Identify fracture-critical regions inside the proximal femur using statistical parametric mapping.
We identified regions inside the proximal femur that are most strongly associated with hip fracture. Bone densitometry based on such fracture-critical regions showed improved power in discriminating fracture patients from controls.


BACKGROUND
Hip fractures typically occur in lateral falls, with focal mechanical failure of the sub-volumes of tissue in which the applied stress exceeds the strength. In this study, we describe a new methodology to identify proximal femoral tissue elements with highest association with hip fracture. We hypothesize that bone mineral density (BMD) measured in such sub-volumes discriminates hip fracture risk better than BMD in standard anatomic regions such as the femoral neck and trochanter.


METHODS
We employed inter-subject registration to transform hip QCT images of 37 patients with hip fractures and 38 age-matched controls into a voxel-based statistical atlas. Within voxels, we performed t-tests between the two groups to identify the regions which differed most. We then randomly divided the 75 scans into a training set and a test set. From the training set, we derived a fracture-driven region of interest (ROI) based on association with fracture. In the test set, we measured BMD in this ROI to determine fracture discrimination efficacy using ROC analysis. Additionally, we compared the BMD distribution differences between the 29 patients with neck fractures and the 8 patients with trochanteric fractures.


RESULTS
By evaluating fracture discrimination power based on ROC analysis, the fracture-driven ROI had an AUC (area under curve) of 0.92, while anatomic ROIs (including the entire proximal femur, the femoral neck, trochanter and their cortical and trabecular compartments) had AUC values between 0.78 and 0.87. We also observed that the neck fracture patients had lower BMD (p=0.014) in a small region near the femoral neck and the femoral head, and patients with trochanteric fractures had lower BMD in trochanteric regions such as in the internal calcar septum (p=0.006).


CONCLUSIONS
We have identified the sub-volumes of proximal femoral tissue which have the strongest association with hip fracture. The power to predict fracture can be improved, by focusing on BMD measurements in the fracture-critical regions, rather than in standard ROIs.
Li
Wenjun
W
Department of Radiology, University of California, San Francisco, San Francisco, CA 94143, USA. wenjun.li@radiology.ucsf.edu
Kornak
John
J
Harris
Tamara
T
Keyak
Joyce
J
Li
Caixia
C
Lu
Ying
Y
Cheng
Xiaoguang
X
Lang
Thomas
T
D000368:Aged; D019540:Area Under Curve; D015519:Bone Density; D005260:Female; D005269:Femur / Q000000981:diagnostic imaging* / Q000473:pathology; D006620:Hip Fractures / Q000000981:diagnostic imaging* / Q000473:pathology; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D012372:ROC Curve; D012307:Risk Factors; D014057:Tomography, X-Ray Computed