Temporal Trends in Femoral Diaphyseal Torsional Asymmetry Among the Arikara Associated with Postural...

Temporal Trends in Femoral Diaphyseal TorsionalAsymmetry Among the Arikara Associated withPostural Behavior

Daniel J. Wescott,1* Deborah L. Cunningham,2 and David R. Hunt3

1Department of Anthropology, Forensic Anthropology Center at Texas State, Texas State University, San Marcos,TX 786662Department of Anthropology, Texas State University, San Marcos, TX 786663Department of Anthropology, National Museum of Natural History, Washington, DC 20560

KEY WORDS femoral torsion; bioarchaeology; biomechanics; skeletal biology; secularchange; Arikara

ABSTRACT Average femoral torsion has beenreported to differ among populations, and several stud-ies have observed a relatively high prevalence of femoralanteversion asymmetry in Native Americans, especiallyfemales. This study investigates sexual dimorphism andtemporal trends in femoral torsional asymmetry amongthe Arikara from the seventeenth to the early nine-teenth century. To establish if there are population dif-ferences, femoral torsion was first measured using adirect method on a diverse comparative sample of NativeAmericans from the Southwest, Midwest, and GreatPlains as well as American Whites and Blacks. To exam-ine temporal trends among the Arikara, femoral torsionwas examined using the orientation of the maximumbending rigidity at subtrochanteric in 154 females and164 males from three temporal variants of the ArikaraCoalescent tradition. There is significant sexual dimor-

phism in femoral torsional directional and absoluteasymmetry among most Native American samples, butnot among American Whites and Blacks. Among the Ari-kara there is significant sexual dimorphism in femoraltorsional asymmetry in all three temporal variants, andasymmetry in femoral torsional asymmetry increasedsignificantly from the protohistoric to the early historicperiod among females. The increased femoral torsionalasymmetry is likely associated with a common side-sitting posture observed in historic photographs of GreatPlains females. Historic Arikara females may havehabitually sat in this compulsory position for extendedperiods while conducting domestic chores. The dramaticchange from the protohistoric to historic period suggestsa cultural change in sitting posture among females thatwas widespread across the Northern Plains. Am J PhysAnthropol 000:000–000, 2014. VC 2014 Wiley Periodicals, Inc.

The non-pathological adult human femoral diaphysisexhibits a slight twist from the proximal end to the dis-tal end, which is referred to as version or torsion. Ante-version and retroversion indicates an increase ordecrease, respectively, of the angle of the femoral neckrelative to the transcondylar plane. Positive values indi-cate anteversion while retroversion is associated withnegative values, although numerous authors incorrectlyrefer to retroversion as any angle below the normalrange (Ruby et al., 1979; Gulan et al., 2000; Cibulka,2004). Diaphyseal version/torsion, along with neck-shaftangle, bicondylar angle, and torsion of the femoral neck,align the lower limb under the body to reduce stress-related strains by optimizing lever arm lengths anddecreasing the bending moments at the hip duringbipedal locomotion (Brien et al., 1995; Duda et al.,1997).

The femoral anteversion angle changes with age dur-ing growth but is mostly stable during adulthood(Decker et al., 2013). Femoral anteversion is apparentby the seventh week of gestation and increases duringfetal development, possibly due to in-utero hyperflexionof the lower limbs, and reaches �30–40� by birth (Upad-hyay et al., 1990; Delp et al., 1994; Gulan et al., 2000;Cibulka, 2004; Tardieu, 2010; Bonneau et al., 2011).During postnatal growth, detorsion, or a decrease in theangle, occurs until the angle reaches adult values ofbetween 8� and 14� during adolescence (Gulan et al.,

2000; Fabeck et al., 2002; Tardieu, 2010). However, itshould be noted that the normal adult values for ante-version given in the literature vary considerably depend-ing on the method used to determine the degree oftorsion (Kate, 1976; Gulan et al., 2000; Decker et al.,2013).

Average femoral torsion has been reported to differamong populations (Steindler, 1955; Stewart, 1962;Eckhoff et al., 1994; Gill, 2001; Jain et al., 2003; Tamariet al., 2006). Compared to Europeans, African popula-tions exhibit greater anteversion and South Asian popu-lations from the Republic of India (hereafter referred toas “Indian”) exhibit less anteversion (Eckhoff et al.,1994; Jain et al., 2003; Zalawadia et al., 2010; Srimathiet al., 2012). Within populations, females generallyexpress slightly greater anteversion than males. Whilesexual dimorphism in femoral anteversion is not

*Correspondence to: Daniel J. Wescott, Department of Anthropol-ogy, Forensic Anthropology Center at Texas State, Texas State Uni-versity, 601 University Drive, San Marcos, TX 78666, USA.E-mail: [email protected]

Received 5 March 2014; revised 4 May 2014; accepted 6 May 2014

DOI: 10.1002/ajpa.22541Published online 00 Month 2014 in Wiley Online Library

(wileyonlinelibrary.com).

� 2014 WILEY PERIODICALS, INC.

AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 00:00–00 (2014)

statistically significant in all populations, females inmost populations have greater anteversion angles thanmales (Davivongs, 1963; Kate, 1976; Tamari et al., 2006;Bonneau et al., 2012). Kate (1976), for example, foundthat males have an average anteversion angle of 7.8while females have an average angle of 13.8. Some stud-ies have found no significant asymmetry in femoral tor-sion (Parsons, 1914; Bonneau et al., 2012), while othershave (Kingsley and Olmstead, 1948; Kate, 1976; Young,2004; Basgall, 2008). Normal side differences are usually<5�, and �95% of adults have differences <11� (Deckeret al., 2013). In most populations, when asymmetry ispresent, the right femur exhibits slightly greater torsionthan the left femur (Upadhyay et al., 1990; Basgall,2008). However, Indians (Republic of India) have beenfound to have the opposite pattern with greater left thanright anteversion (Jain et al., 2003; Zalawadia et al.,2010; Srimathi et al., 2012).

Variation in torsion among the Arikara

Femoral torsion is a biomechanically relevant featureof the human skeleton that can aid bioarchaeologists inreconstructing activities, congenital disorders, and dis-ease in past populations. Non-pathological femoral tor-sion outside the range of normal variation is primarilyassociated with behavioral activities in which the thighsare laterally or medially rotated for extended periods oftime (Crane, 1959; Alvik, 1962; Staheli, 1980; Cibulka,2004). Therefore the examination of femoral torsion hasimplications for understanding human skeletal varia-tion, cultural or behavioral shifts through time within apopulation, and behavioral variation between popula-tions. While examining the Arikara over the past twodecades, we noted high frequencies of femoral torsionalasymmetry, especially in females, compared to other pop-ulations, and a possible temporal trend in this group.The possible temporal trend suggested that there waspotentially a change in activity patterns or culturalbehaviors that may have occurred. This was not unex-pected as previous research has demonstrated a signifi-cant temporal trend among Arikara females in lower limbbone rigidity (Wescott and Cunningham, 2006). There-fore, we were interested in investigating the cause of thehigh frequency of femoral torsional asymmetry amongthe Arikara and determining if there was indeed a tempo-ral pattern. To examine the high frequency of femoral tor-sional asymmetry we first investigated populationvariation in femoral torsional asymmetry among NativeAmericans that are diverse regionally, temporally, and intheir subsistence strategy. This was important to investi-gate because very few studies have examined anteversionin Native American populations, and those that havewere composed of very small sample sizes. To examine if

there is a temporal trend in femoral diaphyseal torsionalasymmetry among the Arikara, we compared differencesamong their three temporal variants dating from the sev-enteenth century to the early-nineteenth century. Finally,we examined the results within a biomechanical, archaeo-logical, and cultural context to better understand the pos-sible reasons for the pattern of observed femoral torsionalasymmetry.

MATERIALS AND METHODS

Population variation in femoral torsionalasymmetry

Samples. To assess population variation in femoraltorsional angle and asymmetry, we used paired rightand left femora from four Native American samples anda comparative sample of American Whites and Blacks(Table 1; Hunt and Williams, 2002). The modern Ameri-can sample consisted of 102 Whites and 100 Blacks fromthe Robert J. Terry Collection. These individuals wereprimarily of lower socioeconomic status and lived in Mis-souri at the time of their death (Hunt and Albanese,2005). The Native American sample consisted of 333adult skeletons housed at the National Museum of Natu-ral History (Smithsonian Institution) representing popu-lations from different geographical regions, time periods,and subsistence strategies (Table 1). The Southwest sub-sample is derived from the Pueblo ruins of Hawikuh(AD 1400–1680) and Puye (AD 1200–1500) in New Mex-ico (Hewett, 1938; Smith et al., 1966; Barnes, 1994).These groups were primarily agriculturalists who culti-vated a variety of crops, but they also hunted and gath-ered wild plants (Hewett, 1938; Barnes, 1994). TheMidwest subsample is from bluff mounds excavated inwestern Jersey County in Illinois (Titterington, 1935).These remains date to the Late Woodland (AD 500—1100) and represent a hunter-gatherer/early horticulturepopulation. They grew maize, squash, sunflower, andother crops (Kelly et al., 1984). The Great Plains subsam-ple is composed of Arikara (AD 1600–1845). The Arikararesided in villages along the Missouri River of SouthDakota, and is represented primarily by prehistoric(Extended Coalescent) and protohistoric (PostcontactCoalescent) variants. The Arikara are traditionally con-sidered horticulturalists but they also hunted, fished, andgathered wild plants (Johnson, 1998). In protohistoricand historic periods the Arikara were actively involved intrade networks along the Missouri River (Johnson, 1998;Parks, 2001; Wescott and Cunningham, 2006).

Methods. The femora used in the population variationpart of the study were matched left and right femoraselected based on completeness, epiphyseal closure, and

TABLE 1. Sample size and populations used in interpopulation comparison

Group Region Dates (A.D.) Females (n) Males (n) Total (n)

Illinois Bluff Midwest 500–1100a 47 51 98Puye Southwest 1200–1500a 38 26 64Hawikuh Southwest 1400–1680a 50 31 81Arikara Plains 1600–1845a 40 50 90Terry White Midwest 1828–1943b 51 51 102Terry Black Midwest 1828–1943b 50 50 100

a Estimated site occupation dates.b Birth years.

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American Journal of Physical Anthropology

absence of lower limb pathology. To be included in thestudy, the greater trochanter and head of the femur hadto be largely intact, and the posterior aspect of both dis-tal condyles had to be undamaged. We used a relativelysimple method to obtain the angle of torsion that can beused in both the laboratory and the field (Fig. 1; Huntand Williams, 2002). The proximal end of the femur wasplaced on an osteometric board with the femoral headoriented so it rests on the base of the board. The headwas then secured in place between the fixed and mobileuprights of the osteometric board. The greater trochan-ter was secured against the fixed upright and the distalend rested on a surface raised so that it formed a contin-uous plane with the osteometic board. We measured theangle of the intersection between the plane formed bythe posterior-most points of the distal condyles and thehorizontal surface. The perpendicular angle (90�) wasthen subtracted from the obtuse angle measured toobtain the angle of torsion (anteversion angle 5 meas-ured angle—90�; Fig. 1).

