Discussion
The search yielded 31 articles focused on injury prevalence in water polo (including 12 observational cohorts) and 10 articles on risk factors. The populations observed include adolescents, collegiate, national team and professional players. Water polo injury prevalence is high, with the highest values found in national team players (16.2%–19.4%),13 31 less in collegiate players (13.1%)14 and lowest in adolescents (5.6%).30 This trend may reflect the higher intensity and illegal physical contact that is proportional to higher competition levels. Rule changes will be necessary in order to decrease these foul play injuries, as evidence shows that they are still largely present in this sport at the international level.31 Most injuries occur in competition situations, and affect predominantly the face and hands with lacerations, contusions and sprains/strains.25 Concussion incidence should be high given the predominance of head contacts, but current evidence is conflicting. Available literature suggests that shoulder injuries are the primary overuse injury in this sport,27 which is reflected by the available risk factor studies identified in this review. The primary causes of shoulder injuries investigated thus far are a lack of flexibility and weakness of the rotator cuff muscles,47 as well as larger volumes of overhead throwing repetitions.53 Surveillance data in teenagers (13–18) further suggests that most reports are overuse rather than traumatic in nature.38 42 This suggests that the process of musculoskeletal adaptations to the demands of water polo may be a source of soreness in this age group in particular. Optimal training methods and planning must be sought to promote wellness and performance most notable in younger players.64
Sex comparisons
During the 2009 and 2013 FINA World Championships, women suffered very similar amounts of injuries to the male participants. Despite using similar methodology, surveillance data from the Olympics shows higher rates for male players.9 13 Furthermore, male players were more likely to have time-loss injuries and more severe conditions.31 Although the number of teams at the World Championships is equal for men and women, there are four less female teams at the Olympics.8 Given that the response rates from the participating teams are inconsistent in these events,31 the increased number of male teams may be the reason for higher recorded injury rates.
For collegiate athletes, Sallis et al found that women had nearly three times greater injury incidence rates, most significantly for the shoulder.33 This study scored a perfect 9/9 on the NOS quality assessment. Therefore, the findings suggest a difference in exposures for the female players. This may be the consequence of lesser quality workload management for the women, or rather an under-representation of overuse injuries in male players. Including a surveillance method such as the Oslo Sports Trauma Questionnaire can be more sensitive to identify these injuries that do not require medical consultations.20 Concussion findings in this population are inconsistent, but survey data suggests that women are more susceptible to this injury.24 36 This is consistent with previous reviews65 66 investigating sex differences in concussion incidence in sport, but authors have not determined whether this is the consequence of reporting bias or a true increased risk for women.
Player position
Limited information is available to compare injuries at different player positions. Nevertheless, Cecchi et al demonstrated that players in the ‘centre’ role receive the most hits to the head, but failed to record any concussions during their three-season study in collegiate men.67 This is the direct consequence of their role in attempting to maintain a position in front of the opponent’s net as they are wrestled out of their spot. Accidental blows from elbows or punching can occur during these grappling periods. This is also supported by surveillance data from Croatian male professional leagues, where players in the centre had more facial injuries on average (5.5/player).44 Goalkeepers are also prone to injury from contact with the ball, rather than from other players.36 In particular, balls rebounding on the posts of the net are prone to hit the goalkeepers on the head and are related to the higher incidence of concussions at this position.36 Further research is needed to investigate these position-specific patterns, given that players on the perimeter swim longer distances in matches,6 and one can expect more overhead throwing injuries in this subgroup.
Injury risk factors
Shoulders appear to be the most common area of overuse injuries in water polo players,27 28 and original research on risk factors has focused extensively on this joint. Potential risk factors investigated include throwing volumes, strength, flexibility and proprioception and scapular alignment. The mechanical demands of the swimming, throwing and grappling nature of the sport appear to lead to predictable anatomical adaptations.48 49 Although these changes on imaging are usually considered pathological, they did not correlate with clinical symptoms of shoulder pain in this group.48 Currently, one single study was designed prospectively to evaluate the roles of flexibility and strength as risk factors in water polo.47 They concluded that insufficient strength and lack of flexibility are related to injury, which supports previous hypotheses.60–63 68 However, strength ratios between external and internal rotators of the shoulder were not statistically related to injury in their sample. Perhaps this is the result of testing shoulder strength in isometric contractions only, which does not mimic the action of the rotator cuff during overhead throwing.37 When available, isokinetic dynamometry can provide more information about strength profiles for clinicians working with water polo players.
Preliminary findings from studies on overhead throwing kinematics show conflicting results. However, both research groups have observed an increased duration of the throwing action in injured players.51 54 This suggests a decreased efficiency at coordinating a complex task such as throwing a ball while maintaining an upright position in the water. This can be the result of faulty technique, leading to increased stress on the shoulder.69 Furthermore, the same patterns of inadequate throwing can lead to distraction injuries to the medial elbow complex, compression injuries to the lateral complex and to the olecranon and its fossa.5 The eggbeater motion required to stay upright could also promote overuse syndromes such as tendinopathy of the dorsiflexors, periostitis and possibly compartment syndrome. Presently, no authors have reported the specific types of foot or ankle injuries seen in water polo players, and analyses of lower body risk factors are rare.70 71
Recommendations
In order for future research to allow for a meta-analysis of injuries in water polo, authors must provide unambiguous definitions of injuries.72–74 Injury surveillance studies that scored lowest on the NOS failed to ascertain exposure and outcome distinctly. Thus, the injury incidence rates and prevalence should reflect data collected prospectively over long periods (>6 months) on players of both sexes, with a transparent methodology to avoid recall bias.75 Authors should implement tools that are more sensitive to monitor overuse injuries such as the Oslo Sports Trauma Research Center questionnaire.76 Consistency is important in methods, as the increasing rates of injury prevalence at major games (World Championships and Olympic Games) is likely a reflection of improved data collection alone.31
On the other hand, risk factor studies with lower quality scores rarely presented sample size calculations, and were limited to cross-sectional designs in all but one research group. A prospective design is crucial to understand the causal relationship between these variables and injury incidence.47 77 Studies including younger players are lacking to understand the specific mechanisms of injury in this age group. Including specific estimates of training volume such as Wheeler et al53 would add a needed layer of interpretation to the complex aetiology of injuries in water polo.22