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Activity-related changes in geometry of the proximal femur A study of two Near Eastern samples Kevin G. Hatala1,2, Steven E. Churchill3, Jaime Ullinger4, Susan Guise Sheridan5 1Hominid Paleobiology Doctoral Program, 2Center for the Advanced Study of Hominid Paleobiology, Department of Anthropology, The George Washington University, 3Department of Evolutionary Anthropology, Duke University, 4Department of Anthropology, The Ohio State University, 5Department of Anthropology, University of Notre Dame Introduction: Results: Analysis: The reconstruction of behaviors of past populations is a central goal of bioarchaeology. Comparisons of Geometric Properties: Data analysis was conducted in two steps: A common technique used to accomplish this goal is the analysis of cross-sectional bone geometry to reconstruct activity patterns. The often-cited but still disputed “Wolff’s IX IY 1.Comparison of Geometric Properties (IX, IY, IMAX, IMIN, J, ZP) Law” generally states that living bone tissue is added in areas of high mechanical demand and resorbed in areas of low demand (Ruff et al. 2006). Analyses of cross- 2.7 2.9 • I values – Resistance to bending forces along designated axes seen in p < 0.0001 p = 0.002 sectional geometry examine the amount and distribution of cortical bone , as they should 2.6 2.8 Figure 1 (measured in mm4) reflect the magnitude and orientation of habitual mechanical loads during life. • J – Polar second moment of area, calculated as the sum of IX and IY. 2.5 2.7 Measures the bone’s resistance to torsion (measured in mm4). log(Ix) log(IY) The goal of this research is to assess the correlations between bone geometry and 2.4 2.6 • ZP – Polar section modulus, calculated as J divided by the average archaeological and historical evidence for activity in two prehistoric Near Eastern radius of the cross-section (measured in mm3). Axis-independent samples. Doing so will provide an examination of how cross-sectional bone geometry 2.3 2.5 method for measuring the overall strength of a cross-section (Ruff 2008) reflects activity patterns in past populations, especially in fragmentary and commingled skeletal samples. 2.2 2.4 St. Stephen's Bab edh-Dhra' St. Stephen's Bab edh-Dhra' 2.Comparison of Geometric Ratios (IX/IY, IMAX/ IMIN) • These ratios describe the shape of the cross-section. Background: IMAX IMIN Cross-sectional geometry: 2.9 p = 0.002 2.7 p < 0.0001 Conclusions: Cross-sectional geometry is often used to hypothesize the magnitude and orientation of habitual loads during life. Analysis is conducted by applying a structural beam model 2.8 2.6 Comparisons of geometric properties (IX, IY, IMAX, IMIN, J, ZP) from engineering to the shafts of long bones (Ruff 1992). This allows for the log(Imax) 2.5 log(Imin) 2.7 calculation of how the geometry of cortical bone contributes to a bone’s resistance to 2.4 The St. Stephen’s sample showed higher mean values for all geometric bending forces at a particular location. Bending resistance is measured as second 2.6 variables, attributable to greater amounts of generalized mechanical stress moments of area (abbreviated I) about x, y, maximum (max), and minimum (min) 2.3 axes. The x and y axes relate to the anatomical plane, corresponding to mediolateral 2.5 during life. In vivo studies of humans have shown the recruitment of a 2.2 and anteroposterior axes, respectively. These axes are shown in Figure 1. wide range of upper leg muscles during squatting exercises (Escamilla 2.4 2.1 2001), which warrants the assumption that frequent, repetitive genuflection St. Stephen's Bab edh-Dhra' St. Stephen's Bab edh-Dhra' would elicit a generalized (rather than directionally-specific) structural J ZP response. 3.1 2.2 p < 0.0001 p < 0.0001 Comparisons of geometric ratios 3.0 2.1 Figure 1. Geometric Axes on Sample Cross-section of Proximal Femur IX/IY : The St. Stephen’s sample showed a higher mean value, likely (Adapted from Figure 1 of Ruff and Hayes 1983) log (ZP) 2.9 log(J) The Samples: 2.0 reflecting the greater proportion of anteroposterior relative to mediolateral Bab edh-Dhra’ - Early Bronze Age II-III (2950-2300 BC) site in present-day Jordan. 2.8 stress experienced during genuflection. Archaeological evidence indicates the following habitual activities: 2.7 1.9 • Agricultural lifestyle IMAX/ IMIN : The Bab edh-Dhra’ sample showed a higher mean value, • Daily travel to fields outside city walls for farming 2.6 1.8 showing a more uniform direction of habitual loading. This likely St. Stephen’s - Byzantine (5th to 7th century AD) monastery in Jerusalem. Historical St. Stephen's Bab edh-Dhra' St. Stephen's Bab edh-Dhra' indicates that a regular pattern of mobility played a more significant role in evidence describes the following patterns of activity: the mechanical loading regime of the Bab edh-Dhra’ sample (Ruff et al. • Sedentary monastic lifestyle (relatively less mobile) • Hundreds of genuflections each day Comparisons