Fatigue strength of locking screws and prototypes used in small-diameter tibial nails: a biomechanical study.

BACKGROUND: One major problem with the use of small-diameter nails in the treatment of tibial fractures is the high rate of fatigue fractures of the locking screws. The objective of this study was to correlate such parameters as diameter of locking screws, influence of notch effect, and material with fatigue strength and fatigue limit. METHODS: In a biomechanical study, the mechanical properties of 11 different locking screws and screw designs to be used in solid tibial nails were tested under typical fatigue conditions. RESULTS: The results showed that an increase in the screw's diameter significantly increased the fatigue strength of the tested locking screws and prototypes (p < 0.0005). A 20% increase of diameter improved fatigue strength by 25 to 70%. Absence of thread at the location where the screw contacts the nail's aperture (where the main load is transmitted to the screw and where the screw, therefore, usually tends to break) may double the fatigue strength and fatigue limit by avoiding the negative notch effect of the screw's thread. It was further significant that titanium alloys had a higher fatigue strength compared with stainless steel alloys (p < 0.001). However, the fatigue strength of titanium implants is massively reduced by minimal damage to the surface. CONCLUSION: Optimizing the core diameter of the locking screws at the aperture of the solid tibial nail by using screws without a continuous thread generates a fatigue strength two to three times higher compared with screws with a continuous thread. Increasing fatigue strength of locking screws might decrease malunion in fractures stabilized by small-diameter nails.     

Acute effects of moderate exercise on plasma lipoprotein parameters

The acute, transient effects of moderate exercise on plasma lipoprotein parameters were assessed in 12 healthy, normolipidemic male volunteers subjected to a 5.5-km run at a comfortable pace. The course was completed in 31.5 min (range 23-43 min) and elicited a significant increase in pulse rate and plasma lactate levels and a fall in diastolic blood pressure. Of the plasma lipid parameters, total phospholipid, apo B-associated phospholipid, plasma triglyceride, and free fatty acid levels increased substantially immediately after the run and, except for triglyceride, were still raised 2 h later. Lesser but also significant increases were also noted in high-density lipoprotein-cholesterol (HDL-C), HDL3-C, and HDL-phospholipid concentrations after the run. The increase in HDL-phospholipid persisted for 2 h but the others returned to basal levels. Apolipoprotein Al, lecithin: cholesterol acyltransferase activity, total cholesterol, low-density lipoprotein-cholesterol, and the free cholesterol:cholesterol ester ratio remained essentially unaltered by exercise. The results were compatible with an increased secretion of triglyceride and phospholipid-rich VLDL, followed by the rapid clearance of the triglyceride moiety from the plasma and some redistribution of surface components to the HDL fraction.     

Activation of neurokinin receptors modulates K and Cl channel activity in cultured astrocytes from rat cortex

Short application of the neurokinin receptor agonist substance P (SP) leads to a biphasic depolarization of astrocytes cultured from rat cortex. The rapid and transient depolarizing event lasted few seconds, the slow one several minutes. In some cells, only the slow depolarizing component was observed. During the slow depolarizing event, the sensitivity of the membrane potential for a change in the K+ gradient decreased, indicating a decrease in the relative K+ permeability of the membrane. The rapid SP-induced depolarization could be reversed, when the membrane potential was depolarized to about 0 mV by elevation of the extracellular K+ concentration, indicating a reversal potential close to the Cl- equilibrium potential. When the membrane was clamped close to the resting membrane potential using the whole-cell patch-clamp technique, SP induced a biphasic inward current with a similar time course as the SP-induced membrane depolarization. Evaluating current-to-voltage curves indicated a conductance decrease during the slow inward current with a reversal potential of the SP-dependent current close to the K+ equilibrium potential. The mean open time of single K+ channels, measured in the cell-attached configuration of the patch-clamp technique, decreased after application of SP. In contrast, the mean open time of single Cl- channels increased. We conclude that activation of neurokinin receptors in astrocytes modulates the activity of K+ and Cl- channels, leading to a complex depolarization of the membrane potential.     

Computed tomography of the disarticulated incus

Complete incus disarticulation may be a complication of trauma, chronic otitis, or prosthetic stapedectomy. Purposeful incus disarticulation (with incus interposition) is used as a method of ossicular reconstruction. CT has been a valuable diagnostic tool for preoperative location of the incus in the former disorders and for determination of the status of the ossiculoplasty in the latter.     

Jenctlonal Epidermolysis Bullosa, Pyloric Atresia, and Genitourinary Disease

The occasional concurrence of junctional epidermolysis bullosa and pyloric atresia has been documented in the literature. Several infants reported as having this combined disorder were also noted to have significant genitourinary disease. We treated a 4 1/2-year-old boy with mild cutaneous manifestations of junctional epidermolysis bullosa, corrected pyloric atresia, and significant renal disease secondary to recurrent obstruction of the ureterovesical junction.