Shoulder injuries in adolescent elit handball players

Sammanfattning: Background: Handball is a physically demanding sport that includes jumping, running, side-cutting movements and frequent throwing. A high prevalence of shoulder problems and pain has been reported in adult handball players but the research on adolescent elite players is scarce. Several factors have been associated with shoulder injuries in handball players, but strong scientific evidence is lacking for most of the suggested risk factors. Objectives: The objectives of this thesis were to determine the prevalence of shoulder problems in adolescent elite handball players, to present reference values of shoulder strength in adolescent elite handball players and to investigate if adolescent elite hand- ball players with pre-season shoulder weakness, decreased shoulder range of motion (ROM), scapular dyskinesia or deceased joint position sense (JPS) have higher shoulder injury rates compared to players without these characteristics. Methods: The thesis is based on data from the Karolinska Handball Study, a prospective cohort study with, in total, 471 Swedish adolescent elite handball players (622 player seasons) from 10 handball-profiled secondary schools. At baseline the players filled in a questionnaire and then shoulder strength, JPS, ROM and scapula dyskinesia were measured. Thereafter, the players were monitored on a weekly basis regarding injuries and amount of handball training and matches. Prevalence ratios (PR) and hazard rate ratios (HRR) were calculated and any differences in shoulder strength between sex, playing position, school grade and playing level as well as side-to-side differences in shoulder strength were evaluated using t-tests. Results: In total, 110 players (23%) reported substantial shoulder problems during the competitive season. The prevalence was higher among females (PR 1.46, 95% 1.04-2.06) and backcourt players compared to 6-metre players (PR 1.58, 95% CI 1.08-2.32). Male players were stronger in all measures, regardless of normalisation to bodyweight or not (p<0.0001). Both male and female players were stronger in the dominant arm (p<0.001). In general, wing players and backcourt players were stronger than line players and goalkeepers. In females, the HRR for new shoulder injuries in players with lower isometric external rotational strength (IER) was 2.37 (95% CI 1.03-5.44), lower isometric internal rotational strength (IIR) 2.44 (95% CI 1.06-5.61), and in those with scapular dyskinesia 1.53 (95% CI 0.36-6.52). In males, the HRR for weaker IER was 1.02 (95% CI 0.44-2.36), for lower IIR 0.74 (95% CI 0.31-1.75), and for scapular dyskinesia 3.43 (95% CI 1.49-7.92). There were no associations between new shoulder injuries and deficits in ROM or JPS. Conclusions: The prevalence of substantial shoulder problems in adolescent elite hand- ball players is higher among females and backcourt players. Male players are stronger than female players in terms of both absolute strength and when normalised by body- weight. In both male and female players, wing players and backcourt players are, in general, stronger than line players and goalkeepers when normalised by bodyweight. Male players with pre-season scapula dyskinesia, and female players with pre-season internal or external rotation shoulder weakness, had an increased shoulder injury rate.