Both absolute and directional asymmetry was eval-uated. Absolute asymmetry was derived by obtaining theabsolute value of the femoral torsion difference in orderto evaluate the degree of difference between the left andright femora of an individual without regard to anydirectionality. Directional asymmetry was calculated bysubtracting the left angle from the right angle. Negativevalues indicate greater torsion of the left femur whilepositive values indicate the opposite. T-tests were usedto examine the differences in absolute and directionalasymmetry between males and females for each popula-tion. The data were analyzed both within populations bycomparing males of a population with females of thesame population and between populations with sexesseparated. An alpha level of 0.05 was used to indicatestatistical significance and rejection of the null hypothe-sis of no difference.

Temporal trends among Arikara

Sample. We examined temporal trends in femoral tor-sion, head diameter, and length asymmetry among three

Arikara archaeological variants ranging in date from1600 to 1845 (Johnson, 1998). The sample consists of154 females and 164 males from three temporal variantsof the Arikara Coalescent tradition: Extended Coalescent(EC; 1500–1650 A.D.), Postcontact Coalescent (PCC;1650–1780 A.D.) and the Disorganized Coalescent orHistoric Arikara (HA; 1780–1845 A.D.) (Table 2). TheEC variant represents a precontact population. The PCCvariant is demarcated by the appearance of Europeantrade items, especially in burials (Johnson, 1998; Billecket al., 1995). The quantity of trade items increasedthrough the PCC and by around 1740 the Arikara beganto acquire horses from the Southwest (Johnson, 1998).With increased involvement in trade networks, femalesproduced surplus crops, hides, beadwork, and otheritems for trade (Johnson, 1998; Parks, 2001; Wescottand Cunningham, 2006).

Methods. For the Arikara temporal trend portion ofthe study, paired femora were selected based on com-pleteness, closed epiphyses, and the lack of observablelower limb pathology. The diaphyseal torsional anglewas estimated using the orientation of the maximumbending rigidity (theta, u) relative to the mediolateral(ML) axes at subtrochanteric (Fig. 2). Larger valuesindicate that the maximum bending rigidity is locatedmore anteriorly, while an angle of zero indicates themaximum bending rigidity is situated in the ML plane.While this is not a true measure of femoral anteversion,theta does provide information about the relative twistof the femoral shaft from proximal to distal (Fig. 3; Ruff,

Fig. 1. Angle of torsion for interpopulation comparative partof study.

TABLE 2. Sample size of Arikara by variant and sex used intemporal trend analysis

Variant Dates (A.D) Females Males Total

Extendedcoalescent (EC)

1500–1650 48 51 99

Postcontactcoalescent (PCC)

1650–1780 79 100 179

Disorganizedcoalescent (HA)

1780–1845 27 13 40

Total 154 164 318

Fig. 2. Angle of orientation of the maximum bending rigid-ity at subtrochanteric (theta).

TEMPORAL TRENDS IN FEMORAL TORSION AMONG THE ARIKARA 3


1981; Ruff and Larsen, 1990). Before measuring theta,the maximum length and head diameter were measuredfor each pair of femora (see Wescott and Cunningham,2006 for details). The femora were then oriented instandard sagittal and coronal planes with the posterioraspect of the condyles resting on a horizontal surfaceand the proximal end of the bone raised using clay untilthe anteroposterior (AP) midpoints of the proximal anddistal shaft were equidistant above the surface (Ruff,1981; Ruff and Hayes, 1983; Wescott, 2001). Computedtomography (CT) cross-sectional images were then col-lected at the level of subtrochateric using a Siemensmedical CT scanner housed at the National Museum ofNatural History. A 0.5-mm cross-sectional image wastaken perpendicular to both the frontal and sagittalplanes. Cross-sectional properties, including theta, werecalculated with Momentmacro (www.hopkinsmedicine.org/fae/mmacro.htm).

Asymmetry was calculated using the same methodused for the population comparison (absolute asymme-try 5 |right–left|; directional asymmetry 5 right–left).Analysis of Variance (ANOVA) was used to test variationbetween groups and sexual dimorphism within andbetween groups. Interactions between sex and popula-tion were used to test for differences in sexual dimor-phism between groups. Post-hoc multiple comparisontests were used to determine which populations differ.An alpha level of 0.05 was used to indicate statisticalsignificance.

RESULTS

Population differences: Comparative analysis

Analysis of within population sexual dimorphism indi-cates significant differences in femoral torsional direc-tional asymmetry between males and females in allNative American groups except for the Hawikuh (Table3). There was also no significant difference in directionalasymmetry between males and females in the Terry col-

lection. Interpopulation analysis show more significantdifferences in directional asymmetry in females than inmales (Table 4).

Analysis of absolute asymmetry within populationsshows significant sexual dimorphism for the Arikara,Hawikuh, and Illinois samples, but not the Puye orAmerican Whites and Blacks (Table 3). In all cases ofsignificant difference, the female mean absolute asym-metry of torsion was higher than the male mean. Inter-population comparisons of absolute asymmetry withinthe sexes showed no significant difference for males butseveral significant differences in females (Table 5).

