The influence of activity levels on humeral retroversion: a bioarchaeological study

Increases in humeral retroversion have been suggested to result from certain shoulder activities, especially throwing. Could retroversion also increase as a result of other upper extremity activities in addition to throwing? It was the purpose of this study to investigate humeral retroversion in the Nubian Tombos population (1400656 BCE) and correlate retroversion with entheseal changes which are used as an assessment of physical activity. Humeral retroversion was measured from photographs. Two photographs were used to define angles from the bony landmarks relative to the table surface, one directly superior to inferior, and one directly inferior to superior. From these photographs the skew humeral head and transepicondylar axes lines were drawn relative to the table plane, from which the axis/table plane angle was measured using ImageJ software. From these two angles the final retroversion was calculated. All lines were drawn by one senior orthopedic surgeon. Upper extremity entheseal scores, taken from a previous Tombos study using the same remains, were grouped as very low, low, high, and very high. Sex was estimated using standard archaeological protocols. Age at death was evaluated using transition analysis, and was grouped as 1524, 2534, 3549, 5069, and = 70 years old. There were 121 complete humeri available for study (61 right and 60 left). The average retroversion was 20 ° ± 10 °, and was 17.5 ° ± 9.6 °, 22.3 ° ± 8.7 °, 26.5 ° ± 11.8 °, 22.2 ° ± 5.9 ° for the very low, low, high, and very high entheseal score groups respectively (p = = 0.041). Those = 70 years old had a large number in the low entheseal score group while those 35 to 49 years old had the greatest number in the very high entheseal score group (p = 0.000001). There were no differences by sex, laterality, age, or burial cemetery. We hypothesize that those who were able to live to old age were better resourced with lower physical demands than other members of the community and thus developed less retroversion. Our results also indirectly support the postulate that an increase in general upper extremity physical activity may result in increased retroversion, and not exclusively due to throwing activities.