Caractérisation morphologique de l'usure des freins

Lors du dimensionnement d'un système de freinage, la géométrie de la garniture est modélisée classiquement avec une surface de contact plane. Hors dans la réalité la surface des garnitures des plaquettes présente une morphologie fortement hétérogène et stochastique. Cette hétérogénéité provient, directement de la constitution et du mode de fabrication de ces dernières. De plus, en service, les garnitures de freins s'usent. Les mécanismes d'usures sont complexes et ne seront pas abordés dans cette étude. Il en résulte une modification continue de la surface de la plaquette tout au long de sa vie en service. L'objectif de ce travail était de mettre en place une méthode de caractérisation de l'état de surface des plaquettes de frein. Cette méthode doit permettre de caractériser, la morphologie d'une part à grande échelle (l'échelle de la plaquette) et d'autre part à plus petite échelle (l'échelle de la rugosité). Pour notre étude nous avions à disposition trois jeux de quatre plaquettes utilisées dans le système de freinage du train de roues de devant d'un véhicule. Un premier jeu constitué de plaquettes neuves. Les deux autres jeux sont issus de tests réalisés chez Hyundai Motors. La procédure est inspirée du test standardisé SAE J2521 (Disc and Drum Brake Dynamometer Squeal Noise Test Procedure). Le nombre de freinage est de 400 pour le premier jeu de plaquettes et de 2600 pour le second. Pour la morphologie à grande échelle, nous avons utilisé un système optique à variation de focus (InfiniteFocus, Alicona?) en utilisant un faible grossissement. Cet appareil nous a permis de mesurer la morphologie sur une grande surface : typiquement, une demi plaquette (29 cm²). Cette surface est reconstruite par assemblage d'images avec chevauchement. Cette méthode de reconstruction d'image est appelée ""stitching"". Pour la rugosité à petite échelle, nous avons effectué les mesures sur un interféromètre en lumière blanche (NewView7300, Zygo ?). Un grossissement 5 fois plus important est utilisé. Sur chaque demie-plaquette nous avons mesuré neufs zones de 5x5 mm² constituées chacune de 30X22 images individuelles se chevauchant (méthode de ""stiching""). Les surfaces ont été choisies pour quadriller d'une façon homogène la plaquette.   Les mesures des morphologies réalisées par variation de focus nous ont permis d'accéder aux profils des garnitures des plaquettes de frein. Ces mesures ont également mis en évidence différentes zones morphologiques sur la surface d'une même plaquette. En interférométrie les mesures ont été traités avec le logiciel MesRug. Cette analyse multi-échelle a permis de classer les différentes zones de la plaquette et de ressortir le paramètre de rugosité (norme ISO 25178) caractéristique

Botulinum toxin type A or selective neurotomy for treating focal spastic muscle overactivity?

To discuss the effectiveness, indications, limitations and side effects of botulinum toxin type A and selective neurotomy for treating focal spastic muscle overactivity to help clinicians choose the most appropriate treatment. Expert opinion based on scientific evidence and personal experience RESULTS: Botulinum toxin type A can decrease muscle tone in different types of spastic muscle overactivity, which allows for treating a large variety of spastic patterns with several etiologies. The toxin effect is sometimes insufficient to improve functional outcome and is transient, thereby requiring repeated injections. Selective neurotomy is a permanent surgical treatment of the reflex component of the spastic muscle overactivity (spasticity) that is effective for spastic equinovarus foot. The neurotomy provides a greater and more constant reduction in spasticity. However, the long-lasting effect on the non-reflex muscle overactivity, especially dystonia, is doubted. The effectiveness, clinical indications, advantages, side effects and limitations of both techniques are discussed. Botulinum toxin type A has the highest level of evidence and the largest range of indications. However, the botulinum toxin effect is reversible and seems less effective, which supports a permanent surgical treatment such as selective neurotomy, especially for the spastic foot. Further research is needed to compare the effect of botulinum toxin type A and selective neurotomy for the different types of spastic muscle overactivity and clinical patterns

Selective tibial neurotomy in the treatment of spastic equinovarus foot in hemiplegic patients: a 2-year longitudinal follow-up of 30 cases.

