RESUMEN
We have developed a simple, inexpensive and innovative device for reproducing the global mechanical behavior of spinal motion segments and the local mechanical environment experienced by lumbar intervertebral discs. The device has several broad functions: (1) exploration of the basic mechanics underlying this complex skeletal system, (2) connecting changes in tissue characteristics with overall motion segment function, and (3) evaluation of strategies for repair and replacement of disc components. This "disc emulator" consists of three main parts: (1) an artificial annulus fibrosus (AAF), made out of silicone, with lumbar disc geometry and adjustable material properties, (2) a hydrogel nucleus pulposus (NP) also with lumbar disc geometry and adjustable material properties, and (3) simulated vertebral bodies 3D printed with trabecular bone simulated by a rigid polymer (Acrylonitrile Butadiene Styrene, ABS) and end plates crafted from a compliant polymer (Thermoplastic Polyurethane, TPU). Mechanical compression experiments have been conducted using the disc emulator under similar protocols to published studies of human cadaver samples. Bulging of the artificial annulus fibrosus was examined under axial compression loads using digital image correlation (DIC), and results show close agreement. We see this approach of using anatomical geometry and multiple adjustable components as a useful means of creating accurate local stress/strain environments for preliminary material evaluation, without the variability and difficulty inherent indirect testing of cadaveric materials.
Asunto(s)
Materiales Biocompatibles , Prótesis Articulares , Núcleo Pulposo , Estrés Mecánico , Fenómenos Biomecánicos , Humanos , Disco Intervertebral , Ensayo de MaterialesRESUMEN
Imaging techniques for quantifying changes in the hierarchical structure of deforming joints are constrained by destructive sample treatments, sample-size restrictions and lengthy scan times. Here, we report the use of fast low-dose pink-beam synchrotron X-ray tomography in combination with mechanical loading at nanometric precision for in situ imaging, at resolutions below 100 nm, of the mechanical strain in intact untreated joints under physiologically realistic conditions. We show that in young, older and osteoarthritic mice, hierarchical changes in tissue structure and mechanical behaviour can be simultaneously visualized, and that the tissue structure at the cellular level correlates with the mechanical performance of the whole joint. We also use the tomographic approach to study the colocalization of tissue strains to specific chondrocyte lacunar organizations within intact loaded joints and to explore the role of calcified-cartilage stiffness on the biomechanics of healthy and pathological joints.
Asunto(s)
Articulaciones/diagnóstico por imagen , Sincrotrones , Tomografía por Rayos X/métodos , Animales , Condrocitos/ultraestructura , Imagenología Tridimensional , Articulaciones/ultraestructura , Masculino , Ratones , Nanoestructuras , Osteoartritis/diagnóstico por imagen , Osteoartritis/patología , Estrés MecánicoRESUMEN
While metal or plastic interbody spinal fusion devices are manufactured to appropriate mechanical standards, mechanical properties of commercially prepared structural allograft bone remain relatively unassessed. Robust models predicting compressive load to failure of structural allograft bone based on easily measured variables would be useful. Three hundred twenty seven femoral rings from 34 cadaver femora were tested to failure in axial compression. Predictive variables included age, gender, bone mineral density (BMD), position along femoral shaft, maximum/minimum wall thickness, outer/inner diameter, and area. We used support vector regression and 10-fold cross-validation to develop robust nonlinear predictive models for load to failure. Model performance was measured by the root-mean-squared-deviation (RMSD) and correlation coefficients (r). A polynomial model using all variables had RMSD = 7.92, r = 0.84, indicating excellent performance. A model using all variables except BMD was essentially unchanged (RMSD = 8.12, r = 0.83). Eliminating both age and BMD produced a model with RMSD = 8.41, r = 0.82, again essentially unchanged. Compressive strength of structural allograft bone can be estimated using easily measured geometric parameters, without including BMD or age. As DEXA is costly and cumbersome, and setting upper age-limits for potential donors reduces the supply, our results may prove helpful to increase the quality and availability of structural allograft.
