RETROTORSION OF THE HUMERUS IN THE THROWING ARMS OF HAND-BALL-PLAYERS - AN ADAPTATION TO UNILATERAL STRAIN

Abstract

INTRODUCTION: When comparing the maximum amount of external shoulder rotation of the throwing arms of handball players to that of the non-dominant side, an increase of about 10 - 15° of external rotation can be found in the throwing arm. This fact is not surprising in itself, because it could be explained by anterior laxity due to chronic overuse, but surprisingly at the same time the maximum amount of internal shoulder rotation is reduced in the dominant arm by approximately 10°. Similar differences in rotation ability have been reported for unilateral overhead or throwing sports like tennis or baseball. This lateral difference could possibly be explained by a side difference in humeral retrotorsion. METHODS: In order to investigate this question further, the angle of humeral retrotorsion was determined in both shoulders of 51 male handball professionals, 39 of them right-handed and 12 left-handed. The age distribution ranged from 18 to 39 years, with an average age of 27 years. All players had started competitive handball before the age of 10. They had to have at least 5 years of team competition to be included in our study. Of the subjects, 38 had no history of shoulder problems, while 13 complained of chronic shoulder pain. Humeral retrotorsion was determined by X-rays in two defined planes with a special technique first published in 1982. The side differences were compared to the values for a control group of 37 men with no history of shoulder instability or unilateral strain due to sport or work activities. RESULTS: In the group of 38 handball players with no chronic shoulder pain, the retrotorsional angle of the humerus was 14.4° larger on the dominant side than on the non-dominant, the differences ranging from 4° to 29°. The difference is highly significant (p < 0.001). In the control group, however, we could find no statistically significant differences, with the average increase being only 2.3°. This finding is consistent with Kronberg et al., who reported an increase of 4° in the dominant arms of 50 non-athletes. The group of handball players with chronic shoulder pain did not exhibit this increase. They even had a decrease of humeral retrotorsion of 5.2° in the throwing arm. As compared to the group of 38 handball players without chronic shoulder pain, this was again statistically highly significant (p 0.001). CONCLUSIONS: The increase of humeral retrotorsion in the throwing arms of handball players is an adaptive process due to extensive external rotation in throwing practice during growth. This increased retrotorsion allows more external rotation of the shoulder before the humeral head puts excessive strain on the anterior capsulolabral complex, and thus may lead to anterior instability. An increase in humeral retrotorsion could thus be interpreted as a protective mechanism for the anterior capsulolabral complex. Those athletes who - for some as yet unknown reason - do not exhibit this biopositive response to practice in childhood seem to have more strain on their anterior capsules at an earlier degree of external rotation and thus may be prone to develop chronic shoulder pain due to anterior instability.