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Sacral spinous processes: a morphologic classification and biomechanical characterization of strength
Tim Wang1, Louis C Fielding2, Anand Parikh2
1Stanford Orthopaedic Surgery, 450 Broadway St Pavilion C 4th Floor, Redwood City, CA 94063, USA.
The Spine Journal : Official Journal of the North American Spine Society
|September 8, 2015
Summary
The S1 spinous process, crucial for spinal fixation, shows variable morphology and strength comparable to lumbar segments. Preoperative 3D imaging aids visualization for interspinous fixation suitability.
Area of Science:
- Spinal anatomy and biomechanics
- Orthopedic surgery
- Radiology
Background:
- Increasing interest in spinous process fixation as a less invasive alternative to transpedicular instrumentation.
- Limited data on sacral spinous process dimensions, morphology, and strength compared to lumbar counterparts.
Purpose of the Study:
- To characterize the morphology of the S1 spinous process.
- To determine the biomechanical strength of the S1 spinous process under cranial loading.
Main Methods:
- Radiographic and computed tomography (CT) analysis of 20 patients' lumbosacral spines.
- Biomechanical testing of 13 cadaveric lumbosacral spinal segments.
- Measurement of S1 spinous process dimensions and evaluation of L5-S1 segment size.
Main Results:
- S1 spinous process visibility on lateral radiographs was low (10%).
- Mean S1 spinous process dimensions: length 11.6 mm (AP), height 23.1 mm (CC).
- Six morphologic subtypes identified; mean peak load to failure was 439N, with 92% failing by fracture.
Conclusions:
- This study provides the first evaluation of sacral spinous process morphology, visibility, and biomechanical strength for instrumentation.
- Sacral spinous processes are smaller with more variable morphology than lumbar ones but exhibit similar failure load.
- Preoperative 3D imaging is recommended over plain radiographs for optimal visualization and assessment of suitability for interspinous fixation.
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