A novel ex vivo model of compressive immature rib fractures at pathophysiological rates of loading

Cardiopulmonary Resuscitation Induced Posterior Rib Fractures in Nontraumatic Pediatric Deaths

ABSTRACT

Posterior rib fractures are considered suspicious for nonaccidental injury when observed in infants without significant trauma history or underlying bone disease. The biomechanical mechanism postulated for causing posterior rib fractures is anterior/posterior compression of the chest with posterior levering of the rib head over the transverse process of the vertebra creating a focal area of stress. The recommended "2-thumb" cardiopulmonary resuscitation method involves the administrator placing both thumbs on the sternum of the patient, encircling the chest with the hands, and placing the finger tips lateral to the spine. From this position, the administrator compresses the chest in an anterior/posterior direction by pressing on the sternum. Theoretically, the 2-thumb method should focus all force on the sternum while the back is supported by the fingers limiting posterior levering of the ribs and reducing the risk of posterior rib fractures. However, posterior rib fractures have been found during the autopsy of infants who received 2-thumb cardiopulmonary resuscitation, had no traumatic history, had a nontraumatic cause of death, and had no indication of underlying bone disease. This case study series presents the demographics, birth histories, circumstances surrounding death, and autopsy findings of four such medical examiner cases.

How stiff is skin?

The measurement of the mechanical properties of skin (such as stiffness, extensibility and strength) is a key step in characterisation of both dermal ageing and disease mechanisms and in the assessment of tissue-engineered skin replacements. However, the biomechanical terminology and plethora of mathematical analysis approaches can be daunting to those outside the field. As a consequence, mechanical studies are often inaccessible to a significant proportion of the intended audience. Furthermore, devices for the measurement of skin function in vivo generate relative values rather than formal mechanical measures, therefore limiting the ability to compare studies. In this viewpoint essay, we discuss key biomechanical concepts and the influence of technical and biological factors (including the nature of the testing apparatus, length scale, donor age and anatomical site) on measured mechanical properties such as stiffness. Having discussed the current state-of-the-art in macro-mechanical and micromechanical measuring techniques and in mathematical and computational modelling methods, we then make suggestions as to how these approaches, in combination with 3D X-ray imaging and mechanics methods, may be adopted into a single strategy to characterise the mechanical behaviour of skin.

Modeling female and male rib geometry with logarithmic spirals

In this study we present a novel six-parameter shape model of the human rib centroidal path using logarithmic spirals. It provides a reduction in parameter space from previous models of overall rib shape, while simultaneously reducing fitting error by 34% and increasing curvature continuity. Furthermore, the model directly utilizes geometric properties such as rib end-to-end span, aspect ratio, rib "skewness", and inner angle with the spine in its parameterization, making the effects of each parameter on overall shape intuitive and easy to visualize. The model was tested against 2197 rib geometries extracted from CT scans from a population of 100 adult females and males of uniformly distributed ages between 20 and 70. Significant size and shape differences between genders were identified, and shape model utility is demonstrated by the production of statistically average male and female rib shapes for all rib levels. Simulated mechanical loading of the resulting model rib shapes showed that the stiffness of statistically average male and female ribs matched well with the average rib stiffness from each separate population. This in-plane rib shape model can be used to characterize variation in human rib geometry seen throughout the population, including investigation of the overall changes in shape and resultant mechanical properties that ribs undergo during aging or disease progression.