Asunto(s)
Densidad Ósea , Trasplante Óseo , Fémur/trasplante , Absorciometría de Fotón , Factores de Edad , Aloinjertos , Trasplante Óseo/tendencias , Calcificación Fisiológica , Femenino , Humanos , Modelos Lineales , Masculino , Fenómenos Mecánicos , Valor Predictivo de las PruebasRESUMEN
Meniscal injury is a common cause of canine lameness. Tissue engineered bioscaffolds may be a treatment option for dogs suffering from meniscal damage. The aim of this study was to compare in vitro meniscal-like matrix formation and biomechanical properties of porcine intestinal submucosa sheets (SIS), used in canine meniscal regenerative medicine, to synoviocyte-seeded SIS bioscaffold (SSB), cultured with fetal bovine serum (SSBfbs) or chondrogenic growth factors (SSBgf). Synoviocytes from nine dogs were seeded on SIS and cultured for 30days with 17.7% fetal bovine serum or recombinant chondrogenic growth factors (IGF-1, TGFß1 and bFGF). The effect on fibrochondrogenesis was determined by comparing mRNA expression of collagen types Iα and IIα, aggrecan, and Sry-type homeobox protein-9 (SOX9) as well as protein expression of collagens I and II, glycosaminoglycan (GAG), and hydroxyproline. The effect of synoviocyte seeding and culture conditions on biochemical properties was determined by measuring peak load, tensile stiffness, resilience, and toughness of bioscaffolds. Pre-culture SIS contained 13.6% collagen and 2.9% double-stranded DNA. Chondrogenic growth factor treatment significantly increased SOX9, collagens I and IIα, aggrecan gene expression (P<0.05), and histological deposition of fibrocartilage extracellular matrix (GAG and collagen II). Culture with synoviocytes increased SIS tensile peak load at failure, resilience, and toughness of bioscaffolds (P<0.05). In conclusion, culturing SIS with synoviocytes prior to implantation might provide biomechanical benefits, and chondrogenic growth factor treatment of cultured synoviocytes improves in vitro axial meniscal matrix formation.
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Perros , Fibrocartílago/citología , Membrana Sinovial/citología , Ingeniería de Tejidos/veterinaria , Andamios del Tejido , Animales , Fibrocartílago/fisiología , Porcinos , Técnicas de Cultivo de Tejidos/veterinaria , Ingeniería de Tejidos/métodosRESUMEN
High-resolution X-ray tomography (microCT) is increasingly available in research settings, and is a valuable tool in the study of mineralized tissue development. At resolutions of 2-20 µm, achievable for typical murine scale samples, it provides nondestructive visualization of three-dimensional tissue morphology and a limited ability for quantitative measurement of developmental parameters. Sample preparation is simple and can be tailored for compatibility with other biological assays. Here, we describe the application of microCT to the investigation of lower incisor development in the context of overall skull morphology.
Asunto(s)
Cráneo/diagnóstico por imagen , Tomografía por Rayos X/métodos , Diente/diagnóstico por imagen , Animales , RatonesRESUMEN
PURPOSE: To develop, test and evaluate affordable haptic technology to provide robotic-assisted repetitive motion fine-motor training. METHODS: A haptic computer/user interface was modified by adding a pantograph to hold a pen and to increase the haptic workspace. Custom software moves a pen attached to the device through prescribed three-dimensional (3D) stroke sequences to create two-dimensional glyphs. The pen's position is recorded in 3D coordinates at 1 kHz. Twenty-one healthy child volunteers were taught a standard handwriting curriculum in a group setting, two times per week for 45-60 min each session over 8 wks. The curriculum was supplemented by the device under the supervision of occupational therapy students. Outcomes were measured using the Evaluation Tool of Children's Handwriting (ETCH), and the Beery-Buktenica Developmental Test of visual-motor integration. RESULTS: Word legibility made significant gains on near point copying task (p=0.04; effect size=0.95). Letter legibility made no significant improvement. One healthy volunteer with illegible handwriting improved significantly on 8 of 14 ETCH measures. The children found the device engaging, but made several recommendations to redesign the pantograph and scribing movements. CONCLUSIONS: A consumer haptic device can be modified for robotic-assisted repetitive motion training for children. The device is affordable, portable, and engaging. It is safe for healthy volunteers. Objective time-stamped data offer the potential for telerehabilitation between a remote therapist and the school or home.
Asunto(s)
Periféricos de Computador , Destreza Motora , Robótica/instrumentación , Telemedicina , Interfaz Usuario-Computador , Curriculum , Humanos , Proyectos Piloto , Robótica/métodos , Programas Informáticos , Estadística como AsuntoRESUMEN
The transcription factor Ctip2/Bcl11b plays essential roles in developmental processes of the immune and central nervous systems and skin. Here we show that Ctip2 also plays a key role in tooth development. Ctip2 is highly expressed in the ectodermal components of the developing tooth, including inner and outer enamel epithelia, stellate reticulum, stratum intermedium, and the ameloblast cell lineage. In Ctip2(-/-) mice, tooth morphogenesis appeared to proceed normally through the cap stage but developed multiple defects at the bell stage. Mutant incisors and molars were reduced in size and exhibited hypoplasticity of the stellate reticulum. An ameloblast-like cell population developed ectopically on the lingual aspect of mutant lower incisors, and the morphology, polarization, and adhesion properties of ameloblasts on the labial side of these teeth were severely disrupted. Perturbations of gene expression were also observed in the mandible of Ctip2(-/-) mice: expression of the ameloblast markers amelogenin, ameloblastin, and enamelin was down-regulated, as was expression of Msx2 and epiprofin, transcription factors implicated in the tooth development and ameloblast differentiation. These results suggest that Ctip2 functions as a critical regulator of epithelial cell fate and differentiation during tooth morphogenesis.
