Automatic methods for characterization of sexual dimorphism of adult femora: distal femur

Quantifying sex differences in femoral size and shape has extensive applications in forensics and prosthesis design. By applying strong statistical techniques such as principal component analysis (PCA), certain three-dimensional (3D) morphological variations of adult femora can be quantified over various femoral sizes. Coupling this statistical approach with a novel feature generation and extraction technique, localization of statistically significant (p < 0.05) features are automatically defined and measured. Also, predefined anatomical landmarks and surgical axes have been calculated automatically. In all methods, femoral scale is controlled as a possible parameter of shape. By extensively comparing measurements across 92 male and 74 female femora, the dimorphic characteristics of the distal femur are shown. These differences have not been accounted for in many prosthetic systems and consequently these systems have limited sizing accuracy.     

人类股骨断面面积与形状的不对称性——基于三维激光扫描的形态测量分析

人类股骨横断面面积、形状及其左右侧差异记载的人类演化、人群差异及生存活动的重要信息一直为古人类学研究所关注。多年来, 对股骨断面的研究通常采用破坏性地切割或者制作模型的方法。本文利用三维激光表面扫描技术, 无损、快捷、方便地获取了20对现代中国人左右侧股骨外轮廓的三维数据, 采用CAD软件及几何形态测量方法对两侧股骨断面轮廓的大小及形状进行了对比和分析。初步研究结果发现: 两侧股骨的横断面相对面积差异极其显著, 绝对面积差异不显著, 不对称方式表现为波动不对称性, 而不是偏向不对称性; 个体之间两侧股骨横断面外轮廓形状的波动不对称性极其显著, 偏向不对称性虽有差异但不显著; 平均形状和面积分析结果似乎表明股骨稍有偏左侧优势。虽然本文所采用的标本量有限, 所得出的结论需要更多标本的进一步验证, 但是, 本文的研究结果提示利用三维激光扫描技术获取股骨横断面外轮廓数据, 并采用形态测量方法分析确实能够揭示出一些以往研究方法不能发现的重要信息, 这种研究骨骼不对称性的新方法值得进一步的应用。     

内蒙古和林格尔土城子农业人群与林西井沟子游牧人群股骨中部的生物力学对比

肢骨的形态结构可以反映人类进化、古代人群的生存适应性活动和生存环境等重要信息。基于“骨骼功能适应”和“杠杆原理”,有学者对不同生计方式的古代人群下肢股骨开展了大量的研究工作,但是,国内外尚未有关于农业人群和游牧人群股骨之间差异性研究的报道。本文选取两个具有代表性的古代人群,即内蒙古和林格尔土城子戍边农业人群和内蒙古林西井沟子游牧人群进行对比研究。通过对股骨骨干中部横断面生物力学分析发现,农业人群股骨粗壮度与游牧人群之间具有显著差异。前者的平均粗壮度较大,后者女性组下肢骨的活动强度明显较小,这可能与游牧人群经常从事骑马活动而下肢骨活动强度相对较少有关。农业人群股骨指数的变异范围均大于游牧人群,这可能与前者男性的士兵身份有关;同时,也提示土城子男性组股骨所反映的行为活动信息并不代表真正意义上的纯农业人群下肢骨行为模式,而是一种农业和士兵行为的混合模式。在性别分工上,井沟子组的男女性均从事骑马活动,两侧股骨受力较为一致,在两侧不对称性程度和骨干横断面形状上的男女差异不大;男性股骨的粗壮度要明显大于女性,这与井沟子组男性还从事一定的狩猎行为有关。与游牧人群女性较为纤细的股骨不同,土城子组女性作为典型的农业人群代表,其下肢骨整体的活动强度较大,几乎与同组的男性和井沟子组男性相当,组内的性别差异相对较小;骨干横断面形状的显著性差异说明,土城子组内部男性和女性的行为活动方式存在明显的性别分工。本文研究结果说明农业人群女性的下肢骨活动强度较大,在行为活动方式上,戍边农业人群具有更为明显的性别分工。     

