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Three-dimensional geometric morphometric analysis of the first metacarpal distal articular surface in humans, great apes and fossil hominins. J Hum Evol 2019; 132:119-136. [DOI: 10.1016/j.jhevol.2019.04.008] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 04/23/2019] [Accepted: 04/23/2019] [Indexed: 11/18/2022]
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2
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Pouydebat E, Bardo A. An interdisciplinary approach to the evolution of grasping and manipulation. Biol J Linn Soc Lond 2019. [DOI: 10.1093/biolinnean/blz058] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Affiliation(s)
- Emmanuelle Pouydebat
- UMR 7179 CNRS/MNHN, Département d’Ecologie et de Gestion de la Biodiversité, Paris, France
| | - Ameline Bardo
- Animal Postcranial Evolution Laboratory, Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, Kent, UK
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Stephens NB, Kivell TL, Pahr DH, Hublin JJ, Skinner MM. Trabecular bone patterning across the human hand. J Hum Evol 2018; 123:1-23. [PMID: 30072187 DOI: 10.1016/j.jhevol.2018.05.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Revised: 05/09/2018] [Accepted: 05/10/2018] [Indexed: 02/06/2023]
Abstract
Hand bone morphology is regularly used to link particular hominin species with behaviors relevant to cognitive/technological progress. Debates about the functional significance of differing hominin hand bone morphologies tend to rely on establishing phylogenetic relationships and/or inferring behavior from epigenetic variation arising from mechanical loading and adaptive bone modeling. Most research focuses on variation in cortical bone structure, but additional information about hand function may be provided through the analysis of internal trabecular structure. While primate hand bone trabecular structure is known to vary in ways that are consistent with expected joint loading differences during manipulation and locomotion, no study exists that has documented this variation across the numerous bones of the hand. We quantify the trabecular structure in 22 bones of the human hand (early/extant modern Homo sapiens) and compare structural variation between two groups associated with post-agricultural/industrial (post-Neolithic) and foraging/hunter-gatherer (forager) subsistence strategies. We (1) establish trabecular bone volume fraction (BV/TV), modulus (E), degree of anisotropy (DA), mean trabecular thickness (Tb.Th) and spacing (Tb.Sp); (2) visualize the average distribution of site-specific BV/TV for each bone; and (3) examine if the variation in trabecular structure is consistent with expected joint loading differences among the regions of the hand and between the groups. Results indicate similar distributions of trabecular bone in both groups, with those of the forager sample presenting higher BV/TV, E, and lower DA, suggesting greater and more variable loading during manipulation. We find indications of higher loading along the ulnar side of the forager sample hand, with high site-specific BV/TV distributions among the carpals that are suggestive of high loading while the wrist moves through the 'dart-thrower's' motion. These results support the use of trabecular structure to infer behavior and have direct implications for refining our understanding of human hand evolution and fossil hominin hand use.
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Affiliation(s)
- Nicholas B Stephens
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany.
| | - Tracy L Kivell
- Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury CT2 7NZ, United Kingdom; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Dieter H Pahr
- Institute for Lightweight Design and Structural Biomechanics, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria
| | - Jean-Jacques Hublin
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
| | - Matthew M Skinner
- Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury CT2 7NZ, United Kingdom; Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, 04103 Leipzig, Germany
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Reina N, Cavaignac E, Trousdale WH, Laffosse JM, Braga J. Laterality and grip strength influence hand bone micro-architecture in modern humans, an HRpQCT study. J Anat 2017; 230:796-804. [PMID: 28421607 DOI: 10.1111/joa.12608] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/15/2017] [Indexed: 11/29/2022] Open
Abstract
It is widely hypothesized that mechanical loading, specifically repetitive low-intensity tasks, influences the inner structure of cancellous bone. As such, there is likely a relationship between handedness and bone morphology. The aim of this study is to determine patterns in trabecular bone between dominant and non-dominant hands in modern humans. Seventeen healthy patients between 22 and 32 years old were included in the study. Radial carpal bones (lunate, capitate, scaphoid, trapezium, trapezoid, 1st, 2nd and 3rd metacarpals) were analyzed with high-resolution micro-computed tomography. Additionally, crush and pinch grip were recorded. Factorial analysis indicated that bone volume ratio, trabeculae number (Tb.N), bone surface to volume ratio (BS.BV), body weight, stature and crush grip were all positively correlated with principal components 1 and 2 explaining 78.7% of the variance. Volumetric and trabecular endostructural parameters (BV/TV, BS/BV or Tb.Th, Tb.N) explain the observed inter-individual variability better than anthropometric or clinical parameters. Factors analysis regressions showed correlations between these parameters and the dominant side for crush strength for the lunate (r2 = 0.640, P < 0.0001), trapezium (r2 = 0.836, P < 0.0001) and third metacarpal (r2 = 0.763). However, despite a significant lateralization in grip strength for all patients, the endostructural variability between dominant and non-dominant sides was limited in perspective to inter-individual differences. In conclusion, handedness is unlikely to generate trabecular patterns of asymmetry. It appears, however, that crush strength can be considered for endostructural analysis in the modern human wrist.
