The Antiquity of the Cam Deformity: A Comparison of Proximal Femoral Morphology Between Early and Modern Humans.
BACKGROUND
The precise etiology of cam impingement continues to be incompletely understood. The prevailing hypothesis posits that the deformity arises as a developmental injury prior to skeletal maturation. There is a possible evolutionary role, with an aspherical femoral head affording upright humans better stability. We set out to identify the antiquity of the cam deformity to better understand the comparative roles of modern behavior and evolution in its development.


METHODS
We used 249 physical specimens of femora from the Libben osteological collection, a set of bones from an ancient population who lived between the eighth and the eleventh century. These femora were photographed in four different orientations, and six specific proximal femoral angles were measured. The values were also compared with those from modern human femora using the Student t test, with a two-tailed p value of 0.05 denoting significance.


RESULTS
In total, 249 femora from 175 individuals were included in the final analysis. The ages of the individuals ranged between seventeen and fifty-five years. Interobserver and intraobserver correlation was good or excellent for all variables measured. Compared with modern populations, ancient human hips were significantly more anteverted (19.96° versus 12.85°; p < 0.001) and varus (true neck-shaft angle, 121.96° versus 129.23°; p < 0.001). The alpha angle was significantly lower in ancient humans (35.33° versus 45.61°; p < 0.001), and none of the ancient femora met the modern criteria for a cam deformity (an alpha angle of >50°).


CONCLUSIONS
It appears that the cam deformity was nonexistent among ancient humans and is perhaps predominantly a product of modern-day stresses. Further clinical investigation into behavioral modifications in adolescence is warranted to potentially prevent the development of deformity and impingement.
Department of Human Evolutionary Biology, Harvard University, Peabody Museum 53C, 11 Divinity Avenue, Cambridge, MA 02138.
Allison R
AR
Moats
Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, Yale Physicians Building, 800 Howard Avenue, 1st Floor, New Haven, CT 06519. E-mail address for R. Badrinath: raghav.badrinath@yale.edu.
Raghav
R
Badrinath
Department of Anthropology, School of Biomedical Sciences, Kent State University, 750 Hilltop Drive, 226 Lowry Hall, Kent, OH 44242.
Linda B
LB
Spurlock
Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, Yale Physicians Building, 800 Howard Avenue, 1st Floor, New Haven, CT 06519. E-mail address for R. Badrinath: raghav.badrinath@yale.edu.
Daniel
D
Cooperman
D000293:Adolescent; D000328:Adult; D000704:Analysis of Variance; D005075:Biological Evolution; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging* / Q000266:history*; D005269:Femur / Q000002:abnormalities / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D005270:Femur Head / Q000002:abnormalities* / Q000000981:diagnostic imaging; D049673:History, 20th Century; D049690:History, Ancient; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011859:Radiography; D055815:Young Adult