PubMed · 9484213
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
D J Halazonetis. 1998. Understanding orthodontic loop preactivation.. https://doi.org/10.1016/s0889-5406(98)70143-x
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
OBJECTIVE: To quantify the kinematics of the injury to the posterior cruciate and the other major knee ligaments as a function of the knee flexion angle at the moment of impact. DESIGN: Computer-aided design modelling was used to investigate the strain response of all major knee ligaments during antero-posterior abnormal tibio-femoral translation at 0-90 degrees knee flexion. BACKGROUND: It is generally believed that the likelihood of injury to the posterior cruciate ligament following anterior impact is higher in the flexed knee. However, there are no kinematical studies to quantify this clinical observation or investigate the role of the other knee ligaments in the above situation. METHODS: Computer calculations of the individual ligament strain were plotted against the magnitude of posterior tibial translation. Additionally, the strain rate for each ligament (defined as the ligament strain produced per mm of posterior tibial linear translation) was calculated as the slope of the strain-displacement curve for all tested degrees of knee flexion. RESULTS: The posterior cruciate ligament has been shown to be the primary restraint to posterior tibial translation in all degrees of knee flexion. However, at 90 degrees of knee flexion the strain rate of the posterior cruciate ligament is approximately half that in the fully extended knee and the posterior cruciate ligament is the only ligament to resist posterior tibial translation. CONCLUSIONS: The strain behaviour of the posterior cruciate ligament during injury is highly dependent on the knee flexion during the moment of impact. Forced posterior tibial translation in the 90 degrees flexed knee may result in isolated posterior cruciate ligament deficit rather than a complex ligament disruption. The strain rate of a ligament as introduced in the present study is a quantified parameter related to the resistance that the ligament imposes to an abnormal joint movement. Relevance. This study provides insight into the differential strain of the knee ligaments during impacts that result in posterior cruciate ligament injury. Studies that quantify the strain behaviour of individual knee ligaments are important to the understanding, diagnosis and prevention of injuries sustained during contact sports and high-energy road traffic accidents.
We describe four previously unpublished methods allowing the computation of the writhe for a supercoiled DNA molecule modeled by a polymer chain consisting of straight segments. These methods are compared with each other in terms of computational efficiency and the scope of their applicability is discussed.
The growth of populations is known to be influenced by dispersal, which has often been described as purely diffusive. In the open ocean, however, the tendrils and filaments of phytoplankton populations provide evidence for dispersal by stirring. Despite the apparent importance of horizontal stirring for plankton ecology, this process remains poorly characterized. Here we investigate the development of a discrete phytoplankton bloom, which was initiated by the iron fertilization of a patch of water (7 km in diameter) in the Southern Ocean. Satellite images show a striking, 150-km-long bloom near the experimental site, six weeks after the initial fertilization. We argue that the ribbon-like bloom was produced from the fertilized patch through stirring, growth and diffusion, and we derive an estimate of the stirring rate. In this case, stirring acts as an important control on bloom development, mixing phytoplankton and iron out of the patch, but also entraining silicate. This may have prevented the onset of silicate limitation, and so allowed the bloom to continue for as long as there was sufficient iron. Stirring in the ocean is likely to be variable, so blooms that are initially similar may develop very differently.