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Affiliation(s)
- Nicolas Reina
- Orthopedic and Trauma Surgery Department, Hôpital Pierre Paul Riquet, Centre Hospitalier Universitaire de Toulouse, Toulouse, France.,Laboratoire d'Anthropobiologie AMIS, UMR 5288 CNRS, Université Paul Sabatier, Toulouse, France
| | - Etienne Cavaignac
- Orthopedic and Trauma Surgery Department, Hôpital Pierre Paul Riquet, Centre Hospitalier Universitaire de Toulouse, Toulouse, France.,Laboratoire d'Anthropobiologie AMIS, UMR 5288 CNRS, Université Paul Sabatier, Toulouse, France
| | | | - Jean-Michel Laffosse
- Orthopedic and Trauma Surgery Department, Hôpital Pierre Paul Riquet, Centre Hospitalier Universitaire de Toulouse, Toulouse, France.,Biomechanics Laboratory, IMFT UMR 5502, University of Toulouse, Toulouse, France
| | - José Braga
- Laboratoire d'Anthropobiologie AMIS, UMR 5288 CNRS, Université Paul Sabatier, Toulouse, France
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Wong AL, Meals CG, Ruff CB. Computed tomographic analysis of the internal structure of the metacarpals and its implications for hand use, pathology, and surgical intervention. Anat Sci Int 2017; 93:231-237. [PMID: 28341969 DOI: 10.1007/s12565-017-0400-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2016] [Accepted: 03/15/2017] [Indexed: 10/19/2022]
Abstract
The variation of bone structure and biomechanics between the metacarpals is not well characterized. It was hypothesized that their structure would reflect their common patterns of use (i.e., patterns of hand grip), specifically that trabecular bone density would be greater on the volar aspect of all metacarpal bases, that this would be most pronounced in the thumb, and that the thumb diaphysis would have the greatest bending strength. Cross-sections at basal and mid-diaphyseal locations of 50 metacarpals from 10 human hands were obtained by peripheral quantitative computed tomography. The volar and dorsal trabecular densities of each base were measured and characterized using the volar/dorsal density ratio. The polar stress-strain index (SSIp), a surrogate measure of torsional/bending strength, was measured for each diaphysis and standardized for bone length and mass. Comparisons were made using mixed-model analyses of variance (ANOVAs) and post hoc tests. Volar/dorsal trabecular density ratios showed even distribution in all metacarpal bases except for the thumb, which showed greater values on the volar aspect. The thumb, second, and third metacarpals all had high bending strength (SSIp), but the thumb's SSIp relative to its length and trabecular mass was much higher than those of the other metacarpals. Trabecular density of the metacarpal bases was evenly distributed except in the thumb, which also showed higher bending strength relative to its length and mass. Understanding of how these indicators of strength differ across metacarpals may improve both fracture diagnosis and treatment and lays the groundwork for investigating changes with age, hand dominance, and occupation.
