Pasi Pulkkinen

Combination of bone mineral density and upper femur geometry improves the prediction of hip fracture

Bone mineral density (BMD) measured by dual-energy X-ray absorptiometry (DXA) is the main determinant of the clinical evaluation of hip fracture risk. However, it has been shown that BMD is not the only predictive factor for hip fracture, but that bone geometry is also important. We studied whether the combination of bone geometry and BMD could further improve the determination of hip fracture risk and fracture type. Seventy-four postmenopausal females (mean age 74 years) with a non-pathologic cervical or trochanteric hip fracture without previous hip fracture or hip surgery constituted the study group. Forty-nine had a cervical fracture (mean age 73 years) and 25 had a trochanteric fracture (mean age 76 years). The control group consisted of 40 age-matched females (mean age 74 years). The geometrical parameters were defined from plain anteroposterior radiographs, and the potential sources of inaccuracy were eliminated as far as possible by using a standardized patient position and calibrated dimension measurements with digital image analysis. BMD was measured at the femoral neck (FEBMD), Ward’s triangle (WABMD), and the trochanter (TRBMD). Stepwise linear regression analysis showed that the best predictor of hip fracture was the combination of medial calcar femoral cortex width (CFC), TRBMD, neck/shaft angle (NSA), and WABMD (r=0.72, r2=0.52, P<0.001). The area under the receiver operating characteristic curve (ROC) for this model was 0.93, while the area under ROC for TRBMD alone was 0.81. At a specificity of 80%, sensitivity improved from 52.5% to 92.5% with this combination compared with TRBMD alone. The combined predictors of cervical and trochanteric fracture differed, being NSA, CFC, TRBMD, and WABMD for cervical and TRBMD and femoral shaft cortical thickness for trochanteric fracture. In addition, we found a statistically significant correlation between FEBMD and femoral shaft and femoral neck cortex width (r=0.40, P<0.01 and r=0.30, P<0.01, respectively). The results confirm that the combination of BMD and radiological measures of upper femur geometry improve the assessment of the risk of hip fracture and fracture type compared to BMD alone, and that bone geometry plays an important role in the evaluation of bone strength.

Ct-based finite element models can be used to estimate experimentally measured failure loads in the proximal femur

The objective of this experimental finite element (FE) study was to assess the accuracy of a simulation model estimate of the experimentally measured fracture load of the proximal femur in a sideways fall. Sixty-one formalin-fixed cadaver femora (41 female and 20 male) aged 55-100 years (an average of 80 years) were scanned with a multi-detector CT scanner and were mechanically tested for failure in a sideways fall loading configuration. Twenty-one of these femurs were used for training purposes, and 40 femurs were used for validation purposes. The training set FE models were used to establish the strain threshold for the element failure criteria. Bi-linear elastoplastic FE analysis was performed based on the CT images. The validation set was used to estimate the fracture loads. The Drucker-Prager criterion was applied to determine the yielding and the maximum principal stress criteria and the minimum principal strain criteria for element failure in tension and in compression, respectively. The estimated fracture load values were highly correlated with the experimental data (r=0.931; p<0.001). The slope was 0.929, with an intercept of 258 N, which was not significantly different from 1 and 0, respectively. The study shows that it is possible to estimate the fracture load with relatively high accuracy in a sideways fall configuration by using the CT-based FE method. This method may therefore be applied for studying the biomechanical mechanisms of hip fractures.

Association of geometric factors and failure load level with the distribution of cervical vs. trochanteric hip fractures.

We experimentally studied the distribution of hip fracture types at different structural mechanical strength. Femoral neck fractures were dominant at the lowest structural strength levels, whereas trochanteric fractures were more common at high failure loads. The best predictor of fracture type across all failure loads and in both sexes was the neck‐shaft angle.

Experimental hip fracture load can be predicted from plain radiography by combined analysis of trabecular bone structure and bone geometry.

SummaryComputerized analysis of the trabecular structure was used to test whether femur failure load can be estimated from radiographs. The study showed that combined analysis of trabecular bone structure and geometry predicts in vitro failure load with similar accuracy as DXA.IntroductionSince conventional radiography is widely available with low imaging cost, it is of considerable interest to discover how well bone mechanical competence can be determined using this technology. We tested the hypothesis that the mechanical strength of the femur can be estimated by the combined analysis of the bone trabecular structure and geometry.MethodsThe sample consisted of 62 cadaver femurs (34 females, 28 males). After radiography and DXA, femora were mechanically tested in side impact configuration. Fracture patterns were classified as being cervical or trochanteric. Computerized image analysis was applied to obtain structure-related trabecular parameters (trabecular bone area, Euler number, homogeneity index, and trabecular main orientation), and set of geometrical variables (neck-shaft angle, medial calcar and femoral shaft cortex thicknesses, and femoral neck axis length). Multiple linear regression analysis was performed to identify the variables that best explain variation in BMD and failure load between subjects.ResultsIn cervical fracture cases, trabecular bone area and femoral neck axis length explained 64% of the variability in failure loads, while femoral neck BMD also explained 64%. In trochanteric fracture cases, Euler number and femoral cortex thickness explained 66% of the variability in failure load, while trochanteric BMD explained 72%.ConclusionsStructural parameters of trabecular bone and bone geometry predict in vitro failure loads of the proximal femur with similar accuracy as DXA, when using appropriate image analysis technology.

