Humeral torsion revisited: a functional and ontogenetic model for populational variation.

Bibliographic Collection: 
MOCA Reference, APE
Publication Type: Journal Article
Authors: Cowgill, Libby W
Year of Publication: 2007
Journal: Am J Phys Anthropol
Volume: 134
Issue: 4
Pagination: 472-80
Date Published: 2007 Dec
Publication Language: eng
ISSN: 1096-8644
Keywords: Adaptation, Physiological, Adolescent, Adult, Child, Child, Preschool, Female, Genetic Variation, Humans, Humerus, Infant, Infant, Newborn, Male, Models, Biological, Movement, Range of Motion, Articular, Torsion, Mechanical

Anthropological interest in humeral torsion has a long history, and several functional explanations for observed variation in the orientation of the humeral head have been proposed. Recent clinical studies have revived this topic by linking patterns of humeral torsion to habitual activities such as overhand throwing. However, the precise functional implications and ontogenetic history of humeral torsion remain unclear. This study examines the ontogeny of humeral torsion in a large sample of primarily immature remains from six different skeletal collections (n = 407). The results of this research confirm that humeral torsion displays consistent developmental variation within all populations of growing children; neonates display relatively posteriorly oriented humeral heads, and the level of torsion declines steadily into adulthood. As in adults, variation in the angle of humeral torsion in immature individuals varies by population, and these differences arise early in development. However, when examined in the context of the developing muscles of the shoulder complex, it becomes apparent that variation in the angle of humeral torsion is not necessarily related to specific habitual activities. Variability in this feature is more likely caused by a generalized functional imbalance between muscles of medial and lateral rotation that can be produced by a wide variety of upper limb activity patterns during growth.

DOI: 10.1002/ajpa.20689
Alternate Journal: Am. J. Phys. Anthropol.
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