Background: Knowledge of spinal deformity in swine remains still fluxional. Although pathologic reports of swine cases with neuromuscular spinal deformity are scarce, it is important to elucidate from the comparative viewpoint whether the development of spinal deformity in pigs is correlated with pathology of the spinal cord and/or skeletal muscle. In addition, intervertebral disc degeneration may be a complex process, but structural changes occurring in the deteriorated disc tissue is not fully explored.
Methods and findings: To evaluate a reciprocal relationship between spinal deformity and a triad of intervertebral disc, spinal cord, and skeletal muscle, a preliminary histopathologic study was conducted on 6 pigs (6 months of age) with thoracic kyphosis (1 case), lordokyphosis (1 case), or lordosis (4 cases). Annulus fibrosus between deformed vertebral bodies showed degeneration characterized by the occurrence of varying degrees of microcyst-like spaces, giving rise to an appearance of microcavitation or microporosity (6 cases). Focal necrosis was recognized in the annular matrix (4 cases). Chondrocytes showed positive labeling with the TUNEL assay, indicating apoptosis (6 cases). In addition, thoracic and lumbar segments of the spinal cord exhibited a minor extent of myelinated nerve fiber degeneration with no specific tract involvement in the white matter (6 cases). The muscle overlying the deformed spinal column had no significant changes.
Conclusions: Determining whether the structural changes observed in the annulus fibrosus played a primary role in the development of vertebral deformity or were secondary to mechanical overlord generated by the spinal deformity would require further investigation of deformed vertebral bodies. It is likely that myelinated nerve fiber alteration in the spinal cord was correlated with spinal deformity that gave mechanical damage to the spinal cord. The histopathologic findings observed in this small study may serve as a reference when studying deformities of the thoracic spinal column in humans.