We conducted a meta-analysis of the association between leisure time physical activity (LTPA) and risk of pancreatic cancer to update previous analyses in light of newly published studies, to examine subgroups of interest and potential sources of heterogeneity. We searched the PubMed and MEDLINE databases for studies until February 2015. Study information was collected using a standardized form to abstract relevant data on study design, number of cases, participant and study characteristics, assessment of LTPA, risk estimates, and adjustments for confounding by two independent abstractors. We used randomeffects models to pool estimates from included studies of lowest versus highest comparison of LTPA. The search identified 26 studies eligible for inclusion into the meta-analysis. The combined summary risk estimate was [relative risk (RR), 0.89; 95% confidence interval (CI), 0.82-0.96]. There was evidence of heterogeneity across studies (I 2 ¼ 22.1%, P heterogeneity ¼ 0.130). Some of the heterogeneity could be explained by study design, with stronger protective effects observed among casecontrol studies (RR, 0.69; 95% CI, 0.59-0.81) compared with cohort studies (RR, 0.96; 95% CI, 0.91-1.02). Across study designs, age of population was a source of heterogeneity, with stronger effects observed among younger (<50 years) populations. The present meta-analysis supports a protective association between LTPA and pancreatic cancer with an 11% risk reduction observed. LTPA appears to have the strongest effect among young populations. Additional investigations are needed to provide insights regarding the impact of LTPA in healthy adult populations, to reduce the risk of pancreatic cancer and encourage increases in LTPA. Cancer Epidemiol Biomarkers Prev; 24(10);
Biomechanical investigations are increasingly using commercially available synthetic femurs as surrogates for human cadaveric femurs. However, the rate of force application in testing these artificial femurs appears to be chosen arbitrarily without much consideration to their visco-elastic time-dependent nature. The aim of this study, therefore, was to examine the effect of loading rate on the mechanical behaviour of synthetic femurs. Ten left, medium, fourth-generation composite femurs (Model 3403, Pacific Research Laboratories, Vashon, WA, USA) were fixed distally into cement-filled steel cubic chambers for mounting into a mechanical tester. In randomized order, each of the ten femurs was loaded at rates of 1, 2.5, 5, 7.5, 10, 20, 30, 40, 50, and 60 mm/min to obtain axial, lateral, and torsional stiffness. Axial stiffness showed an aggregate average value of 1742.7 +/- 174.7 N/mm with a high linear correlation with loading rate (R2 = 0.80). Lateral stiffness yielded an aggregate average value of 56.9 +/- 10.2 N/mm and was linearly correlated with loading rate (R2 = 0.85). Torsional stiffness demonstrated an aggregate average value of 176.9 +/- 14.5 N/mm with a strong linear correlation with loading rate (R2 = 0.59). Despite the high correlations between stiffness and speed, practically this resulted in an overall average difference between the lowest and highest stiffness of only 4 per cent. Moreover, no statistical comparisons between loading rates for axial, lateral, or torsional test modes showed differences (p > or = 0.843). Future biomechanical investigators utilizing these synthetic femurs need not be concerned with loading rate effects over the range tested presently. This is the first study in the literature to perform such an assessment.
Orthopaedic fracture fixation constructs are typically mounted on to human long bones using cortical screws. Biomechanical studies are increasingly employing commercially available synthetic bones. The aim of this investigation was to examine the effect of the screw pull-out rate and canal reaming on the cortical bone screw purchase strength in synthetic bone. Cylinders made of synthetic material were used to simulate unreamed (foam-filled) and reamed (hollow) human long bone with an outer diameter of 35 mm and a cortex wall thickness of 4 mm. The unreamed and reamed cylinders each had 56 sites along their lengths into which orthopaedic cortical bone screws (major diameter, 3.5 mm) were inserted to engage both cortices. The 16 test groups (n = 7 screw sites per group) had screws extracted at rates of 1 mm/ min, 5 mm/min, 10 mm/min, 20 mm/min, 30 mm/min, 40 mm/min, 50 mm/min, and 60 mm/ min. The failure force and failure stress increased and were highly linearly correlated with pull-out rate for reamed (R2 = 0.60 and 0.60), but not for unreamed (R2 = 0.00 and 0.00) specimens. The failure displacement and failure energy were relatively unchanged with pull-out rate, yielding low coefficients for unreamed (R2 = 0.25 and 0.00) and reamed (R2 = 0.27 and 0.00) groups. Unreamed versus reamed specimens were statistically different for failure force (p = 0.000) and stress (p = 0.000), but not for failure displacement (p = 0.297) and energy (0.054 < p < 1.000). This is the first study to perform an extensive investigation of the screw pull-out rate in unreamed and reamed synthetic long bone.
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