Does IMU redundancy improve multi-body optimization results to obtain lower-body kinematics? A preliminary study says no.

Inertial Measurement Units (IMUs) have been proposed as an ecological alternative to optoelectronic systems for obtaining human body joint kinematics. Tremendous work has been done to reduce differences between kinematics obtained with IMUs and optoelectronic systems, by improving sensor-to-segment calibration, fusion algorithms, and by using Multibody Kinematics Optimization (MKO). However, these improvements seem to reach a barrier, particularly on transverse and frontal planes. Inspired by marker-based MKO approach performed via OpenSim, this study proposes to test whether IMU redundancy with MKO could improve lower-limb kinematics obtained from IMUs. For this study, five subjects were equipped with 11 IMUs and 30 reflective markers tracked by 18 optoelectronic cameras. They then performed gait, cycling, and running actions. Four different lower-limb kinematics were computed: one kinematics based on markers after MKO, one kinematics based on IMUs without MKO, and two based on IMUs after MKO performed with OpenSense (one with, and one without, sensor redundancy). Kinematics were compared via Root Mean Square Difference and correlation coefficients to kinematics based on markers after MKO. Results showed that redundancy does not reduce differences with the kinematics based on markers after MKO on frontal and transverse planes comparatively to classic IMU MKO. Sensor redundancy does not seem to impact lower-limb kinematics on frontal and transverse planes, due to the likelihood of the "rigid component" of soft-tissue artefact impacting all sensors located on one segment.

Analysis of the obstetrician's posture and movements during a simulated forceps delivery.

BACKGROUND: The objective of this study was to identify and qualify, by means of a three-dimensional kinematic analysis, the postures and movements of obstetricians during a simulated forceps birth, and then to study the association of the obstetricians' experience with the technique adopted. METHOD: Fifty-seven volunteer obstetricians, 20 from the Limoges and 37 from the Poitiers University hospitals, were included in this multi-centric study. They were classified into 3 groups: beginners, intermediates, and experts, beginners having performed fewer than 10 forceps deliveries in real conditions, intermediates between 10 and 100, and experts more than 100. The posture and movements of the obstetricians were recorded between December 2020 and March 2021 using an optoelectronic motion capture system during simulated forceps births. Joint angles qualifying these postures and movements were analysed between the three phases of the foetal traction. These phases were defined by the passage of a virtual point associated with the forceps blade through two anatomical planes: the mid-pelvis and the pelvic outlet. Then, a consolidated ascending hierarchical classification (AHC) was applied to these data in order to objectify the existence of groups of similar behaviours. RESULTS: The AHC distinguished four different postures adopted when crossing the first plane and three different traction techniques. 48% of the beginners adopted one of the two raised posture, 22% being raised without trunk flexion and 26% raised with trunk flexion. Conversely, 58% of the experts positioned themselves in a "chevalier servant" posture (going down on one knee) and 25% in a "squatting" posture before initiating traction. The results also show that the joint movement amplitude tends to reduce with the level of expertise. CONCLUSION: Forceps delivery was performed in different ways, with the experienced obstetricians favouring postures that enabled observation at the level of the maternal perineum and techniques reducing movement amplitude. The first perspective of this work is to relate these different techniques to the traction force generated. The results of these studies have the potential to contribute to the training of obstetricians in forceps delivery, and to improve the safety of women and newborns.

The Potential Role of Wearable Inertial Sensors in Laboring Women with Walking Epidural Analgesia.

There is a growing interest in wearable inertial sensors to monitor and analyze the movements of pregnant women. The noninvasive and discrete nature of these sensors, integrated into devices accumulating large datasets, offers a unique opportunity to study the dynamic changes in movement patterns during the rapid physical transformations induced by pregnancy. However, the final cut of the third trimester of pregnancy, particularly the first stage of labor up to delivery, remains underexplored. The growing popularity of "walking epidural", a neuraxial analgesia method allowing motor function preservation, ambulation, and free movement throughout labor and during delivery, opens new opportunities to study the biomechanics of labor using inertial sensors. Critical research gaps exist in parturient fall prediction and detection during walking epidural and understanding pain dynamics during labor, particularly in the presence of pelvic girdle pain. The analysis of fetal descent, upright positions, and their relationship with dynamic pelvic movements facilitated by walking during labor is another area where inertial sensors can play an interesting role. Moreover, as contemporary obstetrics advocate for less restricted or non-restricted movements during labor, the role of inertial sensors in objectively measuring the quantity and quality of women's movements becomes increasingly important. This includes studying the impact of epidural analgesia on maternal mobility, walking patterns, and associated obstetrical outcomes. In this paper, the potential use of wearable inertial sensors for gait analysis in the first stage of labor is discussed.

