Vertebra S3
Vertebra SIII
- Related terms: S3
Definition
The sacral vertebra S3 (Third sacral segment), is part of the sacrum, which is composed of five fused vertebrae.
The S3 vertebra features both anterior and posterior sacral foramina, which allow for the passage of the sacral nerves. The anterior sacral foramen of S3 is smaller compared to those of S1 and S2, with an average height of approximately 10 mm.[1] The posterior sacral foramen is similarly smaller, facilitating the exit of sensory fibers.[2]
The S3 segment has a relatively narrow transverse width, averaging around 7.12 mm in the axial plane and 7.71 mm in the coronal plane in normal sacra.[3]
The internal architecture of the S3 vertebra includes a trabecular bone pattern that is less dense compared to the upper sacral segments, with a notable decrease in bone density and cortical thickness at the junction between S2 and S3.[4] This makes the S3 segment a weaker structural area within the sacrum.
In terms of clinical relevance, the S3 segment can accommodate internal fixation devices, such as transiliac transsacral screws, particularly in cases of sacral dysmorphism where the osseous pathway is larger.[3][5]
References
1.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.
2.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.
3.Safe Zone Quantification of the Third Sacral Segment in Normal and Dysmorphic Sacra.Hwang JS, Reilly MC, Shaath MK, et al.Journal of Orthopaedic Trauma. 2018;32(4):178-182. doi:10.1097/BOT.0000000000001100.
4.Internal Architecture of the Sacrum in the Elderly. An Anatomic and Radiographic Study.Ebraheim N, Sabry FF, Nadim Y, Xu R, Yeasting RA.Spine. 2000;25(3):292-7. doi:10.1097/00007632-200002010-00006.
5.Is S3 a Viable Osseous Fixation Pathway?.Eastman JG, Adams MR, Frisoli K, Chip Routt ML.Journal of Orthopaedic Trauma. 2018;32(2):93-99. doi:10.1097/BOT.0000000000001036.
