Abstract
Summary Statement
Bilaretal epiphysiodesis of he neurocentral cartilages causes shortening of the sagittal length of the pedicles and a subsequent spinal stenosis at the operated segments, resembling that found in patients with achrondroplasia.
Introduction
The introduction of pedicle screws in the immature spine may have implications for the growth of the vertebra. The effect of blocking the growth of neurocentral cartilage (NC) is not yet fully defined. Block hypothetically leads to a bilateral symmetrical alteration of the vertebral growth. Using an experimental animal model, our goal is to analyze if a bilateral epiphysiodesis of the NC using pedicle screws is able to induce narrowing of the spinal canal in the thoracolumbar spine.
Experimental animals and Methods
A total of 24 domestic pigs were operated on by bilateral blocking of the NC using pedicle screws. The animals were divided into 4 groups depending on the level of blockage: A, low thoracic levels; B, thoracolumbar transitional hinge; C, upper lumbar spine; and D, blocking of the caudal lumbar level below L5 segment. Different morphological, morphometric and standard radiological parameters were analyzed at the thoracic and lumbar vertebrae of the animals. The deviation from the physiological parameters was established by comparing all parameters obtained in the NC-blocked animals with those acquired in 14 pigs without NC blocking. These animals were considered as the control group.
Results
None of the animals that underwent NC epiphysiodesis showed asymmetrical spinal growth inducing deformities in the coronal plane. There was neither rotation nor wedging of the vertebral bodies. Whatever the level involved, NC epiphysiodesis caused shortening of the sagittal length of the pedicles and a subsequent decreasing of the antero-posterior diameter of the spinal canal. These features resulted in a frank spinal stenosis at the operated levels. However, the transverse diameter of the spinal canal was conserved in the coronal plane. In the sagittal plane, blocking of the neurocentral cartilage conditioned a lumbar hyperlordosis with compensatory kyphosis of the upper level to the operated vertebra.
Conclusions
Symmetrical growth arresting of neurocentral cartilages induces a narrow spinal canal by decreasing the sagittal diameter similar to that observed in patients with achondroplasia. The most affected structure was the development of the vertebral pedicles.