Gait kinematics based on inertial measurement units with the sensor-to-segment calibration and multibody optimization adapted to the patient's motor capacities, a pilot study.

INTRODUCTION: Inertial Measurement Units (IMUs) offer a promising alternative to optoelectronic systems to obtain joint lower-limb kinematics during gait. However, the associated methodologies, such as sensor-to-segment (S2S) calibration and multibody optimization, have been developed mainly for, and tested on, asymptomatic subjects. RESEARCH QUESTION: This study proposes to evaluate two personalizations of the methodology used to obtain lower-body kinematics from IMUs with pathological subjects: S2S calibration and multibody optimization. METHODS: Based on previous studies, two decision trees were developed to select the best (in terms of accuracy and repeatability) S2S methods to be performed by the patient given his/her abilities. The multibody optimization was personalized by limiting the kinematic chain range of motion to the results of the subject's clinical examination. These two propositions were tested on 12 patients with various gait deficits. The patients were equipped with IMUs and reflective markers tracked by an optoelectronic system. They had to perform the postures and movements selected by the decision trees then walk back and forth along a walkway. Gait kinematics obtained from the IMUs directly (referred to as Direct kinematics), and after multibody optimization performed via the OpenSim software using the generic range of motion (referred to as Generic Optimized kinematics), and using the personalized range of motion (referred to as Personalized Optimized kinematics) were compared to those obtained with the Conventional Gait Model through Root Mean Square Errors (RMSE), Correlation Coefficients (CC) and Range of Motion differences (ΔROM). RESULTS: The RMSEs were smaller than 8.1° in the sagittal plane but greater than 7.4° in the transverse plane. The CCs, between 0.71 and 0.99 in the sagittal plane, deteriorate sharply in the frontal and transverse planes where they only measured between 0.15 and 0.68. The ΔROMs were mostly below 8.3°. Optimized kinematics did not improve compared to Direct kinematics. SIGNIFICANCE: The personalization of the proposed S2S calibration method showed encouraging results, whereas multibody optimization did not impact the resulting joint kinematics.

A new approach to assessing the obstetrician's posture and movement during an instrumental forceps delivery.

INTRODUCTION: The number of deliveries by forceps decreases significantly in favour of the vacuum. Now, when the use of forceps is necessary, physicians less experimented with this procedure are likely to induce serious and preventable perineal or foetal injuries. Training therefore becomes essential. However, there are no clear recommendations on the technique to perform a delivery by forceps, namely the body posture and gesture to adopt. Our goal is then to provide a protocol that can help to determine if there is an optimal technique to perform a delivery by forceps. METHOD: We will include voluntary participants whose level of experience and type of practice differ. We will propose to record their postures and gestures using an optoelectronic motion analysis system during a forceps delivery simulated on a mannequin. We will also measure the traction force produced by the subject on the forceps using force platforms and technical markers placed on the forceps. We will then perform a principal component analysis to look for similar motion patterns. EXPECTED RESULTS: We plan to analyse about fifty participants (25 seniors and 25 juniors). Our hypothesis is that the realism of the simulation will be deemed satisfactory by the participants, that the experimental conditions will not modify their gestures, and that the degree of experience will result in different techniques. CONCLUSION: A better knowledge on the posture and gesture to adopt to realise a forceps delivery should improve the safety of women and new-borns. The results of this study could also be a valuable contribution for the training of obstetricians.

The contribution of multibody optimization when using inertial measurement units to compute lower-body kinematics.

