Leaflet Mechanical Stress in Different Designs and Generations of Transcatheter Aortic Valves: An in Vitro Study.

Background: It is unknown whether bioprostheses used for transcatheter aortic valve implantation will have similar long-term durability as those used for surgical aortic valve replacement. Repetitive mechanical stress applied to the valve leaflets, particularly during diastole, is the main determinant of structural valve deterioration. Leaflet mechanical stress cannot be measured in vivo. The objective of this in vitro/in silico study was thus to compare the magnitude and regional distribution of leaflet mechanical stress in old vs new generations of self-expanding (SE) vs balloon expandable (BE) transcatheter heart valves (THVs). Methods: A double activation simulator was used for in vitro testing of two generations of SE THV (Medtronic CoreValve 26 mm and EVOLUT PRO 26 mm) and two generations of BE THV (Edwards SAPIEN 23 mm vs SAPIEN-3 23 mm). These THVs were implanted within a 21-mm aortic annulus. A noncontact system based on stereophotogammetry and digital image correlation with high spatial and temporal resolution (2000 img/sec) was used to visualize the valve leaflet motion and perform the three-dimensional analysis. A finite element model of the valve was developed, and the leaflet deformation obtained from the digital image correlation analysis was applied to the finite element model to calculate local leaflet mechanical stress during diastole. Results: The maximum von Mises leaflet stress was higher in early vs new THV generation (p < 0.05) and in BE vs SE THV (p < 0.05): early generation BE: 2.48 vs SE: 1.40 MPa; new generation BE: 1.68 vs SE: 1.07 MPa. For both types of THV, the highest values of leaflet stress were primarily observed in the upper leaflet edge near the commissures and to a lesser extent in the mid-portion of the leaflet body, which is the area where structural leaflet deterioration most often occurs in vivo. Conclusions: The results of this in vitro/in silico study suggest that: i) Newer generations of THVs have ∼30% lower leaflet mechanical stress than the early generations; ii) For a given generation, SE THVs have lower leaflet mechanical stress than BE THVs. Further studies are needed to determine if these differences between new vs early THV generations and between SE vs BE THVs will translate into significant differences in long-term valve durability in vivo.

Head injury: Importance of the deep brain nuclei in force transmission to the brain.

Finite element modeling provides a digital representation of the human body. It is currently the most pertinent method to study the mechanisms of head injury, and is becoming a scientific reference in forensic expert reports. Improved biofidelity is a recurrent aim of research studies in biomechanics in order to improve earlier models whose mechanical properties conformed to simplified elastic behavior and mechanic laws. We aimed to study force transmission to the brain following impacts to the head, using a finite element head model with increased biofidelity. To the model developed by the Laboratory of Applied Biomechanics of Marseille, we added new brain structures (thalamus, central gray nuclei and ventricular systems) as well as three tracts involved in the symptoms of head injury: the corpus callosum, uncinate tracts and corticospinal tracts. Three head impact scenarios were simulated: an uppercut with the prior model and an uppercut with the improved model in order to compare the two models, and a lateral impact with an impact velocity of 6.5 m/s in the improved model. In these conditions, in uppercuts the maximum stress values did not exceed the injury risk threshold. On the other hand, the deep gray matter (thalamus and central gray nuclei) was the region at highest risk of injury during lateral impacts. Even if injury to the deep gray matter is not immediately life-threatening, it could explain the chronic disabling symptoms of even low-intensity head injury.

Mandibular Titanium Miniplates Change the Biomechanical Behaviour of the Mandible in the Case of Facial Trauma: A Three-Dimensional Finite Element Analysis.

Our study aimed to compare the biomechanical behaviour of mandibles with or without titanium miniplates when subjected to an impact after bone healing using a finite element model (FEM) of the human mandible. We simulated mandibular trauma on an FEM of a human mandible carrying or not two parasymphyseal miniplates and applying a concentrated force of 2000 N to four different areas, including the insertion area, the area straddling the edge of the miniplates and the adjacent bone, at a distance from the miniplates on the symphysis, and on the basilar border of the mandible below the miniplates. Then, we compared the Von Mises stress distributions between the two models. In the case of an impact on the miniplates, the maximum Von Mises stress occurred in two specific areas, on the cortical bone at the posterior border of the two miniplates at a distance from the impact, while in the model without miniplates, the Von Mises stresses were homogenously distributed in the impact area. The presence of titanium miniplates in the case of trauma affects the biomechanical behaviour of the mandible and could cause more complex fractures. We recommend informing patients of this potential risk.

