Glenoid version: the role of genetic and environmental factors on its variability. An MRI study on asymptomatic elderly twins

Background: Glenoid version is the most variable parameter of the shoulder joint. No authors investigated if intrinsic genetic factors or influences from extrinsic sources are responsible for its variability. Aim: We compared glenoid version between elderly monozygotic and dizygotic twins intending to separate the contributions of genetics from shared and unique environments. Methods: Glenoid version of the dominant shoulder was assessed by MRI using Friedman’s method in 30 pairs of elderly twins (16 monozygotic–14 dizygotic; mean age SD: 63.72 3.37, 53–72). Heritability was estimated as twice the difference between the intraclass correlation coefficients for monozygotic and dizygotic pairs. The influence of shared environment was calculated as the difference between monozygotic correlation coefficient and the heritability index. According to job category, one way analysis of variance was used to estimate the differences between groups in the total sample and within zygosity groups. Results: Glenoid version angle in monozygotic and dizygotic twins was 2 (SD: 2 ) and 3 (SD: 3 ), respectively (p¼0.334). Heritability index was 0.98, while the contributions of shared and unique environment were 0 and 0.02, respectively. According to working classes, no significant differences were found between the groups (p¼0.732, F¼0.31). Conclusions: Glenoid version is mainly genetically determined and only marginally influenced by environments. Level of evidence: III.