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Bone fracture healing is a complex regenerative process which is, in most cases, completed successfully within some months. However, complications in the process are not uncommon and 5% – 10 % of the fractures are diagnosed as delayed unions or non-unions (pseudarthrosis). The objective of this PhD thesis is the evaluation and quantitative monitoring of fracture healing in long bones with the use of ultrasound methods. To this end, a wearable ultrasound system for the monitoring and enhancement of fracture healing was developed and validated on an experimental study using a tibial fracture model. The experimental results were supplemented with two computational studies on two-dimensional (2-D) and three-dimensional (3-D) models of intact and fractured long bones. First, the structure and composition of long bones is presented together with the physiology of fracture healing, the types of fractures, the methods of fracture treatment, and the clinical methods for evaluating bone fracture ...
Bone fracture healing is a complex regenerative process which is, in most cases, completed successfully within some months. However, complications in the process are not uncommon and 5% – 10 % of the fractures are diagnosed as delayed unions or non-unions (pseudarthrosis). The objective of this PhD thesis is the evaluation and quantitative monitoring of fracture healing in long bones with the use of ultrasound methods. To this end, a wearable ultrasound system for the monitoring and enhancement of fracture healing was developed and validated on an experimental study using a tibial fracture model. The experimental results were supplemented with two computational studies on two-dimensional (2-D) and three-dimensional (3-D) models of intact and fractured long bones. First, the structure and composition of long bones is presented together with the physiology of fracture healing, the types of fractures, the methods of fracture treatment, and the clinical methods for evaluating bone fractures. Νext, we provide the mechanical properties of intact and healing bones, we review the literature of the biomechanical methods that have been used to determine the properties of intact and healing bones and we also compare their diagnostic ability with the traditional clinical and imaging examinations. Thereafter, we describe the physical principles of ultrasound propagation in solids, with emphasis on propagation in waveguides, the basic ultrasonic testing and evaluation methods and the state-of-the-art of 304 ultrasonic evaluation of intact and fractured long bones on experimental and clinical studies. The presentation covers also technical issues regarding the ultrasonic method itself as well as its comparison to the corresponding biomechanical methods. In the following, the telemedicine system for the monitoring and enhancement of fracture healing is described. It is pointed out that the study that was conducted for investigating the effect of ultrasound on the enhancement of fracture healing is not presented herein since it does not fall within the objectives of the present thesis. More specifically, in this thesis we describe (a) the components and the architecture of the system, (b) the system application to a tibial fracture model on 40 sheep, (c) the analysis of the signals collected from axialtransmission ultrasound measurements, and (d) the validation of the system’s functionality and the diagnostic ability of the ultrasonic measurements. The system consists of a pair of miniature custom-made ultrasound transducers that are placed on each side of the fracture site, a wearable device for generating and acquiring ultrasound signals and a centralized unit. The novel features of the system are that the transducers are implanted directly into the fracture region enabling the transosseous (i.e. through the bone) propagation of ultrasound and that the wearable platform supports the wireless communication of data from the patient to the centralized system and the doctor. During the experimental study, serial ultrasound measurements were collected at various healing stages annotated by follow-up radiographs, and after the end of the study, densitometry and biomechanical testing were also carried out. From each signal, the velocity of the first arriving signal (FAS) at the receiver was calculated. The analysis of the results showed that the propagation velocity of the FAS was gradually increased as the healing was progressing and that the FAS velocity can early discriminate between complete healing and non-unions. Also, from the pre-clinical study it was demonstrated that the system is functional and safe and can be potentially applied to clinical cases.
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