Assessment of cortical bone fracture resistance curves by fusing artificial neural networks and linear regression

Bone injures (BI) represents one of the major health problems, together with cancer and cardiovascular diseases. Assessment of the risks associated with BI is nontrivial since fragility of human cortical bone is varying with age. Due to restrictions for performing experiments on humans, only a limited number of fracture resistance curves (R-curves) for particular ages have been reported in the literature. This study proposes a novel decision support system for the assessment of bone fracture resistance by fusing various artificial intelligence algorithms. The aim was to estimate the R-curve slope, toughness threshold and stress intensity factor using the two input parameters commonly available during a routine clinical examination: patients age and crack length. Using the data from the literature, the evolutionary assembled Artificial Neural Network was developed and used for the derivation of Linear regression (LR) models of R-curves for arbitrary age. Finally, by using the patient (age)-specific LR models and diagnosed crack size one could estimate the risk of bone fracture under given physiological conditions. Compared to the literature, we demonstrated improved performances for estimating nonlinear changes of R-curve slope (R² = 0.82 vs. R² = 0.76) and Toughness threshold with ageing (R² = 0.73 vs. R² = 0.66).     

Functional morphology and biomechanics of cuticular fracture at the elytrophoral autotomy plane of the scaleworm Alentia gelatinosa (Annelida: Polynoidae)

Abstract. Autotomy of the elytra (scales) in the annelid Alentia gelatinosa occurs at a breakage plane near the junction between the elytron and its elytrophore (stalk), and requires fracture of the external epidermal cuticle. The mechanism of cuticular fracture was investigated by light and electron microscopy, glycoconjugate histochemistry, direct observation of autotomy in isolated preparations, and mechanical tests. The breakage plane crosses the elytrophoral wall at a cuticular thickening and passes through the subelytral cavity between the elytron and the terminal septum of the elytrophore. At the cuticular breakage zone (CBZ), the collagenous framework of the normal cuticle is replaced with non‐collagenous microfibrils. The CBZ has a complex glycoconjugate composition and includes a strongly sulfated, uronic acid‐containing glycosaminoglycan and a high proportion of disulfide or sulfydryl linkages. Tonofilament‐rich epidermal cells (tendon cells) are attached to the thick cuticle on the dorsal and ventral sides of the CBZ. Dorsal tendon cells have long processes that extend into the elytron near the roof of the subelytral cavity. Ventral tendon cells are linked by connective tissue to the longitudinal and terminal sphincter muscles of the elytrophore. Mechanical tests showed that the elytrophoral wall is not inherently weaker at the autotomy plane than elsewhere. It is hypothesized that at autotomy (i) contractile force generated by the sphincter muscle is transmitted through elytrophoral tendon cells to the ventral side of the CBZ and (ii) contraction of the longitudinal and main circular muscles of the elytrophore increases hydrostatic pressure in its lumen, everts the terminal septum, and generates tension that is transmitted through elytral tendon cells to the dorsal side of the CBZ. This results in stress concentration at the basal edge of the CBZ and initiates fracture. The distinctive microstructure and macromolecular composition of the CBZ may reduce its fracture toughness and make it more susceptible to brittle failure.     

Emerging evidence that adaptive bone formation inhibition by non-steroidal anti-inflammatory drugs increases stress fracture risk

There is mounting evidence suggesting that the commonly used analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), may inhibit new bone formation with physical training and increase risk of stress fractures in physically active populations. Stress fractures are thought to occur when bones are subjected to repetitive mechanical loading, which can lead to a cycle of tissue microdamage, repair, and continued mechanical loading until fracture. Adaptive bone formation, particularly on the periosteal surface of long bones, is a concurrent adaptive response of bone to heightened mechanical loading that can improve the fatigue resistance of the skeletal structure, and therefore may play a critical role in offsetting the risk of stress fracture. Reports from animal studies suggest that NSAID administration may suppress this important adaptive response to mechanical loading. These observations have implications for populations such as endurance athletes and military recruits who are at risk of stress fracture and whose use of NSAIDs is widespread. However, results from human trials evaluating exercise and bone adaptation with NSAID consumption have been less conclusive. In this review, we identify knowledge gaps that must be addressed to further support NSAID-related guidelines intended for at-risk populations and individuals.