Kinematics obtained using Inertial Measurement Units (IMUs) still present significant differences when compared to those obtained using optoelectronic systems. Multibody Optimization (MBO) might diminish these differences by reducing soft-tissue artefacts - probably emphasized when using IMUs - as established for optoelectronic-based kinematics. To test this hypothesis, 15 subjects were equipped with 7 IMUs and 38 reflective markers tracked by 18 optoelectronic cameras. The subjects walked, ran, cycled on an ergocycle, and performed a task which induced joint movements in the transverse and frontal planes. In addition to lower-body kinematics computed using the optoelectronical system data, three IMU-based kinematics were computed: from IMU orientations without MBO; from MBO performed using the OpenSense add-on of the OpenSim software (OpenSim 4.2, Stanford, USA); as outputs from the commercialised MVN MBO (Xsens, Netherlands). Root Mean Square Errors (RMSE), coefficients of correlations, and differences in range of motion were calculated between the three IMU-based methods and the reference kinematics. MVN MBO seems to present a slight advantage over Direct kinematics or OpenSense MBO, since it presents 34 times out of 48 (12 degrees of freedom * 4 sports activities) a mean RMSE inferior to the Direct and OpenSense kinematics. However, it was not always significant and the differences rarely exceeded 2°. This study does not therefore conclude on a significant contribution of MBO in improving lower-body kinematics obtained using IMUs. This lack of results can partly be explained by the weakness of both the kinematic constraints applied to the kinematic chain and segment stiffening. Personalization of the kinematic chain, the use of more than one IMU by segment in order to provide information redundancy, or the use of other approaches based on the Kalman Filter might increase this MBO impact.

Detection of Horse Locomotion Modifications Due to Training with Inertial Measurement Units: A Proof-of-Concept.

Detecting fatigue during training sessions would help riders and trainers to optimize their training. It has been shown that fatigue could affect movement patterns. Inertial measurement units (IMUs) are wearable sensors that measure linear accelerations and angular velocities, and can also provide orientation estimates. These sensors offer the possibility of a non-invasive and continuous monitoring of locomotion during training sessions. However, the indicators extracted from IMUs and their ability to show these locomotion changes are not known. The present study aims at defining which kinematic variables and indicators could highlight locomotion changes during a training session expected to be particularly demanding for the horses. Heart rate and lactatemia were measured to attest for the horse's fatigue following the training session. Indicators derived from acceleration, angular velocities, and orientation estimates obtained from nine IMUs placed on 10 high-level dressage horses were compared before and after a training session using a non-parametric Wilcoxon paired test. These indicators were correlation coefficients (CC) and root mean square deviations (RMSD) comparing gait cycle kinematics measured before and after the training session and also movement smoothness estimates (SPARC, LDLJ). Heart rate and lactatemia measures did not attest to a significant physiological fatigue. However, the statistics show an effect of the training session (p < 0.05) on many CC and RMSD computed on the kinematic variables, indicating a change in the locomotion with the training session as well as on SPARCs indicators (p < 0.05), and revealing here a change in the movement smoothness both in canter and trot. IMUs seem then to be able to track locomotion pattern modifications due to training. Future research should be conducted to be able to fully attribute the modifications of these indicators to fatigue.

Using accelerations of single inertial measurement units to determine the intensity level of light-moderate-vigorous physical activities: Technical and mathematical considerations.

Quantifying physical activity and estimating the metabolic equivalent of tasks based on inertial measurement units has led to the emergence of multiple methods and data reduction approaches known as physical activity metrics. The present study aims to compare those metrics and reduction approaches based on descriptive and high order statistics. Data were obtained from 147 young healthy subjects wearing inertial measurement units at their wrist or ankle during standing, walking and running, labeled as light, medium or vigorous activities. The research question was, first, if those metrics allowed differentiating between light, moderate, and vigorous physical activities, and, secondly, what was the relationship with the metabolic equivalent of the task performed. The results showed that each metric differentiated the level of activity and presented a high correlation with the metabolic equivalent of the task. However, each metric and data reduction approach demonstrated its specific statistical characteristics related to the localization of the sensors. Our findings also confirm the absolute necessity to detail explicitly all calculus and post processing of metrics in order to quantify the level of activity by inertial measurement units.