Temporal trends in the Arikara

Sexual dimorphism. Descriptive statistics for thetaare presented in Table 6. Significant sexual dimorphismwas observed for theta, theta directional asymmetry,theta absolute asymmetry, femoral head diameter, andfemoral length in the pooled Arikara (results not shown).No significant sexual dimorphism was observed in femo-ral head diameter asymmetry or femoral length asym-metry (results not shown; see Wescott and Cunningham,2006). Females exhibit a greater prevalence of asymme-try in femoral torsion, where one side is �10�from theother, than males. For the pooled Arikara, 51% offemales exhibited asymmetry femoral torsion (46%

Fig. 3. Proximal end of femora showing anteversion and orientation of femoral diaphysis from computed tomography image foran Arikara adult female.

TABLE 3. Intrapopulation comparison of sexual dimorphism inasymmetry

Group Directional asymmetry Absolute asymmetry

Arikara S SHawikuh NS SPuye S NSIllinois S STerry White NS NSTerry Black NS NS

S 5 significant at 0.05; NS 5 not significant at 0.05.



http://www.hopkinsmedicine.org/fae/mmacro.htm

http://www.hopkinsmedicine.org/fae/mmacro.htm

right> left and 5% left> right), while femoral torsionalasymmetry was observed in only 25% (17% right> leftand 8% left> right) of males.

Temporal trends. Analyses comparing variants showsignificant differences in females but not males (Table 7).Figures 4 and 5 are box plots of females and males,respectively, showing temporal trends in theta and asym-metry by variant. There is a slight increase in the preva-lence of femoral torsional asymmetry during the historicperiod in males (Table 8), but the difference is not signifi-cant (Table 7; Fig. 5). There was no significant temporaltrend in femoral head diameter or femoral length asym-metry among females (results not shown). Significant dif-ferences were observed in left theta and theta asymmetrybetween the HA females and EC and PCC females and inright theta between the PCC and all other females (Fig.4, Table 7). There was also greater variation in asymme-

try among the HA females in these measures (Table 6).The prevalence of femoral torsion asymmetry increasesdramatically from the PCC to the HA among females, fol-lowing a slight decrease between the EC and the PCC(Table 8). The change in theta asymmetry during the his-toric period was primarily caused by a significantdecrease in the torsion of the left femur and a slightincrease in the torsion of the right femur compared to thePCC (Table 6; Fig. 4). The only significant differencebetween EC and PCC females was in the angle of thetaon the right femur (Table 7). The PCC females have anaverage lower theta on the right side than both the EC orDC females, and therefore less asymmetry (Table 6).When examined by mean site date, there is a slight posi-tive correlation between theta directional (R2 5 0.15) andabsolute (R2 5 0.24) asymmetry in females, but not inmales (Fig. 6). The temporal trend in females by meansite date is primarily driven by the change between thePCC and HA.

TABLE 4. Interpopulation comparison of directional asymmetry in females (top of diagonal) and males (bottom of diagonal)

Group Arikara Hawikuh Puye Illinois T. Whites T. Blacks

Arikara – S NS NS S SHawikuh NS – S S S SPuye NS NS – S NS NSIllinois NS S S – S ST. Whites NS NS NS S – NST. Blacks NS NS NS NS NS –


TABLE 5. Interpopulation comparison of absolute asymmetry in females (top of diagonal) and males (bottom of diagonal)

Group Arikara Hawikuh Puye Illinois T. Whites T. Blacks

Arikara – NS S NS S SHawikuh NS – S NS S SPuye NS NS – S NS NSIllinois NS NS NS – S ST. Whites NS NS NS NS – NST. Blacks NS NS NS NS NS –


TABLE 6. Descriptive statistics for Arikara variants

Group Statistic R Theta L Theta Directional asymmetry Absolute asymmetry

EC female Mean 51.3 42.7 8.6 11.7StDev 8.7 11.2 12.0 8.8Range 35–75 22–72 213–44 1–44

PCC female Mean 44.5 40.0 4.4 8.9StDev 9.6 8.7 10.5 7.1Range 7–66 17–61 236–24 0–36

HA female Mean 52.3 25.1 27.1 31.6StDev 14.9 13.3 23.4 16.6Range 18–78 5–54 230–65 0–65

EC male Mean 43.8 41.3 2.4 5.9StDev 9.4 7.7 7.2 4.7Range 25–66 21–57 217–20 0–20

PCC male Mean 44.9 42.7 2.2 6.3StDev 10.0 9.6 7.5 4.7Range 10–75 14–70 220–19 0–20

HA male Mean 47.1 44.3 2.8 7.9StDev 8.4 14.8 8.7 4.0Range 28–58 14–71 213–14 1–14



DISCUSSION

Measuring femoral torsion

In this study, femoral torsion was assessed using twodifferent methods. The angles produced by the twomethods are not directly comparable, but they do pro-vide valid methods for assessing differences in femoraldiaphyseal torsion when analyzed separately. For com-parison of populations, torsion or anteversion was meas-ured using the angle formed by a line connecting theposterior head and greater trochanter and a line con-necting the posterior condyles (Fig. 1). This methodgives angles similar, but not exact, to other direct meas-urements (Kingsley and Olmstead, 1948; Rokade and

