Bone growth and remodelling after fracture.

We used a rabbit model to investigate the mechanism by which the angulation of fractures is corrected in children. We produced a transverse proximal tibial fracture in one leg of 12 eight-week-old New Zealand white rabbits and measured bone alignment and length and the patterns of bone growth and remodelling. The angle between the joint surfaces changed rapidly to correct the alignment of the limb as a result of asymmetrical growth of epiphyseal plates. In an adult with closed plates, the angle between the joint surfaces cannot therefore improve. The angle at the fracture itself showed slow improvement because of bone drift and the asymmetrical growth of the epiphyseal plates. Remodelling corrected the shape of the bone in the region of the fracture. Periosteal division on the convex side increased the growth of the epiphyseal plate on that side, thus slowing the correction. The effect was relatively small, providing an indication that factors other than the periosteum are important in inducing correction. External torsional deformities developed because of helical growth at the plate. This was probably caused by abnormal posture which induced a torque at the growth plate. Helical growth is the mechanism by which rotational deformities can occur and correct.

Hemodynamic changes in hypernatremic dehydration in the mini-pig.

Hypernatremic dehydration with metabolic acidosis and azotemia was experimentally induced in the mini-pig by feeding a hypertonic NaCl and NH4Cl solution wit nasogastric tube. After a loss of 19% of initial body weight within 32 hours, the following hemodynamic changes were observed: the heart rate rose, the arterial blood pressure was maintained, but cardiac output fell to 80% of its initial value. There was a redistribution of this lowered cardiac output with unchanged blood flow to heart, brain, adrenals and skeletal muscle. The flow to these vital organs was diverted to selective vasoconstriction of spleen, pancreas, gastrointestinal tract and kidneys. Quantitatively the contribution from the latter two organs was the most important.

[The Göttinger minipig as a laboratory animal. 5. Communication: cardiac output, its regional distribution and organ blood flow (author's transl)]. / Das Göttinger Miniaturschwein als Versuchstier. 5. Mitteilung: Das Herzminutenvolumen, seine prozentuale Verteilung auf den Organismus und die effektive Organdurchblutung.

In 16 juvenile minipigs weighing 3.08 kg an average cardiac output of 23 ml/100 g body weight was measured with the dye-dilution method. The microsphere technique was used to assess distribution of cardiac output and organ blood flow. In 12 adult minipigs with a mean body weight of 21.5 kg the cardiac output of 14 ml/100 g body weight was measured with an electromagnetic flowmeter. The values of total systemic and organic blood flow correlated well with those of man and partly with those of other laboratory animals.