Nuevos conceptos en neuromodulación cerebral: rol de DTI y estimulación de tractos / New concepts in brain neuromodulation: role of DTI and tract stimulation

Introducción: La estimulación cerebral profunda es una técnica difundida y validada para eltratamiento de múltiples dolencias neurológicas y psiquiátricas, entre ellas el temblor esencial. Objetivo: Evaluar si existe un correlato clínico-anatómico, para un paciente con TE, entre la mejor estimulación lograda y los tractos involucrados. Para esto se realiza una descripción de la técnica utilizada, incluyendo el procesamiento de imágenes necesario. Material y métodos: Se presenta el caso de un paciente de 53 años de edad, con una historia de 23 años de temblor esencial progresivo e incapacitante. Se realizó un implante de DBS bilateral en Vim. Se realizó un post procesamiento de imágenes con un método desarrollado por nuestro equipo a través del cual se permitió evaluar gráficamente el área de estimulación cerebral y sus relaciones con los tractos implicados en la patología (dento-rubro-talámico, haz piramidal y haz lemniscal). Resultados: El paciente presentó una mejoría del 55% medido por escala de temblor de Tolosa. Se obtuvo una correlación anatómica y funcional de lo esperado según imágenes y la respuesta clínica del paciente. Se constataron efectos adversos cuando la estimulación implicaba fibras del haz piramidal y lemniscal, presentando los mejores efectos clínicos cuando el haz dento-rubro-talámico era influenciado por el área de acción del campo eléctrico. Conclusiones: En este reporte mostramos la aplicabilidad de DTI y tractografía para explicar los efectos de la programación de los pacientes con estimulación cerebral profunda.

Introduction: Deep brain stimulation is a widespread and validated technique for the treatment of multiple neurological and psychiatric disorders, including essential tremor. Objective: To evaluate if there is a clinical-anatomical correlate, for a patient with essential tremor, between the best stimulation achieved and the tracts involved. For this, a description of the technique used is made, including the necessary image processing. Methods: We present the case of a 53-year-old patient with a 23-year history of progressive and disabling essential tremor. A bilateral DBS implant was performed on Vim. We performed a post-processing of images with a method developed by our team through which we were able to graphically evaluate the area of brain stimulation and its relationships with the tracts involved in the pathology (dento-rubro-thalamic tract, pyramidal tract and lemniscal tract). Conclusions: In this report we showed the applicability of DTI and tractography to explain the clinical effects of the programming features in patients with deep brain stimulation.

Hybrid matrix grafts to favor tissue regeneration in rabbit femur bone lesions.

At present, typical approaches employed to repair fractures and other bone lesions tend to use matrix grafts to promote tissue regeneration. These grafts act as templates, which promote cellular adhesion, growth and proliferation, osteoconduction, and even osteoinduction, which commonly results in de novo osteogenesis. The present work aimed to study the bone-repairing ability of hybrid matrixes (HM) prepared with polyvinyl alcohol (PVA) and bioactive glass in an experimental rabbit model. The HM were prepared by combining 30% bioactive glass (nominal composition of 58% SiO2 -33 % CaO - 9% P2O5) and 70% PVA. New Zealand rabbits were randomly divided into the control group (C group) and two groups with bone lesions, in which one received a matrix implant HM (Implant group), while the other did not (no Implant group). Clinical monitoring showed no altered parameters from either the Implant or the no Implant groups as compared to the control group, for the variables of diet grades, day and night temperatures and hemograms. In the Implant group, radiologic and tomographic studies showed implanted areas with clean edges in femoral non-articular direction, and radio-dense images that suggest incipient integration. Minimum signs of phlogosis could be observed, whereas no signs of rejection at this imaging level could be identified. Histological analysis showed evidence of osteo-integration, with the formation of a trabecular bone within the implant. Together, these results show that implants of hybrid matrixes of bioactive glass are capable of promoting bone regeneration.

Site and sex effects on tibia structure in distance runners and untrained people.

PURPOSE: The purpose was to study the relationship between mechanical environment and bone structure by comparing the tibia in people with different physical activities. MATERIALS AND METHODS: Indicators of bone mass (bone mineral content), bone material "quality" (cortical volumetric mineral density (vBMD)), and diaphyseal design (endocortical and periosteal perimeters (EcPm and PoPm, respectively), cortical thickness (CtTh), circularity, and bending and torsion cross-sectional moments of inertia (CSMIs)) were determined in serial peripheral quantitative computed tomography scans taken at 5% steps of the tibia in 40 voluntary men and women age 25-40 yr who were either physically inactive or experienced distance runners (n = 10-12 per group). RESULTS: Bone mass and design indicators were higher in runner than in nonrunner men, with a variable effect size along the tibia. In the distal tibia, runners had enhanced bone mineral content and CtTh (resistance to compression), but EcPm, PoPm, circularity, and CSMI were unaffected. In the midshaft, CSMIs (resistance to bending/torsion) were enhanced in runners, whereas bone mass was unaffected. In the proximal third, effects were observed for CtTh, EcPm, and PoPm. In female runners, these benefits were restricted to CSMIs only. Cortical vBMD, naturally lower in men than in women, was reduced in runners of either sex. DISCUSSION: Results are coherent with previous findings in physically inactive people and with Frost's mechanostat theory. The observed group differences in cortical vBMD could reflect an increase in intracortical porosity (enhanced remodeling for damage repair), eventually compensated biomechanically by CSMI improvements. The sex specificity of exercise effects may suggest the interference by the endocrine environment. Results confirm that the mechanical environment is a strong determinant of regional tibia structure and suggest that the endocrine environment may reduce the effects of physical interventions on bone health in fertile women.