Mane, 2008). To investigate temporal trends among theArikara, we used theta, or the orientation of the maxi-mum diaphyseal bending rigidity, at subtrochantericmeasured counterclockwise from the ML plane (Fig. 2).The use of theta at subtrochanteric provides a method ofestimating the relative twist of the femoral diaphysisbut not the neck. Therefore this is not a true measure ofanteversion. However, we have confidence in our inter-pretations since Ruff (1981) found a high correlationbetween subtrochanteric theta and the anteversionangle. This correlation is the result of a combination ofbody weight and forces resulting from multiple muscles,which causes high mechanical stress on the subtrochan-teric region of the shaft. The applied forces are nearly

TABLE 7. Arikara intervariant comparison of theta and asymmetry

Sex Femalea Malea

Comparison EC–PCC EC–HA PCC–HA EC–PCC EC–HA PCC–HA

Right thetab S NS S NS NS NSLeft thetab NS S S NS NS NSDIR Asymb,c NS S S NS NS NSABS Asymb,c NS S S NS NS NS

a EC 5 Extended Coalescent, PCC 5 Postcontact Coalescent, HA 5 Historic Arikara/Disorganized Coalescent.b S 5 significant at 0.05; NS 5 not significant at 0.05.c DIR Asym 5 directional asymmetry; ABS Asym 5 absolute asymmetry.

Fig. 4. Box plots showing differences in theta and theta asymmetry by variant for females. Top left: right theta; Top right: lefttheta; Bottom left: directional asymmetry; Bottom right: absolute asymmetry; EC 5 Extended Coalescent; PCC 5 Postcontact Coa-lescent; HA 5 Historic Arikara (Disorganized Coalescent).



perpendicular to the axis of the femoral neck causingbending in the subtrochanteric region. As a result,changes in the orientation of the major axes of the proxi-mal femur (theta) parallel changes in the anteversionangle (Ruff, 1981; Ruff and Larsen, 1990). Therefore,theta provides an accurate method for evaluating rela-tive femoral diaphyseal torsion.

Population differences in femoraltorsional aymmetry

Population differences in femoral anteversion havebeen observed in several studies. Native Americans,Australian Aborigines, Maori, and some African popula-

tions have greater femoral torsion than AmericanWhites and Blacks (Schofield, 1959; Stewart, 1962; Davi-vongs, 1963; Eckhoff et al., 1994; Gill, 2001). Likewise,sexual dimorphism in femoral torsion has been observedin Indians, Japanese, Australian Whites, AustralianAborigines, and other groups (Parsons, 1914; Davivongs,1963; Kate, 1976; Reikeras et al., 1982; Jain et al., 2003;Tamari et al., 2006; Zalawadia et al., 2010). In almostall cases females have greater femoral torsion thanmales. While many studies show that femoral torsionalasymmetry >10� is uncommon (Reikeras et al., 1982;Yoshioka and Cooke, 1987; Prasad et al., 1996), signifi-cant asymmetry has also been found in some popula-tions, especially from North America and India (Kate,

Fig. 5. Box plots showing differences in theta and theta asymmetry by variant for males. Top left: right theta; Top right: lefttheta; Bottom left: directional asymmetry; Bottom right: absolute asymmetry; EC 5 Extended Coalescent; PCC 5 Postcontact Coa-lescent; HA 5 Historic Arikara (Disorganized Coalescent).

TABLE 8. Prevalence of directional asymmetry in theta among Arikara variants

Female Male

Varianta DAb Rightc Leftd Nonee DAb Rightc Leftd Nonee

EC 23/48 (47.9%) 21/48 (43.7%) 2/48 (4.2%) 25/48 (52.1%) 12/51 (23.5%) 8/51 (15.7%) 4/51 (7.8%) 39/51 (76.5%)PCC 32/79 (40.5%) 28/79 (35.4%) 4/79 (5.1%) 47/79 (59.5%) 24/100 (24.0%) 17/100 (17.0%) 7/100 (7.0%) 76/100 (76.0%)HA 24/27 (88.9%) 22/27 (81.5%) 2/27 (7.4%) 3/27 (11.1%) 5/13 (38.4%) 3/13 (23.0%) 2/13 (15.4%) 8/13 (61.6%)

a EC 5 Extended Coalescent, PCC 5 Postcontact Coalescent, HA 5 Historic Arikara/Disorganized Coalescent.b Directional asymmetry 10� or greater difference between right and left thetas.c Right theta 10� or more than left theta.d Left theta 10� or more than right theta.e Asymmetry in theta is <10�.



1976; Jain et al., 2003; Basgall, 2008; Zalawadia et al.,2010; Srimathi et al., 2012). Studies have shown that inNative Americans the right femur has a higher averageanteversion angle than the left, while in Indians the leftside exhibits more torsion.

While population differences in femoral torsion havebeen observed, few studies have examined femoral tor-sional asymmetry in Native Americans. Therefore, itwas important that we first examine femoral torsion in asample of Native Americans from different geographicalregions and time periods. The results of this study dem-onstrate that there is commonly sexual dimorphism inboth directional and absolute asymmetry of femoral tor-sion among Native Americans, but not within AmericanWhites and Blacks. The amount of sexual dimorphism inasymmetrical torsion also varies between Native Ameri-can populations. However, when present, the increasedasymmetry occurs more often in females than males.Likewise, while there is considerable variation withinpopulations and sexes in torsional asymmetry, theamount of variation is higher in females than males.

Native American females also appear to exhibit greaterasymmetry in femoral torsion than other populations.