Another look at shape variation in the distal femur of Australopithecus afarensis: implications for taxonomic and functional diversity at Hadar

Previous studies have recognized two patterns of distal femoral morphology among the specimens from Hadar (Ethiopia) assigned to Australopithecus afarensis. Size and shape differences between the well-preserved large (AL 333-4) and small (AL 129-1a) distal femora have been used to invoke both taxonomic and functional differences within the A. afarensis hypodigm. Nevertheless, prior studies have not analyzed these specimens in a multivariate context, nor have they compared the pattern of shape differences between the fossils to patterns of sexual dimorphism among extant taxa (i.e., the manner in which males and females differ). This study reexamines morphometric differences between the above specimens in light of observed levels of variation and patterns of sexual dimorphism among extant hominoids. Eight extant reference populations were sampled to provide a standard by which to consider size and shape differences between the fossils. Samples include three populations of modern humans, two subspecies of Pan troglodytes, three subspecies of Gorilla gorilla, Pan paniscus, and Pongo pygmaeus. Using size ratios and scale-free "shape" data (both derived from 2-D coordinate landmarks), size and shape differences between the fossils were evaluated against variation within each reference population using an exact randomization procedure. Growth Difference Matrix Analysis (GDMA) was used to test whether the pattern of morphological differences between the fossils differs significantly from patterns of sexual dimorphism observed among the ten extant groups. Overall morphometric affinities of the fossils to extant taxa were explored using canonical variates analysis (CVA).Results of the randomization tests indicate that the size difference between the Hadar femora can be easily accommodated within most hominoid taxa at the subspecific level (though not within single-sex samples). In addition, the magnitude of shape differences between the fossils can be commonly sampled even within most single-sex samples of a single hominoid subspecies. The pattern of morphological differences between the fossils does not differ statistically from any average pattern of femoral shape dimorphism observed among living hominoids. Moreover, contrary to prior claims, and despite a size disparity between the fossils greater than is typically observed within some chimpanzee and human populations, the two Hadar fossils appear to be much more similar to one another in overall shape than either specimen is to any extant hominoid group.     

Testing assumptions of the Gilbert and Gill method for assessing ancestry using the femur subtrochanteric shape

In 1990, Gilbert and Gill proposed a simple metric technique using femoral subtrochanteric anteroposterior and mediolateral diaphyseal diameters for discriminating between Native American and American Black and White femora in medicolegal and bioarchaeological contexts. However, there are several inherent assumptions in the method that may affect its validity. The assumptions include minimal sexual dimorphism, temporal and geographical homogeneity within populations, and that differences between populations in femoral subtrochanteric size and shape are primarily due to genetic variation. In this study, these assumptions are tested using femora from seven populations (African, American Black, American White, Australian, Native American, Hispanic, and Polynesian). The results indicate that sexual dimorphism and geographical and temporal heterogeneity in proximal femur diaphyseal shape within Native Americans are not great enough to significantly affect the validity of the Gilbert and Gill method (GGM). Variation between populations is most likely due to combined genetic and environmental factors, but differences in proximal femur shape between Native Americans and American Blacks/Whites are sufficient to allow accurate discrimination between these groups. Caution, however, must be taken during investigations where populations other than Native Americans or American Blacks/Whites are present, and therefore, the GGM may have limited forensic anthropological application in many parts of the world.     

