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To study the biomechanical properties of flexor tendon repairs, static tensile testing is commonly used because of its simplicity. However, cyclic testing resembles the physiological loading more closely. The aim of the present study is to assess how the biomechanical competence of repaired flexor tendons under cyclic testing relates to specific parameters derived from static tensile testing. Twenty repaired porcine flexor tendons were subjected to static tensile testing. Additional 35 specimens were tested cyclically with randomly assigned peak load for each specimen. Calculated risks of repair failure during repetitive loading were determined for mean of each statically derived parameter serving as a peak load. Furthermore, we developed a novel objective method to determine the critical load, which is a parameter predicting the survival of the repair in cyclic testing. The mean of statically derived yield load equalled the mean of critical load, justifying its role as a valid surrogate for critical load. However, regarding mean of any determined parameter as a clinically safe threshold is arbitrary due to the natural variation among samples. Until the universal performance of yield load is verified, we recommend employing cyclically derived critical load as primary parameter when comparing different methods of flexor tendon repair., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Bone dynamically adapts its structure to the environmental demands placed upon it. Load-related stimuli play an important role in this adaptation. It has been postulated that osteocytes sense changes in these stimuli and initiate adaptive responses, across a number of scales, through a process known as mechanotransduction. While much research has focused on gross and tissue-level adaptation, relatively little is known regarding the relation between cellular-level features (e.g. osteocyte lacunar density, volume and shape) and loading. The increasing availability of high resolution 3D imaging modalities, including synchrotron-based techniques, has made studying 3D cellular-level features feasible on a scale not previously possible. The primary objective of this study was to test the hypothesis that unloading (sciatic neurectomy) during growth results in altered osteocyte lacunar density in the tibial diaphysis of the rat. Secondarily, we explored a potential effect of unloading on mean lacunar volume. Lacunar density was significantly (p<0.05) lower in immobilized bones (49,642 ± 11,955 lacunae per mm(3); n=6) than in control bones (63,138 ± 1956 lacunae per mm(3); n=6). Mean lacunar volume for immobilized bones (209 ± 72 μm(3); n=6) was significantly smaller (p<0.05) than that for the control bones (284 ± 28 μm(3); n=6). Our results demonstrate that extreme differences in loading conditions, such as those created by paralysis, do indeed result in changes in osteocyte lacunar density and volume. Further investigation is warranted to examine relations between these measures and more subtle variation in loading as well as pathological states, which have been linked to alterations in mechanotransduction., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Total variation in any measured variable, in conjunction with expected treatment effect, defines the minimum sample size (minSS) required to detect the expected effect with statistical confidence should the effect truly exist. A comprehensive literature survey of 3472 original studies was carried out to identify studies with biomechanical testing of whole bones. Total variation in common biomechanical traits and expected treatment effects in typical interventions were statistically determined. According to this survey, total variation in biomechanical traits between different species of experimental animals was similar, justifying the use of rat femur as a model in further analyses. Due to poorer precision, stiffness and energy absorption assessment require substantially larger sample size than breaking load. Due to same reason, minSS for femoral neck compression test is considerably larger than for femoral shaft three-point bending test. For the bending test, minSS to show a 10% treatment effect in the breaking load with 80% statistical power is 11rats/group, while corresponding minSS is 23 for the stiffness, and 53 for the energy absorption. For the femoral neck compression test, minSSs are 16, 51, and 134rats/group, respectively. Among the reviewed studies, the mean sample size was 11animals/group. This underscores the need for considerably larger sample sizes in experimental bone interventions which employ mechanical traits as primary outcome variables. In particular, poor precision and generally small expected treatment effects compromise the utility of stiffness and energy absorption assessments in experimental bone interventions.