To assess the long-term efficacy of selective tibial neurotomy in the treatment of spastic equinovarus foot in hemiplegic patients. Intervention study (before-after trial) with an observational design and 2-year follow-up. Spasticity group in a university hospital. Hemiplegic patients (N=30) with spastic equinovarus foot. A selective neurotomy was performed at the level of the motor nerve branches of the tibial nerve. Spasticity (Ashworth scale), muscle strength (Medical Research Council scale), passive ankle dorsiflexion, gait parameters (6 min walking test), and gait kinematics (video assessment) were assessed before and at 2 months, 1 year, and 2 years after selective tibial neurotomy. Compared with preoperative values, there was a statistically significant decrease in triceps surae spasticity, an increase in gait speed, and a reduction in equinus and varus in swing and stance phases at 2 months postoperatively. This improvement persisted at 1 and 2 years after selective tibial neurotomy. Selective tibial neurotomy does not induce permanent triceps muscle weakness or triceps surae-Achilles' tendon complex shortening. This study confirms the long-lasting beneficial effect of selective tibial neurotomy on spasticity, gait speed, and equinovarus deformity in the treatment of spastic equinovarus foot in hemiplegic patients

A case study of intrathecal baclofen pump motor shutdown secondary to the effect of the magnetic field created by a personal digital tablet and magnetic cover.

We present the case of a post-traumatic C6 AIS A tetraplegic patient with spasticity treated with an intrathecal baclofen pump (ITB), who noticed a transient increase in his spasticity each time he used a digital tablet (Ipad®) protected by a magnetic shell placed on his abdomen. Telemetry confirmed transient motor shutdown responsible for withdrawal symptoms each time the tablet was used. Symptoms resolved after the removal of the protective shell. Effects of magnetic fields like magnetic resonance imaging (MRI) are known to stall the pump rotor, which recover at the end of MRI. Other sources of magnetic fields like laptops or new smartphones with magnet charging technology may also interfere with implanted devices. We therefore recommend patients to avoid close contact of magnetic devices with the intrathecal baclofen pump. More robust studies are warranted to assess the effect of the new magnetic technologies on the function of intrathecal pumps

Preliminary study of large and small peripheral nerve fibers in Charcot-Marie-Tooth disease, type I.

Histologic studies of Charcot-Marie-Tooth disease, type I, show a contrast between the lesions of myelinated fibers and the normality of unmyelinated fibers. Conventional electrophysiologic tests only demonstrate the alteration of myelinated fibers but do not study unmyelinated fiber function. We present routine clinical tests that are easily available and effective for the evaluation of small unmyelinated fibers: thermal threshold testing for warmth to evaluate small C unmyelinated somatic fibers and sympathetic skin responses to evaluate small C unmyelinated sympathetic fibers. Five unrelated patients with a diagnosis of Charcot-Marie-Tooth disease, type I, confirmed by biopsy were investigated. All of these patients showed marked reduction or absence of motor and sensory conduction velocities and severe denervation at needle examination. By contrast, thermal threshold testing for warmth and sympathetic skin responses were normal, confirming the normality of small C unmyelinated somatic and sympathetic fibers. We conclude that these noninvasive tests are helpful in the diagnosis of Charcot-Marie-Tooth disease, type I

Effects of Diagnostic Tibial Nerve Block and Selective Tibial Nerve Neurotomy on Spasticity and Spastic co-contractions: A Retrospective Observational Study.

To assess the effects of diagnostic nerve block and selective tibial neurotomy on spasticity and co-contractions in patients with spastic equinovarus foot. Among 317 patients who underwent a tibial neurotomy between 1997 and 2019, 46 patients who met the inclusion criteria were retrospectively screened. Clinical assessment was made before and after diagnostic nerve block and within 6 months after neurotomy. A total of 24 patients underwent a second assessment beyond 6 months after surgery. Muscle strength, spasticity, angle of catch (XV3), passive (XV1) and active (XVA) ankle range of motion were measured. The spasticity angle X (XV1-XV3) and paresis angle Z (XV1-XVA) were calculated with the knee in flexed and extended positions. Tibialis anterior and triceps surae strength remained unchanged, while both Ashworth and Tardieu scores were highly reduced after nerve block and neurotomy at all measurement times. XV3 and XVA increased significantly after block and neurotomy. XV1 increased slightly after neurotomy. Consequently, spasticity angle X and paresis angle Z decreased after nerve block and neurotomy. Tibial nerve block and neurotomy improve active ankle dorsiflexion, probably by reducing spastic co-contractions. The results also confirmed a long-lasting decrease in spasticity after neurotomy and the predictive value of nerve blocks