V J Palmier

S Prabakaran

F Faucher

A Servel

A Peden

Virtual modeling of an ADAS radar

Keywords: Radar, RCS, Simulation, Physics-based, ADAS, Autonomous Driving

Safety has been an increasingly important issue for the development of autonomous cars. Within the 3SA project, the team is working on a simulation platform with the vocation to solve the problems related to the safety of the autonomous car. Regarding the perception, we propose methods for modeling ADAS sensors in constrained environments. Radars are part of these sensors. By their ability to detect targets with different parameters as range, speed or even angular position over a range up to 200 meters but also by their low sensitivity to meteorological conditions, radars provide several advantages for perception. However, some environmental parameters disturb the radar and affect its accuracy and reliability. Our team, a joint collaboration between academic (IMT Atlantique -IRT SYSTEMX) and industrial (Renault, AVSimulation, OKTAL-SE, STELLANTIS) partners, is working on the development of a physic based virtual radar model and on stress patterns in synthetic scenes. This paper addresses a particular validation step: the construction of a virtual radar model based on real characterization. To obtain an accurate radar model, our method combined theorical radar concepts together with the use of a RF reference bench. We will see how real data of characterization of canonical forms obtained by the bench and the knowledge of the analytic RCS results of these forms allow to justify the results obtained with the real radar and to build the virtual model with a better level of accuracy.

Introduction

A sensor's physically based virtual modeling requires real characterization of this sensor in order to build a consolidated model. For an autonomous vehicle, the development of a virtual simulation synthetic environment and the validation of the system behaviour should take into external disturbances. Those external disturbances are due to phenomenon that can influence the decisions making process of the vehicle and the safety of its behaviour. In order to highlight some of these phenomena, while building the virtual radar model, the conception and the validation of these models require real data acquisition according to a specific experimental protocol.

Within the 3SA project, a joint collaboration between academic (IMT Atlantique -IRT SYSTEMX) and industrial (Renault, AVSimulation, OKTAL-SE, STELLANTIS) partners, the team attached to the radar modeling, is working on the development of a physics based virtual radar model and on disturbance patterns in synthetic environment.

Firstly, this paper presents theoretical elements regarding radars. Secondly, it exposes the works for the characterization of the sensor and some real small targets characterized at IMT Atlantique Brest. Thirdly, it explains the transfer of this study to the virtual simulation through the modeling of the 3D replicas for the small targets and their physics-based modeling. Finally, after a benchmarking study between the experimental results and the simulation outputs, we draw conclusions about the state of the method and discuss its future perspectives.

Radar Cross Section

Definition and usages

Usually, the RCS is used to characterize objects to measure and to define their detectability. For the scope of this study, the methodology is inverted: some references objects with their known RCS for a real radar are used to model and validate a virtual radar. Data from real experimentation will enable to build the virtual radar step by step while ensuring the robustness. This consolidation via RCS measurement requires the use of known RCS analytical measurement targets. These objects characterized by simple geometries (cubic, sphere, rectangular plate, dihedral....) are said to be canonical.

For the exploitation of real data, the radar equation enables to obtain the radar cross section [START_REF] Douchin | Simulating complex environments for the assessment of millimeter waves sensors[END_REF] with the exploitation of real measurements of the parameter |S21|² explained as follows [START_REF] Latger | Millimeter waves sensor modeling and simulation[END_REF] :

|𝑆 21 | 2 = 𝐺 𝑇𝑋 𝐺 𝑅𝑋 𝜆 2 𝜎 (4𝜋) 3 𝑑 4 = 𝑃 𝑅𝑋
𝑇 𝑇𝑋 [START_REF] Latger | Millimeter waves sensor modeling and simulation[END_REF] d=distance between the target and the radar [m]; λ=wavelength [m]; Ptx=Transmitted Power [W];

Prx=received power [W]; Gtx=transmission gain; Grx=reception gain; = radar cross section [m²]; |S21|²=measured parameter

The equation [START_REF] Latger | Millimeter waves sensor modeling and simulation[END_REF] enables to obtain: 3 Gtx * Grx * 𝜆 2 [START_REF] Douchin | Simulating complex environments for the assessment of millimeter waves sensors[END_REF] In this expression, the distance d must be long enough to be in the far field of the object in order to have a correct value of RCS.

= Prx Ptx d 4 * (4π)
When the object is far enough to the radar, the measured RCS is considered to be in agreement with the theoretical value of RCS. This far field criterion is defined by the following formula where L [m] represents the biggest dimension of the target and λ represents the wavelength.

d ≥ 2L²/λ [3]

Interest of the RCS Measurements

Usually, the RCS is used to characterize objects to measure and to define their detectability. For the scope of this study, the methodology is inverted: some references objects with their known RCS for a real radar are used to model and validate a virtual radar. Data from real experimentation will enable to build the virtual radar step by step while ensuring the robustness. This consolidation via RCS measurement requires the use of known RCS analytical measurement targets. These objects characterized by simple geometries (cubic, sphere, rectangular plate, dihedral....) are said to be canonical.

The theoretical determination of the RCS of canonical forms is based on the assumption of an "ideal" experimental configuration:

• The sensor is mono static: the same antenna acts as transmitter and receiver • The target is positioned in the far field • Radiation is considered to be isotropic • There is no power loss

Measurements and data acquisition

Targets and analytic RCS results

For this part of the experimentations, six small targets are used. Five of them meet the following criteria: ▪ Their sizes: the object is small (a few centimetres for the largest dimension) enough to allow far field measurements inside an anechoic chamber described below.

▪ Their geometries: with a canonical form, the comparison with analytic results provides an additional reference point for the modeling.

▪ Their materials: the compositions are known and described in order to have a corresponding physical-based calculation.

The sixth target was a small metallic object with a simple geometry that can be compared with a car (see Figure 8). Its interest is to verify the robustness of the method with an unknown geometrical form.

In this paper, three of the six targets are presented for the scope of this paper: a sphere of four centimetres diameter, a dihedron with six centimetres side and the Small Metallic Car (SMC).

Sphere

Real radar

In order to evaluate the radiation patterns of the power measurement of the radar and compare them to the datasheet, the radar is placed in a far field distance, facing a horn antenna connected to a vector analyzer in the far field. The radar is activated in transmission as follows:

• Each of the 3 Tx alone • The 3 Tx together. The mixer located at the back of the horn induces a noise of around -20 dB. For the main lobes, the results showed a good match between the manufacturer's data and the measurements but the noise induced by the mixed and the vectorial analyzer was too important to obtain the global diagrams. In this paper, only the results with the central antenna Tx2 will be presented. This choice is justified by the following facts:

• It is the central antenna • It is the only one for which the datasheet diagrams in elevation and azimuth were available • It is the one offered greater measurement dynamics compared to the noise specific to the measurement device

Description of the experimental design scene

In order to ensure the most optimal experimental conditions possible, the measurements were carried out in an anechoic chamber, thus ensuring the elimination of parasitic reflections and the maximum reduction of environmental noise.

For the respect of the theory of the Radar Cross Section, each target is placed at a far field distance defined regarding its size. The anechoic chamber is 2 meters long and after subtracting the occupied length reference bench system, there remains a distance amplitude of 1.6 meter. That means the dihedron couldn't be in far field distance inside the anechoic chamber. Thus, for the respect of the far field theory for each target, the experiment was split into 2 configurations:

Far field distance (m) f (GHz

• Configuration 1: Target and measurement system are both in the anechoic chamber at a distance of 1.6 meter each other. During the acquisitions, the chamber was closed. • Configuration 2: The target is in the anechoic chamber and the measurement system is outside the chamber at a distance of 3m (Figure 8). During the acquisition, the chamber was opened.

The acquisition system and the target were at the same height in both configurations validated with a LASER. The declination of the system is zero. The acquisition system is fixed and the target is in rotation. The target is placed on a foam support of permittivity substantially equal to 1 positioned on a rotary motor with a precisely calibrated rotation pitch.

The rotation pitch is defined and chosen according to the target studied.

Figure 5 Measurement configuration with the bench outside the chamber

The protocol is the same for both devices. To ensure the experimental protocol, when it takes the place of the reference system, the radar is place at 1.6m of the target to take into account the distance included by the connecting elbows of the reference one. The targets are changed between two acquisitions without moving the system {rotary motor + support}. Before changing the measurement system, all the targets are tested first.

Results and comparison of the real experimental results

At the time of writing this article, the values obtained via the radar are still being studied: so, they are not presented here.

Although the looks RCS of the 3 targets are the same for the theory, the reference bench and the real radar, some discrepancies between the theoretical values and the measurements were to be expected.

These errors come from both the point of view of the reference bench and the point of view of the radar. Indeed, at the section 2.2, we introduced the fact that the theory was built in an ideal case but in real experimentation both for the environment and for in relation to the sensor itself, the framework cannot ideal.

The reference bench is not really mono static contrary to the theory and its radiation is not isotropic; the alignment between the center of the transmission antenna and the center of the target is not perfect. This error leads to a mean error between the specified maximum gain and the one deduced from the RCS measurements of the sphere of 1.45 dB

The real radar is not mono static and its radiation is not isotropic. The anechoic chamber:

• In the configuration 1, the anechoic chamber has some leaks that could lead to minimal additional signal losses as well.

• In the configuration 2, the anechoic chamber is opened which create a large leak. Moreover the edge of the chamber, at the joint, has a metal coating and there are losses caused by the reflections outside the chamber.

The support, although its low permittivity, have its signature observable in the measurement.

