Shape variation of the neural arch in the thoracic and lumbar spine: characterization and relationship with the vertebral body shape.

Quantifying the human vertebral geometry is important for accurate medical procedures. We aimed to characterize the neural arch (NA) shape at T1-L5. All T1-L5 dry vertebrae (N = 4,080) of 240 individuals were measured and analyzed by age, gender, and ethnicity. A 3D digitizer was used to measure the dimensions of the spinous (SP) and transverse (TP) processes, vertebral canal (VC), laminae, and isthmus. Most parameters were independent of age and ethnicity, yet greater in males than in females. Isthmus length increases from T1 (9.8 mm) to T12 (19.87 mm) and decreases from T12 to L5 (9.68 mm) with right > left in the thorax and oppositely in the lumbar region. The SP is longer than its thickness both decreasing in the upper thorax (by ca. 4mm), increasing in the lower thoracic and upper lumbar vertebrae (by 7 mm for length and ca. 14.5 mm for thickness) and decreasing again along the lower lumbar vertebrae (both by 8 mm). The TP length decreases at T1-T12 (by 13 mm) and increases at L1-L5 with left > right at T1-L5 (P < 0.003). The laminar length decreases from T1 (8.72 mm) through T5 (4.76 mm) and increases toward L5 (8.4 mm) with right > left at T1-L5 (P < 0.003). The VC is oval-shaped at T1 and T11-L5 (width > length), rounded-shape at T2 and T10 (width = length), and inverted oval-shaped at T3-T9 (length > width). In conclusion, the NA is systematically asymmetrical and dynamic in shape along the thoracic and lumbar spine. The inter-relationship with the vertebral body and articular facets is discussed.