Investigation of differences between hip fracture types: A worthy strategy for improved risk assessment and fracture prevention

Edited by David Fyhrie could we improve this situation? For example, finite element techniques permitmodeling of different loading conditions and such analyseswould provide improved insight into fracture mechanics and guide the development of refined techniques, e.g. based on computed tomography. Hip fractures are the most problematic outcome of osteoporosis. In this perspective, we suggest that one potential reason for the current limits of hip fracture risk assessment may relate to the neglect of etiological and pathophysiological diversity of (a minimum of two) different types of hip fractures. We suggest that we can improve risk

Cortical bone finite element models in the estimation of experimentally measured failure loads in the proximal femur

Highly accurate nonlinear finite element (FE) models have been presented to estimate bone fracture load. However, these complex models require high computational capacity, which restricts their clinical applicability. The objective of this experimental FE study was to assess the predictive value of a more simple cortical bone simulation model in the estimation of experimentally measured fracture load of the proximal femur. The prediction was compared with that of DXA, and with the prediction of our previous, more complex FE model including trabecular bone. Sixty-one formalin-fixed cadaver femora (from 41 women and 20 men, age 55-100 years) were scanned using a multi-detector CT and were mechanically tested for failure in a sideways fall loading configuration. Trabecular bone was completely removed from the FE models and only cortical bone was analyzed. The training set FE models (N=21) was used to establish the stress and strain thresholds for the element failure criteria. Bi-linear elastoplastic FE analysis was performed based on the CT images. The validation set (N=40) was used to estimate the fracture load. The estimated fracture load values were highly correlated with the experimental data (r(2)=0.73; p<0.001). The slope was 1.128, with an intercept of -360 N, which was not significantly different from 1 and 0, respectively. DXA-based BMD and BMC correlated moderately with the fracture load (r(2)=0.41 and r(2)=0.40, respectively). The study shows that the proximal femoral failure load in a sideways fall configuration can be estimated with reasonable accuracy by using the CT-based bi-linear elastoplastic cortical bone FE model. This model was more predictive for fracture load than DXA and only slightly less accurate than a full bone FE model including trabecular bone. The accuracy and calculation time of the model give promises for clinical use.

Lifestyle factors and site-specific risk of hip fracture in community dwelling older women - a 13-year prospective population-based cohort study

BackgroundSeveral risk factors are associated to hip fractures. It seems that different hip fracture types have different etiologies. In this study, we evaluated the lifestyle-related risk factors for cervical and trochanteric hip fractures in older women over a 13-year follow-up period.MethodsThe study design was a prospective, population-based study consisting of 1681 women (mean age 72 years). Seventy-three percent (n = 1222) participated in the baseline measurements, including medical history, leisure-time physical activity, smoking, and nutrition, along with body anthropometrics and functional mobility. Cox regression was used to identify the independent predictors of cervical and trochanteric hip fractures.ResultsDuring the follow-up, 49 cervical and 31 trochanteric fractures were recorded. The women with hip fractures were older, taller, and thinner than the women with no fractures (p < 0.05). Low functional mobility was an independent predictor of both cervical and trochanteric fractures (HR = 3.4, 95% CI 1.8-6.6, and HR = 5.3, 95% CI 2.5-11.4, respectively). Low baseline physical activity was associated with an increased risk of hip fracture, especially in the cervical region (HR = 2.5, 95% CI 1.3-4.9). A decrease in cervical fracture risk (p = 0.002) was observed with physically active individuals compared to their less active peers (categories: very low or low, moderate, and high). Moderate coffee consumption and hypertension decreased the risk of cervical fractures (HR = 0.4, 95% CI 0.2-0.8, for both), while smoking was a predisposing factor for trochanteric fractures (HR = 3.2, 95% CI 1.1-9.3).ConclusionsImpaired functional mobility, physical inactivity, and low body mass may increase the risk for hip fractures with different effects at the cervical and trochanteric levels.

