Retroversion of the humeral head in the normal shoulder and its relationship to the normal range of motion.

Retroversion of the humeral head and the range of motion of the shoulder joint in both the frontal and the scapular plane have been studied in 100 shoulder joints in 50 healthy subjects, 25 men and 25 women. The average angle for humeral head retroversion was 33 degrees on the dominant side and 29 degrees for the nondominant side. There was no difference between genders. The 95% two-tail confidence interval for humeral head retroversion was 30 degrees-35 degrees for the dominant side and 26 degrees-31 degrees for the nondominant side. A larger retroversion angle was consistent with an increased range of external rotation. Mean external rotation in 90 degrees abduction was 105 degrees in the frontal plane and 120 degrees in the scapular plane. External rotation in 90 degrees abduction was greater in women than in men, but there was no difference between dominant and nondominant shoulder joints. The range of motion of rotation was found to be greater than the accepted normal values.