Breaststroker's knee. An analysis of epidemiological and biomechanical factors.

Competitive swimmers have a high incidence of breaststroke-related knee injuries. Although previous investigators have implicated the terminal phase of the kick in the injury mechanism, athletes often complain of pain during the initial phase of rearward thrust. Disagreement in the current literature surrounds the precise anatomical derangement(s) constituting "breaststroker's knee." The purpose of this investigation was to delineate the epidemiology, anatomy, and pathobiomechanics of breaststroke knee injuries. Descriptive data were obtained by surveying 391 athletes. An extremely high incidence of knee pain was documented both among breaststroke specialists (73%) and nonbreaststrokers (48%). Age, years of competitive swimming, and specific training characteristics were positively correlated with knee pain. Both the medial collateral ligament and the inferomedial patellar border were involved. A further 21 swimmers were assessed in detail using four methods: interview, physical examination, Cybex II isokinetic quadriceps and hamstring testing, and cinematographic analyses. The interview and physical examination data supported the conclusions derived from the descriptive data, while Cybex testing and kinematic film analyses failed to demonstrate statistical differences between the injured and noninjured groups. Although kinematic film analyses did not demonstrate statistical differences between cases and controls, dramatic differences in the injury rate were noted when hip abduction angles at kick initiation were less than 37 degrees or greater than 42 degrees. This bimodal increase in injury rates suggests that modification of hip abduction at kick initiation, in conjunction with altered training regimens, will lead to a reduction in medial knee joint stress and hence fewer breastroke injuries.