Sensor-to-Segment Calibration Methodologies for Lower-Body Kinematic Analysis with Inertial Sensors: A Systematic Review.

Kinematic analysis is indispensable to understanding and characterizing human locomotion. Thanks to the development of inertial sensors based on microelectronics systems, human kinematic analysis in an ecological environment is made possible. An important issue in human kinematic analyses with inertial sensors is the necessity of defining the orientation of the inertial sensor coordinate system relative to its underlying segment coordinate system, which is referred to sensor-to-segment calibration. Over the last decade, we have seen an increase of proposals for this purpose. The aim of this review is to highlight the different proposals made for lower-body segments. Three different databases were screened: PubMed, Science Direct and IEEE Xplore. One reviewer performed the selection of the different studies and data extraction. Fifty-five studies were included. Four different types of calibration method could be identified in the articles: the manual, static, functional, and anatomical methods. The mathematical approach to obtain the segment axis and the calibration evaluation were extracted from the selected articles. Given the number of propositions and the diversity of references used to evaluate the methods, it is difficult today to form a conclusion about the most suitable. To conclude, comparative studies are required to validate calibration methods in different circumstances.

Does the McRoberts' manoeuvre need to start with thigh abduction? An innovative biomechanical study.

BACKGROUND: Guidelines and description about the achievement of the McRoberts manoeuvre are discordant, particularly concerning the need for abduction before the beginning of the manoeuvre. We sought to compare the biomechanical efficiency of the McRoberts' manoeuvre, with and without thigh abduction. METHODS: In a postural comparative study, twenty-three gravidas > 32 weeks of gestational age and not in labour were assessed during three repetitions of two McRoberts' manoeuvre that differed in terms of starting position. For the (i) McRoberts, the legs were initially placed in stirrups; for the (m) McRoberts, the legs were resting on the bed, with thighs in wide abduction. For each manoeuvre, flexion of the plane of the external conjugate of the pelvis on the spine (ANGce), hip flexion and abduction, were assessed using an optoelectronic motion capture system. Lumbar curve were assessed with Epionics Spine® system. Temporal parameters including movement duration or acceleration of the external conjugate were also computed. All values ​​obtained for the two types of manoeuvres were compared using a Wilcoxon matched-pairs signed-ranks test. The significance level was defined as p < 0.05. RESULTS: The starting position of McRoberts' otherwise had no effect on the maximum ANGce (p = 0.199), the minimal lordosis of the lumbar curve (p = 0.474), or the maximal hip flexion (p = 0.057). The other parameters were not statistically different according to the starting position (p > 0.005). CONCLUSION: Regardless of the starting position, the McRoberts' manoeuvre allows ascension of the pubic symphysis and reduction of the lumbar lordosis. This results imply that the McRoberts' manoeuvre could be performed with the legs initially placed in the stirrups.

Biomechanical comparison of squatting and "optimal" supine birth positions.

In obstetric science, it is unknown whether the inherent biomechanical features of the squatting position can be achieved and/or transposed to the supine birth position. In this study Biomechanical features of the squatting position were compared with 2 hyperflexed supine positions for giving birth. Thirteen pregnant women past the 32 weeks of gestational age not in labor were assessed first in the squatting position with the feet flat on the floor, then in the hyperflexed supine position, and finally in the optimal supine position "crushing" the hand of the caregiver onto the bed. For each position, the flexion of the spine associated with the plane of the external conjugate (ANGce) and the pelvis, hip flexion, and abduction were quantified using an optoelectronic motion capture system. A non-invasive strain-gauge-based measuring system was used to track the lumbar curve. An optimal position was defined with a flat lumbar spine and a pelvic inlet plane perpendicular to the lumbar spine (ANGce = 0° ± 5°). For the 13 participants, hip flexion, hip abduction, and the lumbar curve did not differ significantly for the three positions (squatting position, hyperflexed supine position, and OS) in the post-hoc analyses. The optimal supine position induced an ANGce closer to the perpendicular plane than the squatting position (p = 0.002). In the squatting position or in hyperflexed supine position positions, none of the subjects fulfilled the two conditions considered necessary to reach the optimal position. The squatting position was not significantly different from the supine hyperflexed supine position with or without voluntary lordosis correction.

