Kari E. Helgeson 1 , Courtney C. Siegert 1 , Chloe P. McDaneld 1 , Nicholas P. Herrmann 1 , M. Kate Spradley 1 , Michelle D. Hamilton 1 1 Department of Anthropology, Texas State University Midline Shifts in Modern Populations: Comparisons of Migrants and a Donated Skeletal Collection Introduction • Border shifts occur when vertebral elements adopt characteristics of adjacent vertebral types. The etiology of these shifts is believed to be a combination of genetic and environmental factors.¹ • Shifts can happen in five border regions: occipitocervical (OC), cervicothoracic (CT), thoracolumbar (TL), lumbosacral (LS), and sacrocaudal (SC) regions.² • The Operation Identification (OpID) skeletal sample is composed of Central American and Mexican migrants and research suggests these individuals experience a significant amount of stress during growth and development.³ • The purpose of this research is to identify if the presence of vertebral border shifts occur at a higher rate in presumed migrants. Acknowledgements We would like to thank all the student volunteers at Texas State University who have contributed to Operation Identification over the years. Thanks also to Dr. Krista Latham and all of the student volunteers from the University of Indianapolis, the continued collaboration and support from the Brooks County Sheriff’s Office and community, the Equipo Argentino de Antropología Forense, the South Texas Human Rights Center, the Colibrí Center for Human Rights, and all of our partners in the Forensic Border Coalition. We would also like to thank all of the individuals and their families that have donated their body to the Forensic Anthropology Center at Texas State willed body donation program. Conclusion ● OpID individuals are experiencing more lumbosacral shifts potentially exacerbated by environmental stress during growth and development. ● More research needs to be collected on more modern populations and diverse ancestral groups with varied backgrounds to further understand the underlying etiology. Discussion ● OpID individuals show higher frequency of border shifts in the LS region, coupled with higher prevalence of LEH, which may suggest structural inequality and early stress. ● Even though OpID individuals exhibit more vertebral border shifts in the LS region than the Hispanic TXSTDSC sample it is unclear if the difference is due to increased environmental stress for migrant populations in their country of origin due to the small sample size of self- identified Hispanics in the TXSTDSC. ○ The identified OpID individuals are predominantly Central American⁵ and the TXSTDSC individuals are self-identifying Hispanic leaving the term Hispanic open to interpretation. ● OpID individuals are more similar to a clinical study which states that 35.6% of their sample, representing a general population, presents with a shift in the LS region⁶. ○ Data for this clinical study⁶ were collected from abdominal radiographs and the demography is unknown for the “general population” suggesting it may be biased towards an underlying medical condition. References Material & Methods • Border shifts were recorded from each of the five regions² (Table 1; Figures 2-5) in 74 individuals from the Texas State University Donated Skeletal Collection TXSTDSC) (F=31, M=43) and 54 from OpID (F=20, M=34). • TXSTDSC represents a more diverse self-reported sample: White (n=54), Hispanic (n=10), and Black (n=10). Table 1: List of vertebral shifts recorded from Barnes (1994) (region in parentheses). Cranial shifts are bolded, caudal shifts are italicized. • The presence or absence of linear enamel hypoplasia (LEH) on the maxillary central incisor and mandibular canines were scored in both populations to assess signs of early stress⁴ since socioeconomic status is unknown for OpID individuals. • Chi-squared tests of independence were performed for each region comparing the TXSTDSC and OpID individuals, cranial vs caudal shifting, and self-identifying Hispanic to OpID individuals. • A visual representation of relative frequency of appearance was created in ArcGIS version 10.6.1 (Figure 1). Results • OpID individuals exhibit higher frequencies of vertebral shifts at the LS region when compared to the entire TXSTDSC (p=0.000; Table 2, Figure 1) as well as a higher frequency of LEH on the maxillary central incisors. • OpID individuals show higher frequencies of shifts in the LS region when compared to self-identifying Hispanics in the TXSTDSC and less in the OC region, although not statistically significant (Table 2). • There was no difference between OpID and the TXSTDSC when considering cranial and caudal shifts separately. Figure 4. Unilateral sacralization Figure 5. Lumbarization Figure 2. Paracondylar process Figure 3. Lumbar rib Figure 1. Visual representation of relative frequencies of vertebral border shifts in the OpID and TXSTDSC. OpID TXSTDSC Occipital vertebra (OC) Paracondylar process (OC) Rudimentary 1 st rib (CT) Sacralization (LS) Precondylar tubercle (OC) Epitranverse process (OC) 2 nd rib mesosternum (CT) Lumbarization (LS) Basilar cleft (OC) Condylar hypoplasia (OC) Rudimentary 12 th rib (TL) Partial separation of S1 (LS) Bipartite occipital condylar facets (OC) Precondylar articulating facet (OC) Transitional facet T11 (TL) Rudimentary apophyseal joint S1/S2 (LS) Bipartite hypoglossal canal (OC) Cervical ribs (CT) Lumbar ribs (TL) S5 separation (SC) Atlas fusion (OC) 2 nd rib manubrium (CT) Transitional facet L1 (TL) Sacralization of 1 st coccygeal segment (SC) ● ¹Giampietro FP, Dunwoodie SL, Kusumi K, Pourquié O, Tassy O, Offiah AC, Cornier AS, Alman BA, Blank RD, Raggio CL, Glurich I, Turnpenny PD. 2009. Progress in the understanding of the genetic etiology of vertebral segmentation disorders in humans. Ann N Y Acad Sci. 1151: 38-67. ● ²Barnes E. 1994. Developmental defects of the axial skeleton in paleopathology. University Press of Colorado. ● ³Ayala Bas A. 2016. Health and proportionality: A study of undocumented migrants from the Texas-Mexico border (Master’s Thesis). ● ⁴Duray SM. 1996. Dental indicators of stress and reduced age at death in prehistoric Native Americans. Am J Phys Anthropol 99:275–286. ● ⁵McDaneld CP, Gocha TP, Siegert CC, Strand RM, Baker LE, Spradley MK. 2017. Understanding the degree of craniometric variation in South Texas Migrants. New Orleans (LA): American Association of Physical Anthropologists. ● ⁶Apazidis A, Ricart PA, Diefenbach CM, Spivak JM. 2011. The prevalence of transitional vertebrae in the lumbar spine. The Spine Journal 11: 858-862. Sample OC CT TL LS SC OpID (n=54) 0.35 0.07 0.43 0.41 0.48 TXSTDSC (n=74) 0.45 0.07 0.43 0.11 0.57 TXSTDSC Hispanics (n=10) 0.70 0.00 0.50 0.10 0.60 Table 2: Relative frequencies of vertebral border shifts in the OpID and TXSTDSC. 0.0 - 0.10 0.11 - 0.23 0.24 - 0.35 0.36 - 0.46