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Affiliation(s)
- Alison L Wong
- Center for Bioengineering Innovation and Design, Johns Hopkins University, 3400 N. Charles Street, Clark Hall, Suite 200, Baltimore, MD, 21218, USA. .,Division of Plastic and Reconstructive Surgery, Dalhousie University, Room 4714 Halifax Infirmary Site, 1796 Summer Street, Halifax, NS, B3H 3A7, Canada.
| | - Clifton G Meals
- The Curtis National Hand Center, MedStar Union Memorial Hospital, 3333 North Calvert Street, Baltimore, MD, 21218, USA
| | - Christopher B Ruff
- Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, 1830 E. Monument Street, Room 302, Baltimore, MD, 21205, USA
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Functional Morphology of the Primate Hand: Recent Approaches Using Biomedical Imaging, Computer Modeling, and Engineering Methods. ACTA ACUST UNITED AC 2016. [DOI: 10.1007/978-1-4939-3646-5_9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/09/2023]
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7
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Stephens NB, Kivell TL, Gross T, Pahr DH, Lazenby RA, Hublin JJ, Hershkovitz I, Skinner MM. Trabecular architecture in the thumb of Pan and Homo: implications for investigating hand use, loading, and hand preference in the fossil record. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2016; 161:603-619. [PMID: 27500902 DOI: 10.1002/ajpa.23061] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Revised: 06/14/2016] [Accepted: 07/24/2016] [Indexed: 12/31/2022]
Abstract
OBJECTIVES Humans display an 85-95% cross-cultural right-hand bias in skilled tasks, which is considered a derived behavior because such a high frequency is not reported in wild non-human primates. Handedness is generally considered to be an evolutionary byproduct of selection for manual dexterity and augmented visuo-cognitive capabilities within the context of complex stone tool manufacture/use. Testing this hypothesis requires an understanding of when appreciable levels of right dominant behavior entered the fossil record. Because bone remodels in vivo, skeletal asymmetries are thought to reflect greater mechanical loading on the dominant side, but incomplete preservation of external morphology and ambiguities about past loading environments complicate interpretations. We test if internal trabecular bone is capable of providing additional information by analyzing the thumb of Homo sapiens and Pan. MATERIALS AND METHODS We assess trabecular structure at the distal head and proximal base of paired (left/right) first metacarpals using micro-CT scans of Homo sapiens (n = 14) and Pan (n = 9). Throughout each epiphysis we quantify average and local bone volume fraction (BV/TV), degree of anisotropy (DA), and elastic modulus (E) to address bone volume patterning and directional asymmetry. RESULTS We find a right directional asymmetry in H. sapiens consistent with population-level handedness, but also report a left directional asymmetry in Pan that may be the result of postural and/or locomotor loading. CONCLUSION We conclude that trabecular bone is capable of detecting right/left directional asymmetry, but suggest coupling studies of internal structure with analyses of other skeletal elements and cortical bone prior to applications in the fossil record.
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Affiliation(s)
- Nicholas B Stephens
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, 04103, Germany
| | - Tracy L Kivell
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, 04103, Germany.,Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, CT2 7NR, United Kingdom
| | - Thomas Gross
- Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, A-1060 Vienna, Getreidemarkt 9/BE, Vienna, Austria
| | - Dieter H Pahr
- Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, A-1060 Vienna, Getreidemarkt 9/BE, Vienna, Austria
| | - Richard A Lazenby
- Department of Anthropology, University of Northern British Columbia, 3333 University Way, Prince George, BC, Canada, V2N 4Z9
| | - Jean-Jacques Hublin
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, 04103, Germany
| | - Israel Hershkovitz
- Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel-Aviv University, Tel-Aviv, Israel
| | - Matthew M Skinner
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Deutscher Platz 6, Leipzig, 04103, Germany.,Skeletal Biology Research Centre, School of Anthropology and Conservation, University of Kent, Canterbury, CT2 7NR, United Kingdom
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8
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Reeves NM, Auerbach BM, Sylvester AD. Fluctuating and directional asymmetry in the long bones of captive cotton-top tamarins (Saguinus oedipus). AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2016; 160:41-51. [PMID: 26801822 DOI: 10.1002/ajpa.22942] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Revised: 12/17/2015] [Accepted: 12/28/2015] [Indexed: 11/07/2022]
Abstract
OBJECTIVES Skeletal asymmetries reflect developmental stability and mechanical, functional, and physiological influences on bone growth. In humans, researchers have documented the greatest limb bone bilateral asymmetry in diaphyseal breadths, with less asymmetry in articular and maximum length dimensions. However, it remains unclear as to whether the pattern observed for humans is representative of nonhuman primates, wherein bilateral loading may minimize directional asymmetry. This study adds to the small body of asymmetry data on nonhuman primates by investigating patterns of long bone asymmetry in a skeletal sample of Saguinus oedipus (cotton-top tamarin). MATERIALS AND METHODS Humeri, radii, ulnae, femora, and tibiae of 76 adult captive cotton-top tamarin skeletons (48 males, 28 females) were measured bilaterally. We included maximum length, midshaft diaphyseal breadths, and at least one articular measurement for each bone to assess directional (DA) and fluctuating asymmetry (FA) in each dimension. RESULTS Most dimensions exhibit significant FA, and very few have significant DA; DA is limited to the lower limb, especially in knee dimensions. Overall, the magnitudes of asymmetry in tamarins have a consistent ranking that follows the same pattern as found in humans. DISCUSSION This first study of DA and FA among multiple dimensions throughout the limbs of a non-hominoid primate suggests that previously-reported patterns of human bilateral asymmetry are not exclusive to humans. The results further indicate potential underlying differences in constraints on variation within limb bones. While processes shaping variation await further study, our results argue that different long bone dimensions may reflect dissimilar evolutionary processes.
