RESUMO
PURPOSE: To enhance bone healing through controlled interfragmentary movements, numerous experiments have been conducted in animal models employing external fixation devices to apply mechanical stimulation to the fracture site. However, the efficacy of these fixators has been questioned. On the other hand, intramedullary nailing is a widely established clinical practice for reducing closed tibial fractures. MATERIAL AND METHODS: In an effort to enhance bone healing, to overcome the disadvantages of external fixators (i.e., non-uniform linear movement), and to enhance the advantages of intramedullary nailing (i.e., reduced risk of infection), an active intramedullary nail has been designed and fabricated. Active nail will provide controlled in-situ stimulation (simultaneously axial and shear) from a selectable acceleration (0.35 to 8.17g - axial and 0.44g to 10.46 g - shear), associated to a discreet set of high-frequency values (29.82 - 172.05 Hz - axial and 29.68 to 172.13 - shear). RESULTS: Five active intramedullary nails were fabricated, capable of producing average acceleration between 0.35 and 10.4 g. Acceleration is applied simultaneously by all three axes (x, y, and z), resulting in axial and shear stimulation. For each acceleration level, there are a limited number of frequencies that can be selected. For each frequency, there are a limited number of acceleration levels that can be delivered. Bone morphology produces different levels of acceleration in each axe. Acceleration levels are controlled externally only by the variable power source (1.5VDC to 6VDC). Accelerated in-vitro testing showed that the life of the device exceeded the required active period. Mechanical test showed that in case of failure of the active component, the active intramedullary nail will act as a standard nail, allowing bone healing to continue its normal course. Ex vivo experiments were conducted inserting one active intramedullary nail in two intact adult sheep tibia. Results indicate that the strain induced by the active intramedullary nail (from 18.62 µÎµ to 38.13 µÎµ) has been reported to be osteogenic. Additional experiments are required in order to statistically validate the strain that can be induced in vivo by the active intramedullary nail. Also, in vivo experiments using simple fractures of the tibial shaft need to be conducted in order to assess if effectively, applying active mechanical stimulation in situ enhances bone healing.
Assuntos
Pinos Ortopédicos , Fixação Intramedular de Fraturas/métodos , Fraturas da Tíbia/cirurgia , Animais , Desenho de Equipamento , Humanos , Masculino , OvinosRESUMO
Pathological and age-related changes may affect an individual's gait, in turn raising the risk of falls. In elderly, falls are common and may eventuate in severe injuries, long-term disabilities, and even death. Thus, there is interest in estimating the risk of falls from gait analysis. Estimation of the risk of falls requires consideration of the longitudinal evolution of different variables derived from human gait. Bayesian networks are probabilistic models which graphically express dependencies among variables. Dynamic Bayesian networks (DBNs) are a type of BN adequate for modeling the dynamics of the statistical dependencies in a set of variables. In this work, a DBN model incorporates gait derived variables to predict the risk of falls in elderly within 6 months subsequent to gait assessment. Two DBNs were developed; the first (DBN1; expert-guided) was built using gait variables identified by domain experts, whereas the second (DBN2; strictly computational) was constructed utilizing gait variables picked out by a feature selection algorithm. The effectiveness of the second model to predict falls in the 6 months following assessment is 72.22%. These results are encouraging and supply evidence regarding the usefulness of dynamic probabilistic models in the prediction of falls from pathological gait.