Retrotorsion of the Humerus in the Throwing Arm of Handball Players - an Adaptation to Unilateral Strain

INTRODUCTION: As compared to the axis of the elbow joint, the humeral head is directed inward and backward. This is called retroversion of the humeral head or retrotorsion of the humerus respectively (13). Orthopaedic interest in humeral torsion goes back to the 70's. In 1971 DEBEVOISE et al. were the first to suggest a relationship between humeral torsion and shoulder instability (3). Our own studies on this subject started in 1976 (13-16). Meanwhile, we have measured the angle of humeral retrotorsion in more than 300 patients with recurrent anterior shoulder dislocations by X-ray and compared the values with those of 240 shoulders without shoulder problems. The dislocating shoulders were found to exhibit angles that were smaller by 11.3° on the average as compared to the control group (18), meaning that the articular surface of the humeral head is directed more anteriorly in unstable shoulders than it is in stable ones. Our results were later confirmed by other groups either using CT-scan (4, 5) or radiologically (10, 11, 19). When comparing the maximum amount of external shoulder rotation of the throwing arm of handball players to that of the non-dominant side, in almost every handball player an increase of about 10 15° of external rotation can be found in the throwing arm (17). This fact by itself is not surprising, because it could be explained by anterior laxity due to chronic overuse, i.e., stretching the joint capsule and ligaments. If anterior laxity was indeed the sole cause for the difference in external rotation ability, however, the amount of internal rotation should not be affected. Yet among our subjects we observed a considerable reduction of maximum internal rotation of the dominant arm (17). Differences of about the same magnitude (approximately 10°) have been reported for unilateral overhead or throwing sports like tennis (1,2) or baseball (12). In the literature, these findings have been explained by a tightening of the posterior capsule by means of fibrotic changes (2); however, a plausible explanation for this shrinking has not been established yet, since the athletes use their arms normally in everyday life without avoiding movements involving internal rotation (e.g., hygiene care). The aim of the present study was to investigate whether: I) this lateral difference can be explained by an osseous component, i.e., a side difference in the torsional angle of the humerus, and II) the existence or non-existence of such a side difference could be a major factor in the occurrence of chronic shoulder problems in handball players.