Structural analysis of the human tibia by tomographic (pQCT) serial scans.

This study analyses the evaluation of tomographic indicators of tibia structure, assuming that the usual loading pattern shifts from uniaxial compression close to the heel to a combined compression, torsion and bending scheme towards the knee. To this end, pQCT scans were obtained at 5% intervals of the tibia length (S5-S95 sites from heel to knee) in healthy men and women (10/10) aged 20-40 years. Indicators of bone mass [cortical area, cortical/total bone mineral content (BMC)], diaphyseal design (peri/endosteal perimeters, cortical thickness, circularity, bending/torsion moments of inertia - CSMIs), and material quality [(cortical vBMD (bone mineral density)] were determined. The longitudinal patterns of variation of these measures were similar between genders, but male values were always higher except for cortical vBMD. Expression of BMC data as percentages of the minimal values obtained along the bone eliminated those differences. The correlative variations in cortical area, BMC and thickness, periosteal perimeter and CSMIs along the bone showed that cortical bone mass was predominantly associated with cortical thickness toward the mid-diaphysis, and with bone diameter and CSMIs moving more proximally. Positive relationships between CSMIs (y) and total BMC (x) showed men's values shifting to the upper-right region of the graph and women's values shifting to the lower-left region. Total BMC decayed about 33% from S5 to S15 (where minimum total BMC and CSMI values and variances and maximum circularity were observed) and increased until S45, reaching the original S5 value at S40. The observed gender-related differences reflected the natural allometric relationships. However, the data also suggested that men distribute their available cortical mass more efficiently than women. The minimum amount and variance of mass indicators and CSMIs, and the largest circularity observed at S15 reflected the assumed adaptation to compression pattern at that level. The increase in CSMIs (successively for torsion, A-P bending, and lateral bending), the decrease in circularity values and the changes in cortical thickness and periosteal perimeter toward the knee described the progressive adaptation to increasing torsion and bending stresses. In agreement with the biomechanical background, the described relationships: (i) identify the sites at which some changes in tibial stresses and diaphyseal structure take place, possibly associated with fracture incidence; (ii) allow prediction of mass indicators at any site from single determinations; (iii) establish the proportionality between the total bone mass at regions with highly predominant trabecular and cortical bone of the same individual, suitable for a specific evaluation of changes in trabecular mass; and (iv) evaluate the ability of bone tissue to self-distribute the available cortical bone according to specific stress patterns, avoiding many anthropometric and gender-derived influences.

Los huesos son estructuras genéticas, metabólicas, biomecánicas, o todo a la vez? / The bones are genetic structures, metabolic, biomechanical, or all at once?

En las últimas décadas, nuestro grupo de trabajo ha contribuido a desarrollar algunas de las nuevas ideas sobre las verdaderas características estructurales que definen la llamada ôcalidad óseaõ, y sus relaciones con sus determinantes genéticos y con la influencia de los entornos mecánico y sistémico que afectan a las células óseas.La moderna corriente es suficientementeimportante como para haber desviadoel interés de los sponsors internacionales de estudios clínicos controlados. El antiguo estudio densitométrico de masas mineralizadas, y el análisis bioquímico de indicadores del turnover óseo, ceden prioridad hoy al estudio de imágenes seccionales osteo-musculares con criterio biomecánico, y al análisis de las interacciones músculo-hueso. Este conocimiento configura ya una unidadconceptual suficientemente coherentecomo para ser divulgado en forma integrada, para uso del médico práctico. Pese a la obvia complejidad del marco teórico del tema en cuestión, los aspectos más relevantes de la nueva corriente de pensamiento para la correcta interpretación de la Osteología moderna pueden resumirse en 13 puntos críticos, cada uno de ellos defácil comprensión si se lo analiza por separado. A continuación se expone una secuencia didáctica de esos 13 puntos, que enumera y describe, para cada uno de ellos, una triada de aspectos fundamentales para su comprensióny asimilación a la nueva corriente, y deriva de ellos un mensaje práctico para su aplicación fisiopatológica, clínica, o terapéutica.