Femoral curvature in Neanderthals and modern humans: a 3D geometric morphometric analysis

Since their discovery, Neanderthals have been described as having a marked degree of anteroposterior curvature of the femoral shaft. Although initially believed to be pathological, subsequent discoveries of Neanderthal remains lead femoral curvature to be considered as a derived Neanderthal feature. A recent study on Neanderthals and middle and early Upper Palaeolithic modern humans found no differences in femoral curvature, but did not consider size-corrected curvature. Therefore, the objectives of this study were to use 3D morphometric landmark and semi-landmark analysis to quantify relative femoral curvature in Neanderthals, Upper Palaeolithic and recent modern humans, and to compare adult bone curvature as part of the overall femoral morphology among these populations.Comparisons among populations were made using geometric morphometrics (3D landmarks) and standard multivariate methods. Comparative material involved all available complete femora from Neanderthal and Upper Palaeolithic modern human, archaeological (Mesolithic, Neolithic, Medieval) and recent human populations representing a wide geographical and lifestyle range. There are significant differences in the anatomy of the femur between Neanderthals and modern humans. Neanderthals have more curved femora than modern humans. Early modern humans are most similar to recent modern humans in their anatomy. Femoral curvature is a good indicator of activity level and habitual loading of the lower limb, indicating higher activity levels in Neanderthals than modern humans. These differences contradict robusticity studies and the archaeological record, and would suggest that femoral morphology, and curvature in particular, in Neanderthals may not be explained by adult behavior alone and could be the result of genetic drift, natural selection or differences in behavior during ontogeny.     

A novel methodology for generating 3D finite element models of the hip from 2D radiographs

Finite element (FE) modelling has been proposed as a tool for estimating fracture risk and patient-specific FE models are commonly based on computed tomography (CT). Here, we present a novel method to automatically create personalised 3D models from standard 2D hip radiographs. A set of geometrical parameters of the femur were determined from seven a–p hip radiographs and compared to the 3D femoral shape obtained from CT as training material; the error in reconstructing the 3D model from the 2D radiographs was assessed. Using the geometry parameters as the input, the 3D shape of another 21 femora was built and meshed, separating a cortical and trabecular compartment. The material properties were derived from the homogeneity index assessed by texture analysis of the radiographs, with focus on the principal tensile and compressive trabecular systems. The ability of these FE models to predict failure load as determined by experimental biomechanical testing was evaluated and compared to the predictive ability of DXA. The average reconstruction error of the 3D models was 1.77 mm (±1.17 mm), with the error being smallest in the femoral head and neck, and greatest in the trochanter. The correlation of the FE predicted failure load with the experimental failure load was r²=64% for the reconstruction FE model, which was significantly better (p<0.05) than that for DXA (r²=24%). This novel method for automatically constructing a patient-specific 3D finite element model from standard 2D radiographs shows encouraging results in estimating patient-specific failure loads.     

Geometric morphometric analyses of hominid proximal femora: Taxonomic and phylogenetic considerations

The proximal femur has long been used to distinguish fossil hominin taxa. Specifically, the genus Homo is said to be characterized by larger femoral heads, shorter femoral necks, and more lateral flare of the greater trochanter than are members of the genera Australopithecus or Paranthropus. Here, a digitizing arm was used to collect landmark data on recent human (n=82), chimpanzee (n=16), and gorilla (n=20) femora and casts of six fossil hominin femora in order to test whether one can discriminate extant and fossil hominid (sensu lato) femora into different taxa using three-dimensional (3D) geometric morphometric analyses. Twenty proximal femoral landmarks were chosen to best quantify the shape differences between hominin genera. These data were first subjected to Procrustes analysis. The resultant fitted coordinate values were then subjected to PCA. PC scores were used to compute a dissimilarity matrix that was subjected to cluster analyses. Results indicate that one can easily distinguish Homo, Pan, and Gorilla from each other based on proximal femur shape, and one can distinguish Pliocene and Early Pleistocene hominin femora from those of recent Homo. It is more difficult to distinguish Early Pleistocene Homo proximal femora from those of Australopithecus or Paranthropus, but cluster analyses appear to separate the fossil hominins into four groups: an early australopith cluster that is an outlier from other fossil hominins; and two clusters that are sister taxa to each other: a late australopith/Paranthropus group and an early Homo group.     