Figure 6 Looks of the RCS at 79GHzreference bench (cf. 3.2)real radar (cf. 3.3). The measurement for the sphere with real radar were made on 180 degrees because of the duration of the acquisitions and the sphere form looks perfectly

Simulation of radar data

The simulation goal is to provide data which areas realistic as the phenomenon we want to model. Generally, in the automotive field, it relies on having a description of 4 elements:

• A detailed environment which comprises the terrain • Actors including the behaviour of the ego and all the targets surrounding it in the detection range • A perception model characterized by the sensors and all its specifications In this case, for RCS simulation, there is no environment or ego to describe because we focus only on radar interaction with its targets. Thus, the next parts of this paper will only deal with objects modeling, sensor description and acquisition.

Object modeling

The first step is the definition of a workflow of object modeling for physical sensor simulation. Objects are defined by their geometries (3D models) and their material descriptions (reflection, specular, rugosity, etc.). This definition can be written in a .BDD file which is the file extension of SE-WORKBENCH. In order to obtain this file for a specified object, the applied workflow is described in the Figure 7. The objective of this workflow is to have different formats corresponding to the different software that are used in the simulation. These files are generated from the same source 3D model which is then declined in different formats. These toolchains are described in the next paragraph.

Physical simulation with SE-WORKBENCH

The physical RCS simulations were performed thanks to the SE-RAY-EM software which is the EM kernel of SE-Workbench-RF product line. SE-RAY-EM solver uses asymptotic methods coupled to ray tracing in order to compute scattered electromagnetic fields at the bench and radar bandwidth. This method is relevant for the automotive domain since the size of the objects is large compared to the wavelength (a few millimetres for 79GHz). In the case of complex targets and large 3D scenes, the full wave methods are not applicable for several reasons. Where a few GHz is a high limit for "exact" solutions used on this type of objects, it is almost a low limit in terms of physical validity for asymptotic methods. The standard computation range addressed by this method is roughly between 1 to 100 GHz on complex 3D scenes that suit to automotive scenarios. Moreover, asymptotic method coupled to ray tracing produces results that are very similar to the "exact" methods for a very much lower computation time [START_REF] Latger | Millimeter waves sensor modeling and simulation[END_REF]. Ray-tracing is done through the Shooting and Bouncing Rays (SBR) technique that has been further optimized to calculate efficiently the intersections between rays from the transmitter towards the 3D target and back to receiver. Figure 9 shows that rays are traced from the transmitter through a grid (pixels). The intersections of theses beams are computed.

Figure 9 -Ray-tracing grid

There are two types of interactions that are based on three formulations [START_REF] Douchin | Simulating complex environments for the assessment of millimeter waves sensors[END_REF]:

• Geometrical Optics (GO) when the beam is reflected by a metallic or dielectric surface. • Physical Optics (PO) towards the reception points at each interaction. • Equivalent Current Methods (ECM) for computing edge diffraction toward the reception points.

Since the canonicals targets are metallic pieces, the Perfect Electric Conductor (PEC) material was the only model involved under the following simulations.

In order to be able to properly compare the results with the measurements, the following parameters set of the simulations matches the measurements conditions:

• The longitudinal distance between the antenna and the target • The vertical alignment of the target according to the antenna • The distance between the phase center of the emitter and the receiver antenna • The path of the antenna around the target • The number of angles computed (same azimuth sampling) • The same bandwidth Figure 10 -Principle of beam interactions [START_REF] Latger | Millimeter waves sensor modeling and simulation[END_REF] The results of the three simulations presented in this section were performed with the same set of raytracing parameters given on the Table 5 in the next section. Each scenario of the three simulations only comprises a single target, the source antenna and a reception point that take place within a free space environment. Hence, as soon as SE-RAY-EM has computed the complex EM field, it is simple to get the RCS value from the radar equation. This equation leads to the expression given below.

σ(ϴ) = (4𝜋) 2 𝑅 4 2 𝑍 0 𝑃𝑡 |𝐸𝑟(ϴ)| 2 [4]
Where σ(ϴ) is the radar cross section (𝑚 2 ) for a given azimuth angle ϴ (°), |𝐸𝑟(ϴ)| is the module of the complex polarised electric field (𝑉/𝑚) computed by SE-RAY-EM at the reception point for a givenϴ, 𝑍 0 is the free space impedance (around 120𝜋 Ω), 𝑃𝑡 is the transmitted power of the source (1𝑊) and 𝑅 the source-target distance (𝑚).

Figure 11, Figure 12 and Figure 13 respectively show the plots of the car shape target, the dihedron and the sphere. First, we can say that the curves of these plots fit the expected analytical ones. Since the simulations were performed very close to the near field limit, the value of 𝜎 𝑚𝑎𝑥 diverges a little from the expected analytical values. However, as long as the radius distance increases, the 𝜎 𝑚𝑎𝑥 converges very close to the theoretical value (up to 10 -3 -for this set of parameters). These simulations have several goals, one of them is to check the maximum value computed by the kernel in order to compare it with the expected analytical value. Besides, the plots enable us to compare the profile of the computed curves with the measurements in order to check the validity of the solver for different wavelength from 79GHz to 92.5GHz. Furthermore, many different measurements were performed across many different simple geometries will help us to identify the magnitude of the gap between the measurements and the simulation. This information will be ultimately used to check the validity of more complex geometries such as vehicles, traffic signs, bicycles as well as pedestrians. The ray tracing parameter set given in the figure 12 is purposely demanding for this latter reason as well. Finally, the next section will show that these simulations can be performed again in an automotive simulation context through SCANeR Studio and as a validation of the software integration of SE-RAY-EM.

Applying in SCANeR Studio

The previously presented tool SE-RAY-EM has been integrated in the software solution SCANeR Studio from AVSimulation. The goal of such an integration is to apply the physics-based sensor modeling in the field of automotive simulation. During this study, the goal has been to use the integrated tool in SCANeR Studio to reproduce the simulations that have been done with the SE-RAY-EM tool, in order to validate the fact that the theoretical value simulated by the physical-based software can be approached with another platform. The context of the simulation is different because it is based on the scenario description of SCANeR Studio.

A scenario needs an ego vehicle, a terrain and the actors surrounding the ego. Here, the goal is to measure an RCS surrounding the whole object.

Hence having an ego vehicle equipped with a correctly parametrized sensor. The ego has a circular trajectory around the object in order to surround every angle of the object at the precise distance (as described in Figure 14) When applying the simulation process to the three objects of the study, the results (an example is shown in Figure 15) obtained are similar to the simulated RCS with SE-WORKBENCH. The computation core model is the same for both tools but we can highlight some disparities due to the different context and some differences in the simulation parameters used with SCANeR.

First approximation come from the scenario itself. In SCANeR simulation, the ego vehicle is moving around the object applying a small velocity due to the rotation of it. This velocity can imply small dopplers. These can be avoided by stopping the car before each measurement for each angle but the impact of such dopplers is negligible.

The other approximation comes from the simulation parameters: for the integration of the SE-RAY-EM tool into SCANeR Studio, some simplifications have been made to be more adequate and easier to use for an automotive use case. The Studio because such precision is not necessary in the automotive field. In spite of this simplification, the scenario is able to get an accurate representation of the RCS even for very small objects of 4 to 5 centimetres.

Comparison of simulated data with real data

At this stage of development, the virtual RADAR is not finalized. However, as it appears in chapter 4 for this paper, the virtual model of the reference bench is in a good state of achievement. The discussion about the comparison of simulation data with real data will be about the real data of the benchmark.

Results

Figure 16 describes a superposition of the results of RCS obtained with OKTAL-SE, with SCANeR and we compared them with the measurements that have been done at IMT Atlantique with the reference bench. The 3 results have the correct shape and the measurement shows that the model used (in SE-WORKBENCH and then in SCANeR Studio) are relevant regarding the measured value in the anechoic chamber.

Discussion

The results are satisfying. Although, the gaps of the maximum RCS between the results of simulation and the theory are small, they are more important between the reference bench and the simulation. These differences can be more precisely observed in Table 6 which shows local maximum values of RCS around different angles (each face of the dihedron and the center corner of it at 135°).

The identified causes can be due to:

• The causes identified in section 3.5

• In simulation (SCANeR and SE-WORBENCH), the antennas are defined as isotropic antennas unlike the real ones. This choice explains the good scores between the theory and the simulation radiation in theory is defined as isotropic (cf. section 2.2)

The first results exposed in this paper are satisfying because SE-WORKBENCH and SCANeR correctly depicts the shape of the RCS expected with the real RCS measured. The construction of virtual non isotropic antenna could enable to increase the similarity between the real and the simulations. In the same way, the simulations could deviate from the theory. This demonstrates the relevance of using two sources of reference to build the virtual model.

Conclusion

To conclude, this first step of the method development shows a possible and robust workflow to validate radar modeling using simulation and two sources of references (theory and experimentations). The use of RCS reference value helps verifying the correct behaviour and quantification in our sensor model in controlled use case (anechoic chamber). Furthermore, the methodology used is validated from the step of object modeling to the step of parametrization of the sensor with two different toolchains: on one side, the physics-based tool (SE-WORKBENCH) and on the other side, its integration in a software platform (SCANeR Studio) allowing us to address multiple automotive use cases.

This workflow can now be applied for more complex scenarios implying more complex objects such as real cars, pedestrians and adding an environment to the measurement (movements of the objects and actors, and surrounding infrastructures).

Acknowledgement

Thanks to Charaf-Eddine SOURIA for having contributed to the definition of this method. This work has been supported by the French government under the "France 2030" program, as part of the SystemX Technological Research Institute.

Figure 2 -

 2 Figure 2 -RDK-S32R274 Reference Platform from NXP

Figure 3 -

 3 Figure 3 -Measurement protocol of antenna patterns in the azimuthal plan Acquisitions of the RCS were made with two different configurations of activation of the transmit antenna: Tx2 only and 3Tx together. For both, parameters of acquisition are the same and presented in the following table.

