Tissue-separating capacity of growth cartilages.

The tissue-separating capacity of chondral structures has been debated for more than 30 years, and one aspect that has particularly been questioned is whether the secondary cartilage of the mandibular condyle is comparable to primary growth cartilage, e.g. the epiphyseal growth plate. The present report summarizes information gained by using a specific interosseal transplantation method. These findings lead to the conclusion that all the structures examined, i.e. the proximal epiphyseal cartilage of the tibia, the cartilage of the costochondral junction of the ribs, the basicranial synchondroses, the medial cartilage of the clavicle and the mandibular condyle, have the capacity to separate adjoining skeletal structures. The changes induced by the transplanted structures in the recipient area vary, however, suggesting a hierarchial arrangement of cartilages with regard to their tissue-separating capacity. It is suggested that the tissue-separating capacity is a basic phenomenon in the function of growth, not only of primary growth cartilages, but of secondary cartilages as well.

Growth changes in the skull and upper cervical skeleton after partial detachment of neck muscles. An experimental study in the rat.

The influence of altered neck muscle function on the morphology of the craniocervical area was studied in the rat. The neck muscles were detached from their cranial attachments at 14 days of age and the skulls subjected to macroscopic, radiological and microscopic examination at 180, 360 and 450 days of age. Visual observations only were made on the three upper cervical vertebrae. As compared with the situation in the unoperated control animals, the occipital area of the experimental skull was flattened, the superior margin of the foramen magnum was irregularly curved, the sutural serration appeared less accentuated in the posterior lambdoid suture, the normally smooth curvature of which had a caudal flexture in the middle. The spheno-occipital synchondrosis was structurally similar to that in the controls, and no obliteration was seen. The angular relations between the basicranial components changed following the operation in that the posterior basicranial components at first were bent downwards while the situation was later reversed. To compensate for the upward inclination of the posterior part of the basi-occipital bone, the anterior rim of the foramen magnum had become reshaped. The downward flexion of the basicranium was considered to be the result of the decreased nuchal muscle tension whereas the reversed angle phenomenon was possibly brought about by tissue scarring. The dorsal arch of the first cervical vertebra was wider craniocaudally than in the controls and its cranial border was bent ventrally. The second vertebra differed from the controls in that the spinous process was longer and in some cases was directed upwards.(ABSTRACT TRUNCATED AT 250 WORDS)

Synchondroseal growth in the first cervical vertebra of the rat.

Growth and remodelling of the first cervical vertebra were studied in the rat by means of biometry, vital staining (alizarin red S and oxytetracycline), and histology. The measurements showed a change in the ratio of the dorso-ventral to the transversal diameter in the lumen after obliteration of the dorsal synchondrosis. The pattern of labelling between the three segments of the vertebrae joined by synchondroses in the young animals indicated that expansion of the vertebral lumen took the form of a displacement of all three parts making up the bony ring. After closure of the dorsal synchondrosis the two ventral ones were still active and the lumen size increased more in the dorso-ventral direction than transversally. Alizarin red S and oxytetracycline tended to persist in the ventral part of the vertebra, while the staining almost disappeared from the dorso-lateral segment. Resting lines were found laterally to the ventral synchondroses in haematoxylin and eosin stained sections, but not in the ventral segment between the cartilages. The growth of the rat atlas is the result of an early rapid cartilage-mediated expansion of the vertebral lumen in conjunction with the growth of the spinal cord and, at a later age, mainly of a displacement of the ventral vertebral segment, leading to the final form of the vertebra and its lumen.

Morphogenic potential of autogenous costal cartilage transplanted into the interparietal suture area of the rat.

A study was carried out to determine the separability of costochondral tissue and to investigate the preservation of its integrity as a transplant to a relatively immobile osseous site. On 10-day-old rats, two autogenous rib sections, complete with bone and cartilage, were transplanted across the interparietal suture with the cartilaginous ends either in the same direction or in opposite directions; untreated rats were used as controls. The animals, injected with Alizarin red S, were killed 25, 50, and 75 days after the operation, 10 at each time. At 25 days after the operation the calvarial width and neurocranial height were significantly greater, and the strip of new white bone appeared wider in the experimental animals as compared to the untreated control rats; later, the differences were less pronounced. The changes in the neurocranial morphology seemed more symmetrical following positioning of the cartilaginous ends of the graft in opposite directions than when they were in the same direction. In some transplants the endochondral ossification process appeared normal at the termination of the experimental period, but signs of degeneration were also observed. The findings were considered to indicate that costochondral transplants are endowed with an intrinsic tissue-separating capacity, and that they can preserve their integrity for an extended period under relatively nonfunctional conditions.

Morphogenetic potential of rat growth cartilages as isogeneic transplants in the interparietal suture area.

The proximal end of the tibia or the spheno-occipital synchondrosis with some adjoining bone were isogeneically transplanted across the interparietal suture of 10-day-old rats. As a sham procedure, a piece of calvarium traversed by a part of the interparietal suture was interchanged between pairs of animals. Untreated rats served as controls. The animals, injected with Alizarin red S, were killed 25-75 days after the operation, 10 in each group. The transverse dimensions of the neurocranium were larger in the rats with the cartilage transplants than in the controls, particularly at 25 days after the operation; the differences persisted longer in the animals with the synchondroseal transplant. The orientation of the bone interdigitation at the anterior lambdoidal suture changed temporarily in response to the excessive lateral displacement of the parietal bones. The observations indicate that basicranial synchondroses, like epiphyseal cartilage, are endowed with a tissue-separating property that may persist for a prolonged period under transplant conditions. As such cartilaginous structures may also be affected by environmental influences, there must be a two-way interaction between the synchondroses and their immediate environment.

Reactions of transplanted neurocentral synchondroses to different conditions of mechanical stress. A methodological study on the rat.

In order to elucidate the reactions of neurocentral synchondroses to different forces, the first cervical vertebra of 10 or 25 days old rats was transplanted into sex-matched litter mates. Some vertebrae were transplanted as a whole, in some only the ventral part with its synchondroses was transplanted and, in others the lumen was furnished with an expanding sponge or a spring. The transplantation was done subcutaneously and, in the case of the fragments, intracerebrally as well. The synchondroses of the vertebrae transplanted at 10 days did not differ very much from those of the host 5, 10 or 15 days after the operation, whereas in the vertebrae transplanted at 25 days the synchondroses underwent synostosis earlier than in situ. The synchondroses of the transplanted fragments, and especially of those placed intracerebrally, remained open longer than those in the whole vertebral transplants; the sponge and and the spring also delayed closure. In the synchondroses transplanted at 25 days there was a strong reduction in alcian blue staining, whereas in the spring loaded synchondroses the stainability persisted longer, maybe as an adaptation to the tensile force. It seems that the inherent potential of the neurocentral synchondroses to obliterate at a certain time can be altered by changing the biomechanical conditions.