Volumetric quantitative computed tomography of the proximal femur: Precision and relation to bone strength

doi:10.1016/S8756-3282(97)00072-0

Bone

Volume 21, Issue 1, July 1997, Pages 101-108

https://doi.org/10.1016/S8756-3282(97)00072-0 Get rights and content

Abstract

We have developed a three-dimensional computed tomography (CT) scanning and image analysis method for measurement of trabecular and integral bone mineral density (BMD) and geometry in automatically determined femoral-neck and trochanteric subregions of the proximal femur. We measured the correlation of the density and geometry variables to femoral strength assessed in vitro under loading simulating a single-limb condition and a fall to the side. While BMD alone accounted for 48%–77% of the variability in strength for the stance loading configuration, femoral neck cross-sectional area (minCSA) and femoral neck axis length (FNAL) also contributed independently to femoral strength, and a combination of BMD and geometry variables explained 87%–93% of the variance in the data. For the fall loading configuration, trochanteric trabecular BMD alone explained 87% of the variability of strength. The reproducibility in vivo of the technique was assessed in a group of seven postmenopausal women, who underwent repeat scans with repositioning. For trabecular BMD, the precision was 1.1% and 0.6% for the femoral neck and trochanteric subregions, respectively, compared to 3.3% and 1.6% for the corresponding integral envelopes. Thus, trabecular BMD measurements were reproducible and highly correlated to biomechanical strength measurements. These results support further exploration of quantitative CT for assessment of osteoporosis at the proximal femur.

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Musculoskeletal injuries to the lower leg and foot-ankle joint are associated with external mechanical loads resulting from motor vehicle crashes, under body blasts, falls from height, or sports. As an intrinsic material property, the bone mineral density (BMD) is related to bone strength. The clinically recognized biological sites for BMD evaluation are the hip and spine. The focus of this study was to define the correlation between BMD from standard clinical sites (hip and lumbar spine) compared to BMD from non-standard sites (foot-ankle-distal tibia bones). Twenty-one post-mortem human subjects (PMHS) with mean age, height, and mass of 63 ± 11 years, 179 ± 7 cm, and 86 ± 13 kg, respectively were used for analysis. Clinical BMD software (Mindways Software, Inc.) was used for trabecular BMD quantification using quantitative computed tomography (QCT). In quantification of BMD of the foot-ankle-distal tibia (hind foot), the trabecular BMD of the talus (316 ± 86mg/cc) was highest followed by the distal tibia (238 ± 72 mg/cc) and then calcaneus (147 ± 51 mg/cc). To correlate BMD values from foot bone regions with the central skeleton BMD values within the same PMHS, there were 18 lumbar spine and 12 hip BMDs available. The BMD of the distal tibia correlated best with the hip intertrochanter BMD (R² of 0.72). Calcaneus BMD best correlated with the hip femoral neck BMD (R² = 0.64). In summary, the hind foot bone BMD values correlated better with the hip as compared to the lumbar spine BMD from the same PMHS. These findings indicate that, in the absence of a direct measure of foot-bone BMD, hip BMD might be a better predictor of injury risk to hind foot rather than lumbar spine BMD, or alternatively, calcaneal trabecular BMD can be used to predict the risk of injury to hip. Further, these relationships between central and peripheral regions can also be implemented in finite element models for improved failure predictions.
Cortical thinning and accumulation of large cortical pores in the tibia reflect local structural deterioration of the femoral neck
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Cortical bone thinning and a rarefaction of the trabecular architecture represent possible causes of increased femoral neck (FN) fracture risk. Due to X-ray exposure limits, the bone microstructure is rarely measurable in the FN of subjects but can be assessed at the tibia. Here, we studied whether changes of the tibial cortical microstructure, which were previously reported to be associated with femur strength, are also associated with structural deteriorations of the femoral neck.
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Femur strength was associated with the total (vBMD_tot; R² = 0.23, p < 0.01) and trabecular (vBMD_trab; R² = 0.26, p < 0.01) volumetric bone mineral density (vBMD), with the cortical thickness (Ct.Th_FN; R² = 0.29, p < 0.001) and with the trabecular bone volume fraction (Tb.BV/TV_FN; R² = 0.34, p < 0.001), separation (Tb.Sp_FN; R² = 0.25, p < 0.01) and number (Tb.N_FN; R² = 0.32, p < 0.001) of the femoral neck. Moreover, smaller Ct.Th_tibia was associated with smaller Ct.Th_FN (R² = 0.31, p < 0.05), lower Tb.BV/TV_FN (R² = 0.29, p < 0.05), higher Tb.Sp_FN (R² = 0.33, p < 0.05) and lower Tb.N_FN (R² = 0.42, p < 0.01). A higher prevalence of pores with diameter > 100 μm in tibial cortical bone (relCt.Po_100μm-tibia) indicated higher Tb.Sp_FN (R² = 0.36, p < 0.01) and lower Tb.N_FN (R² = 0.45, p < 0.01).
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In this work, we investigate if QCT-derived homogenized voxel finite element (hvFE) simulations of varying hip loading conditions can be used to study the architecture of the femoral neck. The strength of 19 pairs of human femora was measured ex vivo using nonlinear hvFE models derived from high-resolution peripheral QCT scans (voxel size: 30.3 µm). Standing and side-backwards falling loads were modeled. Quasi-static mechanical tests were performed on 20 bones for comparison. Associations of femur strength with volumetric bone mineral density (vBMD) or microstructural parameters of the femoral neck obtained from high-resolution QCT were compared between mechanical tests and simulations and between standing and falling loads.
Proximal femur strength predictions by hvFE models were positively associated with the vBMD of the femoral neck (R² > 0.61, p < 0.001), as well as with its cortical thickness (R² > 0.27, p < 0.001), trabecular bone volume fraction (R² = 0.42, p < 0.001) and with the first two principal components of the femoral neck architecture (R² > 0.38, p < 0.001). Associations between femur strength and femoral neck microarchitecture were stronger for one-legged standing than for side-backwards falling. For both loading directions, associations between structural parameters and femur strength from hvFE models were in good agreement with those from mechanical tests. This suggests that hvFE models can reflect the load-direction-specific contribution of the femoral neck microarchitecture to femur strength.
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Imaging was conducted on a 3-Tesla MRI scanner using two sequences: one balanced steady-state free precession sequence with 300 μm isotropic voxel size and one spoiled gradient echo with anisotropic voxel size of 234 × 234 × 1500 μm. Femora were dissected free of soft-tissue and 4350-ohm strain-gauges were securely applied to surfaces at the femoral shaft, inferior neck, greater trochanter, and superior neck. Cadavers were mechanically tested with a hydraulic universal test frame to simulate loading in a sideways fall orientation.
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View all citing articles on Scopus

