The gross osseous anatomy of the spine has been the subject of much study but the internal architecture and trabecular anatomy of thoracolumbar vertebrate has not previously been well described. This study is based on high resolution x-ray images of 56 isolated thoracolumbar vertebrae and thick sections obtained from them. A previously undescribed array of trabeculae was documented which originated from the medial corner of the base of the pedicles and extended in a radial array throughout the vertebral body. This trabecular array persisted even in severely osteoporotic specimens. The cortex of the vertebral canal thinned abruptly near the base of the pedicle creating what may be a stress concentration at this site. This corresponded to the site of origin of the trabecular array. The presence of this possible stress concentration, in proximity to the trabecular array, may provide an explanation for the trapezoidal shape of the bony fragments that are frequently retropulsed into the spinal canal in axial load type burst fractures, common in this area of the spine.