Allometric and Group Differences in the Xenarthran Femur

The aim of this study is to analyze shape variation in the xenarthran femur to gain insights into their behavior and locomotion. Specimens of both Cingulata (armadillos and glyptodonts) and Pilosa (anteaters and sloths) were studied and within each group body mass varies by several orders of magnitude. The main focus of the analysis was allometric variation in femoral shape in the three groups studied, armadillos, glyptodonts, and pilosans. Three dimensional coordinates were recorded for 40 homologous landmarks on each of 51 xenarthran femurs. The data were analyzed by geometric morphometric methods, and form space analysis was used to identify the allometric variation in each of the three groups. Across all groups, larger specimens tended to have larger articular surfaces, more robust femora generally, and the shape of the femoral condyles was more suited to extended postures. In addition, in larger specimens the medial condyle was much larger than the lateral condyle and the third trochanter was located more distally. The larger armadillo femora had a greater trochanter located considerably proximal to the femoral head and this is thought to improve femoral extension, but in glyptodonts and pilosans the larger specimens had a greater trochanter that was far lateral to the femoral head and this is interpreted as enhancing femoral rotation.     

Shape Ontogeny of the Distal Femur in the Hominidae with Implications for the Evolution of Bipedality

Heterochrony has been invoked to explain differences in the morphology of modern humans as compared to other great apes. The distal femur is one area where heterochrony has been hypothesized to explain morphological differentiation among Plio-Pleistocene hominins. This hypothesis is evaluated here using geometric morphometric data to describe the ontogenetic shape trajectories of extant hominine distal femora and place Plio-Pleistocene hominins within that context. Results of multivariate statistical analyses showed that in both Homo and Gorilla, the shape of the distal femur changes significantly over the course of development, whereas that of Pan changes very little. Development of the distal femur of Homo is characterized by an elongation of the condyles, and a greater degree of enlargement of the medial condyle relative to the lateral condyle, whereas Gorilla are characterized by a greater degree of enlargement of the lateral condyle, relative to the medial. Early Homo and Australopithecus africanus fossils fell on the modern human ontogenetic shape trajectory and were most similar to either adult or adolescent modern humans while specimens of Australopithecus afarensis were more similar to Gorilla/Pan. These results indicate that shape differences among the distal femora of Plio-Pleistocene hominins and humans cannot be accounted for by heterochrony alone; heterochrony could explain a transition from the distal femoral shape of early Homo/A. africanus to modern Homo, but not a transition from A. afarensis to Homo. That change could be the result of genetic or epigenetic factors.     

The anomalous archaic Homo femur from Berg Aukas, Namibia: a biomechanical assessment.

The probably Middle Pleistocene human femur from Berg Aukas, Namibia, when oriented anatomically and analyzed biomechanically, presents an unusual combination of morphological features compared to other Pleistocene Homo femora. Its midshaft diaphyseal shape is similar to most other archaic Homo, but its subtrochanteric shape aligns it most closely with earlier equatorial Homo femora. It has an unusually low neck shaft angle. Its relative femoral head size is matched only by Neandertals with stocky hyperarctic body proportions. Its diaphyseal robusticity is modest for a Neandertal, but reasonable compared to equatorial archaic Homo femora. Its gluteal tuberosity is relatively small. Given its derivation from a warm climatic region, it is best interpreted as having had relatively linear body proportions (affecting proximal diaphyseal proportions, shaft robusticity, and gluteal tuberosity size) combined with an elevated level of lower limb loading during development (affecting femoral head size and neck shaft angle).     

Prediction of femoral strength using 3D finite element models reconstructed from DXA images: validation against experiments

