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A Rare Case of Congenital Radio-Ulnar Synostosis at the Dearmond Site (40RE12) in East Tennessee

by Donna McCarthy, Post-Doctoral Fellow, Physical Anthropology, McClung Museum

Introduction: Years ago while collecting data for my dissertation I recorded a case of a fused radius and ulna in a child at the DeArmond site. At the time I could find little data concerning its occurrence in the prehistoric record, so further investigation was put on hold. Just recently while conducting completely unrelated bioarchaeological research, I encountered an article reporting another prehistoric case of the anomaly (Titelbaum and Verano 2013), reigniting my interest in the case. Rates for congenital radio-ulnar synostosis (CRUS) in modern populations are remarkably low, with approximately 350 currently reported cases in the medical literature (Wurapa 2012). The presence of this rare developmental anomaly in a prehistoric site, therefore, warrants further research.

DeArmondSite

Location of the DeArmond site, with well-known Chickamauga Basin sites for reference.

Site and burial information:  The DeArmond site is located on a terrace of the bottom lands that join the DeArmond and Detheridge Farms on the east bank of the Tennessee River in Roane County. It was excavated between 1939 and 1940 as part of a cooperative effort between the WPA, TVA, and The University of Tennessee. The site dates to AD 1200-1450, and like most Mississippian sites of this time period, consists of a mound and village component. A total of 145 burials were excavated, 52 from the village and 93 from the mound. The affected skeleton was excavated from the village component, close to the plow zone with some visible disturbance. While no burial pit was visible, placement of the body was recorded to be partly-flexed and on the right side. A small, shell-tempered, vertical rim jar was placed against the back of the skull, which had been crushed during interment. Age of the subadult was estimated to be approximately 8 years old based on dental development.

Causes and consequences of CRUS: During fetal development, the cartilaginous precursors of the bones comprising the elbow (the proximal radius, proximal ulna, and distal humerus) are connected, sharing a perichondrium (layer of connective tissue). These elements normally separate during the seventh intrauterine week, however, when this process is interrupted, the cartilage between the developing elements does not separate, becoming bone as endochondral ossification commences. Congenital cases of radio-ulnar synostosis may be sporadic and isolated, however, in some cases they may be inherited via autosomal dominance. Miura et al. (1984) report at least one case of familial predisposition. Effects on the individual depend upon the severity and cause of the condition, as it sometimes occurs in conjunction with serious chromosomal abnormalities or genetic syndromes.

The majority of reported cases (up to 60%) of CRUS are bilateral; however, the case at the DeArmond site is unilateral, affecting the proximal right radius and ulna only. Differential diagnoses considered for this anomaly included complications of fracture and spondyloarthropathy. These conditions were ruled out as a possible etiology in this case, as there is no evidence of remodeling or callous formation associated with fracture healing. In addition, the fused surfaces are smooth and continuous across segments with no evidence of inflammation or pathological bone growth. Based on its appearance, the synostosis is a Type I or “primary or true” fusion as described by Wilkie (1914). Approximately 50% of the entire subadult skeleton was recovered at excavation, and cursory examination revealed no other skeletal pathologies with the exception of linear enamel hypoplasias indicative of nutritional stress.

Implications of this research: Besides their own case from South America, Titelbaum and Verano (2013) report 12 additional prehistoric cases of this rare developmental anomaly. Interestingly, 8 of the 13 cases occur in the United States. Even more interestingly—especially to a Mississippian bioarchaeological researcher—is that two of these cases occur in a Mississippian site in Illinois dating to AD 1200-1300, a range that coincides with the early habitation at the DeArmond site in Tennessee. Milner et al. (1991) reported that Mississippians appeared to have been moving out of west-central Illinois around AD 1300, coinciding with the population decline at Cahokia. McCarthy (2009) also discusses how the people inhabiting Dickson Mounds “inexplicably vanished” sometime during the late 13th to middle 14th centuries. The distances between the sites in Illinois and east Tennessee are much greater than generally considered in biological distance studies (more than 450 miles using straight line distance), however, the presence of this rare anomaly at both sites provides intriguing possibilities regarding population movements during this time period. It is entirely possible, of course, that the anomalous skeletal developments represent completely unrelated isolated occurrences. However, this is an avenue of research that appears to deserve future investigation.

Future plans: The research briefly presented here is currently being expanded for submission to a peer-reviewed journal. The resulting work will include more detailed information regarding the morphology of the elements in this case and of the etiology and possible consequences of CRUS.

References cited:
McCarthy, Stephanie E. 2009. Haunted Peoria. Charleston, SC: Arcadia Pub: 141.

Milner GR, Anderson E, and Smith VG. 1991. “Warfare in Late Prehistoric West-Central Illinois.” American Antiquity 56: 581-603.

Miura, T., R. Nakamura, M. Suzuki, and J. Kanie. 1984. “Congenital Radio-ulnar Synostosis.” The Journal of Hand Surgery: British & European 9: 153-55.

Titelbaum, A. R., and J. W. Verano. 2013. “A Case of Congenital Radioulnar Synostosis from Prehispanic Peru.” International Journal of Osteoarchaeology Int. J. Osteoarchaeol 25: 968-75.

Wurapa R. 2012. “Radial-Ulnar Synostosis.” Medscape Reference. Accessed June 7, 2015. http://emedicine.medscape.com/article/1240467-overview.

Wilkie, D. P. D. 1913. “Congenital Radio-ulnar Synostosis.” British Journal of Surgery Br. J. Surg. 1: 366-75.

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