Figure 4 -

 4 Figure 4 -Picture of the opened anechoic chamber with the installation of the reference bench. Distance between the front of the horns and a target Add approximately 13cm to the distance to take into account the connecting elbows of the horns (reference bench)

Figure 7 -Figure 8 -

 78 Figure 7 -Applied workflow of 3D modeling The modeled objects are listed in the table below. Sphere (40 mm diameter)

Figure 11 -

 11 Figure 11 -RCS (ϴ) plot results of the car shape object

Figure 14 -

 14 Figure 14 -SCANeR Studio view of the measurement for RCS scenario

Figure 16 -

 16 Figure 16 -Layering of the RCS of the dihedron for the 3 measurement sources (blue: OKTAL-SE, red: SCANeR Studio and green: IMT)

(Diameter of 40 mm) Dihedron (a=60mm h=59.5mm e=10.1mm)

	F(GHz)	RCS expression	𝝅𝒓²	𝟖𝒉²𝒂²	𝝅 𝝀
	79	Max RCS in m² Max RCS in dB	0.001 -29.008	14.913 11.736
	92.5	Max RCS in m² Max RCS in dB	0.001 -29.008	21.204 13.264

Table 1 -

 1 Maximum RCS for the two objects with a

	canonical form
	3.2 IMT RF Reference Bench
	Figure 1 -

Details of the quasi-monostatic configuration for the antenna with the connecting elbows

	Transmission Frequency	79 GHz
	Bandwidth	35GHz
	Range resolution	4.2mm
	Gtx	23,35 dB
	Grx	23,35 dB

Table 2 -

 2 Description of the bench with the parameters of calibration

Table 3 -

 3 Parameters

Table 4 -

 4 Minimum distance of the far field criteria for each target

	)	Sphere	Dihedron	SMC
	79	0.85	1.90	1.32
	92.5	0.99	2.23	1.55

table below

 below

					SCANeR	SE-WB
				Grid sample size	10 -2 m	10 -3 m
				Grid subdivision level	2 1	2 4
				Curve sampling	1°	0.5°
				precision
			shows the
	differences	between	SE-WORKBENCH	and
	SCANeR Studio parameters.

Table 5 -

 5 Ray-tracing parameters set Some parameters are less accurate in SCANeR

Table 6 -

 6 Local max values of RCS (in dBm²) simulated and measured for remarkable angles of the dihedron

		RCS max in dBm2
		Sphere	Dihedron	SMC
	Theory	-29	11,89
	Ref Bench	-30.1	8,24	-4,33
	SCANeR	-27.7	11,22	-0,51
	SE-WB	-28.8	10,99	-1,57

Table 7

 7

	-Results of the maximum and of the mean
	RCS for each object
		RCS mean error
		Dihedron	SMC
	Ref Bench/Theory	3.65 dB
	SE-WB/Theory	0.9 dB
	SCANeR/Theory	0.67 dB
	SCANeR/SE-WB	0.36 dB	0.27 dB
	IMT/SCANeR	2.23 dB	2.037 dB
	IMT/SE-WB	1.87 dB	2.34 dB

Table 8 -

 8 mean error (in dB) of the RCS between different data sources (only with the max RCS for the theory)


Bringing down barriers to children's healthy eating Postnatal learning: olfaction

Mean age = 5.7 months Diet complemented with

Exposed

Bringing down barriers to children's healthy eating

The effect of early variety: short term In blue: initially liked vegetable In red: initially disliked vegetable

  Hausner et al, Physiol Behav (2008) Factors affecting the concentration: • Absorption in the gastrointestinal tract • Metabolism • Milk fat content • Characteristics of the volatile: Hydrophobic/hydrophilic character 3-methylbutyl acetate: not detected • The longer infants were breast-fed, the more they accepted umami solution at 6 months Higher glutamate content of human milk compared with formula milk • No more relationship at 12 months Postnatal learning: taste Schwartz et al, Br J Nutr (2013) Bringing down barriers to children's healthy eating Bringing down barriers to children's healthy eating Different stages of learning Bringing down barriers to children's healthy eating Effect of milk type Hausner et al, Clin Nutr (2010) flavour changes from day to day Bringing down barriers to children's healthy eatingThe effect of early variety: short termGerrish & Mennella, Am J Clin Nutr(2001)

  Bringing down barriers to children's healthy eating• Breastfeeding effect • Repeated exposure Flavour learning during complementary feedingMaier et al, Food Qual Pref (2007) 9 months later: 63% were still eating and liking the initially disliked vegetable

Car Car Car Car Car Car Car Car Car Car Chicken Potato group Car Pot Pot Pot Pot Pot Pot Pot Pot Pot Car Chicken Variety group Car Pea Pot Pum Pea Pot Pum Pea Pot Pum Car Chicken Home

		Lab										Lab	Lab
	Day	1	2	3	4	5	6	7	8	9	10	11	12
	Carrot group	Car Carrot Potato Variety

Formula-fed infants Infants' age : 4.6 months Cereals introduced at 4.0 months No consumption of vegetables and meat prior to the study Consumed quantity (g)

Mennella & Beauchamp, Early Hum Dev (2002)

Effect of breastfeeding

Positive association between breastfeeding duration and later vegetable intake, significant in ALSPAC and EDEN

Vegetable intake

(>1 serving/day, except in GENERATION XXI >3 serving/day)

Sensory variety

Prenatal Neonatal exposure

Parental practices

Sensory reactions

Texture learning

Bringing down barriers to children's healthy eating

• At 12 months infants consumed significantly more pureed carrots than chopped carrots

• Familiarity with different textures, especially chopped foods, was the strongest predictor of intake and liking of chopped carrots

• Compared to children introduced to lumpy solids between 6-9 months, children introduced to lumpy foods after the age of 9 months:

• ate less of many of the food groups at 7 years, including all 10 categories of fruit and vegetables

• were reported as having significantly more feeding problems at The more the spoonful pace was adapted to the spoonful weight, the more accurate the caloric adjustment was for 11 month-old infants Brugaillères et al., Appetite (2019) Bringing down barriers to children's healthy eating Thanks for your attention !


A Joud
email: a.joud@chru-nancy.fr

I Stella

O Klein

MD Joud Anthony

DIFFUSE INFILTRATIVE PONTINE GLIOMA BIOPSY IN CHILDREN WITH NEURONAVIGATION, FRAMELESS PROCEDURE: A SINGLE CENTER EXPERIENCE OF 10 CASES

Keywords:

Introduction

This study presented pediatric DIPG 's biopsy with frameless Neuronavigation .

Patients and methods

We report our experience about 10 patients who had Diffuse Intrinsic Pontine Glioma between 2014 and 2018. All patients were biopsied with BrainLab Varioguide Neuronavigation®. We always used fusion between specific CT Scan and MRI to selected target, made planning and biopsies. All patients were included in BIOMEDE after scientific and ethic discussions. We always selected a trans-cerebellar trajectory and made same procedure (lot of biopsies at one level). All patients have MRI at J1 to verify site of biopsy and to eliminate complication.

Results

The average age was 8.1 years. Symptoms were common with principally headaches and nystagmus. All biopsies were contributive for histopathological diagnosis and establish molecular profile for molecular study. We have no definitive morbidity and procedure duration was 93 minutes in average. All MRI didn't showed intracranial complication after procedure and showed great precision of biopsy compared with the selected target.

Discussion

We reviewed the literature and compare our results with series of DIPG biopsies using stereotactic frame or robotic assisted frameless. It was a safe, accuracy and easiness procedure. We always have histopathological and molecular result to proceed next step of treatment. This modality is an alternative possibility to biopsy very young patients with low morbidity.

Introduction:

Diffuse Intrinsic Pontine Gliomas (DIPG) is an infiltrative masse lesion which occurs in the ventral pons. The median age of presentation is between 5 and 9 years [START_REF] Walker | Conference Consensus Group (2013): a multidisciplinary consensus statement concerning surgical approaches to low-grade, high-grade astrocytomas, and diffuse intrinsic pontine gliomas in childhood (CPN Paris 2011) using the Delphi method[END_REF] and the incidence is equal among males and females [START_REF] Jallo | Brainstem gliomas[END_REF]. The overall survival (OS) ranged from 9 to 12 months from diagnosis to death [START_REF] Hargrave | Diffuse Brainstem glioma in children: critical review of clinical trials[END_REF][START_REF] Jansen | Survival prediction model of children with diffuse intrinsic pontine glioma based on clinical and radiological criteria[END_REF]. Response to radiation therapy is transient and chemotherapy has not improved long-term survival.

For decades, usefulness of biopsy in this kind of lesion has been controversial [START_REF] Albright | Magnetic resonance scans should replace biopsies for the diagnosis of diffuse brain stem gliomas: a report from the Children's Cancer Group[END_REF].

Information given from MRI imaging has been considered enough by many authors as well in several institution to assure diagnosis of DIPG thanks to such characteristic features [START_REF] Albright | Magnetic resonance scans should replace biopsies for the diagnosis of diffuse brain stem gliomas: a report from the Children's Cancer Group[END_REF], thus avoiding surgical morbidity. More recently, in France as well as in other countries, oncological progress has justified a wider use of biopsy in order to find biomarkers and new molecular targets, to develop innovative therapies and to improve prognosis of the patients [START_REF] Puget | Biopsy in a series of 130 pediatric diffuse intrinsic pontine gliomas[END_REF].

Nowadays, some teams have a great experience in stereotactic biopsy of DIPG [START_REF] Puget | Biopsy in a series of 130 pediatric diffuse intrinsic pontine gliomas[END_REF], giving an important contribution to research in this topic.

