A probabilistic approach for assessing the mechanical performance of intertrochanteric fracture stabilized with proximal femoral nail antirotation.

Maintaining post-operative mechanical stability is crucial for successfully healing intertrochanteric fractures treated with the Proximal Femoral Nail Antirotation (PFNA) system. This stability is primarily dependent on the bone mineral density (BMD) and strain on the fracture. Current PFNA failure analyses often overlook the uncertainties related to BMD and body weight (BW). Therefore, this study aimed to develop a probabilistic model using finite element modeling and engineering reliability analysis to assess the post-operative performance of PFNA under various physiological loading conditions. The model predictions were validated through a series of experimental test. The results revealed a negative nonlinear relationship between the BMD and compressive strain. Conversely, the BW was positively and linearly correlated with the compressive strain. Importantly, the compressive strain was more sensitive to BW than to BMD when the BMD exceeded 0.6 g/cm3. Potential trabecular bone compression failure is also indicated if BMD is equal to or below 0.15 g/cm3 and BW increases to approximately 2.5 times the normal or higher. This study emphasizes that variations in the BMD significantly affect the probability of failure of a PFNA system. Thus, careful planning of post-operative physical therapy is essential. For patients aged > 50 years restrictions on high-intensity activities are advised, while limiting strenuous movements is recommended for those aged > 65 years.

Depth camera-based model for studying the effects of muscle loading on distal radius fracture healing.

BACKGROUND: Distal radius fractures (DRFs) treated with volar locking plates (VLPs) allows early rehabilitation exercises favourable to fracture recovery. However, the role of rehabilitation exercises induced muscle forces on the biomechanical microenvironment at the fracture site remains to be fully explored. The purpose of this study is to investigate the effects of muscle forces on DRF healing by developing a depth camera-based fracture healing model. METHOD: First, the rehabilitation-related hand motions were captured by a depth camera system. A macro-musculoskeletal model is then developed to analyse the data captured by the system for estimating hand muscle and joint reaction forces which are used as inputs for our previously developed DRF model to predict the tissue differentiation patterns at the fracture site. Finally, the effect of different wrist motions (e.g., from 60° of extension to 60° of flexion) on the DRF healing outcomes will be studied. RESULTS: Muscle and joint reaction forces in hands which are highly dependent on hand motions could significantly affect DRF healing through imposed compressive and bending forces at the fracture site. There is an optimal range of wrist motion (i.e., between 40° of extension and 40° of flexion) which could promote mechanical stimuli governed healing while mitigating the risk of bony non-union due to excessive movement at the fracture site. CONCLUSION: The developed depth camera-based fracture healing model can accurately predict the influence of muscle loading induced by rehabilitation exercises in distal radius fracture healing outcomes. The outcomes from this study could potentially assist osteopathic surgeons in designing effective post-operative rehabilitation strategies for DRF patients.

Quantifying Agglomerate-to-Wall Impaction in Dry Powder Inhalers.

PURPOSE: The probability of agglomerate-to-wall collision was quantified using a unique image processing technique applied to high-speed microscopic images. The study aimed to investigate the effects of flow rate and particle size on the percentage of colliding agglomerates detected within an in-house powder dispersion device. METHOD: The device consists of a swirl chamber and two tangential inlets in various configurations, designed to emulate the geometric features of commercial devices such as the Aerolizer® and Osmohaler®. The test cases were conducted with constant flow rates of 30 SLPM and 60 SLPM. Four powder samples were tested, including carrier Respitose® SV010 (median volume diameter 104 µm, span 1.7) and mannitol of three constituent primary particle sizes (3 µm, 5 µm and 7 µm; span 1.6 - 1.9). RESULTS: At the lower flow rate of 30 SLPM, collision frequencies were significantly different between powders of different constituent particle sizes, but the effects of powder properties diminished on increasing the flow rate to 60 SLPM. At the higher flow rate, all powders experienced a significant increase in the proportion of colliding particles. CONCLUSION: Analysis of collision events showed that the probability of collision for each agglomerate increased with agglomerate diameter and velocity. Experimental data of agglomerate-to-wall collision were utilised to develop a logistic regression model that can accurately predict collisions with various powders and flow rates.