Prevention of fracture at the distal locking site of the gamma nail. A biomechanical study

To investigate the origin of fractures at the distal locking site of the Gamma nail, we loaded ten paired human cadaver femora fixed with a Gamma nail in torsion until they fractured. When an awl was hammered in to start the hole for distal locking a fissure appeared in the lateral cortex of all the femora, and the mean torsional load to create a fracture was reduced by 57.8% compared with that in a control group in which the distal locking hole had been started with a centre drill. When an additional drill hole was made, the mean failure load in torsion decreased by 35.7%. We strongly recommend that an awl should not be used at the distal locking site of the Gamma nail; we recommend the use of a centre drill. Additional drill holes should be avoided because they act as stress raisers

Understanding peripartum pelvic pain: Implications of a patient survey

Study Design. An analysis was made of the self-reported medical histories of patients with peripartum pelvic pain. Objectives. To compile an inventory of the disabilities of patients with peripartum pelvic pain, analyze factors associated with the risk for development of the disease, and to formulate a hypothesis on pathogenesis and specific preventive and therapeutic measures. Summary of Background Data. Pregnancy is an important risk factor for development of chronic low back pain. Understanding the pathogenesis of pelvic and low back pain during pregnancy and delivery could be useful in understanding and managing nonspecific low back pain. Methods. By means of a questionnaire, background data were collected among patients of the Dutch Association for Patients With Pelvic Complaints in Relation to Symphysiolysis. Results were compared with the general population. Subgroups were compared with each other. Results. Peripartum pelvic pain seriously interferes with many activities of daily living such us standing, walking, sitting, and all other activities in which the pelvis is involved. Most patients experience a relapse around menstruation and during a subsequent pregnancy. Occurrence of peripartum pelvic pain was associated with twin pregnancy, first pregnancy, higher ago at first pregnancy, larger weight of the baby, forceps or vacuum extraction, fundus expression, and a flexed position of the woman during childbirth; a negative association was observed with cesarean section. Conclusions. It is hypothesized that peripartum pelvic pain is caused by strain of ligaments in the pelvis and lower spine resulting from a combination of damage to ligaments (recently or in the past), hormonal effects, muscle weakness, and the weight of the fetus

Oblique abdominal muscle activity in standing and in sitting on hard and soft seats

The activity of the oblique abdominal muscles was investigated with the trunk in unconstrained, symmetrical and static postures. Electromyographic recordings in six healthy subjects revealed that in all subjects the activity of both the internal and the external obliques is significantly higher in unconstrained standing than in supine posture. Activity of the internal oblique was higher than that of the external oblique abdominal. The sacrospinal, gluteus maximus and biceps femoris muscles showed practically no activity in unconstrained erect posture. During unconstrained sitting both oblique abdominals are active. In most subjects the activity of the oblique abdominals was significantly smaller when sitting on a soft car seat than when sitting on an office chair with a hard seat. The possibility is discussed that contraction of the oblique abdominals in unconstrained standing and sitting may help in stabilizing the basis of the spine and particularly the sacroiliac joints. During standing and sitting the oblique abdominal muscles apparently have a significant role in sustaining gravity loads

Observation of open scattering channels

The existence of fully transmissive eigenchannels ("open channels") in a random scattering medium is a counterintuitive and unresolved prediction of random matrix theory. The smoking gun of such open channels, namely a bimodal distribution of the transmission efficiencies of the scattering channels, has so far eluded experimental observation. We observe an experimental distribution of transmission efficiencies that obeys the predicted bimodal Dorokhov-Mello-Pereyra-Kumar distribution. Thereby we show the existence of open channels in a linear optical scattering system. The characterization of the scattering system is carried out by a quantum-optical readout method. We find that missing a single channel in the measurement already prevents detection of the open channels, illustrating why their observation has proven so elusive until now. Our work confirms a long-standing prediction of random matrix theory underlying wave transport through disordered systems.Comment: 9 pages including methods and supplementary materials. 3 figure