Automatic variable extraction from 3D coxal bone models for sex estimation using the DSP2 method.

Thanks to technical progress and the availability of virtual data, sex estimation methods as part of a biological profile are undergoing an inevitable evolution. Further reductions in subjectivity, but potentially also in measurement errors, can be brought by approaches that automate the extraction of variables. Such automatization also significantly accelerates and facilitates the specialist's work. The aim of this study is (1) to apply a previously proposed algorithm (Kuchar et al. 2021) to automatically extract 10 variables used for the DSP2 sex estimation method, and (2) to test the robustness of the new automatic approach in a current heterogeneous population. For the first aim, we used a sample of 240 3D scans of pelvic bones from the same individuals, which were measured manually for the DSP database. For the second aim a sample of 108 pelvic bones from the New Mexico Decedent Image Database was used. The results showed high agreement between automatic and manual measurements with rTEM below 5% for all dimensions except two. The accuracy of final sex estimates based on all 10 variables was excellent (error rate 0.3%). However, we observed a higher number of undetermined individuals in the Portuguese sample (25% of males) and the New Mexican sample (36.5% of females). In conclusion, the procedure for automatic dimension extraction was successfully applied both to a different type of data and to a heterogeneous population.

Shape morphing technique can accurately predict pelvic bone landmarks.

Diffeomorphic shape registration allows for the seamless geometric alignment of shapes. In this study, we demonstrated the use of a registration algorithm to automatically seed anthropological landmarks on the CT images of the pelvis. We found a high correlation between manually and automatically seeded landmarks. The registration algorithm makes it possible to achieve a high degree of automation with the potential to reduce operator errors in the seeding of anthropological landmarks. The results of this study represent a promising step forward in effectively defining the anthropological measures of the human skeleton.

Relation of native acetabular anteversion to the orientation of transverse acetabular ligament.

BACKGROUND: Precise positioning of the acetabular component during total hip replacement is the key to achieving optimal implant function and ensuring long-term patient comfort. However, different anatomical variations, degenerative changes, dysplasia, and other diseases make it difficult. In this study, we discuss a method based on the three-dimensional direction of the transverse ligament, predicting native acetabular anteversion with higher accuracy. METHODS: Angular positions of the acetabulum and direction of the transverse ligament were automatically calculated from routine computed tomography data of 270 patients using a registration algorithm. The relationship between acetabular angles and ligament direction and their relationship with sex, age, and pelvic tilt were sought. These relationships were then modelled using multilinear regression. RESULTS: Including the direction of the transverse ligament in the sagittal and transverse planes as a regressor in the multilinear model explained the variation in acetabular anteversion (R2 = 0.76 for men, R2 = 0.63 for women; standard deviation in prediction: men, 3.92° and women, 4.00°). CONCLUSIONS: The results indicate that the ligament was suitable as a guidance structure almost insensitive to the ligament in the sagittal and transverse planes must be considered. Estimation based on the direction in only 1 plane was not sufficiently accurate. The operative acetabular inclination was not correlated with the direction of the ligament. The correlations were higher in men than in women.

From computed tomography to finite element space: A unified bone material mapping strategy.

BACKGROUND: The spatially varying mechanical properties in finite element models of bone are most often derived from bone density data obtained via quantitative computed tomography. The key step is to accurately and efficiently map the density given in voxels to the finite element mesh. METHODS: The density projection is first formulated in least-squares terms and then discretized using a continuous and discontinuous variant of the finite element method. Both discretization variants are compared with the nodal and element approaches known from the literature. FINDINGS: In terms of accuracy in the L2 norm, energy distance and efficiency, the discontinuous zero-order variant appears to be the most advantageous. The proposed variant sufficiently preserves the spectrum of density at the edges, while keeping computational cost low. INTERPRETATION: The continuous finite element method is analogous to the nodal formulation in the literature, while the discontinuous finite element method is analogous to the element formulation. The two variants differ in terms of implementation, computational cost and ability to preserve the density spectrum. These differences cannot be described and measured by known indirect methods from the literature.

Mechanical metric for skeletal biomechanics derived from spectral analysis of stiffness matrix.

A new metric for the quantitative and qualitative evaluation of bone stiffness is introduced. It is based on the spectral decomposition of stiffness matrix computed with finite element method. The here proposed metric is defined as an amplitude rescaled eigenvalues of stiffness matrix. The metric contains unique information on the principal stiffness of bone and reflects both bone shape and material properties. The metric was compared with anthropometrical measures and was tested for sex sensitivity on pelvis bone. Further, the smallest stiffness of pelvis was computed under a certain loading condition and analyzed with respect to sex and direction. The metric complements anthropometrical measures and provides a unique information about the smallest bone stiffness independent from the loading configuration and can be easily computed by state-of-the-art subject specified finite element algorithms.

Bone mineral density modeling via random field: Normality, stationarity, sex and age dependence.

BACKGROUND AND OBJECTIVE: Capturing the population variability of bone properties is of paramount importance to biomedical engineering. The aim of the present paper is to describe variability and correlations in bone mineral density with a spatial random field inferred from routine computed tomography data. METHODS: Random fields were simulated by transforming pairwise uncorrelated Gaussian random variables into correlated variables through the spectral decomposition of an age-detrended correlation matrix. The validity of the random field model was demonstrated in the spatiotemporal analysis of bone mineral density. The similarity between the computed tomography samples and those generated via random fields was analyzed with the energy distance metric. RESULTS: The random field of bone mineral density was found to be approximately Gaussian/slightly left-skewed/strongly right-skewed at various locations. However, average bone density could be simulated well with the proposed Gaussian random field for which the energy distance, i.e., a measure that quantifies discrepancies between two distribution functions, is convergent with respect to the number of correlation eigenpairs. CONCLUSIONS: The proposed random field model allows the enhancement of computational biomechanical models with variability in bone mineral density, which could increase the usability of the model and provides a step forward in in-silico medicine.

Age and sexually dimorphic changes in costal cartilages. A preliminary microscopic study.

This study reports changes in costal cartilages that appear at the microscopic level throughout life, especially during the ossification process. The work builds on the results of our previous X-ray study, which confirmed the presence of two sexually dimorphic ossification patterns. This led to questions about the existence of additional sex-specific patterns that relate to the ossification process in costal cartilages. Samples of costal cartilages and adjacent parts of the bones were obtained from the autopsies of 17 corpses. The age range among the cadavers varied greatly, from a newborn baby to 91 years of age. Sections of costal cartilage were routinely processed and stained. Alkaline phosphatase activity was detected using histochemical methods. Collagens type II and X were detected immunohistochemically by monoclonal antibodies. The results of our study show that ossification of costal cartilages can take place in the form of two individual processes, localization and time-separate. Endochondral ossifications in the region of the costochondral zone appear in the first decade, and they correspond to ossifications detected by X-ray in the second decade. The location of sex-specific ossifications is determined by the penetration of cartilage canals into the metaphysial part of the rib. Endochondral intramembranous ossifications in the reserve zone appear after the third decade. These types of ossifications correspond to central globular ossifications detected by X-ray, and they are not sexually dimorphic. They can serve for accurate estimation of age.