Subject-specific ex vivo simulations for hip fracture risk assessment in sideways falls.

The risk of hip fracture of a patient due to a fall can be described from a mechanical perspective as the capacity of the femur to withstand the force that it experiences in the event of a fall. So far, impact forces acting on the lateral aspect of the pelvic region and femur strength have been investigated separately. This study used inertia-driven cadaveric impact experiments that mimic falls to the side from standing in order to evaluate the subject-specific force applied to the hip during impact and the fracture outcome in the same experimental model. Eleven fresh-frozen pelvis-femur constructs (6 female, 5 male, age = 77 years (SD = 13 years), BMI = 22.8 kg/m2 (SD = 7.8 kg/m2), total hip aBMD = 0.734 g/cm2 (SD = 0.149 g/cm2)), were embedded into soft tissue surrogate material that matched subject-specific mass and body shape. The specimens were attached to metallic lower-limb constructions with subject-specific masses and subjected to an inverted pendulum motion. Impact forces were recorded with a 6-axis force plate at 10,000 Hz and three dimensional deflections in the pelvic region were tracked with two high-speed cameras at 5000 Hz. Of the 11 specimens, 5 femur fractures and 3 pelvis fractures were observed. Three specimens did not fracture. aBMD alone did not reliably separate femur fractures from non-fractures. However, a mechanical risk ratio, which was calculated as the impact force divided by aBMD, classified specimens reliably into femur fractures and non-fractures. Single degree of freedom models, based on specimen kinetics, were able to predict subject-specific peak impact forces (RMSE = 2.55% for non-fractures). This study provides direct evidence relating subject-specific impact forces and subject-specific strength estimates and improves the assessment of the mechanical risk of hip fracture for a specific femur/pelvis combination in a sideways fall.

Monitoring of muscle and bone recovery in spinal cord injury patients treated with electrical stimulation using three-dimensional imaging and segmentation techniques: methodological assessment.

Muscle tissue composition accounting for the relative content of muscle fibers and intramuscular adipose and loose fibrous tissues can be efficiently analyzed and quantified using images from spiral computed tomography (S-CT) technology and the associated distribution of Hounsfield unit (HU) values. Muscle density distribution, especially when including the whole muscle volume, provides remarkable information on the muscle condition. Different physiological and pathological scenarios can be depicted using the muscle characterization technique based on the HU values and the definition of appropriate intervals and the association of such intervals to different colors. Using this method atrophy, degeneration, and restoration in denervated muscle undergoing electrical stimulation treatments can be clearly displayed and monitored. Moreover, finite element methods are employed to calculate Young's modulus on the patella bone and to analyze correlation between muscle contraction and bone strength changes. The reliability of this tool though depends on S-CT assessment and calibration. To assess imaging quality and the use of HU values to display muscle composition, different S-CT devices are compared using a Quasar body scanner. Density distributions and volumes of various calibration elements such as lung, polyethylene, water equivalent, and trabecular and dense bone are measured with different scanning protocols and at different points of time. The results show that every scanned element undergoes HU variations, which are greater for materials at the extremes of the HU scale, such as dense bone and lung inhale. Moreover, S-CT scanning with low tube voltages (80 KV) produces inaccurate HU values especially in bones. In conclusion, 3-D modeling techniques based on S-CT scanning is a powerful follow-up tool that may provide structural information at the millimeter scale, and thus may drive choice and timing to validate rehabilitation protocols.