Biopsy on pediatric DIPG yielded 96% to 100% diagnosis with less than 5% morbidity and no mortality [START_REF] Puget | Biopsy in a series of 130 pediatric diffuse intrinsic pontine gliomas[END_REF][START_REF] Rajshekhar | Computerized tomography-guided stereotactic surgery for brainstem masses: a risk-benefit analysis in 71 patients[END_REF][START_REF] Mcgirt | Independent predictors of morbidity after imageguided stereotactic brain biopsy: a risk assessment of 270 cases[END_REF].

However, we think that further improvement might be realized using new surgical technologies like Neuronavigation system.

Although a reliable technique, stereotactic systems are difficult to use in very young patient or in a context of emergency. To date, frameless Neuronavigation procedures have not been reported in the literature. The aim of this study was to report our experience to perform biopsies of pediatric DIPG by using a frameless Neuronavigation procedure. To date, infratentorial frameless Neuronavigation procedures have not been reported in the literature, although it has already been mentioned for supratentorial ones [START_REF] Guo | Techniques for Stereotactic Neurosurgery: Beyond the Frame, Toward the Intraoperative Magnetic Resonance Imaging-Guided and Robot-Assisted Approaches[END_REF][START_REF] Buchalla | Frameless navigated biopsy with the BrainLAB® Varioguide system: a technical note[END_REF]

Patients and methods:

We retrospectively collected data of the children with highly suspected diagnosis of DIPG on imaging, who benefited from frameless Neuronavigation biopsy at our institution between 2014 and 2018. Ten patients have been identified and included in the series, whose diagnosis of DIPG was confirmed in all cases and all DIPG were included in the study.

All of them were biopsied with BrainLab Varioguide Neuronavigation® and iPlan Software ®; all the procedures were performed by the same operator (AJ).

The decision to biopsy and to include patients in BIOMEDE protocol was discussed during a multidisciplinary staff with radiologist, onco-pediatrician, radiotherapist and neurosurgeon.

All the DIPGs were all included in this protocol; the purpose was extensively discussed with parents and written consent was collected for each patient in the series.

Biopsies have been realized using a standardized protocol as follow.

Three-dimensional injected T1-weighted sequences and FLAIR images of diagnostic MRI were fused with new CT-scan images. Specific Neuronavigation CT scan is mandatory to assure precise procedure with excellent bone's definition to acquire the landmarks.

Target, entry point and trajectory were calculated with BrainLab iPlan software®.

The patient was installed in semi sitting position under general anesthesia (figure 1) which allowed a better acquisition of facial 3D landmarks. Pre-operative cardiac ultrasound was not judged necessary due to estimated low risk of air embolism in such a short and minimally invasive procedure and we didn't report any complication. The head was fixed with three pins head-older. We determined the entry point, the trajectory and reported coordinates to the Varioguide. Everything was made step by step, with verification by two different surgeons.

We made 1 cm skin incision, a 4 mm drill-hole in the skull and we introduced trocar prudently to target.

We realized 4 to 6 different biopsies only at one level. After, we closed the skin with absorbable suture.

We always used a trans-cerebellar trajectory by the middle cerebellar peduncle to access DIPG, to reduce surgical morbidity. Whenever possible, we selected a target with contrast enhancement. When there is no contrast enhancement, we selected a secure target in the lateral part of the Pons. The trans-cerebellar trajectory was based on operator's preferences.

During post-operative period, all children had an MRI, as required by BIOMEDE protocol, to verify proper site of biopsy and to verify the correspondence between the target and the sample.

Results

Data of 10 children treated at our institution with BrainLab Varioguide Neuronavigation® between 2014 and 2018 have been collected. The average age at presentation was 8.1 years, ranging from 3 to 13. Male-female ratio was 1:1 (5 males and 5 females).

Most common presenting symptom in this series was headaches (found in five patients), followed by ataxia and oculomotor palsy (found in 3 cases) and the last 2 had Central Facial palsy.

All tumors observed satisfied DIPG standard definition, with more than 50% of brainstem involved. In all cases, pons was the principal affected structure, with mesencephalic extension found in three cases. Two patients didn't have contrasted enhancement on MRI and we have selected a target with that in 7 out of 8 cases.

Only one patient had bradycardia during procedure, without real hemodynamic instability, but requiring atropine with benefit. All biopsies were contributive for histopathological diagnosis; 1 patient has WHO grade II glioma, 5 patients have grade III glioma and 4 had grade IV glioma, conforming to WHO classification. In all cases, molecular profile was established using a mean of 4.7 samples, while one sample was used for histopathological diagnosis (table 1).

Post-operative neurological impairment was observed only in one case, who presented transient nystagmus during three weeks. There was no definitive morbidity, and the mean procedure duration was 93 minutes (extremes: 75 to 110 minutes).

The above mentioned post-operative MRI at J1 with axial T2-weighted and FLAIR sequences didn't show intracranial complication in any case. The difference between the pre-operative target and the control (viewed on MRI) was under 4 mm (3,4 mm) with 3DT1 images fusion.

All patients were discharged from Neurosurgery unity before 72 hours after the procedure.

Patients benefited from fractionated radiotherapy (54 Gy in 30 days), as previously stated by multidisciplinary team.

Discussion

During many years, DIPG's diagnosis has been based on MRI highly specific imaging and on clinical features [START_REF] Albright | Magnetic resonance scans should replace biopsies for the diagnosis of diffuse brain stem gliomas: a report from the Children's Cancer Group[END_REF] and any kind of surgical treatment was strictly proscribed. During 15 years, some teams have been realizing stereotactic biopsy of DIPG in order to perform molecular analysis and to develop new target and treatment [START_REF] Roujeau | Stereotactic biopsy of diffuse pontine lesions in children[END_REF] with specific protocols have been created in this optic like BIOMEDE. BIOMEDE is a clinical and molecular study which compares efficiency and safety of different drugs (Everolimus, dasatinib and erlotinib) which were given to patients with DIPG based on recognized molecular target.

Reviewing the literature, we found several publications reporting the use of stereotactic frame DIPG biopsy [START_REF] Puget | Biopsy in a series of 130 pediatric diffuse intrinsic pontine gliomas[END_REF][START_REF] Roujeau | Stereotactic biopsy of diffuse pontine lesions in children[END_REF] or robotic assisted frameless ones [START_REF] Lefranc | Frameless robotic stereotactic biopsies: a consecutive series of 100 cases[END_REF][START_REF] Coca | Diffuse intrinsic pontine gliomas in children: Interest of robotic frameless assisted biopsy. A technical note[END_REF] and a lot of papers [6,8,9,11] had showed that biopsies were secure with low morbidity.

On the contrary, there are no description about frameless Neuronavigation-guided procedures.

We thus show our experience with Neuronavigation technique (BrainLAB Neuronavigation and Varioguide).

Compared with frame-assisted techniques, which requires immediate per-operative imaging under general anesthesia, the use of Neuronavigation reduces drug's exposure and overall operative duration. Moreover, it avoid frame positioning which could be difficult in very young patients, due to obvious anatomic reasons.

We used a target with contrast enhancement whenever possible like others series [START_REF] Puget | Biopsy in a series of 130 pediatric diffuse intrinsic pontine gliomas[END_REF] even recent study showed that T2-weighted images are superior to others to provide best discrimination of intratumoral heterogeneity [START_REF] Harward | T2-weighted images are superior to other image types for the determination of diffuse intrinsic pontine glioma intratumoral heterogeneity[END_REF]. The good precision of this technique can be assured by prior fusion of cerebral MRI and CT scan, and confirmed by post-operative MRI, which showed an air spot at biopsy level. We compared the target which was selected and all post operative MRI to evaluate the biopsy precision and we found a margin error of 3,4 mm. Needle progression from cortical surface to the target can be easily followed on Neuronavigation screen during all the procedure, allowing the surgeon to be aware of needle precise position in case of vital parameters anomaly.

We didn't have long lasting complication. Moreover, neither hemorrhagic or ischemic complications have been detected on postoperative MRI in any case.

Histopathological and molecular diagnosis could be assessed in all 10 patients included in our series, proving the usefulness of Neuronavigation-guided biopsy, with accuracy and easiness, as diagnostic tools for DIPG in children.

Conclusion

The use of frameless Neuronavigation to perform biopsy in children with DIPG has not previously been described in the literature. It can be a valuable diagnostic alternative in the pediatric population, carrying the advantage to reduce anesthesia exposure during intervention and to avoid frame positioning, which can be very difficult in very young patients.

Evaluation of our series of ten children with DIPG who were operated on with Neuronavigation system confirmed the usefulness of this technique. Histopathological and molecular results were assured in all cases, with acceptable morbidity rate.

Disclosure of interest: the authors report no conflict of interest concerning the material or methods used in this study or the findings specified in this paper.