Computed tomography (CT)-based finite element (FE) models may improve the current osteoporosis diagnostics and prediction of fracture risk by providing an estimate for femoral strength. However, the need for a CT scan, as opposed to the conventional use of dual-energy X-ray absorptiometry (DXA) for osteoporosis diagnostics, is considered a major obstacle. The 3D shape and bone mineral density (BMD) distribution of a femur can be reconstructed using a statistical shape and appearance model (SSAM) and the DXA image of the femur. Then, the reconstructed shape and BMD could be used to build FE models to predict bone strength. Since high accuracy is needed in all steps of the analysis, this study aimed at evaluating the ability of a 3D FE model built from one 2D DXA image to predict the strains and fracture load of human femora. Three cadaver femora were retrieved, for which experimental measurements from ex vivo mechanical tests were available. FE models were built using the SSAM-based reconstructions: using only the SSAM-reconstructed shape, only the SSAM-reconstructed BMD distribution, and the full SSAM-based reconstruction (including both shape and BMD distribution). When compared with experimental data, the SSAM-based models predicted accurately principal strains (coefficient of determination >0.83, normalized root-mean-square error <16%) and femoral strength (standard error of the estimate 1215 N). These results were only slightly inferior to those obtained with CT-based FE models, but with the considerable advantage of the models being built from DXA images. In summary, the results support the feasibility of SSAM-based models as a practical tool to introduce FE-based bone strength estimation in the current fracture risk diagnostics.     

A comparison of the femoral head and neck trabecular architecture of Galago and Perodicticus using micro-computed tomography (microCT)

Innovations in micro-computed tomography (microCT) in the medical field have resulted in the development of techniques that allow the precise quantification of bone density and fabric related parameters of trabecular bone. For the purpose of this study, the technique was applied to a small sample of Perodicticus potto and Galago senegalensis femora to see if differences in loading environment elicit the predicted effects on trabecular structure. While the overall bone volume was approximately three times larger in the potto, there was no significant difference in the apparent volume density in the two taxa. When regional differences in the proximal femur were examined, the cancellous bone of the femoral head of Perodicticus potto and Galago senegalensis, while not differing in volume density, showed differences in trabecular orientation, with the potto having more randomly oriented trabeculae than the bushbaby. This was as hypothesized, given that the bushbaby submits its femora to more stereotypical loading environments than the potto. In the femoral neck, the cancellous bone was not only more randomly oriented, it was also denser in the potto compared with the bushbaby. This suggests that trabecular morphology may be extremely sensitive to certain differences in the loading environment and that this information, combined with information on cortical bone structure and external geometry, will result in a more complete understanding of how bone shape and composition correspond to loading and locomotor patterns. Ultimately, a synthesis of these different lines of evidence may have considerable applications in paleontological studies that attempt to reconstruct bone use from morphology.     

Anatomical factors relative to the racial selectivity of femoral neck fracture

A comparative racial study of 200 femora from 50 American White and 50 American Negro female skeletons was carried out to determine whether any anatomical differences in femoral from exist between these groups which might account for the racial selectivity of hip fracture, Significant racial differences were found in neck-shaft angle, angle of inclination and oblique length. Negro females have longer femora, larger neck-shaft angles and a smaller angle of inclination than have White females. These differences in femoral morphology may, in some measure, contribute to the greater incidence of hip fracture in female Whites.     

The femur of extinct bunodont otters in Africa (Carnivora,Mustelidae, Lutrinae)

This study compares fossil femora attributed to extinct African bunodont lutrines with extant mustelids and ursids to reconstruct locomotor behavior. Due to the immense size differences among taxa, shape data were used to compare morphology. Based on morphological differences, the fossil femora are suggested to belong to different taxa with different locomotor abilities and habitat preferences. The Langebaanweg femur is the oldest and has a typical mustelid morphology suggesting that it was a locomotor generalist like most mustelids. The West Turkana form is more like extant nonbunodont otters, but much larger, and may have belonged to a semiaquatic taxon. The enormous Omo femur shares some features with truly aquatic taxa (e.g., Enhydra) and is the most likely to have been fully aquatic. The same may hold true for the Hadar species as it is most similar to that from the Omo. If these femora truly belong to bunodont lutrines, then they are more diverse in postcranial morphology than in dental morphology.     

