Analysis of Running Biomechanics in Subjects with Ankle Instability

Abstract

Ankle instability (AI) is the term that is commonly used to denote the occurrence of episodes of ankle “giving way” following an initial ankle sprain. Recently contributions of foot biomechanics to the development of this pathology have been reported, without definitive conclusions. Because of the complexity of the foot/ankle region one would intuitively expect to find differences in biomechanical measurements between uninjured and injured populations. PURPOSE: To determine if differences in ankle joint mechanics existed between athletes with self-reported AI and athletes that sustained a single inversion ankle sprain yet had not developed signs of AI. METHODS: Three-dimensional kinetic and kinematic analysis of straight-ahead running (self-selected speed) was performed using a modified Helen-Hayes marker set on the lower limbs of 8 NCAA Division I-AA football players. The subjects were equally divided into two groups (AI [age: 23±5 yrs., ht.: 185±10 cm, mass: 112±15 kg vs. no AI [age: 20±2yrs., ht.: 186±7 cm, mass: 109±27 kg]). Ankle instability status was derived through the use of a self-reported questionnaire. Ten high-speed cameras operating at 120 Hz and 2 force plates operating at 960 Hz were utilized for data collection. A fully-automated, three-dimensional gait measurement system was used for data acquisition. All kinetic data were normalized for body mass. Comparisons of ankle joint kinetics and kinematics were made using independent samples t-tests (P <0.05). RESULTS: Time to maximal dorsiflexion angle was significantly smaller (P = .02) in the AI group (18.1 ± 2.0°) vs. noAI(22.8±3.0°). Although not significantly different (P = 0.06), time to maximal ankle power was less in the AI group (24.2 ±2.0 ms) vs. the no AI group (29.4 ± 4.0 ms). Additionally, maximal power during the support phase was higher in the AI subjects (3.6 ± 6.0 W) vs. the no AI subjects (2.7 ± 5.0 W), but was not significant (P = 0.07). CONCLUSIONS: The increased joint velocity at which the AI subjects move into dorsiflexion is intriguing and may signal an attempt by them to place the ankle joint in a more stable position earlier in the support phase. Although not significant, the increased power and reduced time to maximal power during the support phase of running suggests that the AI subjects may be utilizing a quick stretch of the posterior calf musculature to facilitate a more powerful contraction for torque generation. Even though this preliminary study reports using a small sample size, the data does provide an interesting look at the running biomechanics associated with AI in athletes.