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A 35 year-old female presents after prolonged extrication from a motor vehicle collision complaining of severe pelvic pain. Physical examination reveals diminished perianal sensation. She is otherwise neurologically intact. Figures A through D are radiographs and representative CT cuts of her injury. Which of the following nerve roots has likely been injured?
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The clinical scenario is consistent with a high-energy sacral fracture. The radiographs in figures A and B demonstrate a sacral fracture with posterior displacement of the right hemipelvis seen on the inlet view. Figures C and D are axial and sagittal CT images which show a displaced fracture of the right hemisacrum along with a transvere fracture component through the S3 body . Diminished perianal sensation is concerning for an S2 nerve root injury.
Mehta et al reviewed the current management of sacral fractures. They note that the S1 and S2 nerve roots are more likely to be injured with sacral fractures as they occupy 1/3 to 1/4 of the neural foramina, as opposed to S3 and S4, which only occupy 1/6 of the neural foramina.
Robles reviewed the current literature to ascertain principles of evaluation and treatment for transverse sacral fractures. The author notes that injury to nerve roots S2 to S5 is manifested by impairment of urinary and anal continence and sexual function.
The first illustration demonstrates the sacral nerve root dermatomal distribution. The second shows a pelvic cadaver dissection demonstrating the sacral nerve roots as they exit the foramina.
Mehta S, Auerbach JD, Born CT, Chin KR
J Am Acad Orthop Surg. 2006 Nov;14(12):656-65. PMID: 17077338 (Link to Abstract)
Spine J. 9(1):60-9. PMID: 17981093 (Link to Abstract)
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A 20-year-old patient presents after jumping from the window of a burning building with a sacral fracture. Which of the following fracture patterns seen in Figures A through E would give this patient the highest risk of associated nerve injury?
Answering this question relies on knowledge of the Denis classification of sacral fractures and their associated risks of nerve injury. Figure A represents a Denis Zone 3 (medial to the foramina) sacral fracture, which has the highest associated risk of nerve injury.
Denis et al outlined a novel classification system of sacral fractures based on the position of the fracture line relative to the sacral foramina. The authors found a 56.7% incidence of nerve injury in fractures that extended medial to the sacral foramina (zone 3), compared with 28.4% for fractures through the foramina (zone 2), and 5.9% for fractures lateral to the foramina (zone 1).
Mehta et al reviewed the current principles for management of sacral fractures. They note that bowel, bladder and sexual dysfunction occur in 76% of patients with zone 3 sacral fractures.
Illustration A below demonstrates the Denis classification of sacral fractures.
2. Figure B shows a zone 1 sacral fracture, which has a 5.9% incidence of nerve injury
3. Figure C shows a zone 2 sacral fracture, which has a 28.4% incidence of nerve injury
4. Figure D shows a sacroiliac joint dislocation, not a sacral fracture
5. Figure E shows a zone 1 sacral fracture with an associated iliac fracture (crescent fracture)
Denis F, Davis S, Comfort T.
Clin Orthop Relat Res. 1988 Feb;227:67-81. PMID: 3338224 (Link to Abstract)
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Which of the following is the most stable construct for fixation of an unstable transforaminal sacral fractures?
Combined iliosacral and lumbopelvic fixation (triangular osteosynthesis)
Anterior pelvic ring plating with bilateral sacroilliac percutaenous screw fixation
Transiliac bars with anterior pelvic ring plating
Combined iliosacral and lumbopelvic fixation (triangular osteosynthesis) for sacral fractures has the greatest stiffness when used for an unstable sacral fracture.
The referenced article by Schildhauer et al is a cadaveric study that examined the biomechanical properties of different fixation constructs under cyclic loading and demonstrates that triangular osteosynthesis for unstable transforaminal sacral fractures provides significantly greater stability than iliosacral screw fixation under in-vitro cyclical loading.
Illustration below shows the radiographic appearance of lumbopelvic fixation. The addition of iliosacral fixation would complete triangular osteosynthesis.
Schildhauer TA, Ledoux WR, Chapman JR, Henley MB, Tencer AF, Routt ML
J Orthop Trauma. 2003 Jan;17(1):22-31. PMID: 12499964 (Link to Abstract)
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HPI - RTA 13 days back , open fracture tibia managed by debridement and external fixator ,a transverse fractures of the sacrum with anterior displacement. Referred from a local hospital for further management.
How would you classify this fracture according to the Denis classification?
This video has been taken from "Long-Segment Spinal Fixation Using Pelvic Screws...
Educational video describing the classifications of sacral fractures.