In vitro opto-electronic analysis of 3-D segmental vertebral movements during gradual rib lengthening in the pig.

The effects of gradual rib elongation on the 3-D position of neighboring vertebrae were studied in vitro in two pig specimens. The ends of one osteotomized rib were gradually distracted and the micromovements of the numerically corresponding vertebra with the osteotomized rib were studied in relation to the subjacent and suprajacent vertebrae with an opto-electronic motion analysis device. The study showed that gradual lengthening of the rib resulted in micromovements of the central vertebra in relation to the neighboring vertebrae registered as a) lateral translation in the coronal plane, b) rotation in the horizontal plane (both a and b were movements towards the opposite side of the lengthened rib), c) ventral translation in the sagittal plane and d) tilt in the coronal and sagittal planes. All movements were registered simultaneously. There was a significant linear correlation with the degree of rib elongation. From the results of this study it is concluded that gradual elongation of one rib affects the position of the numerically corresponding vertebra in relation to the suprajacent and subjacent vertebrae in the three cardinal planes in the same way as the apex vertebra is affected in idiopathic scoliosis. Moreover, the registered tilt, i.e., the rotational movement of the central vertebra in the coronal plane, could explain the wedging of the disc space, and the ventral translation in combination with the tilt in the sagittal plane could account for the lordotic tendency of the scoliotic segment.