Morphological traits in sacra associated with complete and partial lumbarization of first sacral segment

Area of Science:

• Anatomy
• Biomechanics
• Anthropology

Background:

• Transitional vertebrae at the lumbosacral junction are linked to low back pain.
• Lumbarization, a transitional state, involves partial or complete separation of the S1 segment from the sacrum.
• This separation alters lumbosacral junction anatomy and affects regional load-bearing.

Purpose of the Study:

• Identify structural features of sacra with S1 lumbarization.
• Compare dimensions and surface areas of variant sacra with normal samples.
• Analyze load-bearing capacity in relation to altered sacral morphology.

Main Methods:

• Measurement of seven linear dimensions and five surface areas in 332 dried human sacra.
• Screening for partial or complete lumbarization of the S1 segment.
• Formulation of nine indices to analyze morphological variations and traits.

Main Results:

• 3.9% of sacra exhibited lumbarization (7 partial, 6 complete).
• Partial lumbarization showed normal parameters but lower auricular surfaces; complete separation resulted in smaller dimensions, accessory facets, attenuated laminae, and spina bifida in some cases.
• Complete S1 separation led to load transmission via S2 and S3 elements and accessory articulations near sacroiliac joints.

Conclusions:

• Lumbarization causes distinct anatomical changes at the S1-S2 junction.
• Partial lumbarization features include a gap between S1-S2 bodies, lumbar-like S1 neural arches, and low-down auricular surfaces.
• Complete S1 separation involves smaller overall dimensions, occasional accessory articulations, and attenuated sacral laminae, sometimes with spina bifida.