The challenges faced in the design, conduct and analysis of surgical randomised controlled trials

Randomised evaluations of surgical interventions are rare; some interventions have been widely adopted without rigorous evaluation. Unlike other medical areas, the randomised controlled trial (RCT) design has not become the default study design for the evaluation of surgical interventions. Surgical trials are difficult to successfully undertake and pose particular practical and methodological challenges. However, RCTs have played a role in the assessment of surgical innovations and there is scope and need for greater use. This article will consider the design, conduct and analysis of an RCT of a surgical intervention. The issues will be reviewed under three headings: the timing of the evaluation, defining the research question and trial design issues. Recommendations on the conduct of future surgical RCTs are made. Collaboration between research and surgical communities is needed to address the distinct issues raised by the assessmentof surgical interventions and enable the conduct of appropriate and well-designed trials.The Health Services Research Unit is funded by the Scottish Government Health DirectoratesPeer reviewedPublisher PD

Short-Term Creep as Related To Microfibril Angle

Relationship between creep response and microfibril angle within the S2 layer of some coniferous wood tissues was examined. Constant loads corresponding to predetermined initial strain levels of 3,000 μinches/inch (A) and 6,000 μinches/inch (B) were applied to small wood strips. Microfibril angle was measured by the mercury impregnation method.A positive linear relationship was found between microfibril angle and total creep (r = 0.82 and 0.83 for samples tested at constant loads corresponding to strain levels (A) and (B), respectively). A phenomenological approach is presented to explain the role of microfibril angle of the S2 layer in controlling creep response. Total creep was also found to be positively correlated with magnitude of applied load corresponding to a given deformation

Relationships Between Cell-Wall Composition and Cell-Wall Density

The alpha-cellulose content, holocellulose content and crystallinity index were measured for thirteen hardwood and five softwood samples, for which both cell-wall substance and cell-wall densities had been measured in an earlier study. Direct relationships were found between crystallinity index, alpha-cellulose content, and cell-wall density. A simple method of mixtures was used to relate the constituent densities to the cell-wall substance density. Attempts to rationalize the difference between these calculated densities and the measured cell-wall substance densities suggested that the density of one or more of the cell-wall constituents is appreciably different, in situ, than that measured on the material removed from the cell wall

On the Fractional Stress Relaxation of Coniferous Wood Tissues

The intra-incremental stress relaxation behavior of Sitka spruce, Douglas-fir, and balsam fir was studied in tension parallel-to-grain and compression perpendicular-to-grain. The stress relaxation behavior at sustained constant deformation was found to be strongly dependent on location from which the test samples were cut and on the mode and rate of loading

Short-Term Creep as Related to Cell-Wall Crystallinity

X-ray diffraction technique was utilized to determine the relative degree of crystallinity of some coniferous wood tissues, namely Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) normal and compression wood, and normal wood of Sitka spruce (Picea sitchensis (Bong.) Carr.) and western hemlock (Tsuga heterophylla (Raf.) Sarg.). Total creep values were available from a previous study for test samples matched with those used for determining degree of crystallinity. Creep response was measured using two constant loads corresponding to predetermined initial strain levels of 3,000 (A) and 6,000 (B) μinches/inch.The relative degrce of cell-wall crystallinity was found to be linearly correlated (inversely) with short-term creep. Results of this investigation also revealed that cell-wall crystallinity contributes up to 67.2 and 51.8% of the total variability in creep response for samples tested at constant loads corresponding to strain levels (A) and (B), respectively. It is suggested that a relatively high degree of crystallinity increases the rigidity of cell wall, which thereby resists excessive creep deformation