Das Ossifikationsprinzip der Trachealknorpel. R�ntgenologisch-morphometrische und experimentelle Untersuchungen

Abstract

The ossification of human tracheal cartilage is thought to be degenerative or due to genetic factors; in the final resort, however, its etiology still remains to be clarified. Therefore, on the one hand tracheal cartilages obtained from corpses of both sexes and various ages were X-rayed and subjected to measurements at defined points and, on the other hand, the relative distribution of stresses within tracheal cartilage was investigated in a model, using wire strain gauges, and evaluated with the aid of a computer. With increasing age, the cross-section of the tracheal cartilage at the sides and in the middle becomes greater, but to varying extents. Furthermore, in 50% of the males and in only 5% of the females, ossification with lamellar spongiosa occurs, primarily in the cranial and caudal outer margins of the ventral part of the cartilage ring. The cartilage, which is constantly subjected to tensile and compressive forces, reacts with an adaptive hypertrophy at that part of the inside of the cartilage that is exposed predominantly to compressive loading. As a result, the middle of the cartilage is markedly thicker than the sides. Under the influence of the compressive forces, the band-like traction effect of the collagen fibres in the ventral subperichondrial region of the tracheal cartilage becomes insufficient and the effects of stress on the cartilage greater. For a given stress level a greater extension results, which induces ossification in the region of its maximum effect — in the cranial and caudal convexity of the ventral part of the cartilage. In the region of ossification stabilization'occurs as a result of a change in the modulus of elasticity, so that the points subjected to the maximum extension force “migrate” laterally. In these sections, new bone is laid down until the tracheal cartilage has stiffened. The forces necessary to induce cartilaginous hypertrophy on the one hand, and insufficiency of the band-like traction effect on the other occur predominantly only in the male trachea. The ossification of tracheal cartilage is a further example of self-regulated adaptation of the connective and supportive tissues to mechanical stressing.