External fixator pin insertion techniques: biomechanical analysis and clinical relevance.

A series of identically matched pairs of fresh-frozen canine femora (approximating human radii in size and dimension) were used to mechanically compare pull-out strength between 4 mm predrilled, self-tapping, half-pins and 4 mm self-drilling, self-tapping half-pins with drill bit-like cutting flutes. A second biomechanical and videotape analysis was done comparing the differences of pin insertion by power versus hand drilling. Results indicated a mean 22% reduction in bone purchase of self-drilling, self-tapping pins compared with that of predrilled pins and a marked increase in depth of insertion required of the self-drilling pins for comparable pin purchase (10 mm). It was also observed that a visible "wobble factor" exists, which tends to weaken the pin-bone interface when hand drilling is performed.

Repair of the tibiofibular syndesmosis with a flexible implant.

Fractures of the adult ankle with disruption of the tibiofibular syndesmosis require adequate stabilization of the ankle mortise to ensure satisfactory healing of the syndesmotic ligaments. Numerous internal fixation techniques for stabilization of the syndesmosis have been used. However, most techniques require partial device removal before weight bearing can be initiated. The "flexible syndesmosis repair" uses simple, inexpensive, readily available synthetic materials to restore distal tibiofibular stability. Once early fracture healing has been obtained, weight bearing is begun (average 6 weeks). Biomechanical testing on paired cadaver ankles demonstrated a suture tensile strength of 60 lbs and consistent suture-button strength of 49 lbs, whereas tricortical screw fixation was found to have a higher 82 lbs average pull-out strength, but demonstrated a wide variability depending on bone quality. Twelve patients have been managed with flexible syndesmosis repair and followed for 2-4 years. All fractures have healed without deformity and there are no cases of mortise instability. Subsequent analysis of devices removed 8-12 months following implantation has shown that all have remained intact without failure. The flexible syndesmosis repair is a reliable, stable way to restore syndesmosis integrity, allowing early weight bearing without need for interim surgery.

Biomechanical analysis of pin placement and pin size for external fixation of distal radius fractures.

A series of biomechanical analyses were performed to explain the recent reduction in treatment-related complications of external fixation of distal radius fractures using a limited open approach for pin placement and larger 4-mm self-tapping half pins. A comparison of pull-out strength, stress concentration effect, and inherent bending strength of 3- and 4-mm half pins was performed. The effect of proximal pin placement in the radius or in the ulna and the effect of distal pin placement in four, six, or eight metacarpal cortices were determined. These analyses demonstrate that the 4-mm self-tapping half pins result in a significantly higher pull-out strength and only a small decrease in torsional load strength of the bone. They also demonstrate that proximal pin fixation in the radius produces the most stable fixation and that distal pin fixation into six metacarpal cortices produces a strong configuration that does not violate the interosseous muscles of the second intrinsic compartment. The rate of treatment-related complications in the external fixation of distal radius fractures (specifically, pin loosening, bending and breakage, fracture through pin sites, collapse at the fracture site, and intrinsic contracture) are addressed in this study. Such complications can be minimized by using 4-mm pins after central predrilling, with proximal placement in the radius and distal placement through six cortices of the bases of the second and third metacarpals.

Monensin poisoning in horses - an international incident.

Several hundred Michigan horses were accidentally exposed to varying levels of monensin. Severity of effects was proportional to the level of feed contamination; sudden death resulted on at least two premises. Acute signs of cardiovascular impairment occurred on one premises having received feed containing over 200 grams of monensin per tonne. Gross and histological postmortem lesions consisted of acute myocardial necrosis. Although only circumstantially confirmed, investigations led to the suspicion that the source of poisoning was a ration formulation error in a feedmill in southwestern Ontario. Concern over possible undetected heart damage in exposed horses led to clinical monitoring on one farm over a period of several months. Electrocardiographic and serum enzyme monitoring were used soon after the incident to implicate exposure in some horses; they were poor prognostic indicators. Applicable legislation, the cooperative role of government departments, and legal implications relative to potential prosecution and lawsuits arising from sale of contaminated feed between Canada and the USA are summarized.

A fluted intramedullary rod for subtrochanteric fractures.

A new intramedullary rod has been developed for the treatment of subtrochanteric fractures. The stepped fluted rod is designed as a single unit and has exceptional bending strength and rigidity as well as excellent torsional load-carrying capacity. It has been used successfully in eighteen patients with a variety of subtrochanteric fractures. Union was achieved in all instances and no failure of the implant occurred. The simplified technique of insertion, the strength of the device, and the results of this study indicate that the fluted subtrochanteric rod has several advantages over other available devices.

Mineral resources, economic growth, and world populatic.

World population and world income can grow at any likely rate for the next 50 to 75 years, probably for longer, and mineral supplies will continue to keep pace with demand. Not, however, without environmental costs, without affecting Third World development, and, perhaps most important, without ignoring critical questions of power. In what might be termed the revisionist form of the limits to growth thesis, Aurelio Peccei and Alexander King, cofounders of the Club of Rome, seem to be saying that the forecasts of doom themselves are unimportant but they symbolize critical problems of the nature and uses of power in the modern world (30): . . . the Club of Rome is questioning the quality of growth and its distribution around the world. . . . We know that the present structure of the world is obsolete. . . . Both private and state capitalism are stale . . . we have to develop something else. Surely, continually increasing rates of mineral production are symptoms of this obsolete power structure, a result of the fact that, ultimately, population growth and monetary income growth lead to demands for natural resources that necessitate their being found and produced regardless of the implications. Since such higher rates of production are geologically and economically sustainable, we should choose among alternative paths of growth, and hence among alternative rates of mineral resource development, according to what we like or dislike about these implications. The key information will not be found in tables comparing reserves and consumption but in preferences and ethics.