^☆: This work was presented in poster form at the 1996 World Congress on Osteoporosis, Amsterdam, May 17–23, 1996, where it received a Young Investigator Award.

^∗: Present address: Department of Orthopedic Surgery, University of California, Irvine Medical Center, Orange, CA.

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Original articleVolumetric quantitative computed tomography of the proximal femur: Precision and relation to bone strength☆

Abstract

J Biomech

Lancet

Bone mineral content and mechanical strength

Clin Orthop Relat Res

Predicting femoral neck strength from bone mineral data: A structural approach

Invest Radiol

Three-dimensional quantitative CT of the proximal femur: Relationship to vertebral trabecular bone density in postmenpausal women

Radiology

Models of spinal trabecular bone loss as determined by quantitative computed tomography

J Bone Miner Res

Ultrasound and densitometry of the calcaneus correlate with the failure loads of cadaveric femurs

Calcif Tissue Int

3D QCT BMD of the hip;regional comparison with DXA

J Biomed Mater Res

Age-related reduction in the strength of the femur tested in a fall-loading configuration

J Bone Jt Surg

Effects of loading rate on strength of the proximal femur

Calcif Tiss Int

Does estimating volumetric bone density of the femoral neck improve the prediction of hip fracture?

J Bone Miner Res

Bone mineral content and mechanical strength of the femoral neck

Acta Orthop Scand

Three anatomy of the cancellous structures within the proximal femur from computed tomography data

J Orthop Res

Biomechanical properties of the proximal femur determined in vitro by single-energy quantitative computed tomography

J Bone Miner Res

Bone loss in the immediate postmenopausal period

J Comput Assist Tomogr

Simple measurement of femoral geometry predicts hip fracture: The study of osteopotic fractures

J Bone Miner Res

Automated evaluation of hip axis length for predicting hip fracture

J Biomed Mater Res

The femoral neck: Function, fracture mechanism, internal fixation; An experimental study

Noninvasive assessment of bone mineral and structure: State of the art

J Bone Miner Res

Quantitative computed tomography of vertebral spongiosa: A sensitive method for detecting early bone loss after oophorectomy

Ann Int Med

Accurate assessment of precision errors: How to measure the reproducibility of bone densitometry techniques

Osteopor Int

Prediction of hip fractures from pelvic radiographs: the study of osteoporotic fractures

J Bone Miner Res

Original article
Volumetric quantitative computed tomography of the proximal femur: Precision and relation to bone strength☆