The impact of femoral rotation on sacroiliac articulation during pregnancy. Is there evidence to support Farabeuf's hypothesis by finite element modelization?

BACKGROUND: Counter-nutation movement is deemed crucial during the management of the birth process. It is a combination of lateral ilia expansion and backward displacement of the promontory resulting from the external rotations of the femurs producing an enlargement of the pelvic inlet. However, since its description by Farabeuf, this mechanism has never been challenged and analyzed in a dynamic finite element study. METHODS: Based on a female pelvic mesh and sacroiliac ligaments, we simulated external rotations of both femurs with imposed rotation of the two acetabulum centers. We hypothesize that lateral ilia expansion generates a sacrum movement resulting in a backward displacement of the promontory and a pelvic inlet enlargement. RESULTS: Finite element simulation confirms our hypothesis and reveals that ilio-sacro-transverse and axile ligaments play an essential role in this mechanism. Indeed, the increase in stiffness (ranging from 500 MPa to 750 MPa) of these ligaments accentuates the counter-nutation movement and the opening of the inlet. Instead of the anatomic congruence between the ilium and the sacrum, the sacroiliac ligaments may explain the counter-nutation. After a 6° of femur rotation, the inlet area increases to 11 cm2 (141 cm2 vs. 130 cm2). This enlargement could be noteworthy in case of obstructed labor or shoulder dystocia. Moreover, the association between external rotation and flexion of the femurs could be more efficient for opening the pelvic inlet. CONCLUSIONS: Our result did not support the original assumption of Farabeuf. By revealing how postural adjustment increases the bony birth canal, this study provides essential information for the clinical management of the delivery.

Dynamic finite-element simulations reveal early origin of complex human birth pattern.

Human infants are born neurologically immature, potentially owing to conflicting selection pressures between bipedal locomotion and encephalization as suggested by the obstetrical dilemma hypothesis. Australopithecines are ideal for investigating this trade-off, having a bipedally adapted pelvis, yet relatively small brains. Our finite-element birth simulations indicate that rotational birth cannot be inferred from bony morphology alone. Based on a range of pelvic reconstructions and fetal head sizes, our simulations further imply that australopithecines, like humans, gave birth to immature, secondary altricial newborns with head sizes smaller than those predicted for non-human primates of the same body size especially when soft tissue thickness is adequately approximated. We conclude that australopithecines required cooperative breeding to care for their secondary altricial infants. These prerequisites for advanced cognitive development therefore seem to have been corollary to skeletal adaptations for bipedal locomotion that preceded the appearance of the genus Homo and the increase in encephalization.

Management of the pediatric OSAS: what about simultaneously expand the maxilla and advance the mandible? A retrospective non-randomized controlled cohort study.

OBJECTIVE/BACKGROUND: This retrospective non-randomized controlled cohort study aimed to evaluate the efficiency of simultaneous maxillary expansion and mandibular advancement for the management of pediatric OSAS. PATIENTS/METHODS: The sample was composed of 94 children treated with an innovative orthopedic device to correct a Class II malocclusion associated with an OSAS. Polysomnographic recordings were performed before and after the treatment. We also included a group of 113 age-matched control patients who had the same pathologies, but who did not receive the orthopedic treatment at the time they undergone polysomnographic exams. Statistical tests evaluated the significance of the evolution of these data, both in treated and untreated control patients. RESULTS: After nine months (±3 months) of treatment, respiratory OSAS symptoms significantly improved: the AHI significantly decreased as it became inferior to the pathological threshold (<1) for 53% of the treated patients' sample, with a greater proportion within the youngest age group (63%). Only two patients still presented a moderate OSAS after treatment, with an AHI slightly superior to 5. This positive evolution of OSAS respiratory symptoms was not observed within the control group, highlighting the real impact of the orthopedic treatment over the children's natural growth. However, sleep remained fragmented following the treatment. CONCLUSIONS: This study confirmed that simultaneous maxillary expansion and mandibular advancement induced a modification of the maxilla-mandibular anatomy, helping in the significant improvement of the respiratory OSAS symptoms. Then, considering these preliminary results, pediatric OSAS can be managed with this new orthopedic strategy, especially if it is performed early.

Do mandibular titanium miniplates affect the biomechanical behaviour of the mandible? A preliminary experimental study.

