Morphometry of the lower thoracic and lumbar pedicles and its relevance in pedicle fixation.

Abstract

To assess the pedicle morphology in the lower thoracic and lumbar spine in an Indian population and to determine the causes of pedicle wall violation by pedicle screws. Computerised tomographic scans of 135 consecutive patients with thoracolumbar and lumbar spine fractures were prospectively analysed to determine the pedicle morphology. The transverse pedicle angle, pedicle diameter and screw path length at 527 uninjured levels were measured. Post-operative CT scans of 117 patients were analysed to determine the accuracy of 468 pedicle screws at 234 vertebrae. The lowest (mean±SD) transverse pedicle width in the lower thoracic spine was 5.4±0.70mm, whereas in the lumbar spine it was 7.2±0.87mm. The shortest (mean±SD) screw path length in lower thoracic pedicles was 35.8±2.10 and 41.9±2.18mm in the lumbar spine. The mean transverse pedicle angle in the lower thoracic spine was consistently less than 5°, whereas it gradually increased from L1 through L5 from 8.5° to 30°. Forty-one screws violated the pedicle wall, due to erroneous angle of screw insertion. In the current study, pedicle dimensions were smaller compared to the Western population. In Indian patients, pedicle screws of 5mm diameter and 30mm length, and 6mm diameter and 35mm length can safely be used in the lower thoracic and lumbar spine, respectively. However, it is important to assess the pedicle morphology on imaging prior to pedicle fixation.