Asunto(s)
Ameloblastos/citología , Proteínas de Unión al ADN/fisiología , Odontogénesis , Proteínas Represoras/fisiología , Proteínas Supresoras de Tumor/fisiología , Animales , Diferenciación Celular , Regulación hacia Abajo/genética , Desarrollo Embrionario , Células Epiteliales/citología , Mandíbula/crecimiento & desarrollo , Ratones , Ratones Noqueados , Diente/crecimiento & desarrollo , Factores de Transcripción/genéticaRESUMEN
Although the tibia is a common site of stress fractures in runners, the loading of the tibia during running is not well understood. An integrated experimental and modeling approach was therefore used to estimate the bone contact forces acting on the distal end of the tibia during the stance phase of running, and the contributions of external and internal sources to these forces. Motion capture and force plate data were recorded for 10 male runners as they ran at 3.5-4 m/s. From these data, the joint reaction force (JRF), muscle forces, and bone contact force on the tibia were computed at the ankle using inverse dynamics and optimization methods. The distal end of the tibia was compressed and sheared posteriorly throughout most of stance, with respective peak forces of 9.00+/-1.13 and 0.57+/-0.18 body weights occurring during mid stance. Internal muscle forces were the primary source of tibial compression, whereas the JRF was the primary source of tibial shear due to the forward inclination of the leg relative to the external ground reaction force. The muscle forces and JRF both acted to compress the tibia, but induced tibial shear forces in opposing directions during stance, magnifying tibial compression and reducing tibial shear. The superposition of the peak compressive and posterior shear forces at mid stance may contribute to stress fractures in the posterior face of the tibia. The implications are that changes in running technique could potentially reduce stress fracture risk.
Asunto(s)
Carrera/fisiología , Tibia/fisiología , Adulto , Humanos , Masculino , Estrés MecánicoRESUMEN
Thoracic compression fractures are often described as anterior wedge fractures. Although the radiographic signs of these fractures are easily identified, the mechanism of the trabecular failure is not well understood. The current study addressed this mechanism in the lower thoracic spine by measuring the trabecular strain. Trabecular strain was measured in six human thoracic cadaver spines during 1) compressive and 2) flexural loading. The strains were measured at incremental loads using a texture correlation. They were analyzed by global contour plots and regional analysis of the T11 vertebrae. Specimens loaded under only compression exhibited uniform strains in the vertebral body. During flexion, however, the strains were concentrated in the anterosuperior margin of the vertebral body and the compressive and shear strain magnitudes in this region were significantly increased. These results demonstrate that the flexural position places the lower thoracic spine at greater risk of anterior compression fracture as seen clinically.
Asunto(s)
Fenómenos Biomecánicos , Fracturas de la Columna Vertebral/etiología , Vértebras Torácicas , Anciano , Anciano de 80 o más Años , Fenómenos Biomecánicos/instrumentación , Fenómenos Biomecánicos/métodos , Cadáver , Fuerza Compresiva , Femenino , Humanos , Estrés Mecánico , Resistencia a la Tracción , Vértebras Torácicas/anatomía & histología , Vértebras Torácicas/patologíaRESUMEN
A closed intraarticular fracture is a complex injury that consists of a physical disruption of the subchondral bone and articular surface, and an impaction injury to the articular surface that occurs at the time of the fracture. Few experimental models have been able to incorporate the elements of displaced articular fractures and blunt impaction injury to the articular surface. This work details the initial stages of an attempt to develop such model. Using a model of a dorsal wall fracture of the acetabulum in a goat, we have developed a bench-top method for assessing articular contact stress. Additionally, preliminary in vivo survival data are presented.
