["Tension" and "pressure" osteons - reality or myth?]

The underlying study tests the hypothesis on the existence of two types of osteons, the "tension" and the "pressure" ones. Osteons of the first type should be built under the influence of tension and should manifest greater strength in tension. The contrary applies to the "pressure" osteons. The ultimate strength of the bone tissue in tension and compression was studied on samples from the medial wall of the femoral diaphysis, subjected in vivo to compression, and on samples from the lateral wall, subjected to tension. All samples were manufactured with the long axis corresponding to the orientation of osteons, arranged in two helical antirotary systems situated in the contralateral walls of the diaphysis. The osteon orientation was ascertained after filling vascular canals with India-ink. The bone samples were tested using the Schenk Trebel RM 10-K machine. Tension tests found no difference in bone strength between samples from the lateral and from the medial walls. In compression tests, three cases manifested greater strength in samples from the medial wall, two cases in samples from the lateral wall. Such results speak against the hypothesis of the existence of two functional types of osteons. A complementary series of experiments showed that the tension strength is greatest in samples having a longitudinal orientation of osteons and that it decreases rapidly with growing inclination of osteons from the axis of loading. The dominant factor, responsible for the bone strength, is therefore the osteon orientation and not the mode of mechanical loading in vivo or the orientation of collagen fibres. Key words: haversian bone, osteons, strength of bone.