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Activity-related changes in geometry of the proximal femurA study of two Near Eastern samplesKevin G. Hatala1,2, Steven E. Churchill3, Jaime Ullinger4, Susan Guise Sheridan51Hominid 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

Conclusions:

- Comparisons of geometric properties (IX, IY, IMAX, IMIN, J, ZP)
- The St. Stephen’s sample showed higher mean values for all geometric variables, attributable to greater amounts of generalized mechanical stress during life. In vivo studies of humans have shown the recruitment of a wide range of upper leg muscles during squatting exercises (Escamilla 2001), which warrants the assumption that frequent, repetitive genuflection would elicit a generalized (rather than directionally-specific) structural response.
- Comparisons of geometric ratios
- IX/IY :The St. Stephen’s sample showed a higher mean value, likely reflecting the greater proportion of anteroposterior relative to mediolateral stress experienced during genuflection.
- IMAX/ IMIN : The Bab edh-Dhra’ sample showed a higher mean value, showing a more uniform direction of habitual loading. This likely indicates that a regular pattern of mobility played a more significant role in the mechanical loading regime of the Bab edh-Dhra’ sample (Ruff et al. 1984).
- Tests of Hypotheses:
- These results confirmed the hypotheses regarding bone geometry for these samples:
- The Bab edh-Dhra’ sample showed a geometric pattern associated with greater mobility
- Greater response to mediolateral loading in the proximal femur
- The geometry of the St. Stephen’s sample corresponded to the mechanical forces associated with genuflection.
- Greater response to anteroposterior loading in the proximal femur
- The results of this study clearly corresponded to the hypotheses that were made based on archaeological and historical evidence for activity. This study thereby supports the use of cross-sectional geometry to predict activity patterns, even in fragmentary skeletal samples.

Introduction:

The reconstruction of behaviors of past populations is a central goal of bioarchaeology. 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 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-sectional geometry examine the amount and distribution of cortical bone , as they should reflect the magnitude and orientation of habitual mechanical loads during life.

The goal of this research is to assess the correlations between bone geometry and archaeological and historical evidence for activity in two prehistoric Near Eastern samples. Doing so will provide an examination of how cross-sectional bone geometry reflects activity patterns in past populations, especially in fragmentary and commingled skeletal samples.

Analysis:

- Data analysis was conducted in two steps:
- Comparison of Geometric Properties (IX, IY, IMAX, IMIN, J, ZP)
- I values – Resistance to bending forces along designated axes seen in Figure 1 (measured in mm4)
- J – Polar second moment of area, calculated as the sum of IX and IY. Measures the bone’s resistance to torsion (measured in mm4).
- ZP – Polar section modulus, calculated as J divided by the average radius of the cross-section (measured in mm3). Axis-independent method for measuring the overall strength of a cross-section (Ruff 2008)
- Comparison of Geometric Ratios (IX/IY, IMAX/ IMIN)
- These ratios describe the shape of the cross-section.

Background:

Results:

Comparisons of Geometric Properties:

Comparisons of Geometric Ratios:

For every geometric property and ratio, differences in between-group comparisons were statistically significant (p<0.05 in Student’s t-tests). The St. Stephen’s sample showed significantly greater mean values for every geometric property, as well as the IX/IY ratio. The Bab edh-Dhra’ sample showed a greater mean IMAX/IMIN ratio.