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Affiliation(s)
- Nicole M Reeves
- Department of Anatomy, Ross University School of Medicine, Portsmouth, Dominica
- Department of Anthropology, The University of Tennessee, Knoxville, TN
| | | | - Adam D Sylvester
- Center for Functional Anatomy and Evolution, Johns Hopkins University School of Medicine, Baltimore, MD
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Duren DL, Seselj M, Froehle AW, Nahhas RW, Sherwood RJ. Skeletal growth and the changing genetic landscape during childhood and adulthood. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2013; 150:48-57. [PMID: 23283664 PMCID: PMC3539213 DOI: 10.1002/ajpa.22183] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Accepted: 10/03/2012] [Indexed: 01/15/2023]
Abstract
Growth, development, and decline of the human skeleton are of central importance to physical anthropology. All processes of skeletal growth (longitudinal growth as well as gains and losses of bone mass) are subjected to environmental and genetic influences. These influences, and their relative contributions to the phenotype, can be asserted at any stage of life. We present here the gross phenotypic and genetic landscapes of four skeletal traits, and show how they vary across the life span. Phenotypic sex differences are found in bone diameter and cortical index (a ratio of cortical thickness over bone diameter) at a very early age and continue throughout most of life. Sexual dimorphism in summed cortical thickness and bone length, however, is not evident until shortly after the pubertal growth spurt. Genetic contributions (heritability) to these skeletal phenotypes are generally moderate to high. Bone length and bone diameter (which both scale with body size) tend to have the highest heritability, with heritability of bone length fairly stable across ages (with a notable dip in early childhood) and that of bone diameter peaking in early childhood. The bone traits summed cortical thickness and cortical index that may better reflect bone mass, a more plastic phenomenon, have slightly lower genetic influences, on average. Results from our phenotypic and genetic landscapes serve three key purposes: 1) demonstration of the integrated nature of the genetic and environmental underpinnings of skeletal form, 2) identification of periods of bone's relative sensitivity to genetic and environmental influences, 3) and stimulation of hypotheses predicting the effects of exposure to environmental variables on the skeleton, given variation in the underlying genetic architecture.
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Affiliation(s)
- Dana L Duren
- Division of Morphological Sciences and Biostatistics, Lifespan Health Research Center, Department of Community Health, Boonshoft School of Medicine, Wright State University, Dayton, OH 45420, USA.
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Unique suites of trabecular bone features characterize locomotor behavior in human and non-human anthropoid primates. PLoS One 2012; 7:e41037. [PMID: 22815902 PMCID: PMC3399801 DOI: 10.1371/journal.pone.0041037] [Citation(s) in RCA: 75] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Accepted: 06/16/2012] [Indexed: 11/19/2022] Open
Abstract
Understanding the mechanically-mediated response of trabecular bone to locomotion-specific loading patterns would be of great benefit to comparative mammalian evolutionary morphology. Unfortunately, assessments of the correspondence between individual trabecular bone features and inferred behavior patterns have failed to reveal a strong locomotion-specific signal. This study assesses the relationship between inferred locomotor activity and a suite of trabecular bone structural features that characterize bone architecture. High-resolution computed tomography images were collected from the humeral and femoral heads of 115 individuals from eight anthropoid primate genera (Alouatta, Homo, Macaca, Pan, Papio, Pongo, Trachypithecus, Symphalangus). Discriminant function analyses reveal that subarticular trabecular bone in the femoral and humeral heads is significantly different among most locomotor groups. The results indicate that when a suite of femoral head trabecular features is considered, trabecular number and connectivity density, together with fabric anisotropy and the relative proportion of rods and plates, differentiate locomotor groups reasonably well. A similar, yet weaker, relationship is also evident in the trabecular architecture of the humeral head. The application of this multivariate approach to analyses of trabecular bone morphology in recent and fossil primates may enhance our ability to reconstruct locomotor behavior in the fossil record.