INTRODUCTION: Whether to conserve or remove titanium miniplates after rigid internal fixation of mandibular fractures still remains controversial. Miniplates could affect the biomechanical behaviour of the mandible in case of trauma, and therefore cause more complex fractures. MATERIALS AND METHODS: An experimental study, consisting in simulating a mandibular trauma, was designed in order to compare the fractures caused by an impact on the mandible in the presence or absence of an internal fixation. We simulated an impact on the right parasymphysis region in 10 post-mortem human subjects, according to the Charpy impact test method at an impact speed of 7.4 m/s, using a 5 kg test impactor. RESULTS: In the control group, the fracture lines were vertical and straight, without comminution. In the miniplate group, the fractures occurred close to the miniplates (4 cases) and under the miniplates (one case). The fracture lines were more complex, even comminuted in 2 cases. Thus, miniplates impacted the biomechanical behavior of the mandible, resulting in more complex fractures. CONCLUSION: Our experimental study highlighted the impact of the presence of miniplates on the mandible in case of trauma, and the risk of causing more complex fractures. We therefore recommend further investigations to determine if titanium miniplates should be systematically removed after bone healing, in patients with a higher risk of trauma in relation with previous assault injuries, alcohol or substance abuse, the practice of fighting or contact sport/activities, and soldiers.

Leaflet stress quantification of porcine vs bovine surgical bioprostheses: an in vitro study.

Calcified aortic stenoses are among the most prevalent form of cardiovascular diseases in the industrialized countries. This progressive disease, with no effective medical therapy, ultimately requires aortic valve replacement - either a surgical or very recently transcatheter aortic valve implantation. Increase leaflet mechanical stress is one of the main determinants of the structural deterioration of bioprosthetic aortic valves. We applied a coupled in vitro/in silico method to compare the timing, magnitude, and regional distribution of leaflet mechanical stress in porcine versus pericardial bioprostheses (Mosaic and Trifecta). A double activation simulator was used for in vitro testing of a bioprosthesis with externally mounted pericardium (Abbott, Trifecta) and a bioprosthesis with internally mounted porcine valve (Medtronic, Mosaic). A non-contact system based on stereophotogammetry and digital image correlation (DIC) with high spatial and temporal resolution (2000 img/s) was used to visualize the valve leaflet motion and perform the three-dimensional analysis. A finite element model of the valve was developed, and the leaflet deformation obtained from the DIC analysis was applied to the finite element model calculate local leaflet mechanical stress throughout the cardiac cycle. The maximum leaflet stress was higher with the pericardial versus the porcine bioprosthesis (2.03 vs. 1.30 MPa) For both bioprostheses the highest values of leaflet stress occurred during diastole and were primarily observed in the upper leaflet edge near the commissures and to a lesser extent in the mid-portion of the leaflet body. In conclusion, the coupled in vitro/in silico method described in this study shows that the highest levels of leaflet stress occur in the regions of the commissures and mid-portion of the leaflet body. This method may have important insight with regard to bioprosthetic valve durability. Our results suggest that, compared to porcine bioprostheses, those with externally mounted pericardium have higher leaflet mechanical stress, which may translate into shorter durability.

Pelvic and neonatal size correlations in light of evolutionary hypotheses.

OBJECTIVE: This study aimed to analyze the correlations between maternal size, neonatal size, and gestational variables. METHODS: Our sample comprises 131 mother-infant dyads. We investigated correlations between five neonatal traits (gestational age, birthweight, head, suboccipito-brematic, and abdominal girths), three maternal traits (height, BMI, and uterus height), and three pelvic variables (conjugate, inter-spinous diameters, and sub-pubic angle) using computed tomography pelvimetry. RESULTS: We found that the five neonatal traits were significantly intercorrelated. BMI was not correlated with neonatal traits while maternal height was correlated with birthweight, suboccipito-brematic, and abdominal girth. In the multiple regression models, gestational age was correlated with birthweight, head, and abdominal girth. Among the neonatal and pelvimetry correlations, conjugate diameter was slightly correlated with suboccipito-bregmatic girth, but inter-spinous and sub-pubic angle were not correlated with neonatal traits. Uterus height predicted all neonatal variables, but it was not correlated with gestational age. DISCUSSION: Our results suggest that fetal growth is shaped by maternal phenotype rather than external ecological factors. The association of the inlet size with suboccipito-bregmatic girth reflects the tight fit between the neonatal brain and the maternal pelvis dimensions, an adaptation that would reduce the risk of cephalo-pelvic disproportion, while the absence of tight fit at the midplane and outlet could be due to the effect of the pelvic relaxation. Uterus distention is not the only mechanism involved in the initiation of parturition. Birth and pregnancy are complex processes and we suggest that maternal-neonatal associations are the result of a combination of multiple obstetric tradeoffs.