Primary rotational stability of cylindrical and conical revision hip stems as a function of femoral bone defects: an in vitro comparison

Bone stock losses in cementless femoral stem revisions compromise a stable fixation. The surgeon has to rely on his wealth of experience in deciding which stem shape to use. The aim of our study was to compare the primary rotational stability of cylindrical and conical revision hip stems subjected to femoral defects. Four current prostheses (two cylindrical, two conical) were implanted into four synthetic femora. Micro-motion was measured under torque application and femoral neck osteotomy and segmental AAOS Type I and III defects were simulated. The relative movements of all prostheses were significantly influenced by the extent of bone loss (p<0.01). Major differences were seen in fixation behavior (p<0.01). The main fixation area of conical stems is within the distal femoral isthmus, whereas cylindrical implants are dependent on proximal bone stock. In our study, cylindrical stems are advantageous for minor defects because they provide a proximal fixation. In cases of extensive substance loss, the conical implants showed lesser relative movements. These findings should be taken into account for clinical decisions.     

Is sexual dimorphism in the femur a "population specific phenomenon"?

The patterns of sexual dimorphism as well as the differences in amount between the populations were studied on a sample of 162 male and 159 female left femora, which were classified as Zulu, Sotho, Xosa and South Africans of European extraction. Multivariate analyses revealed that even adjacent African tribes exhibit a different pattern of sexual dimorphism, but there were similarities between Zulu and European femora. Furthermore, relative size differences, i.e. shape, discriminated more clearly between the sexes than did absolute size. Bicondylar width yielded a statistically significant higher degree of sexual dimorphism in Europeans when compared to African populations. This finding was interpreted in terms of the biomechanical demands on the femur under different living conditions. On the other hand, sexual dimorphism of femoral length did not differ among the populations. This was unexpected since femoral length correlates highly with stature, which was reported to show a lesser degree of sexual dimorphism in Africans than in Europeans. Detailed analyses of the results of the present study led to suggest that different living conditions may affect bones in complex ways of which linear growth is only one aspect.     

A fossil hominoid proximal femur from Kikorongo Crater, southwestern Uganda

The external morphology of a fragmentary right proximal femur from southwestern Uganda is described here. Discovered in the Kikorongo Crater of Queen Elizabeth National Park in 1961, this specimen was informally assigned to Homo sapiens (although never described) and tentatively dated to the late Pleistocene. However, because aspects of the external morphology of the femur align the fossil with the African great apes, we suggest that the Kikorongo femur may be the first postcranial fossil of the genus Pan. Like the African apes, the Kikorongo specimen lacks both an obturator externus groove and an intertrochanteric line. It has a short femoral neck with a circular cross section, and a narrow and deep superior notch. Using resampling statistics and discriminant function analysis, the Kikorongo femur clustered with the genus Pan, as opposed to Gorilla or Homo. However, if the specimen is from Pan, it would be large for this taxon. Furthermore, features that clearly distinguish the external morphology of Plio-Pleistocene hominin proximal femora from African ape femora, such as the shape of the femoral neck in cross section and femoral neck length, have converged in Holocene humans and African apes. Unfortunately, the internal morphology of the femoral neck of the Kikorongo fossil was not discernable. Although we hypothesize that the Kikorongo femur is from the genus Pan, there is such variability in the proximal femora of modern humans that, although it would be an unusual human, it remains possible that this fossil represents H. sapiens.     

Temporal trends in femoral curvature and length in medieval and modern Scotland

We measured how much the radius of the anterior curvature and the length of the femoral shaft of cadaveric bones have changed from medieval to recent times. Around 20 (x, y) coordinates of a virtual coordinate system were measured at intervals of 1.5 cm along the shaft of the femur to calculate one single radius of a virtual circle in the (x, y) plane. The median radii of curvature were 119, 141, and 158 cm for medieval, early, and late 20th century femora, respectively. Early and late 20th century femora were of similar length (45 cm), but medieval femora were shorter (43.5 cm). Femora have become not only longer but also straighter since the Middle Ages. These findings account in part for the increase in height of modern generations. Size and shape changes may have significant implications for the biomechanical response of the femur to the forces to which it is subjected in everyday life, in trauma, and following surgical intervention.