Assessment of Pelvic-Lumbar-Thigh Biomechanics to Optimize The Childbirth Position: An "In Vivo" Innovative Biomechanical Study.

The study aimed to assess the associations between the pelvis orientation, lumbar curve and thigh postures throughout pregnancy in a population of healthy women. Additionally, optimal mechanical birth conditions in terms of the pelvic inlet and lumbar curve were researched. The individuals' posture was assessed with three-dimensional motion analysis and the lumbar curve with the Epionics SPINE system. The association between the hip joint angles (flexion and abduction), the pelvis external conjugate, and lumbar curve position was assessed with a generalized linear mixed model (GLMM) adjusted to individuals' characteristics. Joint laxity was assessed with a modified Jobbin's extensometer. For all of the subjects, hip flexion and hip abduction were significantly associated with the angle between the external conjugate and spine, with higher correlation in the multivariate regression model. The association between hip flexion and the lumbar curve was less significant in multivariate than univariate regression analysis. Optimal birth conditions were never reached. The findings contribute to the understanding of the association between the hip position (flexion and abduction), pelvic orientation, and lumbar curve adjusted for joint laxity in healthy pregnant women. They lay the groundwork for future research in the field of obstetrical biomechanics.

Is there an impact of feet position on squatting birth position? An innovative biomechanical pilot study.

BACKGROUND: The squatting birth position is widely used for "natural" birth or in countries where childbirth occurs in non-medical facilities. Squatting birth positions, like others, are roughly defined so a biomechanical assessment is required with the availability of noninvasive technology in pregnant women. In practice, we can observe spontaneously two kinds of squatting birth position: on tiptoes and with feet flat. OBJECTIVE: To compare the impact of foot posture on biomechanical parameters considered essential in obstetrical biomechanics during a squatting birth position: on tiptoes versus with feet flat on the floor. STUDY DESIGN: Thirteen pregnant women beyond 32 weeks of gestational age who were not in labor were assessed during squatting birth position firstly spontaneously and secondly with the foot posture that was not taken spontaneously (on the tiptoes vs with feet flat). For each position, ANGle of flexion on the spine of the plane of the pelvis external conjugate (ANGec), hip flexion and abduction, and lumbar curve were assessed using an optoelectronic motion capture system and a biomechanical model adapted from the conventional gait model as well as a measuring system of the lumbar curve. RESULTS: Spontaneously, 11 out of 13 women squatted on tiptoe at the first test. On tiptoes the hip flexion was lower than with feet flat (p < 0.02), whereas hip abduction was not significantly different (p = 0.28). A lower ANGec angle (p = 0.003) was noticed for the tiptoe position than feet flat. The lumbar curve (lordosis) was more marked for the squatting position on tiptoes than for the position with feet flat (p < 0.001). On tiptoes no woman had a pelvic inlet plane perpendicular to the spine and none had a flat back or kyphosis. No woman on tiptoes fulfilled the two conditions necessary for the position that we consider optimal. CONCLUSION: In squatting birth position, foot posture has a biomechanical impact on lumbar curve and pelvic orientation. When comparing squatting positions (on tiptoes vs feet flat), feet flat on the ground is closer to optimal birth conditions than on tiptoes.

Evaluation of ligament laxity during pregnancy.

OBJECTIVE: Pregnancy-related changes in ligament laxity have been shown to be associated with various disorders such as back pain or pelvic floor disorders. The purpose of this study was to assess laxity changes during pregnancy by confronting different methods in order to suggest a simple clinical tool helping to prevent the aforementioned problems. DESIGN: Seventeen pregnant women were evaluated at the first, second and third trimesters as cases and 16 non-pregnant women participated as controls. Ligamentous laxity was measured using an extensometer for the metacarpophalangeal joint of the index, a fingertip to floor test and a sit and reach test to assess hip and lumbar flexibility and the Beighton score. Statistical analysis included independent samples t-tests, analysis of variance and Pearson correlation coefficients. RESULTS: Laxity of the metacarpophalangeal joint increased by 11% from the first to the second trimester of pregnancy and stabilized until delivery. The Beighton score was significantly higher in the second trimester of pregnancy (p < 0.05). The flexibility of the hip and lumbar vertebra showed a significant increase of the distance measured between the foot soles and the middle fingers at third trimester (p < 0.05). A moderate correlation was observed between the results given by the extensometer and the Beighton score in both the cases and the control group at first trimester (r = 0.60, p < 0.05) but none was found for the two hip and lumbar flexibility tests. CONCLUSION: Laxity reached its maximum at the second trimester. The combination of an objective measurement by the extensometer and a global evaluation of the laxity by the Beighton' score for example may be useful for a daily assessment of laxity. However, the chosen clinical tests don't seem appropriate to be used alone in pregnant women.