Impact of the Craniofacial Surgery Simulation in Anterior Plagiocephaly on Orbits and Oculomotor Muscles: Biomechanical Analysis With a Finite Element Model.

PURPOSE: The aim of this study was to show the displacements and strain induced by the supraorbital band advancement during a craniofacial surgery for an anterior plagiocephaly on the orbital bones and the orbital content thanks to a numerical surgical simulation using the finite element method. METHODS: A three-dimensional (3D) finite element model of a child with an anterior plagiocephaly was entirely created from a tomodensitometry of a patient followed by our Craniofacial Pediatric team. Data of the tomodensitometry were computed with Slicer 3D to re-create the orbit geometry. Mesh production, properties of the model, and simulations of the fronto-orbital advancement were conducted on Hyperworks software (Altair Engineering, Inc., Detroit, MI, USA). RESULTS: The resulting 3D Finite Element Model was used to perform the supraorbital advancement simulation. Displacement and strain patterns were studied for orbital bones, oculomotor muscles, and eyeballs. Relative high strain in the both trochlear area and excycloration of the right orbit are among the most interesting results as torsional strabismus as V-pattern strabismus are often described in children with an anterior plagiocephaly. CONCLUSIONS: This pediatric Finite-Element Model of both orbits of a child with an anterior plagiocephaly showed the impact of the fronto-orbital advancement on the oculomotor system. This model described the relationship between the craniofacial surgery and the strabismus in the unilateral coronal synostosis. The advantages of this model are the many opportunities for improvement, including postoperative period and additional surgical procedures.

The association of Le Fort midfacial fractures with frontobasal injuries: a 17-year review of 125 cases, reflections on biomechanics, classifications and treatment.

The frequency of midface and frontobasal fractures has increased over the past 40 years despite the improvement and stringent regulation implemented on modern safety equipment (belts, helmets…). This observation might be correlated with the progress of radiodiagnosis tools. Literature was reviewed according to Prisma guidelines. We searched for reviewed articles, published between January 2000 and December 2017, through Medline (Pubmed) online databases and ScienceDirect, using the following MeSH Keywords: "Le Fort classification", "Le Fort fracture", "Frontobasal fracture", "skull base fracture", "Midface Fractures". Among 652 patients with frontobasal fractures, 125 (19.1%) were associated with a Le Fort fracture. 59 (9%) were associated with Le Fort III fracture, 51 (7.8%) with Le Fort II fracture and 15 (2.3%) with Le Fort I fracture. When frontobasal fractures were associated with midfacial fractures, we found 18 cerebrospinal fluid leaks (11.8 %) and 19 cases of meningitis (12.5 %). When only the frontobasal area was involved, there were 6 cerebrospinal fluid leaks (4.3 %) and 6 meningitis (4.3 %). Our results highlight a regular association between Le Fort fractures and frontobasal fractures for stages II and stage III of Le Fort fractures and also found a higher rate of neuro-septic complication. Further research shall investigate treatment and monitoring recommendations fitting modern epidemiology of craniofacial traumatology.

The Hypoplasic Mandible: What Makes it Different From the Healthy Child?

OBJECTIVE: This study aimed to analyze the morphology of the hypoplasic mandible and its evolution during the growth period to better understand how it differs from the pediatric healthy mandible. METHOD: Three-dimensional mandibular models of hypoplasic and healthy children aged from 39 gestational weeks to 7 years old were analyzed with a morphometric method including data clustering. Morphological distinctions between pathological and healthy mandibles were highlighted. Bilateral and unilateral mandibular hypoplasia were distinguished. RESULTS: The study sample was composed of 31 hypoplasic children and as many sex- and age-matched healthy children. Morphological distinctions between pathological and healthy mandibles were highlighted only from the first year of life. In bilateral hypoplasia, the overall mandibular dimensions were reduced while there was only a ramus asymmetry in unilateral mandibular hypoplasia (mean ± SD of the difference between the Grp03c and Grp03b subgroups: 6.80 ± 6.37 - P value = 1.64e-3 for the height of the left ramus versus 0.18 ± 4.18 - P value = .82 for the height of the right ramus). Supervised classification trees were built to identify the pathology and discriminate unilateral from bilateral mandibular hypoplasia (prediction rates = 81% and 84%, respectively). CONCLUSIONS: Based on a morphometric analysis, we demonstrated that mandibular hypoplasia significantly impacts the mandibular morphology only from the first year of life, with a distinction between bilateral and unilateral hypoplasia.