- Cross-sectional geometry:
- 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 from engineering to the shafts of long bones (Ruff 1992). This allows for the calculation of how the geometry of cortical bone contributes to a bone’s resistance to bending forces at a particular location. Bending resistance is measured as second moments of area (abbreviated I) about x, y, maximum (max), and minimum (min) axes. The x and y axes relate to the anatomical plane, corresponding to mediolateral and anteroposterior axes, respectively. These axes are shown in Figure 1.
- Figure 1. Geometric Axes on Sample Cross-section of Proximal Femur
- (Adapted from Figure 1 of Ruff and Hayes 1983)
- The Samples:
- Bab edh-Dhra’ - Early Bronze Age II-III (2950-2300 BC) site in present-day Jordan. Archaeological evidence indicates the following habitual activities:
- Agricultural lifestyle
- Daily travel to fields outside city walls for farming
- St. Stephen’s - Byzantine (5th to 7th century AD) monastery in Jerusalem. Historical evidence describes the following patterns of activity:
- Sedentary monastic lifestyle (relatively less mobile)
- Hundreds of genuflections each day
- Hypotheses:
- Based upon these activities, the following hypotheses were made:
- The Bab edh-Dhra’ sample will show a geometric pattern associated with greater mobility
- Greater response to mediolateral loading in the proximal femur (Ruff and Larsen 2001)
- The geometry of the St. Stephen’s sample will correspond to the mechanical forces associated with genuflection.
- Greater response to anteroposterior loading in the proximal femur (Escamilla 2001; Trinkaus and Rhoads 1999)

Literature Cited:

Acknowledgements:

We would like to thank Dr. Damiano Marchi and Dr. Tracy Kivell for their advice and encouragement over the course of this project. This research was supported by the NSF-REU (SES 0649088), the Duke University Undergraduate Research Support Office, Trinity College Research Forum, Summer Research in Biological Anthropology at the University of Notre Dame Scholarship in the Liberal Arts, a Smithsonian Institution Pre-doctoral Fellowship, and a Sigma Xi Grant-in-Aid of Research. Thanks to Dr. Susan Guise Sheridan for use of the collection and laboratory as well as for her support and encouragement.

Escamilla RF. 2001. Knee Biomechanics of the Dynamic Squat Exercise. Medicine & Science in Sports & Exercise: 127-141.

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.

Ruff CB. 2008. Femoral/humeral strength in early African Homo erectus. J Hum Evol 54:383–390.

Ruff CB, and Hayes WC. 1983. Cross-Sectional Geometry of Pecos Pueblo Femora and Tibiae- A Biomechanical Investigation: I. Method and General Patterns of Variation. Am J Phys Anthropol 60: 359-381.

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.

Ruff CB, Larsen CS, and Hayes WC. 1984. Structural Changes in the Femur With the Transition to Agriculture on the Georgia Coast. Am J Phys Anthropol 64: 125-136.

Trinkaus E, and Rhoads ML. 1999. Neandertal Knees: power lifters in the Pleistocene? J Hum Evol 37: 833-859.

Trinkaus, E, and Ruff CB. 1999. Diaphyseal Cross-sectional Geometry of Near Eastern Middle Paleolithic Humans: The Femur. J Archaeol Sci 26: 409-424.

1 Provided for free at: http://rsb.info.nih.gov/nih-image/

2 Available at: http://www.hopkinsmedicine.org/FAE/mmacro.htm

p = 0.002

p < 0.0001

p = 0.002

p < 0.0001

IX

IY

p < 0.0001

p < 0.0001

IMAX

IMIN

J

ZP

p = 0.0001

p < 0.0001

Materials and Methods:

IX/IY

IMAX/IMIN

Due to the fragmentary nature of the two samples, the subtrochanteric region was the 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.

Figure 2. Location of the Subtrochanteric Region of the Femur

(Indicated by the red transverse line)

Sample size equaled 42 adult femora in the Bab edh-Dhra’ sample and 57 adult femora in the St. Stephen’s sample.

All femora were physically cross-sectioned at the subtrochanteric region, and digital images were taken of the proximal femur cross-sections. Example images are shown in Figure 3.

Figure 3. Cross-sectional Images of Proximal Femora

Digital Images were imported into the ImageJ program1and analyzed using MomentMacro2. The computer program measured second moments of area about the x, y, maximum, and minimum axes. Size-standardization was accomplished by dividing geometric properties by an estimate of body mass based upon femoral head diameter.

BD1141.144

BD1273.45

EBND1.50

EBND14.120

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