Causes of population variation in femoral torsion

Normal adult femoral anteverison is likely the resultof mechanical forces and some genetic propensity. Upad-hyay et al. (1990) found no significant relationshipbetween femoral anteversion and social class, order infamily, parental age at birth, or birth presentation inchildren aged 2–15 years. They did, however, find signifi-cant correlation in femoral anteversion between siblings,and suggested this might indicate some hereditary influ-ence. Nevertheless, generally the research supports amechanical explanation for most of the variation in fem-oral torsion (LeVeau and Bernhardt, 1984; Tardieu,2010; Bonneau et al., 2011), and Upadhyays and col-leagues’ (1990) results could be interpreted in this light.Biomechanical forces are a primary contributing factorfor the angle of anteversion during early growth anddevelopment (Tardieu, 2010; Bonneau et al., 2011).

Fig. 6. Regression plots showing temporal tend by mean archaeological site date in directional (left column) and absolute (rightcolumn) asymmetry for females (top row) and males (bottom row).



During postnatal growth, muscular and joint capsuletension at the hip influences detorsion. As a result, mus-cular imbalance during development is frequently citedas a cause of variation in femoral torsion. Over-activityof the iliopsoas and medial rotators or laxity of the lat-eral rotators place anteriorly directed loads on thegrowth plate resulting in greater torsion (Appelton,1934; Arkin and Katz, 1956; Glauber and Vizkelety,1966; Shefelbine and Carter, 2004).

Experimental studies on animals and the examinationof children with disorders affecting the hip lend supportto the hypothesis that femoral torsion is related to hipmuscle forces (Wilkinson, 1962; Salter, 1966; Staheliet al., 1968). Wilkinson (1962) observed that immaturerabbits that had their hind legs splinted in a sustainedmedially rotated position developed anteversion whilethose with a sustained lateral rotation had retroversion.In humans, high angles of femoral torsion are associatedwith cerebral palsy and other congenital disorders affect-ing the musculature of the hip (Salter, 1966; Arnold andDelp, 2001; Murray and Robb, 2006). Children withhemiplegia often exhibit normal ranges of femoral tor-sion on the non-hemiplegia side, but increased antever-sion on the hemiplegic side (Staheli et al., 1968). All ofthese studies lend support for a primarily mechanicalinfluence in the development of femoral diaphysealtorsion.

Body build also appears to affect femoral torsion.Cyvin (1977), for example, found that slender children(less muscular and lower weight) have higher values ofanteverion than more muscular, athletically built chil-dren. Likewise, Galbraith et al. (1987) showed that obeseadolescents have reduced femoral torsion compared tothose of normal weight. Increases in body weight havebeen shown to proportionally increase the biomechanicalforces generated across the hip joint (Galbraith et al.,1987). While the causality of differences in femoral tor-sion associated with body build have not been formallyexplored, it is very likely they are the result of forcesgenerated across the hip due to muscularity and bodyweight.

In addition to muscular imbalances, femoral torsionis likely caused by unequal compressive forces acrossthe growth plate due to postural behaviors (Crane,1959; Alvik, 1962; Staheli, 1980; Cibulka, 2004). Highangles of femoral torsion are often linked with pos-tural behaviors where the thigh is habitually rotatedmedially, while low angles are associated with lateralrotation of the thigh. Cradle-boarding, sleeping posi-tion, and sitting position have been cited as causes ofabnormal femoral torsion (Crane, 1959; Salter, 1966;Fabry et al., 1973; LeVeau and Bernhardt, 1984;Cibulka, 2004; Basgall, 2008). For example, while sit-ting in a reverse tailor position (“W-sitting”) the thighsare medially rotated. The medial rotation causes ashortening of the hip joint capsule and muscles on theanterior side of the joint and lengthening of the cap-sule and muscles on the posterior side. This producesuneven torsional forces on the proximal femur (Crane,1959; Cibulka, 2004). For children who habitually W-sit, the unequal tension on the hip joint reduces thenormal detorsion of the femoral neck resulting inhigher than average anteversion in these individuals.In fact, Crane (1959) found that anteversion angles inchildren who W-sit were greater than seen at birth,while children who sat cross-legged exhibited normalranges of anteversion.

Temporal trends in Arikara females

The results of this study show a significant change infemoral diaphyseal torsion, as measured by theta, andtorsional asymmetry between the protohistoric and his-toric periods in Arikara females (Figs. 4 and 6). No sig-nificant temporal trend was observed in males (Figs. 5and 6), although the prevalence of femoral torsionalasymmetry does increase slightly in males during thehistoric period (Table 8). In females, the significantincrease in femoral torsional asymmetry is associatedwith a slight increase in subtrochanteric theta of theright femur and a significant decrease in subtrochanterictheta of the left femur (Table 6).

A few studies examining Native American skeletonsmention changes in anteversion, but with little explana-tion (e.g., Bass and Barlow, 1964; Miles, 1975; Stodder,1987; Ruff and Larsen, 1990). One study that doesattempt to explain causation is Young (2004). In thisstudy, she examined femoral torsional asymmetry in asmall sample of prehistoric St. Lawrence Iroquian skele-tons from the Roebuck site. Twelve of the possible 15females (80%) in her sample exhibited asymmetry in fem-oral anteversion. The single male in the sample did not.Young (2004) argued that the asymmetry in femoral tor-sion observed in females was probably caused by overuseof the lateral rotator muscles during agricultural activ-ities. Another researcher, Basgall (2008), examined 14Northwestern Plains female skeletons from the Univer-sity of Wyoming Human Remains Repository. Ten of the14 females examined had asymmetrical torsion �10�.Similar to our findings, Basgall (2008) found that themarked asymmetry in Northwestern Plains females wasdue to an increase in right and a decrease in left antever-sion. In fact, three of the protohistoric/historic females inher sample exhibited retroversion of the left femur. Sheattributed the high degree of sexual dimorphism andasymmetry in torsion to sitting posture, especially side-sitting (discussed in more detail below). Interestingly,Basgall (2008) also noted a temporal trend, with asymme-try increasing during the late protohistoric and historicperiod, but her sample size did not permit statistical test-ing of this hypothesis. All of the protohistoric and historicperiod skeletons in her sample had significant asymmetryin femoral torsion. The four female skeletons without sig-nificant torsion were from early or late prehistoric peri-ods. Furthermore, in Basgall’s (2008) prehistoric sample,the left femur exhibited greater torsion in all but oneindividual, while the right femur exhibited greater tor-sion in all of the protohistoric and historic remains. Theresults of our study are consistent with those of Basgall(2008) and suggest that femoral torsional asymmetry infemales was widespread among Native Americans, atleast from the historic Northern Great Plains.