Asunto(s)
Acetábulo/lesiones , Fracturas Óseas/fisiopatología , Lesiones de la Cadera/fisiopatología , Análisis de Varianza , Animales , Modelos Animales de Enfermedad , Femenino , Curación de Fractura , Cabras , Técnicas In Vitro , Estrés MecánicoRESUMEN
OBJECTIVE: To determine relative stiffness of various methods of posterior pelvic ring internal fixation. DESIGN: Simulated single leg stance loading of OTA 61-Cl.2, a2 fracture model (unilateral sacroiliac joint disruption and pubic symphysis diastasis). SETTING: Orthopaedic biomechanic laboratory. OUTCOME VARIABLES: Pubic symphysis gapping, sacroiliac joint gapping, hemipelvis coronal plane rotation. METHODS: Nine different posterior pelvic ring fixation methods were tested on each of six hard plastic pelvic models. Pubic symphysis was plated. The pelvic ring was loaded to 1000N. RESULTS: All data were normalized to values obtained with posterior fixation with a single iliosacral screw. The types of fixation could be grouped into three categories based on relative stiffness of fixation: For sacroiliac joint gapping, group 1-fixation stiffness 0.8 and above (least stiff) includes a single iliosacral screw (conditions A and J), an isolated tension band plate (condition F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate stiffness) includes a tension band plate and an iliosacral screw (condition E), one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (greatest stiffness) includes two anterior sacroiliac plates (condition D), two iliosacral screws (condition B), and two anterior sacroiliac plates and an iliosacral screw (condition C). For sacroiliac joint rotation, group 1-fixation stiffness 0.8 and above includes a single iliosacral screw (conditions A and J), two anterior sacroiliac plates (condition D), a tension band plate in isolation or in combination with an iliosacral screw (conditions E and F), and two sacral bars (condition H); group 2-fixation stiffness 0.6 to 0.8 (intermediate level of instability) includes either one or two sacral bars in combination with an iliosacral screw (conditions G and I); group 3-fixation stiffness 0.6 and below (stiffest fixation) consists of two iliosacral screws (condition B) and two anterior sacroiliac plates and an iliosacral screw (condition C). DISCUSSION: Under conditions of maximal instability with similar material properties between specimens, differences in stiffness of posterior pelvic ring fixation can be demonstrated. The choice of which method to use is multifactorial.
Asunto(s)
Fijación de Fractura/efectos adversos , Fracturas Óseas/cirugía , Inestabilidad de la Articulación/etiología , Inestabilidad de la Articulación/fisiopatología , Huesos Pélvicos/lesiones , Soporte de Peso/fisiología , Fracturas Óseas/fisiopatología , Humanos , Modelos Biológicos , Dispositivos de Fijación Ortopédica , Huesos Pélvicos/fisiopatología , Huesos Pélvicos/cirugía , Rango del Movimiento Articular/fisiología , Articulación Sacroiliaca/fisiopatología , Articulación Sacroiliaca/cirugíaRESUMEN
Previous studies have documented how partial and complete meniscectomy affect articular contact pressure, but changes in load transfer through the complete osteochondral structure of the proximal tibia after partial and complete meniscectomy are not well known. The current study measured trabecular bone strain changes in the medial tibial plateau resulting from partial and complete medial meniscectomy. Midcoronal sections were prepared from knees from cadavers. High quality digital images, made from contact radiographs of loaded samples, were compared with digital images of unloaded samples using in-house software to measure trabecular bone strain. Measurements were made on specimens with an intact medial meniscus, after removal of the inner (2/3) of the meniscus, and after complete meniscectomy. Partial meniscectomy caused minimal increases in trabecular bone strain throughout the proximal tibia. However specimens with complete meniscectomy had significant trabecular bone strain increases. Many patients sustaining meniscus tears are young, therefore, it is important to understand mechanical changes associated with partial meniscectomy. The data suggest partial meniscectomy causes little change in load transfer through the proximal tibia, supporting partial meniscectomy as a good surgical option for patients with meniscus tears.
Asunto(s)
Meniscos Tibiales/fisiopatología , Meniscos Tibiales/cirugía , Procedimientos Ortopédicos , Esguinces y Distensiones/fisiopatología , Esguinces y Distensiones/cirugía , Tibia/fisiopatología , Tibia/cirugía , Soporte de Peso/fisiología , Anciano , Placa de Crecimiento/diagnóstico por imagen , Placa de Crecimiento/fisiopatología , Placa de Crecimiento/cirugía , Humanos , Articulación de la Rodilla/diagnóstico por imagen , Articulación de la Rodilla/fisiopatología , Articulación de la Rodilla/cirugía , Meniscos Tibiales/diagnóstico por imagen , Persona de Mediana Edad , Radiografía , Resistencia al Corte , Esguinces y Distensiones/diagnóstico por imagen , Tibia/diagnóstico por imagenRESUMEN
Subchondral stiffening is a hallmark pathologic feature of osteoarthritis but its mechanical and temporal relationship to the initiation or the progression of osteoarthritis is not established. The mechanical effect of subchondral stiffening on the surrounding trabecular bone is poorly understood. This study employs a relatively new application of digital image correlation to measure strain in the trabecular region of the proximal medial tibia in normal specimens and in specimens with simulated subchondral bone stiffening. Coronal sections from eight normal human cadaveric proximal tibiae were loaded in static compression and high resolution contact radiographs were made. Repeat contact radiographs were collected after the subchondral bone near the jointline was stiffened using polymethylmethacrylate. Digital images, made from loaded and unloaded contact radiographs, were compared using in-house software to measure trabecular displacement and calculate trabecular bone strain. Overall strain was higher in the stiffened specimens suggesting experimental artifiact significantly affected our results. Consistent increases in median maximum shear strain, median maximum principal strain, median minimum principal strain, and peak shear strain were measured near the inner and outer edges of the stiffened segment. Our experiment provides direct experimental measurement of increases in trabecular bone strain caused by subchondral stiffening, however, the clinical and biologic importance of strain increases is unknown.
