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)