Ruff and Larsen (1990) observed a temporal trend infemoral anteversion and theta angle among Georgiacoast populations in both sexes. They observed that bothmale and female femora from the precontact periodexhibited relatively high angles compared to contact-period femora. In precontact females, there was a signifi-cant increase in anteversion between preagriculturaland agricultural populations. However, both males andfemales exhibited a decrease in anteversion between theprecontact and contact periods. They observed the samepattern in subtrochanteric theta. Unfortunately, Ruffand Larsen (1990) did not discuss the possible causes forthe changes in femoral torsion they observed.



Possible causes for change in torsion within theArikara

While this study cannot definitively demonstrate thecause of the change in femoral torsional asymmetry, ourresults show that there was a dramatic shift in asymme-try from the PCC to the HA in Arikara females. Thistemporal change is likely associated with behaviors thatcaused differential tension and forces on the hip joint.There is very little evidence to suggest a genetic compo-nent to femoral torsional asymmetry, especially since thechange occurred within a relatively genetically homoge-neous group (Upadhyay et al., 1990). Furthermore, thechange is not seen in males as would be expected ifthere was a strong hereditary influence. There is alsovery little evidence to suggest that the change was dueto congenital disorders or disease. While abnormal femo-ral torsion is associated with a number of clinical disor-ders (e.g., congenital dislocation of the hip, Perthes’disease, cerebral palsy), it is unlikely that congenital dis-orders or diseases played a role in the changes observedin this study, especially since individuals with recogniz-able disorders or diseases of the lower limb were elimi-nated and the change is seen only in females. TheArikara females may have had clinical problems such astoeing-in or toeing-out commonly associated with highanteversion and retroversion, respectively, but theseproblems would have been the result of femoral torsion,not the cause (Crane, 1959; Cibulka, 2004).

If mechanical forces are the primary cause of femoraltorsion, then the change in femoral torsional asymmetryobserved in Arikara females is most likely related togender-specific activities or sitting and sleeping pos-tures. Young (2004) suggested that asymmetry in femo-ral torsion among the Iroquois was related to femaletasks associated with farming activities. She argued thattilling and other farming activities where most of thebody weight is on one leg would involve greater mechan-ical loading and the use of lateral rotators, both of whichare known to cause detorsion of the femur diaphysis.Wescott and Cunningham (2006) examined temporaltrends in long bone diaphyseal size, strength, and shapewithin the Arikara. They found significant changes,especially in the strength of the left femur, from the pro-tohistoric to historic period, which they attributed toincreased workload necessary to produce surplus cropsfor trade. Wescott and Cunningham (2006) argued thatthe primary reason for increases in the strength of theleft lower limb in Historic Arikara females was due toplacing greater mechanical loads on the left lower limbwhile performing right-handed activities such as fieldpreparation and planting. Placing more weight on theleft femur than the right during childhood could causegreater detorsion of the left femur, resulting in torsionalasymmetry where the left femur has less torsion thanthe right (Galbraith et al., 1987).

However, while field preparation may be a contribut-ing factor, a more likely cause of the change in femoraltorsion is a common sitting posture observed in historicphotographs from the Great Plains, known as side-sitting, in which females sat in a modified version of thereverse tailor or W-sitting position (Hunt and Williams,2002; Basgall, 2008). In the side-sitting position theirlegs were pulled underneath their dress and their feetpoint to one side (Fig. 7). Basgall (2008) also argued thatthis was the most likely cause of sexual dimorphism infemoral torsional asymmetry she observed in the North-

western Plains. She notes that there are numerous his-toric accounts that indicate side-sitting was culturallyprescribed for Crow, Cheyenne, Arapaho, and Siouxfemales. That is, in many Northern Plains cultures,side-sitting was the required sitting position for youngadolescent and adult females. However, children andmales were allowed to sit in other positions (Basgall,2008). Males commonly sat cross-legged, long-legged(lower limbs outstretched), or short-legged (lower limbsbent), while females almost always sat sidewise.

The side-sitting position causes the upper thigh to bemedially rotated and the lower to be laterally rotated.Furthermore, when side-sitting, the body weight restson the pelvis and the laterally rotated proximal portionof the lower femur, while the medially rotated upperfemur bears less weight (Fig. 8). Sitting in this positionfor long periods over years, especially if started at ayoung age, would cause increased detorsion of the lowerfemoral neck and prevent normal full detorsion of theupper femur. Historic photographs of Northern Plains

Fig. 7. Historic photograph of Northern Plains Crowfemales sitting in left side-sitting position. Source: University ofWyoming American Heritage Center, Richard Throssel Papers,Accession Number 02394, Box 8, TP11, Throssel #14.

