Abstract Title

Sexual Dimorphism in the Trochlear Angle of the Humerus: A preliminary investigation in Hunter-Gatherers and Agriculturalists

Presenter Name

Alexa Pennavaria

RAD Assignment Number

2407

Abstract

Purpose: Previous research has argued the elbow “carrying angle” to be sexually dimorphic in humans, with females exhibiting greater abduction of the supinated forearm at full extension. Moreover, it is generally assumed that the trochlear angle of the humerus is the primary skeletal basis of the carrying angle, and thus, may independently provide a reliable osteological indicator of sex in forensic, bioarchaeological, and paleoanthropological contexts.

Methods: Here, we employed the software TPSDig2 to derive trochlear angles from photographs of humeri collected on 40 (17 female/23 male) adult Archaic-period Amerindian hunter-gatherers and 54 (24 female/30 male) adult Medieval European agriculturalists. Due to handedness, angles from left and right humeri were averaged for each individual, with asymmetry assessed by subtracting the more acute angle from the more obtuse angle irrespective of actual left/right siding.

Results: Although based on small sample sizes, males and females were not found to be significantly different from each other in either the Amerindian (t=1.5, p=0.13) or European (t=-1.3, p=0.26) samples. With both sexes pooled, the Amerindian sample exhibited more acute trochlear angles (t=4.64, p < 0.0001) and greater bilateral asymmetry (t=-2.07, p=0.042) than the Europeans. Additionally, although not statistically significant, Amerindian males (bilateral difference μ=5.92°) were found to be more asymmetrical than Amerindian females (μ=4.65°), while asymmetry values in European males (μ=3.69°) and females (μ=3.63°) were virtually identical.

Conclusions: While failing to support the trochlear angle as a diagnostic sex indicator, our results are consistent with previous research generally demonstrating elevated levels of upper limb asymmetry in hunter-gatherer populations — asymmetries typically attributed to reliance on activities requiring greater unilateral loading of the dominant limb. Accordingly, the results of this study may indicate that more acute trochlear angles (less forearm abduction) reflect higher levels of biomechanical loading. Thus, sexual dimorphism in the carrying angle, if/when present, may be dependent on sex-specific activity patterns.

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Research Area

Structural Anatomy

Presentation Type

Poster

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Sexual Dimorphism in the Trochlear Angle of the Humerus: A preliminary investigation in Hunter-Gatherers and Agriculturalists

Purpose: Previous research has argued the elbow “carrying angle” to be sexually dimorphic in humans, with females exhibiting greater abduction of the supinated forearm at full extension. Moreover, it is generally assumed that the trochlear angle of the humerus is the primary skeletal basis of the carrying angle, and thus, may independently provide a reliable osteological indicator of sex in forensic, bioarchaeological, and paleoanthropological contexts.

Methods: Here, we employed the software TPSDig2 to derive trochlear angles from photographs of humeri collected on 40 (17 female/23 male) adult Archaic-period Amerindian hunter-gatherers and 54 (24 female/30 male) adult Medieval European agriculturalists. Due to handedness, angles from left and right humeri were averaged for each individual, with asymmetry assessed by subtracting the more acute angle from the more obtuse angle irrespective of actual left/right siding.

Results: Although based on small sample sizes, males and females were not found to be significantly different from each other in either the Amerindian (t=1.5, p=0.13) or European (t=-1.3, p=0.26) samples. With both sexes pooled, the Amerindian sample exhibited more acute trochlear angles (t=4.64, p < 0.0001) and greater bilateral asymmetry (t=-2.07, p=0.042) than the Europeans. Additionally, although not statistically significant, Amerindian males (bilateral difference μ=5.92°) were found to be more asymmetrical than Amerindian females (μ=4.65°), while asymmetry values in European males (μ=3.69°) and females (μ=3.63°) were virtually identical.

Conclusions: While failing to support the trochlear angle as a diagnostic sex indicator, our results are consistent with previous research generally demonstrating elevated levels of upper limb asymmetry in hunter-gatherer populations — asymmetries typically attributed to reliance on activities requiring greater unilateral loading of the dominant limb. Accordingly, the results of this study may indicate that more acute trochlear angles (less forearm abduction) reflect higher levels of biomechanical loading. Thus, sexual dimorphism in the carrying angle, if/when present, may be dependent on sex-specific activity patterns.