of Geometric Ratios: 1984). IX/IY IMAX/IMIN Tests of Hypotheses: Hypotheses: Based upon these activities, the following hypotheses were made: 0.9 p = 0.0001 2.2 p < 0.0001 • The Bab edh-Dhra’ sample will show a geometric pattern associated with greater These results confirmed the hypotheses regarding bone geometry for these mobility 0.8 2.0 samples: • Greater response to mediolateral loading in the proximal femur (Ruff and IMAX/IMIN 0.7 1.8 • The Bab edh-Dhra’ sample showed a geometric pattern associated with IX/IY Larsen 2001) • The geometry of the St. Stephen’s sample will correspond to the mechanical forces 0.6 1.6 associated with genuflection. greater mobility • Greater response to anteroposterior loading in the proximal femur (Escamilla 0.5 1.4 • Greater response to mediolateral loading in the proximal femur 2001; Trinkaus and Rhoads 1999) 0.4 St. Stephen's Bab edh-Dhra' 1.2 St. Stephen's Bab edh-Dhra' • The geometry of the St. Stephen’s sample corresponded to the mechanical forces associated with genuflection. Materials and Methods: • Greater response to anteroposterior loading in the proximal femur Due to the fragmentary nature of the two samples, the subtrochanteric region was the For every geometric property and ratio, differences in between-group only location that could be sufficiently analyzed. This region is defined as 1-2 cm below the lesser trochanter (Trinkaus and Ruff 1999) and is shown in Figure 2. comparisons were statistically significant (p<0.05 in Student’s t-tests). The The results of this study clearly corresponded to the hypotheses that were St. Stephen’s sample showed significantly greater mean values for every made based on archaeological and historical evidence for activity. This study thereby supports the use of cross-sectional geometry to predict geometric property, as well as the IX/IY ratio. The Bab edh-Dhra’ sample activity patterns, even in fragmentary skeletal samples. showed a greater mean IMAX/IMIN ratio. Acknowledgements: Figure 2. Location of the Subtrochanteric Region of the Femur Literature Cited: We would like to thank Dr. Damiano Marchi and Dr. Tracy Kivell for their advice and (Indicated by the red transverse line) Escamilla RF. 2001. Knee Biomechanics of the Dynamic Squat Exercise. Medicine & Science in Sports & Exercise: 127-141. encouragement over the course of this project. This research was supported by the NSF- REU (SES 0649088), the Duke University Undergraduate Research Support Office, Sample size equaled 42 adult femora in the Bab edh-Dhra’ sample and 57 adult femora Ruff CB. 1992. Biomechanical Analyses of Archaeological Human Skeletal Samples. In: Katzenberg, MA, and Saunders, SR, editors. Skeletal Biology of Past Peoples: Research Methods: Wiley-Liss, Inc. p 37-58. Trinity College Research Forum, Summer Research in Biological Anthropology at the in the St. Stephen’s sample. University of Notre Dame Scholarship in the Liberal Arts, a Smithsonian Institution Pre- All femora were physically cross-sectioned at the subtrochanteric region, and digital Ruff CB. 2008. Femoral/humeral strength in early African Homo erectus. J Hum Evol 54:383–390. doctoral Fellowship, and a Sigma Xi Grant-in-Aid of Research. Thanks to Dr. Susan images were taken of the proximal femur cross-sections. Example images are shown Ruff CB, and Hayes WC. 1983. Cross-Sectional Geometry of Pecos Pueblo Femora and Tibiae- A Biomechanical Investigation: I. Method Guise Sheridan for use of the collection and laboratory as well as for her support and in Figure 3. and General Patterns of Variation. Am J Phys Anthropol 60: 359-381. encouragement. Ruff CB, Holt BM, and Trinkaus E. 2006. Who’s Afraid of the Big Bad Wolff?: “Wolff’s Law” and Bone Functional Adaptation. Am J Phys Anthropol 129: 484-498. Ruff CB, and Larsen CS. 2001. Reconstructing Behavior in Spanish Florida: The Biomechanical Evidence. In: Larsen, CS, editor. Bioarchaeology of Spanish Florida. Gainesville: University of Florida Press. p 113-145. BD1141.144 BD1273.45 EBND1.50 EBND14.120 Ruff CB, Larsen CS, and Hayes WC. 1984. Structural Changes in the Femur With the Transition to Agriculture on the Georgia Coast. Am J Figure 3. Cross-sectional Images of Proximal Femora Phys Anthropol 64: 125-136. Trinkaus E, and Rhoads ML. 1999. Neandertal Knees: power lifters in the Pleistocene? J Hum Evol 37: 833-859. Digital Images were imported into the ImageJ program1 and analyzed using Trinkaus, E, and Ruff CB. 1999. Diaphyseal Cross-sectional Geometry of Near Eastern Middle Paleolithic Humans: The Femur. J Archaeol MomentMacro2. The computer program measured second moments of area about the Sci 26: 409-424. x, y, maximum, and minimum axes. Size-standardization was accomplished by 1 Provided for free at: http://rsb.info.nih.gov/nih-image/ dividing geometric properties by an estimate of body mass based upon femoral head 2 Available at: http://www.hopkinsmedicine.org/FAE/mmacro.htm diameter.
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