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. Sacral fractures: an important problem. Retrospective analysis of 236 cases. Clin Orthop Relat Res. 1988 Feb;227:67-81.
PMID:3338224 (Link to Abstract)
Mehta S, Auerbach JD, Born CT, Chin KR. Sacral fractures. J Am Acad Orthop Surg. 2006 Nov;14(12):656-65.
PMID:17077338 (Link to Abstract)