Effects of hemodynamic conditions and valve sizing on leaflet bending stress in self-expanding transcatheter aortic valve: An in vitro study.

Transcatheter aortic valve (TAV) replacement has become a viable alternative to surgery for high and intermediate risk patients with severe aortic stenosis. This technology may extend to the younger and lower risk patients. In this population, long-term durability of the TAV is key. Increased leaflet mechanical stress is one of the main determinants of valve structural deterioration. This in vitro study aims at evaluating leaflet bending stress (LBS) in the self-expanding TAV for different valve sizes, stroke volumes (SV), and degrees of valve oversizing (OS). Three different sizes (23, 26, and 29 mm) of CoreValve (CV) were tested on a pulse duplicator in annulus size ranging from 17 to 26 mm. Leaflet bending stress and bending of the leaflet coaptation line in diastole pinwheeling index (PI) were measured using high-speed camera imaging (1000 images/s). For each given CV and annulus size, geometric orifice area (GOA) increased significantly with OS (P < .001) and SV (P = .001). LBS decreased with increasing prosthesis size and aortic annulus (AA) size while increasing with SV (P < .03). The largest value of peak LBS (3.79 MPa) was obtained with the CV 23 mm in AA of 17 mm (%OS = 35%), SV 90 mL and the smallest value (0.99 MPa) for the CV 29 mm in AA of 26 mm (%OS = 12%), SV 30 mL. On multivariable analysis, LBS increased independently with larger OS, smaller AA size and higher SV. The PI increased with decreasing AA size and increasing OS. Moderate valve OS, such as generally used for transcatheter aortic valve implantation, is associated with increased LBS during valve opening and closing, especially in small annuli. Hence, TAV OS may negatively impact long-term valve durability.

Study of cerebrospinal injuries by force transmission secondary to mandibular impacts using a finite element model.

Brain and cervical injuries are often described after major facial impacts but rarely after low-intensity mandibular impacts. Force transmission to the brain and spinal cord from a mandibular impact such as a punch was evaluated by the creation and validation of a complete finite element model of the head and neck. Anteroposterior uppercut impacts on the jaw were associated with considerable extension and strong stresses at the junction of the brainstem and spinal cord. Hook punch impacts transmitted forces directly to the brainstem and the spinal cord without extension of the spinal cord. Deaths after this type of blow with no observed histological lesions may be related to excessive stressing of the brainstem, through which pass the sensory-motor pathways and the vagus nerve and which is the regulatory center of the major vegetative functions. Biological parameters are different in each individual, and by using digital modeling they can be modulated at will (jaw shape, dentition…) for a realistic approach to forensic applications.

Morphometric characterization of the very young child mandibular growth pattern: What happen before and after the deciduous dentition development?

OBJECTIVES: Numerous tools have been developed to characterize the morphometry of 3D models. The aim of this study was to apply these techniques to better understand the morphometric growth pattern of healthy children's mandibles. MATERIAL AND METHODS: The study sample was composed of 480 very young children aged from 36 gestational weeks to 7 years old. The sample was divided into three subsamples according to the development stages of their deciduous dentition. Several biometric data were collected on 3D mandibular models. RESULTS: There was homothetic growth during the first years of life. Once all deciduous teeth were fully erupted, the mandibular corpus warped more independently of the ramus, and the inter-individual variability was more pronounced. Throughout the growth period, several subgroups could be identified, highlighting the morphological growth pattern of the mandible. CONCLUSIONS: A particular morphogenesis of the mandible during the growth period was observed, which was correlated with deciduous dentition development. In younger individuals, this morphological pattern was mainly characterized by the progressive closure of the chin symphysis and ramus growth. The tongue movements in the oral space, depending on whether the child was bottle- or breast-fed, may explain this result. As the children grew older, the mandible widened to create sufficient space for the developing teeth buds. During the eruption of deciduous dentition, the mandible took on various morphologies, which was likely based on the child's sex and diet. Therefore, we assume that this mandibular morphogenesis is induced by the functional strains affecting the mandible during deciduous teeth development.