Fig. 8. Articulated pelvis and femora of an Arikara femalefrom the Leavenworth site (39CO9) illustrating orientation ofthe femora in a side-sitting position. The right femur is medi-ally rotated while the left is laterally rotated. This causes ten-sion on the bottom side of the right femoral capsule and tensionon the top side of the left femoral capsule. In this position agreater amount of body weight is placed on the left hip jointthan the right.



girls also show them side-sitting. Females likely sat inthis position while conducting tasks that allowed sittingon the ground such as food processing, cooking, hideprocessing, quillwork, and sewing. Based on the Arikaradata in this study, it appears that sitting on the left side(feet to the right) was more common than sitting on theright. This is consistent with historical photographs thatshow the majority of Northern Plains women sitting onthe left side (Fig. 7). This would also be consistent witha sitting posture that allowed full use of the usual domi-nant hand.

If sitting posture is responsible for the temporalchanges in femoral torsional asymmetry observed in Ari-kara females, then 1) historic females spent considerablymore time sitting than in earlier periods, 2) femalesbegan to sit in this position at an earlier age, or 3) theside-sitting posture become more culturally relevant dur-ing the historic period. Of course a combination of thesethree is also possible.

During the historic period, inter-tribal trading becameincreasingly important to Arikara females, who tradedcrops, hides, beadworks, quillworks, and other items toobtain articles that made the lives of their families morecomfortable and provided an economic surplus for cere-monies (Peters, 1995; Parks, 2001). As a result, Arikarafemales spent a considerable amount of time producingsurplus crops and other trade items. It is possible thatfemales spent more time in a side-sitting position thanin previous temporal periods to produce the surplustrade items they needed. Along these same lines, it islikely that side-sitting began at an earlier age duringthe historic period. As surplus items for trade becameincreasingly valuable to the Arikara, it is likely thatyoung girls became involved in these activities at ayounger age than they did previously. Young girls on theGreat Plains spent a great deal of time assisting theirmothers in gender-related chores (Michelson, 1932).Therefore, it is likely that young girls also sat in a side-sitting position along with their mothers. The youngerthe Arikara girls were when they began the practice ofalmost exclusively using a side-sitting posture, the moredramatic the effects would be on femoral torsional asym-metry. As discussed above, femoral torsion slowlydecreases during postnatal life, with most individualsreaching their adult values during adolescence. Deckeret al. (2013) found no correlation with femoral antever-sion and age in males or females older than 20 years ofage. The age of the individual and the duration ofmechanical loading can increase or decrease the timenecessary for bone to adapt. With regards to femoral tor-sion, small constant loads may have a greater effectthan large, short duration forces (Galbraith et al., 1987).Therefore, the changes in asymmetry among the Arikaramust be associated with activities that began early inlife. With the increased need to have excess items fortrade, it is possible that the Historic Arikara femalesbecame involved in activities such as cooking, food prep-aration, beadwork, and hide processing at an earlier agethan in previous temporal variants.

Another possibility is that side-sitting in females wasa culturally prescribed custom only during the historicperiod. This would also be consistent with the changeseen not only in the Arikara but in other NorthernPlains groups (Basgall, 2008). Historical documents indi-cate that side-sitting was a culturally prescribed sittingposition for women among the Arapaho (Hilger, 1952),Cheyenne (Grinnell, 1923), Crow (Marquis, 1928), and

Sioux (Walker, 1917). See Basgall (2008) for a moredetailed discussion. Historic photographs of Arikarafemales also show them in the side-sitting posture (seeFig. 3 in Parks, 2001). Therefore, side-sitting seems tohave been a widespread cultural custom among North-ern Plains females. While there is no record of sittingposture in PCC or EC females, the results of this studyand those of Basgall (2008) suggest that the practicewas not as widespread in either the Arikara or otherNorthern Plains females prior to the historic period.

CONCLUSIONS

Femoral diaphyseal torsion is a relevant biomechani-cal indicator, but it has received very little attention inbioarchaeological studies. Femoral torsion appears to beprimarily driven by imbalances in muscle and joint cap-sule tone due to behavioral activities that result inextended periods of lateral and/or medial rotation of thethighs. There is little evidence to support a stronggenetic component to femoral torsion, especially asym-metry in torsion (Upadhyay et al., 1990). The results ofthis study and others suggest a relatively high preva-lence of torsional asymmetry among Northern PlainsNative American females, especially during the historicperiod.

While this study cannot conclusively demonstrate thecause of asymmetrical femoral torsion, it is likely linkedto a common sitting posture observed in historic photo-graphs from the Great Plains. Females habitually side-sat with one thigh medially rotated and the other later-ally rotated, and most of their body weight resting onthe laterally rotated thigh. If this practice began duringchildhood, it would result in a higher angle of torsion inthe medially rotated thigh than in the laterally rotatedone. If sitting posture is responsible for the change infemoral torsional asymmetry observed in the Arikaraand other Northern Plains females, it is most likelyassociated with habitual sitting in a side-sitting positionearlier in life or that side-sitting became a culturallymandated sitting position for females only during thehistoric period. The results of this study may provideevidence for a change in cultural sitting posture thatwas widespread across the Northern Plains.

ACKNOWLEDGMENTS

The authors acknowledge and thank Hope Williams forher assistance in collecting the data for population compar-ison portion of the study and the AAPA presentation onfemoral torsion.

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