In-vivo assessment of femoral bone strength using Finite Element Analysis (FEA) based on routine MDCT imaging: a preliminary study on patients with vertebral fractures.
OBJECTIVE
To experimentally validate a non-linear finite element analysis (FEA) modeling approach assessing in-vitro fracture risk at the proximal femur and to transfer the method to standard in-vivo multi-detector computed tomography (MDCT) data of the hip aiming to predict additional hip fracture risk in subjects with and without osteoporosis associated vertebral fractures using bone mineral density (BMD) measurements as gold standard.


METHODS
One fresh-frozen human femur specimen was mechanically tested and fractured simulating stance and clinically relevant fall loading configurations to the hip. After experimental in-vitro validation, the FEA simulation protocol was transferred to standard contrast-enhanced in-vivo MDCT images to calculate individual hip fracture risk each for 4 subjects with and without a history of osteoporotic vertebral fractures matched by age and gender. In addition, FEA based risk factor calculations were compared to manual femoral BMD measurements of all subjects.


RESULTS
In-vitro simulations showed good correlation with the experimentally measured strains both in stance (R2 = 0.963) and fall configuration (R2 = 0.976). The simulated maximum stress overestimated the experimental failure load (4743 N) by 14.7% (5440 N) while the simulated maximum strain overestimated by 4.7% (4968 N). The simulated failed elements coincided precisely with the experimentally determined fracture locations. BMD measurements in subjects with a history of osteoporotic vertebral fractures did not differ significantly from subjects without fragility fractures (femoral head: p = 0.989; femoral neck: p = 0.366), but showed higher FEA based risk factors for additional incident hip fractures (p = 0.028).


CONCLUSIONS
FEA simulations were successfully validated by elastic and destructive in-vitro experiments. In the subsequent in-vivo analyses, MDCT based FEA based risk factor differences for additional hip fractures were not mirrored by according BMD measurements. Our data suggests, that MDCT derived FEA models may assess bone strength more accurately than BMD measurements alone, providing a valuable in-vivo fracture risk assessment tool.
Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Hans
H
Liebl
Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany; Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Eduardo Grande
EG
Garcia
Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Fabian
F
Holzner
Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Peter B
PB
Noel
Department of Orthopaedic Surgery, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Rainer
R
Burgkart
Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Ernst J
EJ
Rummeny
Department of Radiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Thomas
T
Baum
Section of Neuroradiology, Klinikum rechts der Isar, Technische Universitaet Muenchen, Muenchen, Germany.
Jan S
JS
Bauer
D015502:Absorptiometry, Photon; D000368:Aged; D015519:Bone Density; D016022:Case-Control Studies; D003198:Computer Simulation; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000502:physiology*; D006801:Humans; D008297:Male; D055595:Mechanical Phenomena; D008875:Middle Aged; D008962:Models, Theoretical; D018570:Risk Assessment; D012307:Risk Factors; D016103:Spinal Fractures / Q000000981:diagnostic imaging / Q000473:pathology; D014057:Tomography, X-Ray Computed / Q000379:methods*