In vivo assessment of the levator ani muscles using shear wave elastography: a feasibility study in women.

INTRODUCTION AND HYPOTHESIS: We hypothesized that shear wave elastography (SWE) technology might be useful for assessing the elastic properties of the pelvic floor in women. Our primary objective was to evaluate the feasibility of assessing the levator ani muscles using SWE in women. Our secondary aim was to investigate the changes in their elastic properties from rest to Valsalva maneuver. METHODS: During this prospective feasibility study in nonpregnant female volunteers, we collected data on participant age, body mass index (BMI), parity, and time since the delivery. The levator ani muscles of each participant were assessed using SWE technology at rest and during a Valsalva maneuver by measuring the shear modulus (in kilopascals). We then assessed the changes in the shear modulus at rest and during the Valsalva maneuver using a Wilcoxon test. RESULTS: Twelve parous women participated in this study. The mean time since the last delivery was 14 months, the mean age was 31 years, and mean BMI was 28 kg.m-2. All the assessments performed at rest were successfully completed, but we encountered two failures during the Valsalva maneuver. The mean shear modulus increased by a factor of more than 2 from rest to the Valsalva maneuver for both the right (16.0 vs 35.4 kPa) and left side (17.1 vs 37.6 kPa). CONCLUSIONS: An assessment of the elastic properties of the levator ani muscles is feasible for nonpregnant women. The reproducibility of the technique and its application in pregnant women and women with pelvic floor disorders must be investigated.

Identification of Noise Covariance Matrices to Improve Orientation Estimation by Kalman Filter.

Magneto-inertial measurement units (MIMUs) are a promising way to perform human motion analysis outside the laboratory. To do so, in the literature, orientation provided by an MIMU is used to deduce body segment orientation. This is generally achieved by means of a Kalman filter that fuses acceleration, angular velocity, and magnetic field measures. A critical point when implementing a Kalman filter is the initialization of the covariance matrices that characterize mismodelling and input error from noisy sensors. The present study proposes a methodology to identify the initial values of these covariance matrices that optimize orientation estimation in the context of human motion analysis. The approach used was to apply motion to the sensor manually, and to compare the orientation obtained via the Kalman filter to a measurement from an optoelectronic system acting as a reference. Testing different sets of values for each parameter of the covariance matrices, and comparing each MIMU measurement with the reference measurement, enabled identification of the most effective values. Moreover, with these optimized initial covariance matrices, the orientation estimation was greatly improved. The method, as presented here, provides a unique solution to the problem of identifying the optimal covariance matrices values for Kalman filtering. However, the methodology should be improved in order to reduce the duration of the whole process.

Simple and efficient thermal calibration for MEMS gyroscopes.

Gyroscopes are now becoming one of the most sold MEMS sensors, given that the many applications that require their use are booming. In the medical field, gyroscopes can be found in Inertial Measurement Units used for the development of clinical tools that are dedicated to human-movement monitoring. However, MEMS gyroscopes are known to suffer from a drift phenomenon, which is mainly due to temperature variations. This drift dramatically affects measurement capability, especially that of cheap MEMs gyroscopes. Calibration is therefore a key factor in achieving accurate measurements. However, traditional calibration procedures are often complex and require costly equipment. This paper therefore proposes an easy protocol for performing a thermal gyroscope calibration. In this protocol, accuracy over the angular velocity is evaluated by referring to an optoelectronic measurement, and is compared with the traditional calibration performed by the manufacturer. The RMSE between the reference angular velocity and that obtained with the proposed calibration was of 0.7°/s, which was slightly smaller than the RMSE of 1.1°/s achieved by the manufacturer's calibration. An analysis of uncertainty propagation shows that offset variability is the major source of error over the computed rate of rotation from the tested sensors, since it accounts for 97% of the error. It can be concluded that the proposed simple calibration method leads to a similar degree of accuracy as that achieved by the manufacturer's procedure.

