[Experimental investigations on the growth of the vertebral column after dorsal spondylodesis (author's transl)].

To investigate the question which growth processes take place in dorsally stiffened vertebral regions, 4 vertebral segments each were dorsally fused in twenty-one pigs, using Harrington's distraction system in 20 cases. X-ray examination and histological measurements conducted with the aid of fluorochromosequential markings showed a more or less pronounced growth of the vertebral bodies and of the fusion mass in all animals. As a rule, the sequence of vertebral bodies overgrows the fusion mass in longitudinal direction, which always results in lordosis of the stiffened region. The longitudinal growth of the vertebral bodies, and even more so of the fusion mass, decreases with increasing postoperative observation time. The fusion mass shows actual internal growth which proceeds partly in diffuse manner in all directions, in the region of the clefts, i.e. as spondyloschisis, in some cases also in the same direction as with enchondral ossification associated with columnar chondrification. The growth of the fused mass does not depend on the formation of a pseudoarthrosis, although it is probably quantitatively promoted by pseudarthroses. The stimulus to longitudinal growth of the fused mass originates from the growing vertebral bodies, with probably varying influence of tensile and compressive forces.