (1-, 2-, 4-rod fixation) were significantly smaller compared to the J-state and did not differ significantly to the I-state, but stayed above the values of the latter. Relative movements did not differ significantly in a direct comparison between the 1-rod, 2-rod and 4-rod fixations.

CONCLUSION

Symphyseal locked plating significantly reduces relative movement of the sacroiliac joint in open book injuries type Tile B1.1 or B1.2 (APC II) but cannot fully restore the situation of the intact sacroiliac joint.

The extent of ligament injury and its influence on pelvic stability following type II anteroposterior compression pelvic injuries--A computer study to gain insight into open book trauma

Surgical stabilization of the pelvis following type II anteroposterior compression pelvic injuries (APCII) is based on the assumption that the anterior sacroiliac, sacrospinous, and sacrotuberous ligaments disrupt simultaneously. Recent data on the ligaments contradict this concept. We aimed at determining the mechanisms of ligament failure in APCII computationally. In an individual osteoligamentous computer model of the pelvis, ligament load, and strain were observed for the two-leg stance, APCII with 100-mm symphyseal widening and for two-leg stance with APCII-related ligament failure, and validated with body donors. The anterior sacroiliac and sacrotuberous ligaments had the greatest load with 80% and 17% of the total load, respectively. APCII causes partial failure of the anterior sacroiliac ligament and the pelvis to become horizontally instable. The other ligaments remained intact. The sacrospinous ligament was negligibly loaded but stabilized the pelvis vertically. The interosseous sacroiliac and sacrotuberous ligaments are likely responsible for reducing the symphysis and might serve as an indicator of vertical stability. The sacrospinous ligament appears to be of minor significance in APCII but plays an important role in vertical stabilization. Further research is necessary to determine the influence of alterations in ligament and bone material properties.