Biomechanical characterization of human temporal muscle fascia in uniaxial tensile tests for graft purposes in duraplasty.

The human temporal muscle fascia (TMF) is used frequently as a graft material for duraplasty. Encompassing biomechanical analyses of TMF are lacking, impeding a well-grounded biomechanical comparison of the TMF to other graft materials used for duraplasty, including the dura mater itself. In this study, we investigated the biomechanical properties of 74 human TMF samples in comparison to an age-matched group of dura mater samples. The TMF showed an elastic modulus of 36 ± 19 MPa, an ultimate tensile strength of 3.6 ± 1.7 MPa, a maximum force of 16 ± 8 N, a maximum strain of 13 ± 4% and a strain at failure of 17 ± 6%. Post-mortem interval correlated weakly with elastic modulus (r = 0.255, p = 0.048) and the strain at failure (r = - 0.306, p = 0.022) for TMF. The age of the donors did not reveal significant correlations to the TMF mechanical parameters. Compared to the dura mater, the here investigated TMF showed a significantly lower elastic modulus and ultimate tensile strength, but a larger strain at failure. The human TMF with a post-mortem interval of up to 146 h may be considered a mechanically suitable graft material for duraplasty when stored at a temperature of 4 °C.

Wrist at risk? - Considerations derived from a novel experimental setup to assess torques during hip reaming with potential implications on the orthopedic surgeons' health.

Orthopedic surgeons endure high physical stresses when performing surgery, as large forces and torques are applied commonly. Occupational risks are consequently higher when compared to other surgical disciplines. One example is the reaming of the acetabula during total hip arthroplasty, using customized instruments. This surgery may predispose the surgeon to overuse-related wrist pathology. In this study, torques acting along the reaming tool were measured, and the resulting forces applied to the orthopedic surgeons' wrists were estimated based on the measured torque data from hip reaming. Different reamer sizes and tool velocities were analyzed to determine how both parameters may influence the torques applied at the surgeon's wrist. Using a highly standardized setup, torques were measured while the reamer was pushed into the acetabula to remove cartilage. Maximum torques and stoppage torques at blocking of the reamer were compared between feed rates and reamer sizes. Peak values of the maximum torques along the reamer axis averaged 1.5-1.8 Nm. No significant difference between maximum torques and reamer sizes was found. A significant difference in maximum torques was noted between feed rates with a large effect (p = 0.010; η2 = 0.214) and a large interaction effect (p = 0.017; η2 = 0.186). Based on this experimental setup, it can be hypothesized that the impulsive behavior of the torque when the milling tool reaches the subchondral lamella could potentially contribute to wrist pathology. These preliminary data warrant further study. Consequently, torque limiters should be implemented in reamers to minimize the risk of occupation-related pathology to the wrist.

Strain-rate sensitive ductility in a low-alloy carbon steel after quenching and partitioning treatment.

We investigate an extraordinarily high ductility in a low alloy carbon steel at an elevated temperature after a quenching and partitioning (Q&P) treatment. The conventional (quenched and tempered) reference material does not show similar behavior. Interestingly, the Q&P treated material's ductility is considerably reduced at increasing strain rates while strength remains almost constant. These results indicate the presence of a diffusion-controlled deformation mechanism at elevated temperatures. Our research shows that interlath retained austenite is more stable during deformation at higher temperatures, resulting in a delayed transformation to martensite and therefore to a more pronounced contribution to plastic deformation at (and in the vicinity of) the many interfaces inherently present in this multi-phase steel.

How much force is required to perforate a colon during colonoscopy? An experimental study.

INTRODUCTION: Colonoscopy is a commonly-performed procedure to diagnose pathology of the large intestine. Perforation of the colon is a rare but feared complication. It is currently unclear how much force is actually required to cause such injury nor how this is altered in certain diseases. Our aim was to analyze the forces required to perforate the colon in experiments using porcine tissues. METHODS: Using 3D printing technology, models of two commercially available colonoscope heads were printed under three configurations: straight (I), 90°- bent (L) and fully bent (U). Samples of porcine colon were assessed with the models and configurations under perpendicular and angular load application and these data compared to the maximum force typically exerted by experienced colonoscopists. RESULTS: The force required for perforation was significantly lower for the I compared to the L of the larger colonoscope head configuration under angular loading (14.1 vs. 46.5 N). Similar differences were found for linear stiffness when loaded (I vs. L small when loaded perpendicular: 0.8 vs. 2.4 N/mm, I vs. L large when loaded angled 0.7 vs. 2.1 N/mm). The mode and site of failure varied significantly between the scopes, with delamination of the mucosa/submucosa below the sample (96%) for the I, blunt mucosa/submucosa/muscularis failure adjacent to the loading site (77%) for the L, and failure of all colon layers lateral to the loading site (59%) for the U configuration, respectively. Perpendicular and angulated loading resulted in similar load-deformation values. Maximum forces typically exerted by colonoscopists averaged 13.9-27.9 N, depending on the colonoscope model and head configuration. DISCUSSION: The force required for colon perforation varies depending on the type mode of loading and is likely lower than the force an experienced colonoscopist would exert in daily practice. There is a real risk of perforation, especially when the end of the scope is advancing directly into the colonic wall. The given experimental setup allowed to obtain reliable data of the colon in a standardized scenario, forming the basis for further experiments.

Preliminary biomechanical results of a novel pin configuration for external fixation of vertical shear pelvic fractures.

BACKGROUND: Vertical shear fractures are unstable and potentially life-threatening injuries that require urgent reduction and stabilization. The aim of this study was to compare the biomechanical efficacy of three different external fixation pin configurations for vertical shear pelvic fractures in a cadaveric model. We hypothesized that a modified external fixation pin configuration with a crestal (CR) pin in the stable hemipelvis and bilateral supra-acetabular (SA) pins provides the greatest overall stability to axial loading. METHODS: The force to failure within a standard standing axial load (maximum 650 N) was tested on 10 human cadaveric pelvises with vertical shear fractures. Three pin configurations were compared including iliac crest (IC), SA and a modified SA frame with a third CR pin on the stable hemipelvis. Both displacement at the posterior pelvis at 650 N and force to failure of >25 mm displacement was recorded. RESULTS: The mean force to failure was highest with CR (499 N), then IC (350 N) and then SA (265 N) pin configurations, being statistically non-significant (P = 0.165). The minimum force to failure followed a similar trend with 296, 68 and 43 N for CR, IC and SA, respectively. About 1/4 CR, 1/4 IC and 2/9 SA pins sustained 650 N or more without failure. CONCLUSION: It was shown that this new design may reliably withstand a seated physiological load of 250 N. However, none of the three pin configurations tested can reliably withstand a standing load of 650 N. Further experiments are needed to quantify these findings under physiological loading.