Mechanobiological modeling of endochondral ossification: an experimental and computational analysis.

Long bone formation starts early during embryonic development through a process known as endochondral ossification. This is a highly regulated mechanism that involves several mechanical and biochemical factors. Because long bone development is an extremely complex process, it is unclear how biochemical regulation is affected when dynamic loads are applied, and also how the combination of mechanical and biochemical factors affect the shape acquired by the bone during early development. In this study, we develop a mechanobiological model combining: (1) a reaction-diffusion system to describe the biochemical process and (2) a poroelastic model to determine the stresses and fluid flow due to loading. We simulate endochondral ossification and the change in long bone shapes during embryonic stages. The mathematical model is based on a multiscale framework, which consisted in computing the evolution of the negative feedback loop between Ihh/PTHrP and the diffusion of VEGF molecule (on the order of days) and dynamic loading (on the order of seconds). We compare our morphological predictions with the femurs of embryonic mice. The results obtained from the model demonstrate that pattern formation of Ihh, PTHrP and VEGF predict the development of the main structures within long bones such as the primary ossification center, the bone collar, the growth fronts and the cartilaginous epiphysis. Additionally, our results suggest high load pressures and frequencies alter biochemical diffusion and cartilage formation. Our model incorporates the biochemical and mechanical stimuli and their interaction that influence endochondral ossification during embryonic growth. The mechanobiochemical framework allows us to probe the effects of molecular events and mechanical loading on development of bone.

Cellular scale model of growth plate: An in silico model of chondrocyte hypertrophy.

The growth plate is the responsible for longitudinal bone growth. It is a cartilaginous structure formed by chondrocytes that are continuously undergoing a differentiation process that starts with a highly proliferative state, followed by cellular hypertrophy, and finally tissue ossification. Within the growth plate chondrocytes display a characteristic columnar organization that potentiates longitudinal growth. Both chondrocyte organization and hypertrophy are highly regulated processes influenced by biochemical and mechanical stimuli. These processes have been studied mainly using in vivo models, although there are few computational approaches focused on the rate of ossification rather than events at cellular level. Here, we developed a model of cellular behavior integrating biochemical and structural factors in a single column of cells in the growth plate. In our model proliferation and hypertrophy were controlled by biochemical regulatory loop formed between Ihh and PTHrP (modeled as a set of reaction-diffusion equations), while cell growth was controlled by mechanical loading. We also examined the effects of static loading. The model reproduced the proliferation and hypertrophy of chondrocytes in organized columns. This model constitutes a first step towards the development of mechanobiological models that can be used to study biochemical interactions during endochondral ossification.

Acid ceramidase treatment enhances the outcome of autologous chondrocyte implantation in a rat osteochondral defect model.

OBJECTIVE: The overall aim of this study was to evaluate how supplementation of chondrocyte media with recombinant acid ceramidase (rhAC) influenced cartilage repair in a rat osteochondral defect model. METHODS: Primary chondrocytes were grown as monolayers in polystyrene culture dishes with and without rhAC (added once at the time of cell plating) for 7 days, and then seeded onto Bio-Gide® collagen scaffolds and grown for an additional 3 days. The scaffolds were then introduced into osteochondral defects created in Sprague-Dawley rat trochlea by a microdrilling procedure. Analysis was performed 6 weeks post-surgery macroscopically, by micro-CT, histologically, and by immunohistochemistry. RESULTS: Treatment with rhAC led to increased cell numbers and glycosaminoglycan (GAG) production (∼2 and 3-fold, respectively) following 7 days of expansion in vitro. Gene expression of collagen 2, aggrecan and Sox-9 also was significantly elevated. After seeding onto Bio-Gide®, more rhAC treated cells were evident within 4 h. At 6 weeks post-surgery, defects containing rhAC-treated cells exhibited more soft tissue formation at the articular surface, as evidenced by microCT, as well as histological evidence of enhanced cartilage repair. Notably, collagen 2 immunostaining revealed greater surface expression in animals receiving rhAC treated cells as well. Collagen 10 staining was not enhanced. CONCLUSION: The results further demonstrate the positive effects of rhAC treatment on chondrocyte growth and phenotype in vitro, and reveal for the first time the in vivo effects of the treated cells on cartilage repair.

Penetrating stab wounds to the abdomen: use of serial US and contrast-enhanced CT in stable patients.

PURPOSE: To evaluate the usefulness of computed tomography (CT) and ultrasonography (US) for the initial assessment of penetrating abdominal stab wounds in patients who presented to the emergency department without indication for immediate laparotomy. MATERIALS AND METHODS: During 36 months, 32 patients with a penetrating stab wound to the abdomen were examined with serial US (at admission and 12 hours later) and helical CT, with contrast material administered orally, intravenously, and rectally. Presence of hemoperitoneum and integrity of solid and hollow viscera were evaluated with both methods. Sonograms were interpreted by the radiologist who performed the examination, and CT images were independently evaluated by two radiologists. Findings of both techniques were compared with clinical outcome and/or surgical findings. RESULTS: One (3.1%) of 32 patients required surgery: Surgical findings were massive hemoperitoneum and an extensive hepatic laceration. Both US and CT depicted these abnormalities. Thirty-one (96.9%) patients were treated conservatively, without surgery, and remained asymptomatic during 28 days of clinical follow-up after discharge from the hospital. US and/or CT showed intraperitoneal abnormalities in 21 of these patients. In 11 patients, both methods showed no evidence of visceral injury or hemoperitoneum, and none of these patients required surgery. CONCLUSION: Serial US and CT help guide treatment for stable patients with penetrating stab injuries to the abdomen.

Resistencia a oxacilina en staphylococcus aislados de bacteremias intrahospitalarias / Resistance a oxaciline in Staphylococcus isolate of bacteremias intrahospital

Se identificó la bacteria asociada a 264 bacteremias ocurridas en pacientes de 4 grandes hospitales de Lima y se evaluó la sensibilidad a oxacilina y a otros antibióticos (amikacina, cefotixina, ceftazimida, ceftriaxona, ciprofloxacina, gentamicina y vancomicina) de las cepas de estafilococo coagulasa negativo (209) y de estafilococo dorado (63) aisladas. La frecuencia relativa de cepas resistentes a oxacilina para cada hospital varió entre 52 por ciento y 0 por ciento para los estafilococos coagulasa negativos, y entre 63 por ciento y 7 por ciento para los estafilococos dorados. Igualmente variable fue la sensibilidad de los estafilococos resistentes a oxacilina a otros antibióticos, excepto para la vancomicina a la que fueron sensibles el 100 por ciento de estas cepas. Se concluye que es necesario considerar la posibilidad de resistencia a oxacilina en los aislamientos intrahospitalarios de estafilococos, casos en los que que la vancomicina debe considerarse como una alternativa, y que es importante mantener una vigilancia de la sensibilidad antibiótica de los gérmenes en general en cada hospital.