Purpose of the present study was to investigate biomechanical manifestations of soccer players with increased alpha angles during running, especially the rearfoot motion, which was not been analyzed before. To our best knowledge, this was the first gait analysis of predominantly asymptomatic athletes which had radiologically increased alpha angles. Despite no apparent differences in foot structure, the semiprofessional group experience higher impact forces and load transfer at initial ground contact as compared to the subjects of the amateur group. Increases in the median power frequency, maximum vertical ground reaction force rate, and peak tibial acceleration indicate the semiprofessional group's lower limb to be a more rigid structure during ground contact in running when compared to the amateur subjects. The lower rearfoot motion in the semiprofessional group also contributes to increased shocks of the body during ground contact. A more lateral placement of the foot, causing higher peak pressures under the lateral heel and third metatarsal head, may explain the more rigid foot structure with less subtalar angular joint motion.
Although hip motion during running was not measured, the present data allow us to assume that the oscillation of the center of mass is different between the investigated groups. In the semiprofessional group, increased vertical forces are accompanied by reduced horizontal forces which both are related to a more accentuated upward-downward movement of the center of mass. Compared to non-symptomatic subjects, FAI-patients are restricted in hip flexion during squatting which may be caused by hip pain. The half of the semiprofessional subjects showed clinically a varus deviation of the lower limb. In a previous study, our study group found a correlation between increased alpha angles and deviation of the mechanical leg axis. The mechanical axis deviation can have effects on the kinematics on gait. To compensate limitations in hip flexion which was found in FAI patients during walking, increasing vertical oscillation of the center of mass could be used to counteract the restrictions in sagittal plane hip motion. By applying this strategy, soccer players with increased alpha angles may achieve the same step length but with higher lower extremity loading as well as, obviously, higher energy consumption due to increases in mechanical work. Obviously, all compensatory mechanisms become manifest as a more rigid lower limb structure during the entire stance phase.
It can be concluded that limitations in range of motion (ROM) which were observed in the studies of Kennedy et al. and Lamontagne et al. seem to be compensated by readjustments of the locomotor system. However, restrictions in ROM combined with reduced shock absorption capacity constitute interlocking risk factors for joint disease. Especially in running-related activities, such as in many team sports, the need to be competitive has to be discussed critically according to the aftereffects, especially the pathomechanism of osteoarthrosis.
Consistent with previous findings, our study suggests that specific characteristics of FAI, for instance functional constraints in ROM, can be diagnosed by biomechanical screening. Limitations in hip ROM, reduced shock attenuation capacity and accentuated vertical movement of the center of mass should be considered as functional indicators of FAI.
BMC Musculoskelet Disord. 2014;15(88) © 2014 BioMed Central, Ltd.
© 1999-2006 BioMed Central Ltd