LEGENDS:

Figure 1 :

 1 Figure 1: Patient in semi sitting position during the frameless neuronavigation procedure

Figure 2 :

 2 Figure 2: DIPG biopsy with Neuronavigation. Screenshot after facial's morphing with CT Scan

Figure 3 :

 3 Figure 3: Planning with transcerebellar trajectory to the target in the medial part of contrast

Table 1 :

 1 Summary of demographic, clinical, radiological and biological results of 10 cases of DIPG.


Paul Zetlaoui
email: paul.zetlaoui@aphp.fr

Anesthésie et infection de prothèses articulaires Anaesthesia for patients with infected joint prosthesis

Keywords: Prothèse articulaire, infection, antibiothérapie prolongée, catheter Midline, catheter PICCline Articular prosthesis, sepsis, prolonged antibiotics administration, Midline catheter, PICCline catheter

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

2

L'infection sur prothèse articulaire est définie comme une pathologie nosocomiale et doit être considérée comme une urgence thérapeutique [START_REF] Has | 'infection dans le mois suivant l'implantation[END_REF]. Quelle est la place de l'anesthésiste, et de l'anesthésie dans la prévention et la prise en charge de ces infections ? L'infection d'une prothèse articulaire de hanche ou de genou, plus rarement d'épaule, est un drame pour le patient, un problème pour le chirurgien orthopédiste, et un fardeau pour la société car le coût du traitement est considérable (hospitalisations et interventions itératives, antibiothérapies de longue durée, arrêts de travail et parfois séquelles fonctionnelles) ; le coût d'une infection de prothèse était estimé à 8161 € par hospitalisation en 2008 ; on peut considérer qu'il a presque doublé depuis! Classiquement l'infection de prothèses articulaire concerne le chirurgien orthopédiste, le microbiologiste et l'infectiologue [START_REF] Has | 'infection dans le mois suivant l'implantation[END_REF], mais ce sujet concerne aussi l'anesthésiste, car parmi tous les facteurs impliqués dans l'infection d'une prothèse articulaire, certains sont détectables au cours de la consultation d'anesthésie et une action correctrice peut en réduire l'agressivité. Par ses choix ou ses contraintes, l'anesthésiste va jouer un rôle important aux trois temps de l'intervention, préopératoire, peropératoire et postopératoire.

Epidémiologie

Malgré l'amélioration des procédures, de l'antibioprophylaxie et de la lutte contre les infections nosocomiales en général, le risque d'infection de prothèse articulaire, bien que peu élevé, reste à un niveau relativement constant, entre 0,67 % et 2,4 % pour la hanche et entre 0,58 % et 1,6 % pour le genou [START_REF] Segreti-Berbari | Introduction to the Centers for Disease Control and Prevention and Healthcare Infection Control Practices Advisory Committee Guideline for Prevention of Surgical Site Infection: Prosthetic Joint Arthroplasty Section[END_REF]. Selon le moment de survenue de l'infection après l'implantation, on distingue l'infection précoce (dans le premier mois), différée (du 2ème au 24ème mois) et tardive (au-delà de 24 mois). On distingue aussi des infections méconnues, révélées par la positivité des prélèvements bactériologiques pratiqués lors de la reprise d'une prothèse descellée considérée comme aseptique.

Pour le cadre nosologique on distingue les infections superficielles du site opératoire (ISO), de la peau à l'aponévrose de revêtement, et les infections profondes (IPOP) qui concernent l'os et le matériel prothétique.

Les facteurs de risque d'infection prothétique en chirurgie orthopédique peuvent être classés en 2 catégories : les facteurs modifiables et les non modifiables (tableau 1) [START_REF] Has | 'infection dans le mois suivant l'implantation[END_REF]. C'est à l'évidence sur la correction des facteurs modifiables que tous les efforts doivent porter.

Tableau 1. Facteurs non-modifiables ou modifiables responsables des infections de prothèses articulaires (D'après 2]

Facteurs non-modifiables

Facteurs modifiables -Score ASA≥ 3 (grade 3-5 vs 1 : 1,8 En pratique, plus l'HbA1C s'éloigne de 7,5%, plus le risque semble augmenter [START_REF] Godshaw | Preoperative glycemic control predicts perioperative serum glucose levels in patients undergoing total joint arthroplasty[END_REF], [START_REF] Chrastil | Is Hemoglobin A1c or perioperative hyperglycemia predictive of periprosthetic joint infection or death following primary total joint arthroplasty?[END_REF] et plus il faudra retarder l'intervention et confier le patient à un diabétologue, si nécessaire, pour l'amener à l'intervention dans les meilleures conditions. Cette option n'est cependant pas partagée par tous les auteurs [START_REF] Lopez | Review: The relationship of hemoglobin A1c to postoperative surgical risk with an emphasis on joint replacement surgery[END_REF].

Allergie au ß-lactamines.

Les ß-lactamines sont les antibiotiques de choix dans le cadre de la chirurgie prothétique articulaire [START_REF] Auboyer | Recommandations Formaliseés d'Experts Actualisation de recommandations Antibioprophylaxie en chirurgie et medecine interventionnelle (patients adultes)[END_REF]. Les alternatives en cas d'allergie (vancomycine ou clindamycine) seraient moins efficaces en termes de réduction du risque d'infection. Dans une étude portant sur 18.830 prothèses, Ponce et coll. ont montré que le taux d'infection était de 1,1% chez les patients qui ont reçu de la céfazoline vs. 2,6% chez les patients se déclarant allergiques et ayant reçu une prophylaxie par vancomycine seule (p<0,001) [START_REF] Ponce | Surgical site infection after arthroplasty: comparative effectiveness of prophylactic antibiotics: do surgical care improvement project guidelines need to be updated?[END_REF]. Ces résultats sont confirmés par d'autres études qui rapportent une augmentation du risque infectieux lors du remplacement de la céfazoline par la vancomycine [START_REF] Blumenthal | The impact of a reported penicillin allergy on surgical site infection risk[END_REF], [START_REF] Kheir | vancomycin prophylaxis for total joint arthroplasty: incorrectly dosed and has a higher rate of periprosthetic infection than cefazolin[END_REF], avec même une nette tendance à l'apparition d'infection à bacille gram négatif [START_REF] Tan | Is Vancomycin-only prophylaxis for patients with penicillin allergy associated with increased risk of infection after arthroplasty?[END_REF]. En pratique, plus de 10% des patients candidats à une arthroplastie, se considèrent ou se déclarent allergiques à la pénicilline, mais la réalité est que 1% environ des patients sont réellement allergiques à la pénicilline [START_REF] Mcdanel | Screening for ßeta-lactam allergy in joint arthroplasty patients to improve surgical prophylaxis practice[END_REF]. De plus l'allergie croisée pénicilline -céphalosporine est rare, et concerne moins de 2% des patients, signifiant que risque réel d'allergie à la céfazoline est extrêmement faible.

Dans ce contexte, la majorité des publications rappellent l'importance de confirmer la réalité de cette allergie évoquée à la pénicilline, et proposent même, en raison du sur-risque infectieux en cas de substitution par la vancomycine ou la clindamycine, la réalisation de tests allergiques pour évaluer l'allergie à la céfazoline.

De plus, il faut rappeler que :

1. pour la clindamyncine, s'il ne semble pas exister de sur-risque infectieux, à la dose actuellement recommandée de 900 mg (1200 mg chez le sujet obèse) [START_REF] Auboyer | Recommandations Formaliseés d'Experts Actualisation de recommandations Antibioprophylaxie en chirurgie et medecine interventionnelle (patients adultes)[END_REF], il existe un risque réel d'interaction avec les curares (la clindamycine ayant un effet curarisant intrinsèque) et que cette potentialisation est peu sensible à la décurarisation par la prostigmine (la décurarisation du rocuronium par le sugammadex ne semble pas être sensible à la présence de clindamycine, data personnels non publiés) [START_REF] Ahdal | Clindamycin-induced neuromuscular blockade[END_REF].

2. pour la vancomycine, la dose actuellement recommandée est de 30 mg/kg en 1 h, sans dépasser 2000 mg au total [START_REF] Auboyer | Recommandations Formaliseés d'Experts Actualisation de recommandations Antibioprophylaxie en chirurgie et medecine interventionnelle (patients adultes)[END_REF], ce qui est en pratique difficile à réaliser, et que le pic de concentration tissulaire est souvent atteint trop tardivement.

En pratique, le choix raisonné reposerait sur la substitution de la céfazoline par la clindamycine.

Anémie préopératoire.

L'anémie est définie par l'OMS comme un taux d'Hémoglobine < 13g/dl chez l'homme et < 12g/dl chez la femme. Dans une étude prospective sur 1534 patients d'orthopédie, l'anémie est retrouvée chez 14 % des patients en préopératoire, et chez 86 % des patients en postopératoire [START_REF] Lasocki | PREPARE: the prevalence of perioperative anaemia and need for patient blood management in elective orthopaedic surgery: a multicentre, observational study[END_REF]. L'anémie périopératoire multiplie par 2 à 3 l'incidence des ISO qui est de 3,7 % chez les patients anémiques en préopératoire vs. 1,2% chez les patients non anémiques en préopératoire [START_REF] Greenky | Preoperative anemia in total joint arthroplasty: is it associated with periprosthetic joint infection?[END_REF]. Dans une étude portant sur 13.563 patients, Vola et coll. rapportent que l'anémie préopératoire est associée à une incidence d'IPOP de 4,5 % vs. 1,2 % chez les patients non anémiques [START_REF] Viola | Preoperative anemia increases postoperative complications and mortality following total joint arthroplasty[END_REF]. De même, le taux de reprise opératoire est beaucoup plus élevé chez les patients anémiques : 16,6 % comparé à 1,14 % chez les patients non anémiques (OR: 11,93; Ic:95 %= 5,84-24,36; p<0,0001). Enfin, les patients anémiques en préopératoires nécessitent 3 à 4 fois plus souvent de transfusion de concentrés érythrocytaires que les patients non anémiques (30,9 % vs. 10,9 %) [START_REF] Lasocki | PREPARE: the prevalence of perioperative anaemia and need for patient blood management in elective orthopaedic surgery: a multicentre, observational study[END_REF][START_REF] Greenky | Preoperative anemia in total joint arthroplasty: is it associated with periprosthetic joint infection?[END_REF][START_REF] Viola | Preoperative anemia increases postoperative complications and mortality following total joint arthroplasty[END_REF]. L'anémie préopératoire et la transfusion périopératoire sont associées à une augmentation de la morbidité postopératoire [START_REF] Lasocki | PREPARE: the prevalence of perioperative anaemia and need for patient blood management in elective orthopaedic surgery: a multicentre, observational study[END_REF][START_REF] Greenky | Preoperative anemia in total joint arthroplasty: is it associated with periprosthetic joint infection?[END_REF][START_REF] Viola | Preoperative anemia increases postoperative complications and mortality following total joint arthroplasty[END_REF][START_REF] Biboulet | Preoperative Epoetin-α with Intravenous or Oral Iron for Major Orthopedic Surgery: A Randomized Controlled Trial[END_REF]. Il est primordial, en chirurgie réglée que le patient ne soit pas anémique le jour de l'intervention ; il nécessaire, pour chaque patient de planifier un plan de PBM (patient blood management) de façon à ce qu'il ne soit pas anémique à l'arrivée au bloc opératoire [START_REF] Kotzé | Effect of a patient blood management programme on preoperative anaemia, transfusion rate, and outcome after primary hip or knee arthroplasty: a quality improvement cycle[END_REF].