Is increased peripheral ligamentous laxity in term pregnant women associated with obstetric anal sphincter injury?

INTRODUCTION AND HYPOTHESIS: Increased ligamentous laxity is associated with pelvic floor distension in pregnant women. This considered, it may also be related to the risk of obstetric anal sphincter injury (OASI). Our objective was to assess the association among increased ligamentous laxity, perineal tear severity, and OASI occurrence. METHODS: This is a prospective study. We assessed ligamentous laxity between the 36th week of pregnancy and the onset of labor, by measuring the passive extension of the nondominant index finger for a 0.26 N.m torque applied to the second metacarpophalangeal joint (MCP laxity). We collected perineal tear occurrence and classification (Royal College of Obstetricians and Gynecologists). We investigated the MCP laxity distribution according to the stage of perineal tears, and then we looked for a predictive level of MCP laxity for OASI. RESULTS: A total of 272 of the 300 pregnant women included had a vaginal delivery and were considered for the analysis. Mean age was 29 years, mean body mass index was 24.5 kg/m2 and 39.2% of women were nulliparous. We reported 12 cases of OASI. MCP laxity significantly increased with the stage of perineal tears from 58° in stage 0 to 69° and 66° for stages 3a and 3b respectively. An MCP laxity higher than 64° was associated with OASI with sensitivity of 75%, specificity of 56%, and an area under the curve of 0.65. CONCLUSION: Increased ligamentous laxity seems associated with OASI occurrence, which is the opposite of the initial hypothesis. This suggests that the stiffest tissues might be at a lower risk of injury.

Is levator hiatus distension associated with peripheral ligamentous laxity during pregnancy?

INTRODUCTION AND HYPOTHESIS: The impact of pregnancy on pelvic floor disorders remains poorly understood. During pregnancy, an increase in ligamentous laxity and pelvic organ mobility is often reported. Our main objective was to investigate a possible association between peripheral ligamentous laxity and levator hiatus (LH) distension during pregnancy. METHODS: This was a prospective longitudinal study of 26 pregnant women followed up from the first to the third trimester. We collected the following information: occurrence of pelvic organ prolapse (POP) symptoms (score higher than 0 for the POP section of the Pelvic Floor Distress Inventory 20 questions score), 4D perineal ultrasound scan results with LH distension assessment and measurement of metacarpophalangeal joint mobility (MCP laxity). The association between MCP laxity and LH distension was estimated by mixed multilevel linear regression. The associations between MCP laxity and categorical parameters were estimated in a multivariate analysis using a generalized estimating equation model. RESULTS: MCP laxity and LH distension were correlated with a correlation coefficient of 0.26 (p = 0.02), and 6.8% of the LH distension variance was explained by MCP laxity. In the multivariate analysis, MCP laxity was associated with POP symptoms with an odds ratio at 1.05 (95% CI 1.01-1.11) for an increase of 1° in MCP laxity. CONCLUSION: LH distension and peripheral ligamentous laxity are significantly associated during pregnancy. However, the relationship is weak, and the results need to be confirmed in larger populations and with more specific techniques such as elastography to directly assess the elastic properties of the pelvic floor muscles.

Position for labor and birth: State of knowledge and biomechanical perspectives.

This review aims to examine how childbirth position during labour affects maternal, fetal and neonatal outcomes. Epidemiological data suggest that vertical birthing positions have many benefits. But when we consider the players and mechanisms of delivery, including the forces generated to move the fetus and obstacles to its progression, many questions remain about the advantage of one position over another. Thus, childbirth could be considered in a way as an athletic feat that probably requires the choice of optimal positions. These should be individually suited to each woman at different stage of labour to improve its efficiency and effectiveness. Tweetable abstract: Beyond epidemiological data, biomechanical investigations is necessary to assess birth's position.