[Long bone healing after transverse osteotomy under constant interfragmentary compression. Animal experiments...

The reaction of cortical contact areas, after osteotomy of a tubular bone, to a constant interfragmentary pressure has not been studied in exact terms so far because of lack of an adequate testing system. The present experimental study therefore examines the influence of various, but during the experiment constant, static pressures on the healing process of the cortical bone. Departing from the basic interrelation between fixation and interfragmentary compression (in the following briefly called: pressure) and from the resulting more or less limited mobility of the bone parts, following osteotomy, it appeared necessary to concentrate observation on either of the two parameters "fixation" or "pressure" alone. For this animal experiment a suitable external compression apparatus was developed so as to secure the application of a constant pressure. The present study contains construction drawings and data on the constructional assembly and integration of these newly developed compression apparatuses and pressure measuring devices. The compression apparatuses permit by variable spring configurations to produce pressures up to a maximum force of 1000 newton. To control the pressure exerted over a period of many weeks, a special measuring system had to be used to provide for a correction of the losses of pressure as occurring, for different reasons, during the progress of the experiment. One chapter is devoted to the various possible methods of pressure measuring. From among the available methods a pressure measuring system, operating on the principle of induction, was selected for practical realization of a model, and produced in a small series. The experiments pressure ranges of 100, 400 and 800 newton as criteria of interfragmentary compression, were carried out on 20 sheep's metacarpal bones, following osteotomy. During the six weeks experiment, current pressure corrections within a maximum of 10 pc of the nominal pressure were necessary, particularly during the first two weeks. X-ray examination showed with the increase of interfragmentary pressure an ever later beginning and ever less substantial formation of callus, regularily in a process of periosteal formation of callus. The lower the interfragmentary compression became, the earlier and the more frequently resorptive changes in the cortical bone occurred. Findings in the cortical contact areas, obtained microscopically from fluoro-chrome-labelled ground-sections and from corresponding microradiographs, in about half of the cases showed a formation of resorption cavities whose extent increased with the decrease of interfragmentary compression. An effect, observed parallel with this finding and with decreasing interfragmentary compression, was an intensified and earlier bone fill-up reaction. Also Havers' remodelling of the corticalis showed a tendency of increasing with the decrease of interfragmentary compression...