Chez les patients anémiques en préopératoire, l'apport de fer, au mieux par voie intraveineuse, et l'EPO sont les moyens les plus performants pour satisfaire cet objectif dans un délai de 3 à 4 semaines [START_REF] Biboulet | Preoperative Epoetin-α with Intravenous or Oral Iron for Major Orthopedic Surgery: A Randomized Controlled Trial[END_REF][START_REF] Kotzé | Effect of a patient blood management programme on preoperative anaemia, transfusion rate, and outcome after primary hip or knee arthroplasty: a quality improvement cycle[END_REF] Le traitement anticoagulant ne doit pas être initié ou repris trop précocement après l'intervention, dans la majorité des cas la première dose peut être administrée sans risque le lendemain de l'intervention [START_REF] Colwell | Flexibility in administration of fondaparinux for prevention of symptomatic venous thromboembolism in orthopaedic surgery[END_REF].

Résumé de la période préopératoire

A la suite de cette étape préopératoire, les patients peuvent être répartis dans 3 groupes différents [START_REF] Marmor | Patient-specific risk factors for infection in arthroplasty procedure[END_REF] :

• Les patients à risque faible ou habituel d'ISO: pas de modifications des pratiques habituelles ; information standard sur le risque infectieux postopératoire. • Les patients à risque intermédiaire d'ISO avec des facteurs de risque modifiables, et pouvant bénéficier d'une correction préopératoire, qui va souvent motiver un délai préopératoire prolongé, le plus souvent entre 1 à 3 mois.

• Les patients à risque élevé d'ISO, lié essentiellement à des facteurs non modifiables, pour lesquels il pourrait être envisagé de renoncer à l'intervention après une évaluation approfondie du rapport risque/bénéfice et une information adaptée.

La période opératoire

Antibioprophylaxie

Après avoir établi le choix et la stratégie de l'antibioprophylaxie (cf. chapitre 1), il convient d'en respecter les modalités d'administration. La posologie doit être adaptée au poids et à l'indice de masse corporel pour les ß-lactamines. L'administration du médicament doit être terminée au moins 30 minutes avant l'incision [START_REF] Auboyer | Recommandations Formaliseés d'Experts Actualisation de recommandations Antibioprophylaxie en chirurgie et medecine interventionnelle (patients adultes)[END_REF].

Acide tranéxamique

L'administration d'acide tranéxamique (ATx) est associée à une diminution du taux d'ISO en chirurgie prothétique. Dans une étude de cohorte sur 6.340 patients Yazdi et coll. ont montré que l'incidence des infections de prothèse était de 3,4 % dans le groupe sans ATx et de 1,6% dans le groupe recevant de l'AT (15 mg/kg en 1 dose unique avant l'incision) [START_REF] Yazdi | Tranexamic acid Is associated with reduced periprosthetic joint infection after primary total joint arthroplasty[END_REF]. L'acide tranéxamique semble efficace par toutes les voies, per os, IV ou locale, que cela soit pour les primo-implantations ou les reprises.

Hypothermie peropératoire

L'hypothermie (<35°) peropératoire majore le infectieux postopératoire [START_REF] Kurz | Perioperative normothermia to reduce the incidence of surgical-wound infection and shorten hospitalization. Study of Wound Infection and Temperature Group[END_REF]. Le risque d'ISO serait multiplié par 1,5 si la température< 36° et par 3 si la température est < 35°. En chirurgie prothétique orthopédique, l'hypothermie augmente le saignement, augmente les hématomes au niveau de la cicatrice qui sont des facteurs associés à l'ISO. Il est donc nécessaire de maintenir la température des patients au-dessus de 36°c (avec les difficultés que l'on connaît dans ces chirurgies), l'hypothermie modérée ne semblant pas majorer le risque infectieux en chirurgie prothétique [START_REF] Scholten | The incidence of mild hypothermia after total knee or hip arthroplasty: A study of 2600 patients[END_REF].

La technique anesthésique

Le choix de la technique ou des agents d'anesthésie modifie-t-il le risque infectieux en chirurgie prothétique orthopédique ? Pour ce qui concerne l'anesthésie générale, le choix entre halogénés ou propofol n'a pas d'influence sur l'incidence sur le risque infectieux [START_REF] Kishimoto | Suspected periprosthetic joint infection after total knee arthroplasty under propofol versus sevoflurane anesthesia: a retrospective cohort study[END_REF]. Hu et coll. ont été les premiers en 2009 à mettre en évidence une relation entre la technique d'anesthésie et l'incidence des infections de prothèses en faveur de la rachianesthésie [START_REF] Hu | A comparison of regional and general anaesthesia for total replacement of the hip or knee: a meta-analysis[END_REF]. Plusieurs études [START_REF] Scholten | General anesthesia might be associated with early periprosthetic joint infection: an observational study of 3,909 arthroplasties[END_REF][START_REF] Pugely | Differences in short-term complications between spinal and general anesthesia for primary total knee arthroplasty[END_REF][START_REF] Zorrilla-Vaca | The impact of neuraxial versus general anesthesia on the incidence of postoperative surgical site infections following knee or hip arthroplasty: a meta-analysis[END_REF][START_REF] Weinstein | Neuraxial anaesthesia techniques and postoperative outcomes among joint arthroplasty patients: is spinal anaesthesia the best option?[END_REF][START_REF] Mauermann | A comparison of neuraxial block versus general anesthesia for elective total hip replacement: a meta-analysis[END_REF][START_REF] Memtsoudis | Perioperative comparative effectiveness of anesthetic technique in orthopedic patients[END_REF][START_REF] Lenguerrand | Risk factors associated with revision for prosthetic joint infection following knee replacement: an observational cohort study from England and Wales. National Joint Registry for England, Wales, Northern Ireland and the Isle of Man[END_REF][START_REF] Smith | Neuraxial and combined neuraxial/general anesthesia compared to general anesthesia for major truncal and lower limb surgery: a systematic review and meta-analysis[END_REF][START_REF] Helwani | Effects of regional versus general anesthesia on outcomes after total hip arthroplasty: a retrospective propensity-matched cohort study[END_REF] ont par la suite confirmé les résultats de cette princeps : la rachianesthésie étant associée à une incidence plus faible d'infection prothétique (Tableau 5). Scholten et coll. dans une étude portant sur 3909 PTG et PTH ont rapporté un risque différent d'ISO entre anesthésie générale (1,7%) et rachianesthésie (0,8%) avec un OR de 2 (IC95% :1,0-3,7) [START_REF] Scholten | General anesthesia might be associated with early periprosthetic joint infection: an observational study of 3,909 arthroplasties[END_REF]. De même, Helwani et coll. ont retrouvé dans une série de 12.929 PTH une incidence plus faible d'ISO profonde dans le groupe rachianesthésie (OR=0,38, IC95% : 0,-0,72) en comparaison avec le groupe AG [START_REF] Helwani | Effects of regional versus general anesthesia on outcomes after total hip arthroplasty: a retrospective propensity-matched cohort study[END_REF]. Dans cette même étude, les taux de complications, cardiovasculaires et pulmonaires et in fine le taux de mortalité (OR=0,78 ; IC95% :0,43-1,42) étaient plus bas dans le groupe rachianesthésie que dans le groupe AG [START_REF] Helwani | Effects of regional versus general anesthesia on outcomes after total hip arthroplasty: a retrospective propensity-matched cohort study[END_REF]. Seules 2 études ne montrent pas de différence quant à l'incidence des ISO, entre rachianesthésie et AG [START_REF] Curry | Evaluation of anesthetic technique on surgical site infections (SSIs) at a single institution[END_REF][START_REF] Kopp | The impact of anesthetic management on surgical site infections in patients undergoing total knee or Total Hip Arthroplasty[END_REF] Pour cela le choix de l'anticoagulation est important et le l'horaire de début aussi. Il est probablement sans risque de débuter la thromboprophylaxie le lendemain de l'intervention ; cela a été montré avec le fondaparinux et les AOD [START_REF] Colwell | Flexibility in administration of fondaparinux for prevention of symptomatic venous thromboembolism in orthopaedic surgery[END_REF]. L'aspirine serait une alternative à évaluer ; dans une étude au moins, la prophylaxie par aspirine est associée à une faible incidence d'ISO que la warfarine (0,4% vs. 1,5% p<0,001) [START_REF] Huang | Comparison of the Efficacy and Safety of Aspirin and Rivaroxaban Following Enoxaparin Treatment for Prevention of Venous Thromboembolism after Hip Fracture[END_REF]. La remise en place d'un traitement par AVK devrait être retardée jusqu'au 3 ème -4 ème jour.