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Intensificación de Imagen Radiográfica/métodos , Interpretación de Imagen Radiográfica Asistida por Computador/métodos , Tibia/diagnóstico por imagen , Tibia/fisiología , Soporte de Peso/fisiología , Anciano , Cadáver , Fuerza Compresiva , Elasticidad , Humanos , Técnicas In Vitro , Persona de Mediana Edad , Polimetil Metacrilato , Resistencia al Corte , Estrés MecánicoRESUMEN
OBJECTIVE: To measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the distal tibia. DESIGN: Cadaveric biomechanical model. SETTING: Contact radiographs were made from sagittal sections of human cadaveric distal tibia under no load and loaded to 400 N. Digital images, made from contact radiographs of unloaded specimens, were compared to corresponding digital images of loaded specimens using custom software that measures trabecular deformation and calculates trabecular bone strain. INTERVENTION: Twelve specimens were initially loaded intact in compression. Testing was repeated after creating three increasing circular subchondral bone defects in the center of a sagittal cross-section of the distal tibia. Defects were 10%, 20%, and 30% of the sagittal diameter of the distal tibia. MAIN OUTCOME MEASURES: Maximum shear strain, maximum principal strain, and minimum principal strain were measured in six discrete regions in the trabecular bone in the distal tibia. RESULTS: Small defects (10%) caused minimal strain elevations. Significant increases in trabecular bone strain were measured with medium (20%) and large (30%) defects. Compressive strain increases as high as 1400 microstrain (10 strain) were measured adjacent to and proximal to the defects with medium and large defects. CONCLUSIONS: Subchondral defects cause size-dependent elevations in trabecular bone strain in the distal tibia. Medium and large defects caused rapidly increasing trabecular bone deformation under load.
Asunto(s)
Fracturas Conminutas/fisiopatología , Fracturas de la Tibia/fisiopatología , Adulto , Anciano , Traumatismos del Tobillo/patología , Traumatismos del Tobillo/fisiopatología , Fenómenos Biomecánicos , Cartílago Articular/patología , Fracturas Conminutas/diagnóstico por imagen , Fracturas Conminutas/patología , Humanos , Persona de Mediana Edad , Intensificación de Imagen Radiográfica , Fracturas de la Tibia/diagnóstico por imagen , Fracturas de la Tibia/patologíaRESUMEN
OBJECTIVE: To measure trabecular bone strain changes resulting from three increasing subchondral bone defects in the medial tibial plateau. DESIGN: Cadaveric biomechanical model. SETTING: Contact radiographs were made from coronal sections of human cadaveric proximal tibia under no load and loaded to 400 newtons (N). Digital images made from contact radiographs of unloaded specimens were compared to corresponding digital images of loaded specimens using in-house software that detects trabecular deformation and measure trabecular bone strain. INTERVENTION: Ten specimens were loaded intact and with three increasing circular subchondral bone defects and centered under the subchondral plates in the medial tibial plateau that were 10%, 20%, and 30% of the coronal width of the medial plateau. MAIN OUTCOME MEASURE: Maximum shear strain and minimum principal strain were measured at approximately 2,600 discrete points in the trabecular bone in the medial tibial plateau. RESULTS: Trabecular strain increased most dramatically as defects increased from the medium (20%) to the large (30%) defect. The regions of greatest strain elevation were between the physeal scar and joint line near the medial cortex. Small (10%) and medium (20%) defects resulted in modest strain elevations. CONCLUSIONS: Subchondral defects cause size-dependent elevations in trabecular bone strain in the medial tibial plateau. A size threshold may exist, above which the trabecular bone is subjected to rapidly increasing deformation under load.