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Shaw CN, Ryan TM. Does skeletal anatomy reflect adaptation to locomotor patterns? cortical and trabecular architecture in human and nonhuman anthropoids. AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2011; 147:187-200. [DOI: 10.1002/ajpa.21635] [Citation(s) in RCA: 85] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2010] [Accepted: 10/03/2011] [Indexed: 11/11/2022]
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Kivell TL, Skinner MM, Lazenby R, Hublin JJ. Methodological considerations for analyzing trabecular architecture: an example from the primate hand. J Anat 2011; 218:209-25. [PMID: 20977475 PMCID: PMC3042755 DOI: 10.1111/j.1469-7580.2010.01314.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/01/2010] [Indexed: 10/18/2022] Open
Abstract
Micro-computed tomographic analyses of trabecular bone architecture have been used to clarify the link between positional behavior and skeletal anatomy in primates. However, there are methodological decisions associated with quantifying and comparing trabecular anatomy across taxa that vary greatly in body size and morphology that can affect characterizations of trabecular architecture, such as choice of the volume of interest (VOI) size and location. The potential effects of these decisions may be amplified in small, irregular-shaped bones of the hands and feet that have more complex external morphology and more heterogeneous trabecular structure compared to, for example, the spherical epiphysis of the femoral head. In this study we investigate the effects of changes in VOI size and location on standard trabecular parameters in two bones of the hand, the capitate and third metacarpal, in a diverse sample of nonhuman primates that vary greatly in morphology, body mass and positional behavior. Results demonstrate that changes in VOI location and, to a lesser extent, changes in VOI size had a dramatic affect on many trabecular parameters, especially trabecular connectivity and structure (rods vs. plates), degree of anisotropy, and the primary orientation of the trabeculae. Although previous research has shown that some trabecular parameters are susceptible to slight variations in methodology (e.g. VOI location, scan resolution), this study provides a quantification of these effects in hand bones of a diverse sample of primates. An a priori understanding of the inherent biases created by the choice of VOI size and particularly location is critical to robust trabecular analysis and functional interpretation, especially in small bones with complex arthroses.
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Affiliation(s)
- Tracy L Kivell
- Department of Human Evolution, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
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Lazenby RA, Skinner MM, Hublin JJ, Boesch C. Metacarpal trabecular architecture variation in the chimpanzee (Pan troglodytes): Evidence for locomotion and tool-use? AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 2010; 144:215-25. [PMID: 20872805 DOI: 10.1002/ajpa.21390] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/12/2009] [Accepted: 07/06/2010] [Indexed: 11/08/2022]
Abstract
Trabecular architecture was assessed by 3D micro-computed tomography from spherical volumes of interest located within the head and base of metacarpals (MC) 1, 2, and 5 from n = 19 adult common chimpanzees. Two subspecies, West African Pan troglodytes verus from the Taï Forest, Côte d'Ivoire (n = 12) and Central African P. t. troglodytes from Cameroon (n = 7), were studied. For the combined sample, the metacarpal head is distinguished by greater bone volume fraction across all metacarpals, though the MC 1 is distinctive in having thicker, more plate-like trabeculae. The architecture in the MC 2 and MC 5 can be related to strains associated with terrestrial knuckle-walking. In particular, the relatively robust MC 5 head architecture may result from functional loading incurred during braking and use of a palm-in hand posture. Examining differences between samples, we found that the Cameroon chimpanzees possess a more robust architecture across all metacarpals in the form of greater bone volume fraction, higher connectivity, and somewhat more plate-like structure. These differences are not explicable in terms of population distinctions in body size or daily travel distance, but possibly reflect a combination of more terrestrial knuckle-walking in the Cameroon sample and more diverse hand postures and precision handling required of nut-cracking in West African chimpanzees.
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Affiliation(s)
- Richard A Lazenby
- University of Northern British Columbia, Prince George, BC, Canada V2N4Z9.
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