Reprises postopératoires

Les reprises opératoires pour infection de la cicatrice ou de la prothèse nécessitent une antibiothérapie prolongée, probabiliste dans un premier temps, puis adaptée au germe dans un second temps. Les germes retrouvés sont des staphylococcus dans 75% à 88% des cas, des bactéries à Gram négatif dans 14% à 39% des cas, des streptococcus dans 19% des cas, des corynebacterium ou des anaérobies dans 20% des cas ; enfin 30% à 45% des infections sont polymicrobiennes. Les recommandations de la HAS pour l'antibioprophylaxie sont une bithérapie associant vancomycine et pipéracilline-tazobactam ou à une céphalosporine de 3e génération (ceftriaxone ou céfotaxime) en attendant l'identification microbiologique [START_REF] Segreti-Berbari | Introduction to the Centers for Disease Control and Prevention and Healthcare Infection Control Practices Advisory Committee Guideline for Prevention of Surgical Site Infection: Prosthetic Joint Arthroplasty Section[END_REF]. Plusieurs éléments sont à prendre en considération. Ce traitement doit être commencé après les prélèvements bactériologiques. L'association vancomycine + pipéracillinetazobactam est néphrotoxique. Chez le patient dont la fonction rénale est déjà compromise, une association moins néphrotoxique doit être envisagée ; l'association céfépimevancomycine est une alternative moins néphrotoxique. Par ailleurs, la cetriaxone et le céfotaxime, moins néphrotoxiques, sont aussi recommandées en association à la vancomycine par la HAS [START_REF] Rutter | Nephrotoxicity during Vancomycin Therapy in combination with piperacillin-tazobactam or cefepime[END_REF].

La surveillance rapprochée de la fonction rénale est impérative. Elle sera secondairement adaptée en fonction de l'association antibiotique prescrite ; une surveillance de la fonction hépatique doit être envisagée dans certains cas.

La perfusion de vancomycine est douloureuse et veinotoxique. Il est envisageable dès la première intervention pour reprise septique de mettre en place, alors que le patient est sous anesthésie générale, soit un cathéter central, soit un Midline ou un PICCLine, l'antibiothérapie sera, dans tous les cas, prolongée. Chez les patients âgés, qui constituent la

Figure 1 .

 1 Figure 1. Relation entre le taux d'HbA1c et le risque d'infection en chirurgie prothétique en orthopédie. Redessinée d'après Cancienne JM et coll. [5].

  AVK, l'INR préopératoire doit être normalisé, c'est à dire le plus proche possible de 1. Un INR> 1,5 avant l'incision majore le risque infectieux qui augmente avec l'INR, passant de 0,8% pour un INR = 1 à 5% pour un INR >1,5 (p<,001) (Figure2)[START_REF] Rudasill | Revisiting the International Normalized Ratio (INR) threshold for complications in primary total knee arthroplasty: An analysis of 21,239 Cases[END_REF].

Figure 2 .

 2 Figure 2. Relation entre l'INR préopératoire et l'incidence des ISO en chirurgie orthopédique. D'après[START_REF] Rudasill | Revisiting the International Normalized Ratio (INR) threshold for complications in primary total knee arthroplasty: An analysis of 21,239 Cases[END_REF]

Figure 3 .

 3 Figure 3. Relation entre le type d'anticoagulant administré en postopératoire, l'incidence des événements thromboemboliques veineux et l'incidence des ISO en chirurgie prothétique orthopédique. D'après [40].

  Le diabète est un facteur de risque majeur et selon certains, il multiplierait par 7 le risque d'infection de prothèse[START_REF] Dowsey | Obese diabetic patients are at substantial risk for deep infection after primary TKA[END_REF]. Le risque est plus important quand le diabète est non ou mal contrôlé[START_REF] Marchant | The impact of glycemic control and diabetes mellitus on perioperative outcomes after total joint arthroplasty[END_REF]. Plus que le dosage ponctuel de la glycémie, le bon marqueur qui permet de savoir si le diabète est contrôlé ou non, est l'hémoglobine glyquée (HbA1c) qui reflète l'équilibre ou le déséquilibre de la glycémie sur une période de 3 mois ; cependant, ce

	-Maladies de systèmes	-Hématome postopératoire
		-Durée opératoire > 2,5h
	2. Consultation d'anesthésie
	Durant la consultation d'anesthésie avant l'implantation d'une prothèse articulaire, il est
	important de rechercher les facteurs potentiellement responsables d'une infection et de
	tenter d'en corriger les déséquilibres ou anomalies.
	2.1. Diabète
	[1,6-	-Diabète déséquilibré
	2,1])	-Hémostase préopératoire anormale
	-Obésité BMI≥ 35 ou 40 selon les études	-Tabagisme actif
	(OR:1,94 à 6,40 selon les études)	-Dénutrition
	-Insuffisance rénale (OR: 12,4 Ic=95%: 3,1-	-Traitements	altérant	l'immunité
	49,7 ; p<0.001)	(corticothérapie, Nib, Mab, …)
	-Cirrhose (RR 7,5, Ic95%: 4,8-9,5)	-Antibioprophylaxie inadéquate (molécule,
	-Polyarthrite rhumatoïde (OR = 4,8 à 10,3	dose, …)
	vs. arthrose simple)	-Hypothermie peropératoire

marqueur est discuté par certains auteurs. Quoi qu'il en soit, le dosage de l'HbA1c est de plus en plus souvent disponible lors de la consultation d'anesthésie. Bien qu'il n'existe pas de relation linéaire entre HbA1c et l'incidence des IPOP

[START_REF] Cancienne | Is There a Threshold Value of Hemoglobin A1c That Predicts Risk of Infection Following Primary Total Hip Arthroplasty?[END_REF]

, la majorité des auteurs s'accordent sur le fait qu'en chirurgie réglée :

• L'incidence des ISO augmente (de façon non linéaire) avec le taux d'HbA1C (Figure

1

)

• Le point d'inflexion sur la courbe du risque semble se situer à 7,5% • Il ne faudrait pas opérer un patient dont le pourcentage d'HbA1C est supérieur à 8% • Il ne faut pas opérer un patient dont le pourcentage d'HbA1C est supérieur à 9%

Traitements préopératoires altérant l'immunité, et majorant le risque infectieux en chirurgie prothétique. Traitements de fond classiques Méthotrexate (Imeth®), sulfasalazine (Salazopyrine®), léflunomide (Arava®), hydroxychloroquine (Plaquénil®), cyclophosphamide (Endoxan®), azathioprine (Imurel®), acide mycophénolique (Cellcept®) Biothérapies (traitements de fond biologiques

  . De façon pratique, les résultats biologiques (NFS, fer sérique, coefficient de saturation de la sidérophiline, etc….) doivent être disponibles lors de la consultation d'anesthésie ; la date opératoire doit être modifiée si une correction de l'anémie est nécessaire, et si le délai entre la consultation d'anesthésie et l'intervention est insuffisant à la normalisation de l'hémoglobine.2.4. Infection urinaireIl est classiquement recommandé de systématiquement réaliser un examen cytobactériologique des urines avant l'implantation d'une prothèse articulaire et de traiter une éventuelle infection ou même bactériurie asymptomatique. Cette attitude est largement remise en question. En effet, si une infection urinaire documentée ou une simple bactériurie sont associées à une majoration du risque d'ISO, leur traitement (infection patente ou bactériurie asymptomatique) ne modifie pas l'incidence des ISO, parce que le germe retrouvé au niveau de la prothèse infectée n'est jamais celui qui est retrouvé dans les urines. Les recommandations actuelles[START_REF] Gómez-Ochoa | Risk of surgical site infection in patients with asymptomatic bacteriuria or abnormal urinalysis before joint arthroplasty: Systematic review and meta-analysis[END_REF][START_REF] Sousa | Is routine urinary screening indicated prior to elective total joint arthroplasty? A systematic review and meta-analysis[END_REF] sont : American College of Rhumatology et de l'American Association of Hip and Knee surgeons préconisent l'arrêt de ces traitements avant une intervention programmée[START_REF] Goodman | American college of rheumatology/American association of hip and knee surgeons. guideline for the perioperative management of antirheumatic medication in patients with rheumatic diseases undergoing elective total hip or total knee arthroplasty[END_REF]. Les modalités d'arrêt de ces médicaments dont les schémas thérapeutiques sont très variables sont relativement simples.-Le délai d'arrêt avant l'intervention doit être supérieur à celui écoulé entre 2 doses du médicament.-Le traitement ne doit pas être repris avant J15 postopératoire. En présence d'une ISO précoce, d'un retard de cicatrisation ou d'un problème infectieux intercurrent, le traitement ne sera repris qu'après la guérison totale de ces événements. Ainsi pour le golimumab (Simponi®), l'intervalle entre 2 injections IV est de 8 semaines, et donc l'arrêt du traitement sera de 9 semaines au minimum. Pour le rituximab (MabThéra®) qui nécessite une injection tous les 6 mois, le délai sera de 7 mois. Dans les deux cas, le traitement ne sera repris qu'après 15 jours en l'absence de toute complication.Pour ce qui concerne les corticoïdes, il existe une relation entre la dose quotidienne et l'incidence des ISO (Tableau 3). Il semble donc utile de réduire, autant que cela serait possible, les doses de prednisone à 5 mg/j pour réduire le risque infectieux[START_REF] Scherrer | Infection risk after orthopedic surgery in patients with inflammatory rheumatic diseases treated with immunosuppressive drugs[END_REF][START_REF] Bongartz | Incidence and risk factors of prosthetic joint infection after total hip or knee replacement in patients with rheumatoid arthritis[END_REF][START_REF] George | Perioperative timing of infliximab and the risk of serious infection after elective hip and knee arthroplasty[END_REF]. A l'inverse, la dexaméthasone, administrée à titre-antiémétique en anesthésie, ne majore pas le risque d'ISO[START_REF] Bustos | A retrospective analysis of the use of intravenous dexamethasone for postoperative nausea and vomiting in total joint replacement[END_REF].

