Anatomical and biomechanical analyses of the unique and consistent locations of sacral insufficiency fractures.
METHODS
Correlation of locations of sacral insufficiency fractures is made to regions of stress depicted by finite element analysis derived from biomechanical models of patient activities.


OBJECTIVE
Sacral insufficiency fractures occur at consistent locations. It was postulated that sacral anatomy and sites of stress within the sacrum with routine activities in the setting of osteoporosis are foundations for determining patterns for the majority of sacral insufficiency fractures.


BACKGROUND
The predominant vertical components of sacral insufficiency fractures most frequently occur bilaterally through the alar regions of the sacrum, which are the thickest and most robust appearing portions of the sacrum instead of subjacent to the central sacrum, which bears the downward force of the spine.


METHODS
First, the exact locations of 108 cases of sacral insufficiency fractures were catalogued and compared to sacral anatomy. Second, different routine activities were simulated by pelvic models from CT scans of the pelvis and finite element analysis. Analyses were done to correlate sites of stress with activities within the sacrum and pelvis compared to patterns of sacral insufficiency fractures from 108 cases.


RESULTS
The sites of stress depicted by the finite element analysis walking model strongly correlated with identical locations for most sacral and pelvic insufficiency fractures. Consistent patterns of sacral insufficiency fractures emerged from the 108 cases and a biomechanical classification system is introduced. Additionally, alteration of walking mechanics and asymmetric sacral stress may alter the pattern of sacral insufficiency fractures noted with hip pathology (P = 0.002).


CONCLUSIONS
Locations of sacral insufficiency fractures are nearly congruous with stress depicted by walking biomechanical models. Knowledge of stress locations with activities, cortical bone transmission of stress, usual fracture patterns, intensity of sacral stress with different activities, and modifiers of walking mechanics may aid medical management, interventional, or surgical efforts.
Linstrom
Nathan J
NJ
Barrow Neurological Institute, St Joseph Hospital and Medical Center, Phoenix, AZ 85013, USA.
Heiserman
Joseph E
JE
Kortman
Keith E
KE
Crawford
Neil R
NR
Baek
Seungwon
S
Anderson
Russell L
RL
Pitt
Alan M
AM
Karis
John P
JP
Ross
Jeff S
JS
Lekovic
Gregory P
GP
Dean
Bruce L
BL
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001696:Biomechanical Phenomena; D005260:Female; D020342:Finite Element Analysis; D015775:Fractures, Stress / Q000473:pathology* / Q000503:physiopathology; D006621:Hip Joint / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D008953:Models, Anatomic; D008954:Models, Biological; D010024:Osteoporosis / Q000473:pathology* / Q000503:physiopathology; D012189:Retrospective Studies; D012447:Sacrum / Q000473:pathology* / Q000503:physiopathology; D016103:Spinal Fractures / Q000473:pathology* / Q000503:physiopathology; D013314:Stress, Mechanical; D014057:Tomography, X-Ray Computed; D014481:United States; D016138:Walking