The examination of dynamic foot pressure distributions, running mechanics, and a lateral hop in subjects with chronic ankle instability

Lateral ankle sprains (LAS) are common injuries in athletic activity. Although some will resolve with conservative treatment, others will develop chronic ankle instability (CAI), a condition associated with persistent pain, weakness, and instability. Because of an increase in prevalence of CAI, considerable attention has been directed towards understanding the underlying causes of this pathology. Despite the amount of research conducted in this area, analysis of the movement patterns in these individuals during dynamic conditions is limited. A mechanical analysis of high-risk dynamic activities may give greater insight into the stresses on the foot and ankle complex in CAI subjects. The overall aims of this study were: (1) to determine if there are kinematic, kinetic, or neuromuscular differences at the foot and ankle complex in the running mechanics of subjects with CAI (2) to determine if there are kinematic, kinetic, or neuromuscular differences at the foot and ankle complex during a lateral hop in subjects with CAI and (3) to determine if there are differences in dynamic plantar pressure distributions at the foot during a running gait in subjects with CAI. We hypothesized that subjects with CAI would display different biomechanical patterns at the foot and ankle when compared to both a group of subjects who suffered one LAS, but did not develop CAI (AS group), and an uninjured control group. The differences detected will highlight characteristics at the foot and ankle which may predispose CAI subjects to recurrent injury. We also hypothesized that the greatest disparity would be between the CAI and AS groups, indicating possible compensatory strategies utilized in the AS population. The differences would be demonstrated in the kinetic, kinematic, electromyographic, and plantar pressure variables of interest.The specific aims were addressed in three studies. The first and second studies utilized three-dimensional motion analysis and surface electromyographic assessment to investigate biomechanical strategies at the foot and ankle during dynamic conditions in subjects with CAI. The first study utilized a running gait, while the second integrated a lateral hopping maneuver. During a running gait, subjects with CAI had a significantly greater rearfoot inversion angle at foot strike (FS), greater variability of the rearfoot inversion angle at FS, a reduced rearfoot internal inversion moment during the loading phase of stance, a greater plantar flexion angle at FS, and a more delayed onset of peroneal muscle activity relative to FS. With regard to the lateral hop, only the onset of peroneal muscle activity was significantly different between groups, with the greatest delay occurring in the CAI group. The results demonstrate that individuals with CAI have different foot and ankle mechanics and may help to explain their predisposition to episodes of "giving way" and subsequent ankle sprains. It is important to note, however, that the differences detected were greatest between the CAI and Control groups for both conditions. We were unable to detect clear compensatory strategies utilized by the AS group. The AS group exhibited kinematic and kinetic characteristics at the rearfoot and ankle that more closely matched the uninjured control group. Therefore, more attention should be placed on correcting foot and ankle positioning and increasing neuromuscular control during dynamic activity in the treatment and rehabilitation of CAI.The third study assessed differences in plantar pressure distributions at the foot during a running gait in subjects with CAI. Individuals with CAI had a significantly more lateral pressure distribution at foot strike (FS) and a more lateral center-of-pressure (COP) trajectory during the loading phase. Both findings demonstrate a more inverted pattern of running gait. Interestingly, the greatest difference in the pressure distribution at FS was between the CAI and AS subjects and may highlight a potential compensatory mechanism.The combined results suggest that individuals with CAI have altered movement patterns and mechanics at the foot and ankle during dynamic activity, and display a more vulnerable inverted gait pattern. The disparity between the CAI and AS groups suggests that mechanics utilized by the CAI group contribute to the development of repetitive, not isolated lateral ankle sprain events. These findings may assist in the development of appropriate treatment and prevention protocols for CAI.