Objective: Research suggests that excessive pronation of the foot contributes to the incidence of anterior cruciate ligament (ACL) tears by increasing internal tibial rotation. Studies have documented greater navicular drop values in individuals with a history of an ACL tear using methods that may not accurately follow the motion of underlying bone. The purpose of our investigation was to compare the navicular drop of subjects with a history of ACL tears with healthy controls when measured by a Metrecom.
Subjects: Eighteen subjects previously diagnosed with a torn ACL were matched by age, sex, and limb to noninjured control subjects.
Design and setting: Static group comparisons of navicular drop in subjects with an injured ACL and subjects having no history of ACL injury.
Measurements: A single investigator performed the measure of navicular drop. The position of the navicular tuberosity was digitized while the subject stood barefoot on a flat surface in subtalar joint neutral and in relaxed stance. Intrarater reliability was assessed using intraclass correlation coefficient and standard error of the measurement. An independent t test assessed the difference between the amount of navicular drop in the ACL group and the controls.
Results: Analysis of repeated measures, intraclass correlation coefficient (2,1), demonstrated intrarater reliability for the measure of navicular drop to be 0.90; the standard error of measurement was 1.19 mm. The independent t test showed a statistically greater amount of navicular drop in the ACL group.
Conclusions: Excellent intrarater reliability was demonstrated when using the Metrecom to measure navicular drop. Excessive subtalar joint pronation, measured as navicular drop, was identified as 1 factor that may contribute to ACL injury.