Acromion morphology and prevalence of rotator cuff tear: A systematic review and meta-analysis.

The causes of degenerative rotator cuff (RTC) tears are unclear but certain acromion morphology may contribute. This study's objective was to determine using a systematic review and meta-analysis the association of acromion type and acromial index with the prevalence of RTC tears. Six databases were searched electronically. Seventeen relevant studies between 1993 and 2017 were included in the meta-analyses determining the association of RTC tears with acromion type (n = 11) or acromial index (n = 10). Effect sizes were calculated as an odds ratio (OR) for the studies reporting acromion type and as raw mean difference (RMD) for the studies reporting acromial index. Meta-analysis was performed using a random-effects model. There was a significant small-to-medium effect found in the meta-analysis for acromion type (overall OR = 2.82, P = 0.000003), indicating an almost three times greater odds for a RTC tear in individuals with a type-III acromion as compared with those with a type-I or -II. A significant effect was also found for acromial index (RMD = 0.071, P < 0.0000001), indicating that a larger acromial index is associated with a greater likelihood of a RTC tear. Because of substantial heterogeneity in RMD for acromial index (Q-df = 92, P < 0.00001; I2 = 89%), subgroup analyses and meta-regressions were performed. Interestingly, the continent where the study was conducted (i.e., Europe vs. Asia) was the only moderator variable that could explain some of the acromial index heterogeneity. Overall, the findings from our analyses indicate that individuals with either a type-III acromion and/or a larger acromial index have a greater likelihood for non-traumatic RTC tears. Clin. Anat. 32:122-130, 2019.