A novel method to quantitate bioprosthetic valve leaflet mechanical stress: a numerical and in vitro study.

An original in vitro/in silico method was developed to estimate the local and global mechanical stress applied on the bioprosthetic valve leaflet, which can be important for better understanding of the valve durability. A non-contact system based on stereophotogammetry and digital image correlation enabled filming and studying the valve leaflet movement frame by frame and performing three-dimensional analysis. The deformation was applied in a finite element model in order to calculate the local mechanical stress applied. High stress regions were primarily observed in the upper leaflet edge and belly and to a lesser extent at the free leaflet edge.

Transmission of force to the hyoid bone during manual strangulation: Simulation using finite element numerical models.

INTRODUCTION: Strangulation is a medicolegal form of mechanical asphyxia, and can be difficult to identify if cutaneous damage to the neck is limited. We began by creating a numerical model of a hyoid bone with adjustable anthropometric parameters and then subjected our model to compression simulating a precision grip on the neck from the front. MATERIALS AND METHODS: We selected six bones from the 77 hyoid bones contained in the database we created during a previous study led by our laboratory, in which we demonstrated the sexual dimorphism of this bone and identified the minimal force required for fracture. The anthropometric characteristics of these six bones (angle, length and width) corresponded to those of the 10th, 50th and 90th percentiles from cluster 1 (male individuals) and cluster 2 (female individuals), respectively. After enhancing, developing and meshing the selected 3D models, we analysed and reproduced simulation conditions that were as close as possible to the in vivo conditions of neck strangulation from the front (area of pressure on the bone, tissue environment, and biological variability of this bone). RESULTS: We modelled the six numerical hyoid bone models using the finite element method. For all models, the simulation of mechanical pressure applied to simulate anterior strangulation resulted in fractures. The forces required to produce these fractures matched the results obtained in the experimental testing of dissected hyoid bones. CONCLUSION: Six finite element numerical models were created, covering the anthropometric morphological variability of the hyoid bone. These six models enabled numerical simulation of the in vivo behaviour of a hyoid bone subjected to one-handed strangulation.

Forces transmission to the skull in case of mandibular impact.

BACKGROUND: Forensic investigations have been reported regarding the loss of consciousness and cardiac arrests resulting from direct mandible impact. However, the mechanisms by which the forces are transferred to the skull through direct mandible impact remain unclear. We conducted a study regarding direct mandible impact on the level of energy required to create a mandible fracture and on the energy dispersion phenomenon to the skull and to the brain. MATERIALS AND METHODS: This study combines an experimental and numerical approach. Mandible strike was studied using experimental trials performed on post-mortem human subjects. A finite element model of the head and face of a male was also developed based on tomodensitometry scans. The model was validated with literature data and experimental trials. A parametric study was then performed to study the effect of diverse variables such as the dentition integrity, cortical bone thickness, etc. RESULTS: The forces measured on our reference model were 3000 N on the chin, 1800 N at the condyles, and 970 N in the occiput. Of all the results, we observed a decrease of approximately one-third of the efforts from the chin to the base of the skull and a lower half of the still forces at the occiput, except in the edentulous and for the lateral and frontal impact where the force is transmitted directly to the skull base area. CONCLUSION: This study allowed us to create a 3D model of the mandible and face bones to better understand the force transfer mechanisms into and from the mandible. The parameters of the model may be modified to suit the individual characteristics for forensic investigations and legal matters.

Material properties of the placenta under dynamic loading conditions.

Trauma during pregnancy especially occurring during car crashes leads to many foetal losses. Numerical modelling is widely used in car occupant safety issue and injury mechanisms analysis and is particularly adapted to the pregnant woman. Material modelling of the gravid uterus tissues is crucial for injury risk evaluation especially for the abruption placentae which is widely assumed as the leading cause of foetal loss. Experimental studies on placenta behaviour in tension are reported in the literature, but none in compression to the authors' knowledge. This lack of data is addressed in this study. To complement the already available experimental literature data on the placenta mechanical behaviour and characterise it in a compression loading condition, 80 indentation tests on fresh placentae are presented. Hyperelastic like mean experimental stress versus strain and corridors are exposed. The results of the experimental placenta indentations compared with the tensile literature results tend to show a quasi-symmetrical behaviour of the tissue. An inverse analysis using simple finite element models has permitted to propose parameters for an Ogden material model for the placenta which exhibits a realistic behaviour in both tension and compression.