	Tableau 3.
		-Anti-TNF alpha dont 5 produits sont commercialisés infliximab
		(Rémicade®), adalimumab (Humira®), étanercept (Enbrel®),
		certolizumab (Cimzia®), golimumab (Simponi®).
		-Anti-IL6 : tocilizumab (Roactemra®) et sarilumab (Kevzara®)
		-Anti-IL1 : anakinra 5kineret®) et canakinumab (Ilaris®)
		-Les anti-lymphocytes B : rituximab (MabThéra®), bélimumab
		(Benlysta®)
		-Anti-lymphoytes T : abatacept (Orencia®)
	Traitements de fond	TINIB : baricitinib (Oluminant®) et tofacitinib (Xeljanz®)
	synthétiques ciblés
	Corticoïdes	Predisone, …..

-Ne pas rechercher une bactériurie asymptomatique -Traiter une infection urinaire symptomatique 2.5. Nib, Mib, Mab et autres traitements spécifiques Les patients atteints de (polyarthrite inflammatoire (polyarthrite rhumatoïde, spondylarthrite ankylosante, lupus érythémateux disséminé, rhumatisme psoriasique, etc.) sont de plus en fréquemment traités par des modulateurs de l'immunité. On les regroupe en 4 catégories (Tableau 2).

Tableau 2.

Tous ces traitements qui ont amélioré l'évolution naturelle de ces maladies majorent le risque infectieux périopératoire et particulièrement celui de l'IPOP. Les recommandations conjointes de l'

Risques d'infection des prothèses articulaires à J30 et à 12 mois en fonction de la dose quotidienne de prednisolone. D'après 26.

  Dans cette même étude sur 49.603 patients, l'incidence des infections urinaires et des pneumopathies postopératoires est aussi significativement plus élevée chez les patients dénutris.Il est classiquement demandé un bilan dentaire avant une chirurgie prothétique avec un bilan radiologique panoramique. Il est acquis que cette recommandation est obsolète. Ne doivent être traités que les patients qui ont à l'évidence un foyer infectieux dentaire. En effet, les germes retrouvés au niveau de la prothèses infectée ne sont jamais les mêmes que ceux retrouvés au niveau des foyers dentaires[START_REF] Sonn | Effect of preoperative dental extraction on postoperative complications after total joint arthroplasty[END_REF][START_REF] Lampley | Total joint arthroplasty: should patients have preoperative dental clearance?[END_REF]. De plus, il semble nécessaire que toute intervention sur un foyer dentaire soit réalisée au moins 45 jours avant l'implantation de la prothèse, les soins dentaires réalisés dans un délai de 15 à 21 jours avant l'intervention étant associés à une majoration de l'incidence des ISO.

	2.8. Arrêt du tabac
	L'arrêt du tabac devrait être un prérequis indispensable à toute chirurgie programmée,
	particulièrement prothétique. Le tabagisme complique le postopératoire de façon générale,
	mais particulièrement en orthopédie, il multiplie le risque d'infection de la plaie opératoire
	(x 2,16), le risque de pseudarthrose, et accessoirement le risque thromboembolique
	(Tableau 4) [33]. Il est donc fondamental de faire comprendre au patient la nécessité de
	l'arrêt du tabac avant l'intervention [34, 35].Par ailleurs cet arrêt du tabac doit être de
	longue durée, au moins 8 semaines, sachant que même 1 an après persiste un sur-risque
	certes modéré (x1,52) mais certain.
		Risque d'ISO à J30	Risque d'IPOP à 12 mois
	≤ 5mg/j prednisone	0,98 (0.67, 1.44)	1.90 (1.14, 3.18)
	> 5 et ≤ 10mg/j	1.13 (0.76, 1.67)	1.93 (1.13, 3.31)
	prednisone
	> 10mg/j prednisone	2.11 (1.30, 3.40)	2.70 (1.30, 5.60)
	2.6. Dénutrition protidique.
	En pratique, selon les pays et les études, on considère que 5 à 25% des patients candidats à
	une prothèse articulaires sont dénutris ; 50% des patients avec un IMC>30 sont en état de
	dénutrition protidique ! Si de nombreux critères cliniques ou biologiques (pré-albuminémie <
	150 mg/L, transferrinémie <2g/L, etc.) sont utilisables pour évaluer la dénutrition, l'albumine
	plasmatique est le marqueur le plus simple et le moins onéreux à obtenir en routine [29]. Il
	serait souhaitable de disposer à la consultation d'anesthésie du dosage de l'albuminémie.
	Chez les patients dénutris, un programme de renutrition protidique est souhaitable [30]. Un
	apport de protide de 1g/kg par jour pendant 15 jours serait nécessaire.
	2.7. Bilan dentaire

La dénutrition protidique définie par une albuminémie <35g/l, est un facteur majeur de risque d'ISO. Bohl et coll. ont montré que le taux d'ISO est de 2,3% quand l'albuminémie est <35g/L vs. 0,9% quand l'albumine est >35g/L

[START_REF] Bohl | Hypoalbuminemia Independently Predicts Surgical Site Infection, Pneumonia, Length of Stay, and Readmission After Total Joint Arthroplasty[END_REF]

.

En pratique, il ne faudrait pas opérer pour une prothèse articulaire un fumeur actif et ne devrait arriver à la consultation d'anesthésie que des patients que le chirurgien a déjà convaincus de la nécessité de l'arrêt du tabac; dans tous les cas c'est à l'opérateur de débuter cette information. Tableau 4.

Impact du tabagisme sur le risque de complications postopératoires.

		Evénements indésirables		Risque X par
	Mortalité postopératoire			2,6
	Nécessité de réanimation postopératoire		2,0 à 2,9
	Infection postopératoire			2,0 à 3,5
	Complications coronariennes			3,0
	Complications respiratoires			3,0
	Infection de la cicatrice			1,7
	Retard	de	consolidation	osseuse	et	2,7 et 8,1
	pseudarthrose
	Thrombose vasculaire			3,1
	2.9. Hémostase, coagulation
	Il existe une relation entre l'anticoagulant utilisé et le degré d'anticoagulation préopératoire
	et la réalisation du risque infectieux en chirurgie prothétique de hanche ou de genou. En
	comparaison avec les AVK (standard nord-américain) les HBPM majoreraient le risque de
	saignement, de transfusion d'infection et de reprise opératoire [36] (6,2% vs. 2,1%; OR =
	3,82

-CI95% 2,64 to

[START_REF] Cancienne | Is There a Threshold Value of Hemoglobin A1c That Predicts Risk of Infection Following Primary Total Hip Arthroplasty?[END_REF][START_REF] Mauermann | A comparison of neuraxial block versus general anesthesia for elective total hip replacement: a meta-analysis[END_REF]

. Le lien entre ces différents événements défavorables est probablement l'effet anticoagulant majorant le saignement péri-prothétique. L'anticoagulation préopératoire par HBPM majore le risque infectieux par 6,2 (Ic95% : 1,5-23)

[START_REF] Asensio | Preoperative low molecular weight heparin as venous thromboembolism prophylaxis in patients at risk for prosthetic infection after knee arthroplasty[END_REF]

; cette pratique doit être abandonnée. Chez les patients traités au long cours par

Relation entre la technique anesthésique (rachianesthésie vs. anesthésie générale) et l'incidence des infections postopératoires en chirurgie prothétique orthopédique. OR : odds ratio ; IC : intervalle de confiance

  . Dans la méta-analyse la plus récente publiée en 2019 regroupant 49 études, la rachianesthésie est associée à une réduction du risque d'ISO [OR: 0,73 ; Ic95%: 0,67-0,79] [59]. 'anticoagulation excessive après PTH ou PTG est un facteur de risque identifié d'ISO. Il semble important de limiter le saignement postopératoire pour minorer le risque d'ISO.

	2.5. La durée opératoire
	Il ne s'agit pas ici d'un paramètre directement lié à l'anesthésie, mais il semble utile d'en
	avoir conscience ; il existe une relation directe entre durée de l'intervention et infection de
	prothèse. L'incidence de l'infection est de 1,1% pour une intervention dont la durée est
	inférieure à 60 minutes, 1,4% pour une durée entre 60 et 90 minutes et 2,1% au-delà de 90
	minutes [60]. Le risque infectieux augmente de 25% toutes les 20 minutes au-delà de 60
	minutes.
	3. La période postopératoire
	3.1. Anticoagulation postopératoire.
	Tableau 5. Etude	Population	Statistiques
	Scholten R 2019 Rétrospectif	3909 pts	OR AG = 2,
	Memstoudis S 2019	94 études	OR rachi= 0,73
	Méta-analyse	795.135 pts	IC95= 0,67-0,79
	Liu J 2013 Registre	16.555 pts	OR ALR= 0.77, IC95%, 0.64-0.92.
	Chang CC 2013 Registre	3.081 pts	OR AG = 2,21, IC95% = 1,25-3,91
			P< 0,007
	Helwani M 2015 Registre	12.929 pts	OR rachi = 0,38, IC95% = 0,20-0,72
			P<0,01
	Smith LM 2017 Méta-analyse	1.082.965	OR rachi=0,76 IC95% = 0,71-0,82
		pts	P<0,01
	Zorrilla-Vaca A. 2016 Méta-	362.029 pts OR rachi = 0.77, IC95% 0.70-0.86;
	analyse		P < 0.001
	Lenguerrand E. 2019 Cohorte	679.010 pts OR AG = 1,1 1,0-1,2
	Curry C 2014 Cohorte	7.751 pts	NS
	Kopp S 2015 Rétrospectif	606 pts	NS
	On est donc incité à proposer aux patients une rachianesthésie plutôt qu'une anesthésie
	générale pour une chirurgie prothétique de hanche ou de genou, non seulement en termes
	de réduction de l'incidence des ISO, mais aussi pour une amélioration globale des suites
	postopératoires.

L