Assessment of Risk of Femoral Neck Fracture with Radiographic Texture Parameters: A Retrospective Study

PURPOSE To investigate whether femoral neck fracture can be predicted retrospectively on the basis of clinical radiographs by using the combined analysis of bone geometry, textural analysis of trabecular bone, and bone mineral density (BMD). MATERIALS AND METHODS Formal ethics committee approval was obtained for the study, and all participants gave informed written consent. Pelvic radiographs and proximal femur BMD measurements were obtained in 53 women aged 79-82 years in 2006. By 2012, 10 of these patients had experienced a low-impact femoral neck fracture. A Laplacian-based semiautomatic custom algorithm was applied to the radiographs to calculate the texture parameters along the trabecular fibers in the lower neck area for all subjects. Intra- and interobserver reproducibility was calculated by using the root mean square average coefficient of variation to evaluate the robustness of the method. RESULTS The best predictors of hip fracture were entropy (P = .007; reproducibility coefficient of variation < 1%), the neck-shaft angle (NSA) (P = .017), and the BMD (P = .13). For prediction of fracture, the area under the receiver operating characteristic curve was 0.753 for entropy, 0.608 for femoral neck BMD, and 0.698 for NSA. The area increased to 0.816 when entropy and NSA were combined and to 0.902 when entropy, NSA, and BMD were combined. CONCLUSION Textural analysis of pelvic radiographs enables discrimination of patients at risk for femoral neck fracture, and our results show the potential of this conventional imaging method to yield better prediction than that achieved with dual-energy x-ray absorptiometry-based BMD. The combination of the entropy parameter with NSA and BMD can further enhance predictive accuracy.

Quantification of differences in bone texture from plain radiographs in knees with and without osteoarthritis

OBJECTIVE To quantify differences in bone texture between subjects with different stages of knee osteoarthritis (OA) and age- and gender-matched controls from plain radiographs using advanced image analysis methods. DESIGN Altogether 203 knees were imaged using constant X-ray parameters and graded according to Kellgren-Lawrence (KL) grading scale (KL0: n = 110, KL1: n = 28, KL2: n = 27, KL3: n = 31, KL4: n = 7). Bone density-related and structure-related parameters were calculated from medial and lateral tibial subchondral bone plate and trabecular bone and from femur. Density-related parameters were derived from grayscale values and structure-related parameters from Laplacian- and local binary patterns (LBP)-based images. RESULTS Reproducibilities of structure-related parameters were better than bone density-related parameters. Bone density-related parameters were significantly (P < 0.05) higher in KL2-4 groups than in control group (KL0) in medial tibial subchondral bone plate and trabecular bone. LBP-based structure parameters differed significantly between KL0 and KL2-4 groups in medial subchondral bone plate, between KL0 and KL1-4 groups in medial and lateral trabecular bone, and between KL0 and KL1-4/KL2-4 in medial and lateral femur. Laplacian-based parameters differed significantly between KL0 and KL2-4 groups in medial side regions-of-interest (ROIs). CONCLUSIONS Our results indicate that the changes in bone texture in knee OA can be quantitatively evaluated from plain radiographs using advanced image analysis. Based on the results, increased bone density can be directly estimated if the X-ray imaging conditions are constant between patients. However, structural analysis of bone was more reproducible than direct evaluation of grayscale values, and is therefore better suited for quantitative analysis when imaging conditions are variable.

Standard Radiography: Untapped Potential in the Assessment of Osteoporotic Fracture Risk

BackgroundAssessment of osteoporotic fracture risk is based primarily on bone mineral density (BMD) measurements using dual X-ray absorptiometry (DXA).MethodsHowever, recent evidence indicates that the method is insufficient for accurate individual risk assessment; in addition to methodological inaccuracies related to DXA, the mechanical strength of bone is influenced not only by low BMD but also by other factors that are not captured by DXA.ResultsDXA-based BMD can provide information on the amount of bone but does not elucidate bone structure, which is significant for bone mechanical strength and for fracture risk. In order to achieve more a comprehensive assessment of fracture risk, recent efforts have been directed toward imaging techniques by which bone structural changes can be observed. In addition to novel three-dimensional imaging techniques, analysis of plain radiographs has also been investigated with promising results.ConclusionAs plain radiographs are cheap and widely available, it was considered of interest to discover how well plain radiography could be utilised for the assessment of bone mechanical competence and fracture risk. In this article, we review studies related to radiographic assessment of fracture risk in order to show the potential of this conventional methodology for screening subjects at risk.Key Points• Conventional radiography has sufficient theoretical requirements for assessment of bone structure.• Bone geometry and trabecular structure can be depicted by and evaluated from standard radiographs.• Texture-based analysis of radiographs discriminates postmenopausal women with and without fractures.• Such analysis can also predict fractures in individuals without frank osteoprosis.• Imaging and subsequent analysis should become more standardised to allow structural quantification