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INDICATORS OF THORACIC OSTEOARTHRITIS COMPARED TO RELATIVE AGE ESTIMATED USING THE VERTEBRTAL EPIPHYSEAL RING

Abstract

Osteoarthritis of the vertebrae is strongly influenced by age but other factors, including occupation, weight, sex, genetic predisposition, diet and lifestyle, also affect the severity of this skeletal pathology. Vertebral osteoarthritis can be expressed as lipping or osteophytosis, eburnation and porosity. Eburnation provides strong evidence of osteoarthritis. However, there is debate about whether the process that initiates osteoporosity, or bone destruction, differs from that involved in bone accumulation, resulting in osteophytosis or lipping. To systematically investigate the relationship between eburnation, lipping and porosity, we reconstructed age by seriating a randomly selected sample of 14 thoracic vertebrae from the bioarchaeology teaching collection of Georgia State University. Relative ages were assigned by ordering stages of epiphyseal ring degeneration. First, the oldest and youngest were identified. The youngest exhibits a prominent epiphyseal ring with a pronounced margin that is evenly thick along its length without interruption or disfigurement. The oldest epiphyseal ring is characterized by distorted margins and severe disruption of the morphological integrity of the ring. The other individuals were ascribed a relative age, including younger, middle and older adult, according to their similarities to these extremes. Striations were also considered and reduced the relative age closer to the younger pole when discernable under 10x magnification. Eburnation, lipping and porosity were scored using Buikstra and Ubelaker’s (1994) ranking system and compared using Spearman correlations. Prior to analysis, a measurement error study confirmed repeatability by yielding no significant differences between two independent scoring attempts. Eburnation exhibits the strongest correlation with relative age (r = 0.516), whereas lipping is more weakly correlated (r = 0.397). Porosity and relative age are not correlated (r = 0.078). Between the indices, porosity and lipping are weakly correlated (r = 0.340) whereas the others are uncorrelated. To the extent that this limited sample reflects broad trends in the human life cycle, these results support the position that porosity acts independent of age. When porosity is associated with aging, it is because of its weak correlation with lipping. In contrast to the other osteoarthritis indicators, eburnation appears to be the most reliable indicator of age in the thoracic spine.

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