Vertebra S1
Vertebra SI
- Related terms: S1
Definition
The first sacral vertebra (S1) is part of the sacrum, which is formed by the fusion of five sacral vertebrae. The S1 vertebra has several key anatomical features:
1. Body: The body of S1 is robust and supports the weight of the spine. It articulates with the fifth lumbar vertebra (L5) at the lumbosacral junction.
2. Ala: The lateral parts of S1, known as the ala, extend laterally and articulate with the iliac bones, forming the sacroiliac joints. The ala contains yellow marrow and is bounded by cortical bone and spongy bone.[1]
3. Pedicles: The pedicles of S1 are significant for surgical screw placement. They are approximately 20 mm in height and provide a pathway for screws in lumbosacral fusion procedures.[2]
4. Sacral Foramina: S1 has both anterior and posterior sacral foramina. The anterior sacral foramen (ASF) allows the passage of the first sacral nerve root, while the posterior sacral foramen (PSF) allows sensory fibers to exit. The S1 PSF measures approximately 12×10 mm.[3]
5. Sacral Canal: The sacral canal at the S1 level is about 30 mm in width and 20 mm in height, decreasing in diameter caudally.[3]
6. Spinous Process: The S1 spinous process is smaller and more variable in morphology compared to lumbar spinous processes. It is often not clearly visible on radiographs.[4]
References
1.Anatomic and Experimental Basis for the Insertion of a Screw at the First Sacral Vertebra.de Peretti F, Argenson C, Bourgeon A, et al.Surgical and Radiologic Anatomy : SRA. 1991;13(2):133-7. doi:10.1007/BF01623887.
2.Location of the Sacral Pedicle, Foramina, and Ala on the Lateral Aspect of the Sacrum: A Radiographic Study.Ebraheim NA, Xu R, Challgren E, Heck B.Orthopedics. 1998;21(6):703-6. doi:10.3928/0147-7447-19980601-13.
3.Best Practices for Dorsal Root Ganglion Stimulation for Chronic Pain: Guidelines From the American Society of Pain and Neuroscience.Chapman KB, Sayed D, Lamer T, et al.Journal of Pain Research. 2023;16:839-879. doi:10.2147/JPR.S364370.
4.Sacral Spinous Processes: A Morphologic Classification and Biomechanical Characterization of Strength.Wang T, Fielding LC, Parikh A, Kothari M, Alamin T.The Spine Journal : Official Journal of the North American Spine Society. 2015;15(12):2544-51. doi:10.1016/j.spinee.2015.08.058.
