Biomechanical comparison of six intramedullary nails, for the treatment of ex-tra-articular, proximal tibial fractures.

BACKGROUND: Intramedullary nailing is the "gold standard" treatment modality of diaphyseal fractures of the tibia. However, when the same method is used for extra-articular fractures of the proximal tibia, various problems may occur, like malalignment, loss of reduction, and non-union. The objective of the present biomechanical study was to compare the stability of six tibial nails when these are used for the treatment of unstable, extra-articular, proximal tibial fractures. METHODS: Thirty composite tibia models were divided into six groups, and a corresponding number of nails from six manufacturers (Citieffe, Braun Aesculap, Orthoselect, Orthofix, Stryker, and Depuy Synthes) was implanted in each group. The maximum number of proximal screws was used for each specimen, and a proximal gap osteotomy was performed. Each bone model was then submitted in dynamic, followed by static loading, and the passive construct stiffness was calculated, representing the specimen's rigidity. Furthermore, for each specimen, the force needed to cause a displacement of more than one millimeter at the fracture site was calculated. RESULTS: Stiffness values of a solid nail with two proximal screws and a cannulated nail with five screws were significantly higher compared to all other groups. On the other hand, a titanium cannulated nail with three screws showed the lowest rigidity. CONCLUSION: Solid nails provide more rigidity compared to cannulated ones, and the maximum number of proximal screws in all possible directions should be used in order to achieve maximum stability. HIPPOKRATIA 2019, 23(2): 58-63.

Do composite resin restorations protect cracked teeth? An in-vitro study.

Aims: To evaluate whether bonded resin composite restorations can effectively immobilise the tooth segments in teeth with a synthesised crack under loading, by exploring the impact of the restoration type (direct versus indirect composite resin) and restoration design (inlay versus onlay) on the fatigue resistance. Methods: Sound human third molars underwent large mesio-occluso-distal preparations and a groove was cut to simulate a crack. Standardised procedures were adopted and measures were taken during teeth selection so that systematic error and methodology bias were minimised. The teeth were randomly assigned to four groups. The specimens were submitted to cyclic loading and loaded until fracture or to a maximum of 185,000 cycles. The failure mode was recorded. Results: No failure was observed in 'direct' groups up to the 1000 N force. Survival analysis revealed statistically significant higher survival rates for 'direct' groups compared to 'indirect' groups (χ2 = 11.352, df = 1, p = 0.001) while there was no significant difference between 'inlay' and 'onlay' groups (χ2 = 0.015, df = 1, p = 0.901) (pooled data). Conclusions: Within the limitations of this in-vitro study, it can be concluded that the direct composite resin restorations sufficiently protected the cracked teeth regardless of the cavity design. As there was no statistically significant difference in survival rates between inlays and onlays it is not possible to favour one design type over the other.

The Effect of Body Mass on the Shoe-Athlete Interaction.

Long-distance running is known to induce joint overloading and elevate cytokine levels, which are the hallmarks for a variety of running-related injuries. To address this, footwear systems incorporate cushioning midsoles to mitigate injurious mechanical loading. The aim of this study was to evaluate the effect of athlete body mass on the cushioning capacity of technical footwear. An artificial heel was prototyped to fit the impact pattern of a heel-strike runner and used to measure shock attenuation by an automated drop test. Impact mass and velocity were modulated to simulate runners of various body mass and speeds. The investigation provided refined insight on running-induced impact transmission to the human body. The examined midsole system was optimized around anthropometric data corresponding to an average (normal) body mass. The results suggest that although modern footwear is capable of attenuating the shock waves occurring during foot strike, improper shoe selection could expose an athlete to high levels of peak stress that could provoke an abnormal cartilage response. The selection of a weight-specific cushioning system could provide optimum protection and could thus prolong the duration of physical exercise beneficial to maintaining a simulated immune system.