The role of foot pronation in the development of femoral and tibial stress fractures: a prospective biomechanical study.

ABSTRACT

OBJECTIVE: To examine whether dynamic parameters of foot pronation are risk factors for the development of stress fractures of the femur and tibia. DESIGN: Observational prospective study. SETTING: Infantry basic training course. PARTICIPANTS: 473 recruits evaluated for stress fractures of the femur and tibia every 2 weeks during 14 weeks of infantry basic training. The final analysis included 405 recruits. ASSESSMENT OF RISK FACTORS Two weeks before commencement of training, the recruits were evaluated during treadmill walking for their subtalar joint kinematics. Five independent variables were measured bilaterally maximal pronation angle during the stance, pronation range of motion, time from heel strike to maximum pronation, pronation mean angular velocity, and time to maximum pronation as a percent of the total stance time. MAIN OUTCOME MEASUREMENTS Stress fractures of the femur and tibia. These were considered positive only when proven by imaging. RESULTS: Ten percent of the participants were diagnosed with stress fractures of the femur and tibia. Recruits with longer duration of foot pronation had reduced odds ratio to develop this injury. CONCLUSIONS AND CLINICAL RELEVANCE Longer duration of foot pronation may have a protective effect from stress fractures of the femur and tibia. This finding may promote the understanding of stress fracture pathomechanism, assist in the identification of subjects with increased risk who need augmented monitoring throughout training, and assist in future planning of impact reducing aids.