Vertebral body and posterior element morphology: the normal spine in middle life.

Multiple morphologic parameters were studied in 50 normal adult vertebral columns ranging in age from 20 to 40 years at the time of death. Posterior element morphology is highly variable and largely unpredictable. Minimum pedicle diameters ranged from 1.8 mm at T6 to 6.4 mm at L5, and did not correlate with any more readily measured vertebral dimensions. Penetration of 5 mm screw threads through pedicle cortex can be expected to occur routinely in the lower thoracic spine, and in a lesser but significant number of lumbar vertebrae.